Medical imaging device and medical imaging procedures

Abstract

Medical imaging device (410), in particular endoscope device, exoscope device and / or microscope device, comprising: an illumination unit (412) with at least one light source (414) configured to provide illumination light (416) for illuminating an object (418) to be imaged; an image acquisition unit (420) configured to acquire several calibration images (422, 423) of the object (418) to be imaged and to acquire at least one object image (424) of the object (418) to be imaged; and an image correction unit (426) configured to: determine depth information from the calibration images (422, 423), wherein the depth information comprises several depth maps relating to different wavelength ranges;Determining a correction for the object image (424), wherein the correction includes taking into account a distance dependence of a light intensity of illumination light (416) and / or a distance dependence of a light intensity of object light (428) according to the depth information; and producing a corrected object image (430) according to the correction, wherein the illumination unit (412) is configured to be operable in different illumination modes in which illumination light in different spectral ranges can be provided, and wherein the image acquisition unit (420) is configured to acquire several calibration images (422, 423) the acquisition of which is based on different illumination modes of the illumination unit (412).

Description

The invention relates to a medical imaging device, in particular an endoscope device, exoscope device and / or microscope device, a method for medical imaging, program code for carrying out such a method, and a computer program product with such program code. Imaging devices for fluorescence imaging are known in the art, capable of acquiring both fluorescence and white light images. Suitable excitation light is used to selectively excite fluorescent dyes or, optionally, naturally occurring fluorescent substances, and to detect the emitted light for imaging. To simultaneously display anatomical structures within the image area to the user, a white light image is often acquired concurrently or sequentially. The white light image allows the user to assess whether the anatomical structure is depicted. Fluorescence and white light images can also be superimposed, making anatomical and fluorescence information simultaneously perceptible and analyzable for the user. Imaging devices such as endoscopic or exoscopic devices that generate multispectral or hyperspectral images are also known from the prior art. In addition to two spatial dimensions, such as those of a conventional camera image, multispectral or hyperspectral images have a spectral dimension. This spectral dimension comprises several spectral bands (wavelength bands). Multispectral and hyperspectral images differ primarily in the number and width of their spectral bands. Such systems can also be suitable for performing fluorescence imaging. Several imaging devices for generating such multispectral or hyperspectral images are known, particularly in the context of medical applications. For example, DE 20 2014 010 558 U1 describes a device for acquiring a hyperspectral image of an examination area of ​​a body. The device comprises an input lens for generating an image in an image plane and a slit-shaped aperture in the image plane for blocking out a slit-shaped area of ​​the image. The light passing through the aperture is dispersed by means of a dispersive element and captured by a camera sensor. This allows the camera sensor to capture a multitude of spectra, each with an associated spatial coordinate, along the longitudinal direction of the slit-shaped aperture.The described device is further configured to acquire additional spectra along the longitudinal direction of the slit-shaped aperture in a direction different from that direction. The method underlying this disclosure for generating multispectral or hyperspectral images is also known as the pushbroom method. Besides the pushbroom method, there are other techniques for generating multispectral or hyperspectral images. In the so-called whiskbroom method, the area under investigation or object is scanned point by point, and a spectrum is acquired for each point. In contrast, the staring method captures multiple images with the same spatial coordinates. Different spectral filters and / or illumination sources are used for each image to resolve spectral information. Furthermore, there are methods in which a two-dimensional multicolor image is decomposed into several individual spectral images using suitable optical elements such as optical slicers, lenses, and prisms. These images are then simultaneously acquired by different detectors or detector sections. This is sometimes referred to as a snapshot approach. As described in DE 10 2020 105 458 A1, multispectral and hyperspectral imaging devices are particularly suitable as endoscopic imaging devices. In this context, multispectral and / or hyperspectral imaging is a fundamental field of application, for example, for diagnostics and for assessing the success or quality of a procedure. DE 10 2020 124 220 A1 relates to a method and a system for stereoendoscopic fluorescence measurement using a stereo optic of a stereo video endoscope directed at an area of ​​the tissue to be examined, and which excites the fluorescent agent to emit fluorescent light by means of a single excitation light. The publication by Li et al., “Review of spectral imaging technology in biomedical engineering: achievements and challenges”, Journal of Biomedical Optics from 2013 describes different multimodal imaging techniques. Furthermore, the publications by Bradley and Thorniley, “A review of attenuation correction techniques for tissue fluorescence”, in Journal of the Royal Society Interface from 2006 and by Kim et al., “Topographic mapping of subsurface fluorescent structures in tissue using multiwavelength excitation”, in Journal of Biomedical Optics from 2010 describe the physical background. Multimodal imaging devices allow the selective acquisition of white light images and / or multispectral images and / or fluorescence images and / or hyperspectral images. Examples of such imaging devices are multimodal endoscopes and multimodal exoscopes. In general, the aforementioned imaging methods involve shining light of a specific spectrum onto the object being observed, which is then reflected, absorbed, transmitted, or emitted as a result of fluorescence excitation. Ultimately, this light reaches an image sensor, possibly passing through one or more suitable observation filters. The image sensor captures image data, which can then be used to generate a display for the user. However, no further information is provided regarding the specific light interaction that resulted from the detected light. Based on the prior art, the invention aims to improve the interpretability of image data. This problem is solved according to the invention by an imaging device, a method for medical imaging, program code, and a computer program product as described herein and defined in claims 1, 11, 12, and 13. Further developments are set forth in the dependent claims. According to the invention, a medical imaging device, in particular an endoscope, exoscope, and / or microscope device, comprises an illumination unit with at least one light source configured to provide illumination for an object to be imaged, and an image acquisition unit configured to acquire multiple calibration images of the object to be imaged and to acquire at least one object image of the object to be imaged. The imaging device also includes an image correction unit. The image correction unit is configured to determine depth information from the calibration images.Furthermore, the image correction unit is configured to determine a correction for the object image, whereby the correction takes into account a location dependency, in particular a distance dependency, a light intensity of illumination light and / or a distance dependency of the light intensity of object light according to the depth information. In addition, the image correction unit is configured to generate a corrected object image according to the correction. Furthermore, a method for medical imaging is provided according to the invention. In some embodiments, the method can be carried out using a medical imaging device according to the invention. The method comprises providing illumination light in different wavelength ranges for illuminating an object to be imaged. The method also comprises acquiring several calibration images of the object to be imaged in the different wavelength ranges. In addition, the method comprises acquiring at least one image of the object to be imaged. Furthermore, the method comprises determining depth information from the calibration images.Furthermore, the method includes determining a correction for the object image, whereby the correction takes into account the distance dependence of the light intensity of the illumination light and / or the distance dependence of the light intensity of the object light according to the depth information. The method also includes generating a corrected object image according to the correction. The features according to the invention make it possible to improve the interpretability of image data. The inventors recognized that in conventional fluorescence imaging, multispectral imaging, or hyperspectral imaging, signal intensity varies with distance, which can lead to misinterpretations of image data. This distance dependence may result in reflectance values ​​not being measured absolutely in multispectral and / or hyperspectral imaging. The inventors also recognized that the accuracy of image data interpretation can be impaired if fluorescence signals are attenuated by overlying tissue and / or if the depth within the tissue under consideration of the observed fluorescent dye is unknown, or if the distance between an anatomical surface and the fluorescent dye is unknown.Furthermore, the inventors have identified another problem with conventional multispectral imaging and / or hyperspectral imaging: for certain applications, particularly for calculating physiological parameters such as tissue oxygen saturation (StO2 parameter), simple assumptions have been made regarding the penetration depth of light, which can lead to distorted measurement results. According to the invention, by determining depth information from a calibration image and using it to correct object images, these effects can be compensated for. The physical interaction of illumination light, reflected light, and / or emitted light with the observed object can be taken into account, thereby making the available information more accurately interpretable. The imaging device may be configured as a microscope, macroscope, and / or exoscope, and / or comprise such a device. In some embodiments, the imaging device may be an endoscopic imaging device. It may comprise an endoscope and / or an endoscope system, and / or be configured as such, and / or form at least a part, and preferably at least a major component and / or principal component, of an endoscope and / or an endoscope system. "At least a major component" may mean at least 55%, preferably at least 65%, more preferably at least 75%, particularly preferably at least 85%, and most preferably at least 95%, particularly with respect to the volume and / or mass of an object. In some embodiments, the imaging device is designed to be inserted into a cavity for inspection and / or observation, for example into an artificial and / or natural cavity, such as the interior of a body, a body organ, tissue or the like. In particular, if the imaging device is an exoscopic imaging device, it can be configured to acquire tissue parameters, images of wounds, images of body parts, etc. For example, the imaging device can be configured to image a surgical field. The image acquisition unit includes, in particular, an image acquisition sensor and / or at least one optical element, especially a lens. The image acquisition sensor can be configured to detect light in both the visible and near-infrared ranges. In some embodiments, the smallest detectable wavelength can be at most 500 nm, at most 450 nm, or even at most 400 nm. In some embodiments, the largest detectable wavelength can be at least 800 nm, at least 900 nm, or even at least 1000 nm. The image acquisition sensor can, for example, comprise at least one white-light image sensor and at least one near-infrared image sensor. In some embodiments, the imaging device comprises a white-light camera and / or sensors for white-light image acquisition. The imaging device can be configured for white-light imaging. The anatomical images can be acquired using the white-light camera and / or the sensors for white-light image acquisition. The image acquisition unit can include a filter unit with optical observation filters. The filter unit can define multiple observation modes and / or fluorescence modes, each defined by different observation filters. For example, different edge filters can be used that absorb / block the respective spectrum of the associated excitation luminescent element and transmit at least substantially only fluorescence light. In some embodiments, the observation filters can also be switchable between a multispectral mode and / or a hyperspectral mode and a fluorescence mode. The imaging device, and in particular the optics of the image acquisition unit and / or the image acquisition sensors, may be configured for multispectral and / or hyperspectral imaging, specifically for acquiring and / or generating multispectral and / or hyperspectral image data. Multispectral imaging or multispectral image data may, in particular, refer to imaging in which at least two, in particular at least three, and in some cases at least five spectral bands can be independently acquired and / or are acquired. Hyperspectral imaging or hyperspectral image data may, in particular, refer to imaging in which at least 20, at least 50, or even at least 100 spectral bands can be independently acquired and / or are acquired.The imaging device can operate according to the pushbroom method and / or the whiskbroom method and / or the staring method and / or a snapshot principle. For some applications, a high spectral resolution can be advantageous. Hyperspectral imaging is then a suitable option. This can be combined with white light imaging. This enables real-time observation via a white light image, even if the acquisition of spectrally resolved image data is only essentially real-time, meaning, for example, that it takes several seconds to generate a spectrally resolved image. For some applications, it can be advantageous to generate spectral image data in real time. This includes, for example, generating a spectrally resolved image in less than a second or even several times per second. In these cases, it can be useful to employ multispectral imaging. A potentially lower spectral resolution is then offset by a higher frame rate.Depending on the application, it may be sufficient to consider only a few different spectral ranges and / or wavelengths, for example, two, three, four, or generally fewer than ten. In this case, additional white light imaging can optionally be omitted. Spectrally resolved image data acquired in real time or providing multiple images per second can also be used for surveillance purposes. It is not essential to create a displayable image for a user; the image data can also be processed in the background. The medical imaging device may have at least one proximal section, one distal section, and / or an intermediate section. The distal section is specifically designed to be inserted into and / or located within a cavity to be examined during operation, such as during diagnostic and / or therapeutic procedures. The proximal section is specifically designed to be positioned outside the cavity to be examined during operation, such as during diagnostic and / or therapeutic procedures. "Distal" is understood to mean, in particular, that the device is oriented towards a patient and / or away from a user. "Proximal" is understood to mean, in particular, that the device is oriented away from a patient and / or towards a user. In particular, "proximal" is the opposite of "distal."The medical imaging device has, in particular, at least one, preferably flexible, shaft. The shaft can be an elongated object. Furthermore, the shaft can form at least part, and preferably at least a large part, of the distal section. An "elongated object" is understood to be, in particular, an object whose principal extent is greater by at least a factor of five, preferably at least a factor of ten, and most preferably at least a factor of twenty than a maximum extent of the object perpendicular to its principal extent, i.e., in particular, a diameter of the object. A "principal extent" of an object is understood to be, in particular, its longest extent along its principal direction of extension.The term "main extension direction" of a component is understood to mean, in particular, a direction that runs parallel to the longest edge of the smallest imaginary cuboid that just completely encloses the component. The image acquisition unit can be located at least partially, and preferably at least predominantly, in and / or form part of the proximal section. In other embodiments, the image acquisition unit can be located at least partially, and preferably at least predominantly, in and / or form part of the distal section. Furthermore, the image acquisition unit can be distributed at least partially between the proximal and distal sections. The image acquisition sensor system comprises, in particular, at least one image sensor. Furthermore, the image acquisition sensor system can also have at least two, and preferably more, image sensors, which can be arranged in series.Furthermore, the two, and preferably more, image acquisition sensors can have different spectral sensitivities, such that, for example, a first sensor is particularly sensitive in a red spectral range, a second sensor in a blue spectral range, and a third sensor in a green spectral range, or comparatively more sensitive than the other sensors. The image sensor can be designed, for example, as a CCD sensor and / or a CMOS sensor. The optical system of the image acquisition unit can comprise suitable optical elements such as lenses, mirrors, gratings, prisms, optical fibers, etc. The optical system can be configured to direct object light emanating from the imaged object to the image acquisition sensor, for example, to focus and / or project it. The image acquisition unit is specifically designed to acquire spatially and spectrally resolved image data. The image acquisition unit can be configured to generate at least two-dimensional spatial image data. The image acquisition unit can be spatially resolved in such a way that it provides a resolution of at least 100 pixels, preferably at least 200 pixels, preferably at least 300 pixels, and advantageously at least 400 pixels in at least two different spatial directions. The image data is preferably at least three-dimensional, with at least two dimensions being spatial dimensions and / or at least one dimension being a spectral dimension. Several spatially resolved images of the image area can be obtained from the image data, each assigned to different spectral bands.The spatial and spectral information of the image data can be structured in such a way that a corresponding spectrum can be obtained for each of several spatial pixels. In some embodiments, the image acquisition unit is configured to continuously generate updated image data. For example, the image acquisition unit can be configured to generate the image data essentially in real time, which includes generating updated image data at least every 30 seconds, in some cases at least every 20 seconds, and in some cases even at least every 10 seconds or at least every 5 seconds. Preferably, the image acquisition unit is configured to generate at least the anatomical images and the fluorescence images, as well as the display based thereon, in real time, for example at a frame rate of at least 5 fps, at least 10 fps, at least 20 fps, or even at least 30 fps. The lighting unit can be multimodal and include several independently selectable activatable lighting elements, which are set up to emit light according to different emission spectra in order to provide the illumination light. The image acquisition unit can be operated in a calibration mode and in at least one imaging mode. In calibration mode, at least one calibration image can be acquired. In imaging mode, at least one object image can be acquired. The object image can be a white light image, a fluorescence image, a multispectral image, and / or a hyperspectral image. A section of the calibration image can correspond to and / or at least overlap with a section of the object image. In particular, the calibration image can define a section that is at least partially contained within a section of the object image. Correction can be performed, in particular, for areas of the object image that are also depicted in the calibration image. The image correction unit can be configured to compare the image sections of the calibration image and the object image in order to identify image areas that can be corrected.This allows for correction even in cases where the calibration image and the object image are not identical. The image acquisition unit can be configured to capture multiple calibration images with different image acquisition parameters and / or illumination parameters. The depth information can be based on several calibration images, particularly those captured with different parameters. The image acquisition unit can be configured to capture stereo images. For example, the image acquisition unit can include at least one pair of image sensors so that stereo pairs of images can be captured. Within the scope of this disclosure, "object light" generally refers to light originating from an object under observation. As mentioned, this can be reflected or emitted light, depending on the nature of the object and / or the imaging method. In some embodiments, the correction involves assigning spatial coordinates x, y, z to captured image points according to the depth information. Based on this, the correction for a specific image point can be based on a function f(x,y,z) that depends on the spatial coordinates x, y, z of that particular image point. If the correction takes distance dependence into account, the aforementioned function can depend on the sum x² + y² + z² and / or the square root of this sum, i.e., sqrt(x² + y² + z²). The correction can be performed point by point, image by area, and / or image by image. The corrected object image can be corrected point by point, image area by image, and / or image by image. The corrected object image is based in particular on the object image and the calibration image. The process steps mentioned can be carried out in the order in which they are listed. However, it is understood that a different order is also possible according to the invention, and the listing of the process steps does not necessarily define a predetermined sequence. A comprehensive correction can be performed, in particular, if the depth information includes at least one depth map. A depth map is understood to be spatially resolved depth information that assigns at least one depth value, defined, for example, by a coordinate z, to a series of pixels, especially all pixels of the calibration image, which can be defined by coordinates x and y. In other words, a topography of the object to be imaged can be derived from the calibration image to obtain the depth information. This depth information can be specific to the image acquisition parameters and / or illumination parameters used. The depth information may comprise multiple depth maps relating to different wavelength ranges. Furthermore, the depth information may include multiple depth maps relating to different tissue types and / or anatomical structures.Different depth maps can also be derived from multiple calibration images, either alternatively or additionally. In particular, at least one calibration image with specific parameters can be taken to obtain a particular depth map. The acquisition of the calibration image can include the detection of reflected light. This allows depth information to be easily obtained by exploiting the fact that light in certain spectral ranges has a very shallow penetration depth in tissue. Preferably, the calibration image is acquired using stereo imaging or 3D imaging. The calibration image can be a 3D image. A depth map can then be obtained using a stereo reconstruction algorithm. For example, a semi-global matching algorithm can be used, as described in the article "Accurate and efficient stereo processing by semi-global matching and mutual information" by Hirschmüller, 2005, IEEE Conference on Computer Vision and Pattern Recognition, pp. 807-814. Alternatively, a 3D image or a topographic surface can be calculated from two-dimensional image data.For this purpose, an artificial intelligence algorithm can be trained beforehand using suitable 2D and 3D image data. The acquisition and / or evaluation of 3D images can include calibration of the image acquisition unit, which is aimed at determining distortion parameters and / or the relative spatial position of image sensors. Light used to acquire such calibration images is essentially reflected directly from the surface of the object being imaged; therefore, the calibration image primarily, or at least essentially exclusively, contains image information relating to the surface of the object being imaged. A depth map, for example, can be derived from a white-light calibration image. White light typically has a very shallow penetration depth into tissue, so reflected light originates approximately from an anatomical surface.Alternatively or additionally, a depth map can be derived from a single-color calibration image or a false-color calibration image using illumination light that lies only in one or more sub-ranges of the visible light spectrum. For example, illumination can be provided only with blue, green, yellow, and / or red light to obtain depth information based on reflected light. A mixture of specific colors and / or spectral ranges that deviate from white light can also be used. Preferably, wavelength ranges are used for which light has the lowest possible penetration depth into the object being imaged, ensuring that the reflected light originates from the object's surface. Alternatively or additionally, different calibration images can be acquired for different wavelength ranges, and depth maps can be calculated for each.These can then be used for correction in different wavelengths, which in particular takes into account wavelength-dependent penetration depths. In some embodiments, the acquisition of the calibration image can include the detection of fluorescence light. This provides a basis for a comprehensive and accurate evaluation of fluorescence images. Preferably, at least one 3D fluorescence image is acquired. As described above, light of a suitable wavelength can be used as excitation light, and the light emitted by the object being imaged can be detected through a suitable observation filter. Depth information, in particular a depth map, can be obtained by means of stereo reconstruction. Alternatively, analogous to the case described above, a 2D image can be used as a basis, and depth information can be obtained using an artificial intelligence algorithm.In particular, a depth map can be derived from the calibration image, relating to areas of the object being imaged that lie within the object and / or below a surface of the object. Specifically, the depth map can be based on stained areas covered by unstained tissue. Fluorescence light then travels from a position to the image sensor and / or to a lens of the image acquisition unit that is farther from the image sensor / lens than a surface of the object being imaged. Extensive correction, enabling the correct interpretation of image data in different imaging modes, can be achieved by configuring the illumination unit to operate in different illumination modes, providing illumination light in different spectral ranges, and by configuring the image acquisition unit to acquire multiple calibration images based on different illumination modes of the illumination unit. For example, a first illumination mode can be used to obtain a calibration image based on reflected light, and a second illumination mode can be used to obtain a calibration image based on emitted light, particularly fluorescent light.From this, at least a first depth map and at least a second depth map can be obtained, wherein the first depth map refers to a surface of the object to be imaged and wherein the second depth map refers to areas of the object to be imaged that are colored by means of at least one fluorescent dye and are located below the surface of the object to be imaged. The image acquisition unit can be configured to acquire multiple calibration images in different spectral ranges simultaneously and / or sequentially, particularly using different optical filters. Multiple calibration images can, for example, originate from different spectral ranges in multispectral imaging and / or hyperspectral imaging. In some embodiments, the correction comprises a distance correction based on the inverse of a power of a light path length, in particular the length of a light path between the image acquisition unit, especially an image sensor and / or a lens of the image acquisition unit, and the object to be imaged, and / or a light path within the object to be imaged. The distance correction can be based, for example, on an inverse square law. In this case, the illumination unit can be approximated as a point light source. Deviations from a point light source can be taken into account by using an exponent other than 2. Furthermore, the correction can include an absorption correction based on an attenuation, particularly exponential, of light along a light path of a certain length, especially a length of a light path within the object being imaged. Alternatively or additionally, the absorption correction can take into account an attenuation of illumination light and / or an attenuation of object light. In general terms, a distance correction for fluorescence imaging, in which light with a wavelength λ0 is incident and light with a wavelength λ1 is emitted, can be based on the following attenuation due to a distance from a lens of the image acquisition unit to the object being imaged, as well as the positioning of a fluorescently stained area in the object being imaged: where Idetected denotes the detected light intensity, I(λ0) the intensity of the incident light with wavelength λ0, d0 a distance between the lens and the surface of the object being imaged, d1 a distance between the surface of the object being imaged and the fluorescently stained area in the object being imaged, α an exponent that defines the inverse square law and can, for example, be chosen as 2 to calculate according to the inverse square law.µ(λ0) denotes a damping factor for the attenuation of light of wavelength λ0 as it passes through the object to be imaged. µ(λ1) denotes a damping factor for the attenuation of light of wavelength λ1 as it passes through the object to be imaged. A particularly high degree of accuracy can be achieved if the image correction unit is configured to determine spatial and / or spectral properties, especially inhomogeneities, of the illumination unit from at least one calibration image and to take these determined spatial and / or spectral properties into account during correction. In other words, the acquisition of calibration images can be used to calibrate the illumination device or to consider real properties of the illumination device for calculating the corrected object image. In some embodiments, it may be provided that in the corrected object image, at least one image area is enhanced and / or attenuated relative to at least one other image area with respect to at least one parameter, such as hue, brightness, and / or saturation, according to the correction. This allows for the creation of a corrected object image that is intuitively understandable for a user. Generally, this can compensate for, for example, differences in intensity that result from different lighting conditions but not from differences in the depicted tissue. The corrected object image can then be calculated, for example, in such a way that the differences in intensity are not perceptible. For the user, similar areas are then recognizable as such, even if they are not depicted identically.For example, a fluorescent area that is partially or completely obscured by unstained tissue can be displayed as if it were uncovered. Alternatively, distance information can be conveyed to the user using false colors. For instance, a fluorescent area covered by unstained tissue can be displayed with increased brightness so that it is clearly visible, but the color can be changed according to the distance of the fluorescent area from the surface of the object being imaged, allowing the user to determine whether and how far the fluorescent area is located within the object. This can, for example, assist the user during dissection. In some embodiments, the medical imaging device includes a lighting device, which comprises the lighting unit. The lighting device may include an optical interface for optically connecting an imaging device. The lighting unit may be configured to supply illumination light to the optical interface. The lighting unit may be multimodal and comprise several independently selectable light elements configured to emit light according to different emission spectra to provide the illumination light. The lighting unit may be operable in at least one multispectral mode in which a first group of light elements is activated at least intermittently and in which the lighting unit provides illumination light for multispectral imaging.Furthermore, the illumination unit can be operated in at least one fluorescence mode in which a second group of light elements is activated at least intermittently and in which the illumination unit provides illumination light for fluorescence imaging. The light elements can include at least one light element that is contained in both the first and the second group. Furthermore, a method for generating illumination light for an imaging device by means of an illumination device may be provided. The illumination device comprises an optical interface for the optical connection of an imaging device and an illumination unit configured to supply illumination light to the optical interface. The illumination unit comprises several independently selectable illuminating elements configured to emit light according to different emission spectra in order to supply the illumination light. The method includes the step of at least temporarily activating a first group of the illuminating elements to supply illumination light for multispectral imaging and the step of at least temporarily activating a second group of the illuminating elements to supply illumination light for fluorescence imaging.At least one of the lighting elements is activated at least temporarily both when the first group of lighting elements is activated at least temporarily and when the second group of lighting elements is activated at least temporarily. The optical interface can be either detachable or connectable. Furthermore, the optical interface can be combined with a mechanical interface, so that an optical connection is automatically established, for example, when the imaging device is mechanically attached. The lighting elements can comprise single-color LEDs (light-emitting diodes) and / or laser diodes. Furthermore, at least one of the lighting elements can be a white LED or another white light source. In some embodiments, the lighting unit comprises at least one blue lighting element, at least one red lighting element, at least one dark red lighting element, and at least one near-infrared lighting element, in particular LEDs or laser diodes. Additionally, the lighting unit can comprise at least one white LED or another white light source. The first group can comprise at least two light sources that emit spectrally different wavelengths. A high degree of efficiency in multispectral imaging can be achieved if the multispectral mode includes different states in which a specific light source or a specific type of light source is activated, at least temporarily. This allows for targeted illumination in a specific spectral range, enabling the acquisition of different spectral images. Different light sources activated in different states can serve as different support points for multispectral imaging. At least one of these support points can be selected to be adapted to characteristic points in the absorption spectra of physiologically relevant components, for example, an isosbestic point on the hemoglobin oxygenation curve.Multispectral imaging can additionally include the use of suitable observation filters. Furthermore, the second group can comprise at least two phosphor elements that emit spectrally different wavelengths. The fluorescence mode can include different submodes and / or states, in each of which a specific phosphor element or a specific type of phosphor element is activated, at least temporarily. This allows for targeted excitation in a specific spectral range, enabling fluorescence imaging, for example, for a specifically selected dye. In other words, the at least one phosphor element that is included in both the first and second groups can be used for both the multispectral mode and the fluorescence mode. In some embodiments, the first group comprises only some, but not all, of the light-emitting elements. Alternatively or additionally, in some embodiments, the second group comprises only some, but not all, of the light-emitting elements. In multispectral mode, in particular, only light-emitting elements of the first group are activated, at least temporarily, whereas light-emitting elements not belonging to the first group are deactivated. In fluorescence mode, in particular, only light-emitting elements of the second group are activated, at least temporarily, whereas light-emitting elements not belonging to the second group are deactivated. It is generally understood that the light-emitting elements can comprise different types and that, in particular, exactly one light-emitting element of each type can be present.It is understood that mixed operating modes can also occur according to the invention, in which the aforementioned modes are used sequentially. For example, multispectral imaging and fluorescence imaging can be performed sequentially. Synergies regarding the use of a single light source for different modes, and the associated efficiency gains, can be achieved particularly when at least one light source, included in both the first and second groups, emits light in the red spectral range, especially in a spectral range between 600 nm and 680 nm, for example, between 610 nm and 650 nm, or between 620 nm and 660 nm, or between 630 nm and 670 nm. The spectral range can be narrowband and include a wavelength of 660 nm. "Narrowband" can encompass a spectral width of at most 80 nm, particularly at most 40 nm, or even at most 20 nm. This at least one light source can be configured to excite red-spectral absorbing dyes and contribute to red-spectral illumination for multispectral imaging. In some embodiments, the illumination unit can be operated in at least one white light mode, in which it provides illumination for white light imaging. This illumination can be broadband white light. Alternatively, it can comprise several narrow wavelength bands separated from one another, for example, a blue, a red, and a far-red band. "Far-red" here refers to a wavelength longer than red and describes the spectral position, not the light intensity. The illumination can be a mixture of light from different illuminating elements. In white light mode, a third group of light elements can be activated, at least temporarily, to provide illumination for white light imaging. This group of light elements can include at least one element that is present in the first group, the second group, and / or the third group. In some cases, the third group may include only some, but not all, of the light elements. Specifically, in white light mode, only light elements from the third group are activated, at least temporarily, while light elements not belonging to the third group are deactivated. In other words, the illumination unit can include light elements that serve one, two, or all three of the aforementioned illumination modes. This allows multiple light elements to be used for multiple purposes. At least one luminescent element, included in the first group and / or the second group as well as the third group, can emit light in the red spectral range, specifically in a spectral range between 600 nm and 680 nm, for example, between 610 nm and 650 nm, or between 620 nm and 660 nm, or between 630 nm and 670 nm. The advantages of using multiple luminescent elements are particularly evident when at least one red luminescent element is usable for all three modes. At least one luminescent element, contained in the first group and / or the second group as well as the third group, can emit light in the blue spectral range, particularly in a spectral range between 440 and 480 nm. At least one blue luminescent element can conveniently be used in both fluorescence mode and white light mode. In general terms, the luminaires can, as mentioned, comprise at least one luminaire, in particular a blue one, that emits light in a spectral range between 440 and 480 nm. Furthermore, as mentioned, the luminaires can comprise at least one luminaire, in particular a red one, that emits light in a spectral range between 600 and 680 nm, for example, between 610 nm and 650 nm, or between 620 and 660 nm, or between 630 and 670 nm. Alternatively or additionally, the luminaires can comprise at least one luminaire, in particular a dark red one, that emits light in a spectral range between 750 and 790 nm. Alternatively or additionally, the luminaires can comprise at least one luminaire, in particular a near-infrared one, that emits light in a spectral range between 920 and 960 nm. In addition, the luminaires can comprise a white light luminaire.A compact and versatile lighting unit can be provided, in particular, if at least one of each of the aforementioned light element types is present. For example, in fluorescent mode, the blue and red light elements can be used, and, if suitable dyes are used, possibly also the far-red light element. In multispectral mode, the far-red and near-infrared light elements can be used. In white light mode, the white light light element can be used. This can be supplemented in white light mode by the blue light element and, if necessary, also by the red light element. This allows wavelength ranges to be supplemented with colored light elements in which the white light light element provides reduced intensity, for example, due to its design, but especially due to filters and optical elements of the lighting unit.In addition, the colored light elements can be used to adjust the color temperature during white light imaging. In some embodiments, the second group comprises a single luminaire and / or a single type of luminaire. For example, a white light luminaire, a red luminaire, and an IR-emitting luminaire may be provided, with particular reference to the values ​​above regarding possible spectral ranges. The first group may then, for example, comprise the red and the IR-emitting luminaire. The second group may comprise the IR-emitting luminaire, in particular as the only luminaire or as the only type of luminaire. A favorable arrangement of lighting elements is particularly possible if the lighting unit comprises at least one crossed beam splitter by means of which light from opposite input sides can be deflected to an output side, with at least one of the lighting elements being arranged on each of the opposite input sides of the crossed beam splitter. In some embodiments, two or more crossed beam splitters can be provided, arranged optically one behind the other. The at least one crossed beam splitter can comprise two beam splitter elements whose transmittance is adapted to the respective associated lighting element. The beam splitter elements each comprise, in particular, a notch filter, so that they reflect in a narrow spectral band but transmit otherwise.The spectral position and / or width of the corresponding notch can be adapted to the spectral range of the respective associated luminaire element, so that its light is deflected, but light from other luminaire elements is at least largely transmitted. In some embodiments, the luminaires can comprise at least four narrowband emitting single-color luminaires, each with different spectral ranges, and at least one broadband emitting white light luminaire. Reference is also made to the above descriptions of the colored luminaires. A wide range of functions combined with a compact design and the exploitation of synergistic effects when using light elements can be achieved, in particular, if the illumination unit can be operated in at least one hyperspectral mode in which several light elements are activated whose emission spectra together cover at least a spectral range from 450 nm to 850 nm, and in which the illumination unit provides illumination light for hyperspectral imaging. This can include, in particular, all of the light elements. It is understood that, particularly when using laser diodes, suitable polarization filters can be used for the optical filters mentioned herein. Furthermore, particularly when using laser diodes, at least one crossed beam splitter can be used, the beam splitter elements of which are equipped with polarization filters. Selective transmission can then be achieved by combining different polarizations. The invention also relates to program code which is configured to effect the execution of a method according to the invention when it is executed in a processor. Furthermore, the invention relates to a program code comprising a computer-readable medium on which program code according to the invention is stored. The devices and systems and methods according to the invention are not intended to be limited to the application and embodiment described above. In particular, they may, to achieve a functionality described herein, have a different number of individual elements, components, units, and process steps than specified herein. Furthermore, values ​​within the specified limits of the value ranges stated in this disclosure are also considered disclosed and freely usable. It is specifically pointed out that all features and properties described in relation to a device, as well as methods, are transferable analogously to processes and usable within the scope of the invention and are considered to be jointly disclosed. The same applies in reverse. This means that structural, i.e., device-related, features mentioned in relation to processes can also be considered, claimed, and likewise included in the disclosure within the scope of the device claims. The present invention is described below by way of example with reference to the accompanying figures. The drawing, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and use them meaningfully in combination within the scope of the claims. If more than one instance of a particular object exists, only one of them may be identified with a reference symbol in the figures and description. The description of this instance can then be applied to the other instances of the object. If objects are named using numerical terms, such as first, second, third object, etc., these serve to identify and / or classify objects. Thus, for example, a first object and a third object, but not a second object, may be included. However, numerical terms could also indicate a number and / or sequence of objects. Figure 1 shows a schematic representation of an imaging device with a lighting device; Figure 2 shows a schematic representation of the lighting device; Figure 3 shows schematic transmission curves of beam splitter elements of the lighting device; Figure 4 shows a schematic representation of the imaging device; Figure 5 shows a schematic representation of a further embodiment of the imaging device; Figure 6 shows a schematic representation of yet another embodiment of the imaging device; Figure 7 shows a schematic perspective view of another embodiment of the imaging device; Figure 8 shows a schematic flowchart of a method for generating illumination light for an imaging device by means of a lighting device; Figure 9 shows a schematic flowchart of a method for operating an imaging device; Figure 1Fig. 10 a schematic flowchart of a method for operating an imaging device; Fig. 11 a schematic representation of a medical imaging device; Fig. 12 a schematic representation of an imaging situation; Fig. 13 a schematic representation of a first calibration image; Fig. 14 a schematic representation of a second calibration image; Fig. 15 a schematic representation of a first depth map; Fig. 16 a schematic representation of a second depth map; Fig. 17 a schematic representation of an object image; Fig. 18 a schematic representation of a corrected object image; Fig. 19 a schematic representation of another corrected object image; Fig. 20 a schematic representation of several calibration images and associated depth maps; Fig. 21 a schematic flowchart of a method for medical imaging; and Fig. 22 a schematic representation of a computer program product. Fig. 1 shows a schematic representation of an imaging device 10. In the example shown, the imaging device 10 is an endoscopic imaging device, specifically an endoscope. Alternatively, the imaging device 10 could be an exoscopic, microscopic, or macroscopic imaging device. The imaging device 10 is shown as an example of a medical imaging device. The imaging device 10 is intended, for example, for examining a cavity. The imaging device 10 includes a medical imaging device 14. In the case shown, this is an endoscope. Furthermore, the imaging device 10 comprises an illumination device 12 with an optical interface 16 and an illumination unit 18. The imaging device 14 can be optically connected to the optical interface 16. The optical interface 16 can be part of an opto-mechanical interface that is optionally detachable and connectable. The illumination device 14 can optionally be detached from the illumination device 12. The illumination unit 18 is configured to supply illumination light to the optical interface 16. During imaging using the imaging device 14, the illumination unit 18 can accordingly provide the required illumination light, which is directed to the illumination device 14 and from there projected onto an object to be imaged, such as a site. In the illustrated case, the imaging device 10 further comprises a display unit on which images based on image data acquired by means of the imaging device 14 can be displayed. These images can be video images, still images, superimpositions of different images, partial images, image sequences, etc. The imaging device 10 is multimodal. For example, the imaging device can be operated in three basic modes: a multispectral mode, a fluorescence mode, and a white light mode. Furthermore, the imaging device 10 can be operated in a hyperspectral mode in addition to or as an alternative to the multispectral mode. The illumination device 12 is multimodal. It can be operated in different illumination modes, in which it provides light for different imaging modes. In this case, the illumination device 12 can be operated in three basic modes: a multispectral mode, a fluorescence mode, and a white light mode. Similarly, the imaging device 14 can be operated in different operating modes, specifically at least a multispectral mode, a fluorescence mode, and a white light mode. In the corresponding operating mode of the imaging device 10, the modes of the illumination device 12 are coordinated. Fig. 2 shows a schematic representation of the lighting device 12. The lighting unit 18 comprises several independently activatable luminaires 20, 22, 24, 26, 28. These are configured to emit light according to different emission spectra in order to provide illumination, i.e., the respective emission spectrum differs from luminaire to luminaire. For example, the light elements 20, 22, 24, 26, and 28 are designed as LEDs. Specifically, the first light element 20 is a red LED, the second light element 22 is a far-red LED, the third light element 24 is a blue LED, and the fourth light element 26 is a near-infrared LED. The colored light elements 20, 22, 24, and 26 each emit in a narrowband pattern, for example, with emission peaks at wavelengths approximately 660 nm (first light element 20), 770 nm (second light element 22), 460 nm (third light element 24), and 940 nm (fourth light element 26). Furthermore, a fifth luminaire element 28 is provided, which in this case is a white light luminaire element, such as a white light LED. The fifth luminaire element 28 emits, for example, in a spectral range of approximately 400 to 700 nm. In other embodiments, laser diodes can also be used, in particular as colored luminaire elements. Depending on the lighting mode, some of the lighting elements 20, 22, 24, 26, 28 are activated at least temporarily, while other lighting elements 20, 22, 24, 26, 28 may not be used in the lighting mode in question. In this case, a first group comprises the first light element 20 and the fourth light element 26. The first group may additionally include light element 22 and / or light element 24. The first group is used for multispectral imaging, with the contained light elements 20, 26, and, if applicable, 22 and 24 each serving as a support point. In multispectral mode, for example, the first light element 20 is used for illumination and an image is acquired. Subsequently, the fourth light element 26 is used for illumination and an image is acquired. The images are each based on remission, i.e., the light backscattered by the object being imaged is considered. The two different support points allow spectral information about the object being imaged to be obtained. For example, this allows for the assessment of specific tissue types, perfusion status, tissue properties, or the like. Furthermore, a second group comprises the first light source 20, the second light source 22, and the third light source 24. This second group is used for illumination in fluorescence imaging. For example, objects stained with appropriately selected dyes can be viewed. Different dyes can also be introduced into different tissue types or similar materials and viewed simultaneously. By selectively activating a specific dye, it is stimulated to fluoresce. The resulting fluorescent light is then imaged. The first light source 20, for example, is suitable for activating the dye Cyanine 5.5 (Cy 5.5). The second light source 22 is suitable for activating the dye Indocyanine Green (ICG). The third light source 24 is suitable for activating the dye Fluorescein. Furthermore, a third group comprises the fifth luminaire 28. In the present embodiment, the third group also includes the first luminaire 20 and the third luminaire 24. The third group serves to provide illumination for white light imaging. For this purpose, white light from the fifth luminaire 28 can be mixed with light from certain colored luminaires, thereby compensating for spectral losses and / or allowing a specific color temperature to be set. It is evident that some of the lighting elements 20, 22, 24, 26, 28 are assigned to several groups, for example the first lighting element 20 to all three groups as well as the third lighting element 24 and possibly also the second lighting element 22 to the second and the third group. Alternatively or additionally, it can also be provided that some or all of the illuminating elements 20, 22, 24, 26, 28 are used in a hyperspectral mode. This generates a broad excitation spectrum. In combination with a suitable hyperspectral detector, spectral information regarding the object to be imaged can then be acquired across the entire visible and near-infrared spectrum. The imaging device 14 can, for this purpose, include a pushbroom arrangement as a hyperspectral detector. In other embodiments, a whiskbroom arrangement, a staring arrangement, and / or a snapshot arrangement is used. The imaging device 14 can be a hyperspectral imaging device. Regarding different methods of hyperspectral imaging and the components required for them, reference is made to the article "Review of spectral imaging technology in biomedical engineering: achievements and challenges" by Quingli Li et al.References were made to the article “Medical hyperspectral imaging: a review” by Guolan Lu and Baowei Fei, published in Journal of Biomedical Optics 19(1), 010901, January 2014, published in Journal of Biomedical Optics 18(10), 100901, October 2013, and to the article “Medical hyperspectral imaging: a review” by Guolan Lu and Baowei Fei, published in Journal of Biomedical Optics 19(1), 010901, January 2014. The lighting unit 18 comprises two crossed beam splitters 30, 32. Each of these comprises an output side 42, 44, an input side 37, 41 opposite the output side 42, 44, and two opposing input sides 34, 36, 38, 40. All input sides 34, 36, 37, 38, 40, 41 direct incident light to the corresponding output side 42, 44. The output side 42 of a first crossed beam splitter 30 faces an input side 41 of the second crossed beam splitter 32. The output side 44 of the second crossed beam splitter 32 faces the optical interface 16. The two crossed beam splitters 30, 32 are preferably arranged coaxially with each other and / or with the optical interface. The lighting unit 18 can comprise suitable optical elements such as lenses and / or mirrors (not shown). By way of example, several lenses 78, 80, 82, 84, 86, 88 are shown in Fig. 2. One lens 78 is associated with the optical interface 16 and couples light coming from the output side 44 of the second crossed beam splitter 32 into the optical interface 16. Furthermore, each of the lighting elements 20, 22, 24, 26, 28 can be associated with a lens 80, 82, 84, 86, 88. A particularly high degree of compactness can be achieved, in particular, if the lighting elements 20, 22, 24, 26, 28 are each arranged without an intermediate mirror at the input sides 34, 36, 37, 38, 40 of the at least one crossed beam splitter 30, 32. The lighting elements 20, 22, 24, 26, 28 can then be moved very close to at least one crossed beam splitter 30, 32. The crossed beam splitters 30, 32 each comprise two beam splitter elements 90, 92, 94, 96. These can, in principle, be partially transparent, so that light from all input sides 34, 36, 37, 38, 40, 41 is deflected to the respective output side 42, 44. In the present embodiment, the beam splitter elements 90, 92, 94, 96 are selectively transparent. This is further illustrated with reference to Fig. 3. The beam splitter elements 90, 92, 94, 96 can be filters that reflect only in a defined area, but otherwise exhibit high transmission. In Fig. 3, transmission curves 98, 100, 102, 104 of the beam splitter elements 90, 92, 94, 96 of the two crossed beam splitters 30, 32 are shown. Each of the colored light elements 20, 22, 24, 26 or each of the opposite entrance sides 34, 36, 38, 40 is assigned one of the beam splitter elements 90, 92, 94, 96.The beam splitter elements 90, 92, 94, 96 are selected such that they reflect in the wavelength range in which the associated luminaire element 20, 22, 24, 26 emits, while transmitting largely in the surrounding range. For this purpose, notched filters can be used in the mid-wavelength range, exhibiting, for example, the transmission spectra shown in 100 and 102. At the spectral edges, high-pass or low-pass filters can be used instead of notched filters; see transmission spectra 98 and 104. Due to the specific transmission spectra 98, 100, 102, 104 of the crossed beam splitters 30, 32, the light from the fifth luminaire 28 is spectrally clipped. It can therefore be advantageous, as already mentioned, to selectively supplement the light blocked by the beam splitters 30, 32 using the luminaires 20 and 24, and optionally also 22 and / or 26. This allows supplementation specifically in those spectral ranges where the beam splitters 30, 32 absorb and / or reflect light from the fifth luminaire 28, but in any case do not transmit it to the optical interface 16. The supplementary luminaires 20, 24, and optionally 22 are preferably operated at reduced power or with adjusted power. The aim here can be to at least largely restore the original spectrum of the fifth luminaire 28. In some embodiments, the fifth luminaire element 28 can alternatively be a green luminaire element, or more generally, a colored luminaire element that emits primarily in the spectral range transmitted by the at least one beam splitter 30, 32. For example, in such embodiments, the fifth luminaire element 26 can be an LED with an emission peak at approximately 530 nm. A green laser diode is also suitable for this purpose. It can be provided that color mixing takes place in white light mode, and in particular, that no individual white light source such as a white light LED is used, but rather that white light from separate luminaire elements is selectively mixed. It goes without saying that, with suitable dyes, such a green luminescent element could also be used in fluorescence mode. Alternatively or additionally, it could be used in multispectral mode. The lighting unit 18 defines a common optical path 54 into which emitted light from the luminaire elements 20, 22, 24, 26, 28 can be coupled. The common optical path 54 extends from the output side 44 of the second crossed beam splitter 32 to the optical interface. The common optical path 54 is arranged coaxially with the fifth luminaire element 26. In the illustrated embodiment, the luminaire elements 20, 26 of the first group are arranged such that the light emitted by the luminaire elements 20, 26 travels a path of at least substantially the same length from the respective luminaire element 20, 26 to the optical interface 16. The luminaire elements 20, 26 of the first group each have a light-emitting surface 56, 58. The light-emitting surfaces 56, 62 are arranged equidistant from the common optical path 54. This is achieved in the present case by arranging the two luminaire elements 20, 26 at the same distance from their associated beam splitter 32 (in this example, the second beam splitter 32), specifically from its opposite input sides 38, 40. The light is coupled into the common optical path 54 from the crossed beam splitter 32. The beam splitters 30, 32 are arranged in such a way that light-emitting surfaces 56, 58, 60, 62, 64 of the luminaire elements 20, 22, 24, 26, 28 are each arranged equidistantly with respect to their associated crossed beam splitter 30, 32. By using crossed beam splitters 30, 32 and illuminating elements 20, 22, 24, 26, 28 that can be used together for different modes, the illumination unit 18 or the illumination device 12 exhibits a high degree of compactness. Furthermore, the equidistant arrangement ensures that no spectral shifts occur when the imaging device 14 or its light guide is rotated relative to the optical interface 16. It is understood that a different number of illuminating elements 20, 22, 24, 26, 28 and / or a different number of crossed beam splitters 30, 32 can be used. The use of crossed beam splitters 30, 32 has proven to be particularly advantageous. In other embodiments, however, other types of beam splitters and / or other optical elements can be used to couple light from the illuminating elements 20, 22, 24, 26, 28 into the optical interface 16. Fig. 4 shows a schematic representation of the imaging device 10. The imaging device 14 is optically coupled to the optical interface 16, for example via a light guide 106 such as at least one optical fiber. The imaging device 10 has a control unit 66, which is configured to automatically coordinate the operating state of the imaging device 14 and the illumination mode of the illumination unit 18. In this case, a user can specify the operating mode of the imaging device 14 through a user action. The control unit 66 then sets the corresponding illumination mode of the illumination unit 18. Alternatively or additionally, the user can set a specific illumination mode of the illumination unit 18 through a user action. The control unit 66 can then set a corresponding operating mode of the imaging device 14. The illumination device 12 and / or the imaging device 10, for example, has a user interface through which the user can enter corresponding commands. The imaging device 14 comprises a camera unit 68 and a distal shaft 76. The distal shaft 76 is optically coupled to the camera unit 68. The camera unit 68 may have a connection for the distal shaft 76, which can be selectively detachable and detachable. The distal shaft 76 may also be permanently optically and / or mechanically coupled to the camera unit 68. The camera unit 68 is arranged proximally to the shaft 76. The camera unit 68 comprises imaging sensors 108, in this case, for example, a white light sensor 110 and a near-infrared sensor 112. The imaging sensors 108 can generally comprise one or more spatially resolved light sensors / image sensors, for example, at least one CMOS sensor and / or at least one CCD sensor.The shaft 76 comprises optical elements (not shown) by means of which light can be guided to the camera unit 68 in order to optically capture the object to be imaged. Furthermore, the shaft 76 comprises at least one light path 114, for example defined by a light guide such as an optical fiber, which leads to a distal section 116 of the shaft 76 and by means of which the illumination light originating from the optical interface 16 of the illumination device 12 can be coupled out to the object to be imaged. The camera unit 68 has different operating states, specifically, for example, at least one multispectral operating state and one fluorescence operating state, and in the present embodiment, additionally a white light operating state and, optionally, a hyperspectral operating state. The controller 66 automatically adapts the illumination mode of the illumination unit 18 to the current operating state of the camera unit 68. In doing so, the controller 66 can adjust settings on the image acquisition behavior of the camera unit 68. For example, the controller 66 can adjust the exposure time, sensitivity / gain, and / or other operating parameters of the camera unit 68, or more specifically, its image acquisition sensor 108 and, optionally, its optics, thereby defining different operating states of the imaging device 14. In this case, the controller 66 performs camera-synchronous triggering of the illumination unit 18. The imaging device 14 comprises a filter unit 46 with optical filters 48, 50, and 52. Three optical filters are shown as examples, but it is understood that a different number can be used. The filter unit 46 is switchable between a multispectral mode and a fluorescence mode. Furthermore, the filter unit 46 can also be switched to a white light mode and / or a hyperspectral mode. The optical filters 48, 50, and 52 can be selectively inserted into an observation beam path 70 of the camera unit 68, thereby defining different observation modes. These define the operating states of the camera unit 68. Several optical filters 48, 50, 52 can be assigned to a basic imaging mode. Particularly for fluorescence imaging, a different suitable optical filter can be used depending on the illuminant element 20, 22, 24, 26, 28 used for excitation. For example, in this case, the first illuminant element 20 (red) is combined with an optical filter that transmits wavelengths greater than 730 nm but blocks shorter wavelengths. This ensures, in particular, that only fluorescence light and not the excitation light itself is detected. For example, this optical filter can absorb at least in the range of 600 nm to 730 nm. Furthermore, in this case, for example, the second illuminant element 22 (dark red) is combined with a filter that absorbs in the range of 700 to 850 nm or transmits only significantly above 850 nm. The user can select a specific filter 48, 50, or 52, thereby directly choosing a corresponding observation mode or operating state of the camera unit 68. For this purpose, the camera unit 68 has a filter sensor 72 that can automatically detect an optical filter currently inserted into the observation beam path 70. The user can thus manually insert a selected filter 48, 50, or 52 into the observation beam path 70. In the example shown, the optical filters 48, 50, or 52 are mounted on a filter carrier 118. This carrier can be moved to different positions, allowing the user to select one of the optical filters 48, 50, or 52 at a time. The filter sensor 72 then detects the currently selected optical filter 48, 50, or 52.The control unit can then determine the current operating state of the camera unit 68, and thus of the imaging device 14, based on a sensor signal from the filter sensor 72, and automatically adjust the illumination mode of the illumination unit 18 accordingly. The user can therefore switch the entire imaging device 10 to the desired mode with a simple action, such as manually selecting an optical filter 48, 50, or 52. In principle, a user can combine different filters with different illumination modes and thereby create different types of contrast. In the illustrated case, the imaging device 14, and in particular the shaft 76, comprises a broadband transmitting optic 77 that can be used uniformly in the different illumination modes. The broadband optic 77 is designed for a spectral range of at least 400 nm to 1000 nm. It can be used uniformly for different illumination and / or observation spectral ranges. In some embodiments, the imaging device 14 can be configured as a stereo endoscope comprising a stereoscopic eyepiece with two sides. Different optical filters can be placed independently in front of these sides, allowing different contrast images to be superimposed. In the following, the same reference numerals as above are used for identical or similar components in the context of further embodiments and modifications. For their description, reference is generally made to the explanations above, whereas the following primarily focuses on the differences between the embodiments. Furthermore, for the sake of clarity, some reference numerals have been omitted in the following figures. Fig. 5 shows a schematic representation of another embodiment of the imaging device 10. The imaging device 10 comprises a lighting device 12 with an optical interface 16 and a lighting unit 18, as well as an imaging device 14 connected to the optical interface 16. The imaging device 14 comprises a camera unit 68 with an automated filter unit 210. The automated filter unit 210 comprises several optical filters 48, 50, 52, which can be automatically inserted into an observation beam path 70 of the camera unit 68 according to a user-defined observation mode. The automated filter unit 210 comprises a filter drive 212, which is configured to automatically move the optical filters 48, 50, 52 into or out of the observation beam path 70. The optical filters 48, 50, 52 can be mounted on a filter carrier 118, which is connected to the filter drive 212. The filter drive 212 can be configured to move the filter carrier 118, for example, to shift and / or rotate and / or pivot it. The imaging device 14 has a user interface 214 by means of which the user can set a desired observation mode. For example, a desired position of the filter holder 118 can be specified by means of the user interface 214. The imaging device 14 also includes a control unit 66. The control unit 66 is coupled to the filter drive 212 and the user interface 214. The control unit 66 is specifically configured to process a user-defined observation mode and, according to this user-defined setting, to control both the filter unit 210 and the illumination unit 18. Thus, the control unit 66 can, according to a user-selected observation mode, set an operating state of the imaging device 14 and a corresponding illumination mode of the illumination unit 18. Fig. 6 shows a schematic representation of yet another embodiment of the imaging device 10. The imaging device 10 comprises a lighting device 12 with an optical interface 16 and a lighting unit 18, as well as an imaging device 14 connected to the optical interface 16. The imaging device 14 includes a proximal base unit 310. The proximal base unit 310 is connected to the optical interface 16 of the lighting device 12. Illumination light generated by the lighting device 12 can thus be supplied to the proximal base unit 310. The imaging device 14 further comprises a control unit 66, which in some embodiments may be integrated into the base unit 310. Various interchangeable shafts 312, 314 can be optically and electronically coupled to the proximal base unit 310. The base unit 310 has an interface 316 for coupling different interchangeable shafts 312, 314. This interface 316 supplies the illumination light from the illumination device 12 to a coupled interchangeable shaft 312, 314. Furthermore, the interface 316 is configured to supply an coupled interchangeable shaft 312, 314 with electricity and / or to connect it electronically to the control unit 66 of the imaging device 14. The interchangeable shafts 312 and 314 each have an integrated camera 318 and 320, respectively, as well as integrated optical filters 322 and 324. The integrated cameras 318 and 320 are designed as tip cameras. In this case, the integrated camera 318 of a first interchangeable shaft 312 is configured for multispectral imaging. Furthermore, the integrated camera 310 of a second interchangeable shaft 314 is configured for fluorescence imaging. The optional optical filters 322 and 324 can be adapted accordingly. In other embodiments, interchangeable shafts can also be used that include only optical filters but no integrated camera. These can then be coupled to a proximal camera unit. In some cases, the proximal camera unit can then be designed without an additional filter unit. The selection of a specific optical filter or a specific observation mode can be achieved by choosing a suitably equipped interchangeable shaft. The control unit 66 is configured to detect an attached interchangeable shaft 312, 314. This can be done via software, mechanically, and / or by sensor detection. Depending on the detected interchangeable shaft 312, 314, the control unit 66 can then determine the operating state or observation mode in which the imaging device 14 should be operated. The control unit 66 is also configured to set an illumination mode for the illumination unit 18. Thus, the control unit 66 is configured to set an illumination mode for the illumination unit 18 depending on the observation mode defined by a currently attached interchangeable shaft 312, 314. The interchangeable shafts 312, 314 and the imaging device 10 are, in this case, part of a medical imaging system 316. The medical imaging system 316 allows a user to select a suitable interchangeable shaft 312, 314, connect it to the base unit 310, and thereby define a mode for the entire imaging device 10. By simply changing the interchangeable shaft 312, 314, the illumination device 18 is automatically adapted to the image acquisition mode to be performed. Fig. 7 shows a schematic perspective view of another embodiment of an imaging device 10'. The reference numerals of this embodiment are enclosed in single quotes for differentiation. In this embodiment, the imaging device 10' is designed as an exoscopic imaging device. It comprises a lighting device 12' and an imaging unit 14'. Their basic operation corresponds to that described above; however, in this embodiment, the imaging unit 14' is designed as an exoscope. Aspects of the above description can also be summarized or described as follows. Fig. 8 shows a schematic flowchart of a method for generating illumination for an imaging device 14 by means of an illumination device 12. The sequence of the method also follows from the above explanations. The illumination device 12 comprises an optical interface 16 for the optical connection of an imaging device 14 and an illumination unit 18, which is configured to supply illumination to the optical interface 16. The illumination unit 18 comprises several independently selectable illuminating elements 20, 22, 24, 26, 28, which are configured to emit light according to different emission spectra in order to supply the illumination. The method comprises step S11 of at least temporarily activating a first group of the light-emitting elements 20, 22, 24, 26, 28 to provide illumination for multispectral imaging. Furthermore, the method comprises step S12 of at least temporarily activating a second group of the light-emitting elements 20, 22, 24, 26, 28 to provide illumination for fluorescence imaging. One of the light-emitting elements 20, 22, 24, 26, 28 is activated at least temporarily both during the at least temporary activation of the first group of light-emitting elements 20, 22, 24, 26, 28 and during the at least temporary activation of the second group of light-emitting elements 20, 22, 24, 26, 28. Fig. 9 shows a schematic flowchart of a method for operating an imaging device 10. The sequence of the method also follows from the above explanations. In step S21, an imaging device 10 is provided with an imaging unit 14. In step S22, illumination light is supplied to the imaging unit 14. The supply of the illumination light to the imaging unit 14 is carried out according to a method as described with reference to Fig. 8. Fig. 10 shows a schematic flowchart of a method for operating an imaging device 10. The sequence of the method also follows from the above descriptions. The method comprises a step S31 of providing a lighting device 12 to supply illumination light to an imaging device 14. The imaging device 14 comprises an optical interface 16 for optical connection and a lighting unit 18 configured to supply illumination light to the optical interface 16. The lighting unit 18 is multimodal and can be operated in several different illumination modes. Furthermore, the method comprises a step S32 of providing an imaging device 14 that can be connected to the optical interface 16 of the lighting device 12.Furthermore, the procedure includes step S33 of automated tuning of an operating state of the imaging device 14 and an illumination mode of the illumination unit 18. The following describes an aspect concerning the correction of object images based on depth information obtainable from calibration images. Fig. 11 shows a schematic representation of a medical imaging device 410 according to this aspect. The medical imaging device 410 can, in principle, be constructed and / or designed like the imaging device 10 described above or like the imaging device 10' above. In particular, reference is made to the above description regarding the functionality of the components and details of the design of the imaging device 410. To explain this aspect, it is useful to describe the technical situation with reference to Fig. 11, which is to be understood purely schematically, and the other figures. In this specific example, the imaging device 410 is an endoscope device, but it could also be an exoscope device and / or a microscope device. The imaging device 410 comprises an illumination unit 412 with at least one light source 414. The illumination unit 412 can, for example, be configured as described above with reference to the illumination device 12. For the following description, it is assumed that the illumination unit 412 is configured as described above. However, this is purely exemplary. In principle, the illumination unit 412 is configured to provide illumination 416, by means of which an object 418 to be imaged can be illuminated. The imaging device 410 further comprises an image acquisition unit 420 with a lens 442 (shown only schematically) and with suitable image acquisition sensors 444. The image acquisition unit 420 is configured to detect object light 428 originating from the object 418. This can be reflected illumination light 416 and / or light emitted by the object 418, for example, fluorescent light. The image acquisition sensor 444 is configured to be able to capture images in both the visible and near-infrared ranges. For example, the image acquisition sensor 444 is sensitive at least in a range between 450 nm and 950 nm, and in some embodiments in a range between 400 nm and 1000 nm. It is assumed that the image acquisition unit 420, in combination with the illumination unit 412, can be operated in at least a white light mode and a fluorescence mode. In white light mode, broadband illumination light 416 is shone on, for example, by means of a white light illuminator, at least in the range of 480 nm to 750 nm. The illumination light 416 reflected by the object 418 is then observed. In fluorescence mode, on the other hand, illumination light 416 with a specific wavelength is shone on, which is suitable for exciting a fluorescent dye. Furthermore, light emitted by the fluorescent dye, and specifically by excited dye molecules, is detected. In the present case, the image acquisition unit 420 is configured for capturing stereo images. It can include suitable stereo optics and / or suitable stereo image acquisition sensors 444 for this purpose.The object 418 to be imaged is, for example, an anatomical structure, such as one located in a patient's cavity. The object 418 comprises a region 448 stained with a fluorescent dye. Indocyanine green, for example, is used as the dye. Furthermore, the object 418 comprises tissue 450 covering the stained region 448. For example, the stained region 448 is a blood vessel, and the tissue 450 is adipose tissue covering the vessel; this is purely illustrative. Fig. 12 shows a schematic representation of the imaging situation. A surface of the tissue 450 is located at a distance d0 from the imaging device 410, specifically from the lens 442 of the image acquisition unit 420. The stained region 448 is located within the tissue 450 and is positioned at a distance d1 from its surface. In the following, it is assumed that illumination light is extracted in the area of ​​lens 442. This has several implications for imaging. If illumination light 416 is used, which has a shallow penetration depth into the object 418, it is essentially reflected and / or scattered by the surface of the tissue 450. The intensity of the reflected light then depends on the distance d0 according to an inverse square law, approximately the well-known inverse square law. It is assumed here that there is air in the region of distance d0, located in the cavity within which the imaging is performed. Since we work with illumination light 416, which can penetrate the tissue 450 and is suitable, for example, to reach the stained area 448 and excite dye molecules to fluorescence there, two effects must be taken into account. First, the incident intensity is also subject to an inverse square law. Furthermore, the illumination light 416 is attenuated within the tissue 450 due to interaction with the tissue 450. The intensity actually available for fluorescence excitation is therefore lower than the intensity emitted by the illumination unit 412. Object light 428 emitted from the stained area 448 is also subject to a certain attenuation in the tissue 450. Furthermore, the intensity of the emitted object light 428 also follows an inverse square law, whereby the total distance d0 + d1 must be taken into account. The fluorescence intensity detectable by the image acquisition unit 420 is therefore lower than the fluorescence intensity emitted by the stained area 448. As mentioned above, a detectable intensity Idetected is thus obtained as follows: where Idetected denotes the detected light intensity, I(λ0) the intensity of the incident light with wavelength λ0, d0 a distance between the lens and the surface of the object to be imaged, d1 a distance between the surface of the object to be imaged and the area stained with fluorescent dye in the object to be imaged, α an exponent that defines the inverse square law and can, for example, be chosen as 2 to calculate according to the inverse square law, µ(λ0) a damping factor for the attenuation of light of wavelength λ0 as it passes through the object to be imaged, µ(λ1) a damping factor for the attenuation of light of wavelength λ1 as it passes through the object to be imaged. To account for these effects and correct the images accordingly, the imaging device 410 includes an image correction unit 426. Its operation is described below with reference to Figs. 13, 14, 15, 16, 17 to 18. First, in the present example, two calibration images 422 and 423 are acquired. These can each be stereo images. A first calibration image 422 is obtained, for example, by illumination with white light and detection of reflected light. Since white light has a low penetration depth into object 418, the first calibration image 422 essentially shows the surface of object 418. Light penetrating object 418 and reflected from deeper layers can be neglected because the reflected intensity is significantly lower than the intensity reflected from the surface of object 418, due to both the attenuation of the incident light and the attenuation of the reflected light in the tissue. Furthermore, a second calibration image 423 is recorded, for which light with a wavelength at which the dye used can be excited is shone. The second calibration image 423 is recorded through a suitable observation filter and / or in a suitable wavelength range in order to detect fluorescence light. This originates from the stained area 448. In this example, the image correction unit 426 is configured to determine a depth map 432, 434 from each of the two calibration images 422, 423. A stereo reconstruction algorithm is used for this purpose. The depth maps 432, 434 thus contain information regarding an observed surface of the respective object; that is, in the case of depth map 432, which is determined from the first calibration image, a surface of the object 418 to be observed, and in the case of depth map 434, which is determined from the second calibration image, a surface of the stained area 448 located in the tissue 450. From this, the distances d0 and d1 shown schematically in Fig. 12 can be determined. It is understood that such distances can be determined point by point. The depth maps 432 and 434 contain, in particular, point-by-point depth information, so that a correction can be carried out depending on the pixel. It should be noted that, due to scattering effects, the distance d1 from the second calibration image 423 may be determined taking a scattering factor into account. Because of these scattering effects, the stereo reconstruction may yield a depth for the colored area 448 of d0 + x·d1, where x is an empirically determined factor between 0 and 1. The factor x can, for example, be empirically determined through suitable calibration and then taken into account by the image correction unit 426 to determine the actual distance value d1. In this case, the correction includes taking the above equation into account, i.e., both distances and attenuations are considered. It is then possible to determine the position of the stained area 448 in the tissue 450 by using the two depth maps 432 and 434. Subsequently, an object image 424 of object 418 can be acquired. This image can be based on several individual images and, for example, be a superimposed representation showing a white light image and a fluorescence image. Due to the described distance and attenuation effects, the colored area 448 in object image 424 may appear significantly paler than its actual fluorescence emission would suggest. The image correction unit 426 is therefore configured to generate a corrected object image 430 according to the correction parameters. In the corrected object image 430, the intensity of the fluorescence light originating from the colored area 448 is, for example, increased according to the correction parameters.The corrected object image 430 thus comprises at least one image area 436 which, according to the correction, is enhanced and / or attenuated relative to another image area 437 with respect to at least one parameter, such as hue, brightness, and / or saturation. The colored area 448 is then clearly recognizable to a user despite its position within the tissue 450. The corrected object image 430 can be output to a user via a schematically represented display 446 of the imaging device 410. Fig. 19 shows another example of a corrected object image 430. To additionally provide the user with information about the depth of the stained area 448 within the tissue 450, the stained area 448 is displayed in this case with a brightness / intensity corrected as described above, but in false colors according to a color scale 452. The color scale 452 contains information regarding the depth of the stained area 448 within the object 418. The color scale 452 can be displayed to the user so that they can directly determine a specific depth from the displayed coloration of the stained area 448. Referring to the above descriptions of a multimodal illumination device 12, it is generally understood that, depending on the dye used, different wavelengths or wavelength mixtures can be used as illumination light 416 to acquire calibration images. Furthermore, illumination can also be performed at a wavelength at which dye emission is expected in order to analyze the absorption / attenuation properties of the tissue under consideration. For example, if indocyanine green is used as the dye, a calibration image can be acquired by illuminating the tissue with a wavelength of approximately 940 nm (see fourth illumination element 26). In this case, instead of fluorescent light as described above, reflected light is detected.A depth map determined in this way then provides information about the penetration depth and the absorption behavior of the tissue under consideration in the spectral range in which the dye is emitted during subsequent object imaging. If, for example, Cy 5.5 is used as the dye, a calibration image can be taken to determine the absorption in the tissue that is relevant for its fluorescence, in which dark red light is irradiated, for example with a wavelength of 770 nm (see second luminescent element 22). Alternatively or additionally, a calibration image that allows conclusions to be drawn about the surface of object 418 can also be obtained using monochromatic and / or narrowband illumination. Multiple calibration images can also be taken in different spectral ranges to create spectrally dependent depth maps. Figure 20 illustrates another application. Here, the imaging device 410 is configured for multispectral and / or hyperspectral imaging. Such imaging can be used, for example, to measure specific tissue parameters, such as perfusion. For this purpose, the intensity of certain pixels associated with specific tissue types, such as blood vessels, is measured at suitable wavelengths. Perfusion measurements can be performed, for example, by comparing intensities at 680 nm and 930 nm. However, if the effects mentioned above, which influence the detected intensity, are not taken into account, distorted parameters may be obtained. The imaging device 410 can therefore be configured to acquire several calibration images 422-1, 422-2, 422-3, 422-4 for different spectral ranges. These can be obtained, for example, by using one of the illuminating elements 20, 22, 24, 26 described above as an illumination light source to acquire a corresponding calibration image. Preferably, stereo images are again acquired. Depth maps 432-1, 432-2, 422-3, and 422-4 can be calculated from calibration images 422-1, 422-2, 422-3, and 422-4 using stereo reconstruction. These depth maps are assigned to specific spectral ranges. Depth maps 432-1, 432-2, 432-3, and 432-4 contain information regarding the average penetration depth of the light in question. Additionally, a white light image or an image using short-wavelength illumination, such as blue light, can be acquired as a further calibration image. From this additional calibration image, another depth map can be determined in the manner described above. Due to the shallow penetration depth of the light, this map corresponds, at least substantially, to the surface of the object being imaged. If the depth maps 432-1, 432-2, 432-3, 432-4 are each subtracted from this further depth map, the mean penetration depth in the respective spectral range can be estimated.Accordingly, absorption losses in the tissue under consideration can then be taken into account. Additionally or alternatively, as described above, a distance law can be taken into account to consider intensity losses due to a distance from the lighting unit 412. Fig. 21 shows a schematic flowchart of a medical imaging procedure. The sequence of the procedure is also evident from the above explanations. The procedure is carried out, for example, using the imaging device 410. Step S41 comprises providing illumination light 416 to illuminate an object 418 to be imaged. Step S42 comprises acquiring at least one calibration image 422, 423 of the object 418 to be imaged. Step S43 comprises acquiring at least one object image 424 of the object 418 to be imaged. Step S44 comprises determining depth information from the calibration image 422, 423. Step S45 comprises determining a correction for the object image 424, wherein the correction takes into account a positional dependence of the light intensity of the illumination light 416 and / or a distance dependence of the light intensity of the object light 428 according to the depth information.Step S46 includes generating a corrected object image 430 according to the correction. Fig. 22 shows a schematic representation of a computer program product 438 with a computer-readable medium 440. The computer-readable medium contains program code which, when executed in a processor, is configured to perform one and / or all of the described procedures. Reference symbol list 10 Imaging device 12 Illumination device 14 Imaging device 16 Optical interface 18 Illumination unit 20 Light element 22 Light element 24 Light element 26 Light element 28 Light element 30 Beam splitter 32 Beam splitter 34 Input side 36 Input side 37 Input side 38 Input side 40 Input side 41 Input side 42 Output side 44 Output side 46 Filter unit 48 Filter 50 Filter 52 Filter 54 Optical path 56 Light-emitting surface 58 Light-emitting surface 60 Light-emitting surface 62 Light-emitting surface 64 Light-emitting surface 66 Control unit 68 Camera unit 70 Observation beam path 72 Filter sensor 74 Display unit 76 Shaft 77 Optics 78 Lens 80 Lens 82 Lens 84 Lens 86 Lens 88 Lens 90 Beam splitter element 92 Beam splitter element 94 Beam splitter element 96 Beam splitter element 98 Transmission spectrum 100 Transmission spectrum 102 Transmission spectrum 104 Transmission spectrum 106 Light guide 108 Imaging sensor 110 White light sensor112 Near-IR sensor 114 Light path 116 Distal section 210 Filter unit 212 Filter drive 214 User interface 310 Base unit 312 Interchangeable shaft 314 Interchangeable shaft 316 Imaging system 318 Camera 320 Camera 322 Filter 324 Filter 410 Imaging device 412 Illumination unit 414 Light source 416 Illumination light 418 Object 420 Image acquisition unit 422 Calibration image 423 Calibration image 424 Object image 426 Image correction unit 428 Object light 430 Corrected object image 432 Depth map 434 Depth map 436 Image area 437 Image area 438 Computer program product 440 Computer-readable medium 442 Lens 444 Image acquisition sensor 446 Display 448 Stained area 450 Tissue 452 Scale

Claims

Medical imaging device (410), in particular endoscope device, exoscope device and / or microscope device, comprising: an illumination unit (412) with at least one light source (414) configured to provide illumination light (416) for illuminating an object (418) to be imaged; an image acquisition unit (420) configured to acquire several calibration images (422, 423) of the object (418) to be imaged and to acquire at least one object image (424) of the object (418) to be imaged; and an image correction unit (426) configured to: determine depth information from the calibration images (422, 423), wherein the depth information comprises several depth maps relating to different wavelength ranges;Determining a correction for the object image (424), wherein the correction includes taking into account a distance dependence of a light intensity of illumination light (416) and / or a distance dependence of a light intensity of object light (428) according to the depth information; and producing a corrected object image (430) according to the correction, wherein the illumination unit (412) is configured to be operable in different illumination modes in which illumination light in different spectral ranges can be provided, and wherein the image acquisition unit (420) is configured to acquire several calibration images (422, 423) the acquisition of which is based on different illumination modes of the illumination unit (412). Medical imaging device (410) according to claim 1, wherein an image acquisition of the calibration images (422, 423) comprises a detection of remitted light. Medical imaging device (410) according to one of the preceding claims, wherein an image acquisition of the calibration images (422, 423) comprises a detection of fluorescence light. Medical imaging device (410) according to one of the preceding claims, wherein the correction comprises a distance correction based on an inverse of a power of a length of a light path, in particular a length of a light path between the image acquisition unit (420) and the object to be imaged (418) and / or a light path within the object to be imaged (418). Medical imaging device (410) according to one of the preceding claims, wherein the correction comprises an absorption correction based on an attenuation of light along a light path of a length, in particular an exponential attenuation, in particular a length of a light path within the object to be imaged (418). Medical imaging device (410) according to claim 5, wherein the absorption correction takes into account an attenuation of illumination light (416) and / or an attenuation of object light (428). Medical imaging device (410) according to one of the preceding claims, wherein the image correction unit (426) is configured to determine spatial and / or spectral properties, in particular inhomogeneities, of the illumination unit (412) from the calibration images (422, 423) and to take the determined spatial and / or spectral properties into account during correction. Medical imaging device (410) according to one of the preceding claims, wherein the image correction unit (426) is configured to determine the depth information by means of a stereo reconstruction. Medical imaging device (410) according to one of the preceding claims, wherein in the corrected object image (430) at least one image area (436) is enhanced and / or attenuated according to the correction relative to at least one other image area (437) with respect to at least one parameter, such as a hue, brightness and / or saturation. Medical imaging device (410) according to one of the preceding claims, wherein the illumination unit (412) and / or the image acquisition unit (420) is configured for multispectral imaging. A method for medical imaging, in particular with a medical imaging device (410) according to one of the preceding claims, comprising: providing illumination light (416) in different wavelength ranges for illuminating an object (418) to be imaged; acquiring several calibration images (422, 423) of the object (418) to be imaged in the different wavelength ranges; acquiring at least one object image (424) of the object (418) to be imaged; determining depth information from the calibration images (422, 423), wherein the depth information comprises several depth maps relating to the different wavelength ranges; determining a correction for the object image (424), wherein the correction comprises taking into account a distance dependence of a light intensity of illumination light (416) and / or a distance dependence of a light intensity of object light (428) according to the depth information;and generating a corrected object image (430) according to the correction.; Program code configured to, when executed in a processor, effect the performance of a method according to claim 11. Computer program product (438) comprising a computer-readable medium (440) on which program code according to claim 12 is stored.

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