Method of recording image data

Abstract

A method for recording image data by means of a camera, in particular by means of a film camera, is provided. In this regard, the camera includes an image sensor having adjustable sensitivity, the image sensor including a plurality of photosensitive detector elements arranged in rows and columns, and the image sensor is configured to generate respective charges according to light intensities incident on the respective detector elements during respective single exposures, the respective charges are amplified according to the set sensitivity and converted into respective image signal values. The method comprises the steps that recording sensitivity and target sensitivity are predefined, and the deviation between the recording sensitivity and the target sensitivity is an exposure correction value; recording the image data by means of the camera while setting the sensitivity of the image sensor to the recording sensitivity; determining noise correction according to the target sensitivity and / or the exposure correction value; and generating corrected image data by modifying the recorded image data based on the noise correction.

Description

Technical Field

[0001] The invention relates to a method for recording image data by means of a camera, in particular by means of a movie camera. Background Art

[0002] One or more individual images of the respective scene can be recorded as image data with the aid of a camera, since light emitted (radiated or reflected) from objects of the scene is deflected by the camera's optics onto the camera's image sensor, so that the scene is imaged onto the image sensor. In this regard, the image sensor typically comprises a plurality of light-sensitive detector elements arranged in rows and columns, and each light-sensitive detector element is configured to generate a respective charge as a function of the intensity of light incident on the respective detector element, and to convert the respective charge into a respective image signal value. In this way, a respective image signal value can be generated for each detector element during a respective single exposure - i.e., during a single exposure, the light of the scene is incident on the detector element approximately simultaneously within a certain period of time (shutter speed). The image signal values ​​generated by the respective single exposures then together form a respective single image.

[0003] By means of the respective detector elements, only light whose intensity lies within a certain intensity range can be reasonably converted into respective image signal values, so that the respective image signal values ​​are actually meaningful for the respective light intensity. This is because, if the intensity is too high (overexposure), the detector elements are saturated, so that different intensities that are too high cannot be distinguished, since these different intensities that are too high would lead to the same (maximum) image signal value; on the other hand, if the intensity is too low (underexposure), the conversion of the incident light into the respective image signal values ​​is dominated by the generally unavoidable noise of the image sensor, so that different intensities that are too low cannot be distinguished, since these different intensities that are too low would be buried in the noise. In this respect, the noise may include, on the one hand, parts of electronic noise from the respective detector elements or various electronic components of the image sensor, and, on the other hand, parts of noise caused by the quantum properties of light (e.g. shot noise). The said intensity range, in which meaningful image signal values ​​can be generated, is therefore limited and defines the dynamic range of the image sensor.

[0004] When recording image data, the aim is usually to ensure that, possibly for each detector element, the light incident thereon has an intensity within the stated intensity range. Ideally, the overall intensity of the light is in this respect at least largely in the middle range of the intensity range, so that the resulting image has a medium brightness and a large range of the dynamic range of the image sensor can be utilized overall, from the shadows to the highlights of the scene. However, different brightness distributions may also be sought, depending on artistic design intent.

[0005] On the one hand, the intensity of the light incident on the respective detector element depends on the brightness of the respective object in the scene from which the light is emitted, wherein the brightness may be influenced by the illumination of the scene, in particular artificial illumination. On the other hand, the intensity of the incident light may depend on various further parameters, namely in particular on the substantially adjustable aperture of the iris of the camera and the substantially adjustable shutter speed of the camera shutter. According to the respective set aperture, the cross section of the incident light beam is ideally limited by the iris in the region of the main plane of the camera optics, thereby spatially influencing the amount of light incident on the image sensor during the respective single exposure; the duration of the respective single exposure is limited by the shutter, which may be a mechanical shutter or an electronic shutter (for example, implemented by a respective control of the image sensor), according to the respective set shutter speed, and the amount of light incident on the image sensor during the respective single exposure is limited in time.

[0006] The sensitivity of the image sensor, which is preferably adjustable and is usually predefined as a so-called ISO value, has a further influence on the image brightness. However, the ISO setting does not change the amount of light incident on the image sensor, but rather changes the way this light is converted into corresponding image signal values ​​by the correspondingly generated charges, in particular how much the charges are amplified. In this respect, the amplification may also reach saturation and result in noise depending on the amplification level.

[0007] In particular during movie recording, it may happen that image data with related content are recorded successively in several parts and that the exposure conditions vary in between, influencing the amount of light incident on the image sensor and being caused in particular by (at least among others) the brightness or illumination of the recorded scene, the set aperture of the iris and / or the set shutter speed of the camera shutter. Such variations in exposure conditions may occur for reasons that cannot be influenced or are difficult to influence, for example due to daylight fluctuations. However, variations in exposure conditions may also be a side effect of an intentional adjustment, for example if the aperture of the iris is adjusted for creative reasons, for example in order to change the depth of field.

[0008] Therefore, it may be necessary to compensate for changes in exposure conditions so that the image data recorded under different exposure conditions match each other in terms of their respective brightness. For example, such compensation can be achieved by an ND filter (neutral density filter) that filters out a defined portion of the light. This portion is usually specified as the optical density of the ND filter. For example, an optical density of 0.3 (more precisely: log 102) corresponds to a reduction in light intensity by one f-stop, which in turn corresponds to a halving of the amount of light. Such an ND filter can be mounted in front of the lens of a camera and / or between the lens and the image sensor in a camera. However, mounting one or more ND filters in front of the lens may delay the entire corresponding photographing operation. Furthermore, an ND filter mounted in front of the lens may cause interfering reflections. The ND filters provided in the camera increase the design effort of the camera. Therefore, it is generally advantageous if the use of ND filters can be avoided.

[0009] Nowadays, especially high-quality cameras have a large dynamic range, which generally allows (at least to a certain extent) that changes in exposure conditions do not necessarily have to be compensated by changing the amount of incident light (such as by using ND filters), as long as this change only shifts the brightness to such an extent that even the brightest areas do not reach saturation or the darkest areas are not buried by noise. If the dynamic range is sufficient, the image data can therefore generally be recorded without special adaptation to the changed exposure conditions, but will be correspondingly brighter or darker.

[0010] The altered brightness can usually be adapted to the image data recorded under the original conditions by adjusting the sensitivity of the image sensor accordingly. However, for fundamental reasons (due to the quantum properties of light), the image data recorded at the altered sensitivity have different noise (signal-to-noise ratio) compared to the image data recorded under the original image conditions, due to the altered exposure conditions associated with the respective sensitivity of the image sensor. Image data recorded successively under different exposure conditions may have significantly different characteristics due to the different noise. Such unexpected differences in image noise, especially in the case of high-quality film recordings, e.g. for movie production, may be unacceptable. Summary of the invention

[0011] The object of the invention is to provide a method for recording image data with the aid of a camera, in particular with the aid of a film camera, which method is able to simply compensate for changes in exposure conditions and in this respect avoids the disadvantages of the prior art, in particular does not require ND filters and does not lead to perceptible changes in the image noise.

[0012] This object is achieved by a method having the features of claim 1. Advantageous embodiments emerge from the dependent claims, the description and the drawings.

[0013] The method according to the invention is used for recording image data by means of a camera, in particular by means of a movie camera. The image data may be still image data in the form of a single image or moving image data in the form of a sequence of single images, wherein the single images of the sequence are preferably recorded at a constant frame rate. In this respect, the camera comprises an image sensor with an adjustable (settable) sensitivity, the image sensor comprising a plurality of light-sensitive detector elements arranged in rows and columns, and the image sensor being configured to: generate a respective charge as a function of the light intensity incident on the respective detector element during a respective single exposure; amplify the respective charge in accordance with the set sensitivity; and convert the respective charge into a respective image signal value.

[0014] The image signal values ​​obtained in this way during the respective single exposure then together form the image data of the respective single image. In other words: the respective single image corresponds to a data set of image signal values ​​generated due to the respective single exposure (i.e., during a prescribed period of time, the light of the scene to be recorded continuously impinges on the image sensor and causes the generation of charge).

[0015] The camera may further comprise an aperture having an adjustable aperture and being configured to reduce the amount of light incident on the image sensor during a respective single exposure, depending on the set aperture, e.g. by limiting the cross section of the incident light beam in a region that is ideally located in the main plane of the camera optics. Furthermore, the camera may comprise a (mechanical or electronic) shutter having an adjustable shutter speed (i.e. exposure time), which is configured to limit the duration of the respective single exposure during which the light is incident on the image sensor to the set shutter speed. For example, such a shutter may be configured in the form of a rotating sector shutter (also referred to as a rotating aperture), the rotation speed and / or the size of the shutter opening of which are adjustable.

[0016] According to the invention, the method comprises: predefining a recording sensitivity and a target sensitivity, wherein a deviation of the recording sensitivity from the target sensitivity is an exposure correction value; recording image data by means of a camera while setting the sensitivity of the image sensor to the recording sensitivity; determining a noise correction according to the target sensitivity and / or the exposure correction value; and generating corrected image data by modifying the recorded image data based on the noise correction. The corrected image data can then be output by the camera.

[0017] The recording sensitivity and the target sensitivity can each be specified in the form of a so-called ISO value, which corresponds approximately to the ISO sensitivity of a photographic film. For recording the image data, the image sensor is set to the recording sensitivity. In this respect, the recording sensitivity is the actually set sensitivity of the image sensor. In contrast, the target sensitivity can represent only a nominal sensitivity, i.e., as far as can be predefined by the target sensitivity, the corrected image data should ultimately look as if they were recorded with the aid of an image sensor set to the target sensitivity.

[0018] The exposure correction value is preferably not equal to zero and can be specified specifically in aperture values. In this respect, one aperture value corresponds to a change in sensitivity, so that, depending on the sign of the exposure correction value, a doubling or halving of the amount of light incident on the image sensor is compensated by the change in sensitivity. In which direction and with which sign the correction is made is a matter of definition. In this context, changing the sensitivity of the image sensor by a negative exposure correction value means reducing the sensitivity, i.e. the ISO value is reduced. Thus, in the case of a negative exposure correction value, the recorded sensitivity is lower than the target sensitivity.

[0019] The predefinition of the recording sensitivity and the target sensitivity can be performed by a user of the camera, for example by means of an input device of the camera. Both the recording sensitivity and the target sensitivity do not necessarily need to be predefined directly, since instead only one of these sensitivities can be predefined and an exposure correction value can be predefined directly instead of the other sensitivity, whereby the other sensitivity can also be predefined indirectly, since it can be clearly derived from one sensitivity and the exposure correction value. In particular, provision can be made for the target sensitivity and the exposure correction value to be predefined directly, wherein the recording sensitivity can then be determined from the target sensitivity and the exposure correction value, and the recording sensitivity is thus predefined indirectly. For example, a value of ISO 800 can be predefined as the target sensitivity and a -1 aperture value can be predefined as the exposure correction value, whereby a recording sensitivity of ISO 400 is indirectly predefined.

[0020] The noise correction is determined as a function of the target sensitivity and / or the exposure correction value. The noise correction is preferably determined as a function of both the target sensitivity and the exposure correction value. In this respect, the target sensitivity and the exposure correction value also do not necessarily have to be used directly for determining the noise correction, but one of these values ​​may also be derived indirectly from the respective other value in combination with the recording sensitivity. In this respect, the noise correction may also be determined (directly or indirectly) as a function of the recording sensitivity.

[0021] Noise correction is used to compensate for the difference between the actual noise of a single image recorded by means of an image sensor set to a recording sensitivity and the expected noise of a single image recorded by means of an image sensor set to a target sensitivity. In principle, various ways can be considered to determine such noise correction based on the target sensitivity and / or the exposure correction value (or recording sensitivity). For example, the noise correction can be based on empiricism, by comparing the difference in noise at different sensitivities based on image data recorded with different sensitivities of the image sensor, wherein the noise correction can then be determined based on this difference. Alternatively or additionally, theoretical models of noise can also be used to determine the noise correction. However, in this respect, the empirical data and the theoretical models can be of a general nature and can therefore be valid for different (specific types of) image sensors, or can be specifically determined or defined for the corresponding image sensor.

[0022] Finally, the recorded image data are modified based on the determined noise correction and in this way corrected image data are generated. The fact that the corrected image data are generated by modifying the recorded image data based on the noise correction is not intended to exclude that the generation of the corrected image data comprises even further steps, in particular a further modification of the recorded image data.

[0023] For example, the generation of the corrected image data may also comprise a modification of the brightness of the recorded image data to compensate for a remaining brightness deviation. In this respect, the recorded image data are preferably modified in terms of their brightness in accordance with the exposure correction value. The modification may comprise multiplying the recorded image data, in particular the image signal values, by an exposure correction factor, which (in particular exponentially) depends on the exposure correction value, wherein the exposure correction factor may also depend on the corresponding image signal value. If a gamma correction has been applied to the image signal values, it may further be provided that, before the image signal values ​​are multiplied by the exposure correction factor, the image signal values ​​are first linearized again (inverse gamma correction) and the gamma correction is subsequently applied again.

[0024] Thanks to the method according to the invention, the corrected image data can largely match the other image data recorded before the exposure conditions were changed in terms of brightness and noise, without the need to use ND filters. The effort and difficulties usually associated with the use of ND filters can thus be easily avoided.

[0025] The term “image sensor with adjustable sensitivity” has a broad meaning in the present context and includes not only the photosensitive detector elements themselves (e.g. in CMOS technology) but also integrated or associated amplification electronics (e.g. column amplifiers for columns of photosensitive detector elements, as is known, for example, from DE 102013209164 B4).

[0026] According to a preferred embodiment, it is provided that if the recording sensitivity is lower than (has a smaller ISO value) the target sensitivity (i.e., the exposure correction value is negative), a corresponding noise value is determined as a noise correction for each image signal value of the recorded image data, and corrected image data is generated by adding the corresponding noise value to each image signal value (wherein, the generation of the corrected image data is not necessarily limited to this, and may also include further modification of the recorded image data).

[0027] In this respect, the noise correction may correspond to a data set of noise values ​​which, in terms of resolution, i.e. the number of individual values ​​arranged in rows and columns, corresponds to a respective individual image recorded by the camera and formed by image signal values ​​generated during a respective single exposure. Thus, for a respective individual image, a respective noise value may be assigned to each image signal value of the individual image and added to the respective image signal value to generate the corrected image data. The addition may specifically correspond to a simple addition of the respective image signal value and the respective noise value. For at least one or some of the image signal values, the respective noise value may also be zero; i.e. not every image signal value has to be modified.

[0028] If the recording sensitivity is lower than the target sensitivity, the image data recorded at the recording sensitivity will have reduced noise compared to recording at the target sensitivity. By adding the noise value, the recorded image data is provided with additional noise, so that the reduced noise can be compensated in this way.

[0029] The method according to the present invention can generally also be limited to a recording sensitivity lower than a target sensitivity, so that a corresponding noise value is always determined as a noise correction for each image signal value of the recorded image data, and corrected image data is generated by adding the corresponding noise value to each image signal value.

[0030] According to another advantageous embodiment, it is provided that if the recorded sensitivity is higher (has a larger ISO value) than the target sensitivity (i.e., the exposure correction value is positive), a noise filter is determined as a noise correction, and the recorded image data is filtered by means of the noise filter to generate corrected image data (wherein the generation of the corrected image data is not necessarily limited to this, and may also include further modification of the recorded image data).

[0031] Due to the dependence on the target sensitivity and / or the exposure correction value (or the recording sensitivity), the noise filter can be particularly adapted to filter out the noise component characteristic of the corresponding sensitivity. The filtering can be performed using generally known noise suppression methods, wherein the filter parameters are specifically selected according to the target sensitivity and / or the exposure correction value (or the recording sensitivity). In this regard, the filter parameters can be determined, for example, by calculation or using a lookup table according to the target sensitivity and / or the exposure correction value (or the recording sensitivity).

[0032] If the recording sensitivity is higher than the target sensitivity, the image data recorded at the recording sensitivity will have increased noise compared to recording at the target sensitivity. The increased noise can be compensated in this way by filtering with the aid of a noise filter to reduce the noise in the recorded image data.

[0033] The method according to the invention can generally also be restricted to a recording sensitivity higher than a target sensitivity, so that a noise filter is always determined as noise correction and corrected image data are generated by filtering the recorded image data by means of the noise filter.

[0034] According to another advantageous embodiment, the noise correction is determined based on a noise characteristic of the image sensor. The noise characteristic can generally be defined in a model-generic manner, i.e. in the same way for all image sensors of the same design of a specific image sensor model. However, the noise characteristic is preferably defined in a sample-specific manner, i.e. individually for a specific sample of image sensors used in the camera. The method may comprise first determining the noise characteristic, in particular as part of a calibration step preceding the aforementioned method steps. In this respect, the determination of the noise characteristic is preferably carried out empirically. Once the noise characteristic has been determined, it or data defining it can, for example, be stored in a memory of the camera, from which it or the defining data can then be read out to determine the noise correction.

[0035] According to an advantageous further development, the noise characteristic comprises a theoretical model, in particular a mathematical model, for the noise of the image sensor. The determination of the noise correction then comprises calculating data for the noise correction with the aid of the model. The calculated data can specifically be the mentioned noise values.

[0036] According to another advantageous further development, the noise characteristic comprises a lookup table. That is, the noise characteristic or at least part of the information comprised in the noise characteristic can be stored in a lookup table. The determination of the noise correction then comprises reading out the data of the noise correction from the lookup table. The data read out from the lookup table can specifically be the noise values ​​or data from which these noise values ​​can be derived.

[0037] The lookup table may, for example, include a standard deviation for each detector element of the image sensor. The standard deviation may be determined by time measurement. This may specifically include, for example, acquiring image signal values ​​within a specific time period under specified conditions with at least approximately uniform illumination of the image sensor, and determining the standard deviation of all image signal values ​​generated by each detector element at the corresponding detector element within this time period. The noise value may then be determined based on these standard deviations. In this regard, the lookup table may include different standard deviations for different target sensitivities and / or exposure correction values ​​(or recording sensitivities). However, the target sensitivity and / or exposure correction value (or recording sensitivity) may also (only) be included in the determination of the noise value based on the standard deviation.

[0038] If the noise characteristic comprises both the theoretical model of the noise of the image sensor and the lookup table, the parameters of the model, in particular the different parameters for different target sensitivities and / or exposure correction values ​​(or recording sensitivities), can also be stored as data in the lookup table and can then be read out from the lookup table. Subsequently, the noise value or another noise correction can be calculated, for example, with the aid of the model parameterized in this way, in particular as a function of the target sensitivity and / or exposure correction value (or recording sensitivity).

[0039] The corrected image data may typically be generated outside the camera, i.e., in some embodiments, the step of correcting the image data based on the noise correction may also be performed outside the camera. For example, the recorded image data may be output by the camera and then modified based on the noise correction by means external to the camera, e.g., by means of a separate image processing unit (in particular local or remote) or by means of a remote distributed image processing device (in particular a data center and / or a "cloud" server). The step of correcting the image data based on the noise correction may in particular be performed temporally independently of the step of recording the image data using the camera and does not necessarily have to be performed immediately thereafter.

[0040] According to an advantageous embodiment, the generation of the corrected image data takes place in the camera, preferably immediately after the recording of the image data and possibly continuously during the recording of further image data. If the corrected image data are generated in the camera, the camera can then output them. In particular, it can be provided that the camera always outputs the image data in an already corrected form, either together with the recorded (not yet corrected) image data or only the corrected image data.

[0041] In order to generate the corrected image data, the camera may comprise an image processing unit which is configured to generate the corrected image data. Furthermore, the determination of the noise correction may also be performed in the camera, for which purpose the image processing unit (if provided) is also configured to determine the noise correction. Furthermore, it is advantageous if the recording sensitivity and the target sensitivity can also be predefined on the camera, for which purpose the camera may have an input device. In this way, neither a device external to the camera nor an accessory of the camera need be provided in order to perform the method. The image processing unit may be part of a control device of the camera, to which the input device (if provided) may be connected.

[0042] According to another advantageous embodiment, the method further comprises: firstly recording reference image data by means of a camera under given exposure conditions (i.e., currently existing exposure conditions due to external conditions and / or corresponding settings, in particular lighting, aperture and / or shutter), while setting the sensitivity of the image sensor to a target sensitivity; and after a change in the exposure conditions, determining an exposure correction value in accordance with the change in the exposure conditions. In this respect, the exposure correction value can be determined directly or indirectly by determining a new recording sensitivity in accordance with the change in the exposure conditions, the deviation of the new recording sensitivity from the target sensitivity corresponding to the exposure compensation value.

[0043] In other words, before the above-mentioned method steps, at least before the predefinition of the recording sensitivity, the recording sensitivity is first determined (directly or indirectly by means of an exposure correction value), and in fact the recording sensitivity is determined as a function of a change in exposure conditions, which occurs after previously recorded image data, which are referred to here as reference image data (primarily in order to conceptually distinguish them from image data recorded as part of another method). In this respect, the exposure conditions are specifically defined by the brightness or illumination of the recorded scene, by the set aperture of the iris of the camera and / or by the set shutter speed of the shutter of the camera, and may change specifically due to changes in brightness / illumination, iris and / or shutter speed. As exposure correction values, it can be determined in particular to what extent the sensitivity of the image sensor must change due to the change in exposure conditions in order to record image data whose brightness at least approximately corresponds to the brightness of the reference image data.

[0044] The object of the present invention is also achieved by a method for modifying image data, the method comprising the following steps:

[0045] - receiving image data of a camera, in particular a movie camera, corresponding to a set recording sensitivity;

[0046] - receive settings for recording sensitivity;

[0047] -Receive target sensitivity;

[0048] -determining a noise correction based on the recording sensitivity and the target sensitivity; and

[0049] -Modify received image data using noise correction.

[0050] The image data may specifically be recorded with a recording sensitivity set as described above and / or generated by an image sensor with adjustable sensitivity. In some embodiments, the set recording sensitivity may be received separately from the image data, or the set recording sensitivity may be embedded in the image data (particularly as metadata) and received together with the image data. In some embodiments, the target sensitivity may be received by user input. Furthermore, in some embodiments, the noise correction may be indirectly determined by an exposure correction value representing a deviation of the recording sensitivity from the target sensitivity, i.e., as described above, the noise value may also be determined based on such an exposure correction value.

[0051] The method makes it possible to reproduce an image impression which corresponds to a recording sensitivity instead of the recording sensitivity actually set when the image data were recorded, i.e. a selectable target sensitivity. At the same time, the method allows a reproducible modification of the image data, i.e. the perceived image noise always corresponds to the corresponding (actual or virtual) sensitivity (set recording sensitivity or selected target sensitivity) to the same extent. This is particularly important for film recordings, for example when combining multiple film recordings into a single sequence during film editing.

[0052] The object of the present invention is also achieved by a camera, in particular a movie camera, comprising an image sensor with adjustable sensitivity and a control device. The image sensor comprises a plurality of light-sensitive detector elements arranged in rows and columns, and the image sensor is configured to: generate corresponding charges according to the light intensity incident on the corresponding detector elements during the corresponding single exposure; amplify the corresponding charges according to the set sensitivity; and convert the corresponding charges into corresponding image signal values. The control device is configured to control the camera to record image data according to the method according to the present invention, in particular according to the method in any of the above embodiments.

[0053] The control device can also be configured to determine the noise correction and / or generate the corrected image data. If the camera includes a separate image processing unit, this can also be done by the control device controlling the image processing unit to determine the noise correction or generate the corrected image data. However, the image processing unit can also be integrated in the control device.

[0054] The control device and / or image processing unit mentioned in conjunction with the present invention may include, for example, an integrated circuit (IC), a microprocessor, a central processing unit (CPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC) and / or a field programmable gate array (FPGA), or at least may be roughly formed thereby.

[0055] Furthermore, the camera may include an input device (in particular the input device already mentioned above), by means of which the recording sensitivity, the target sensitivity and / or the exposure correction value may be predefined. The control device may then receive the recording sensitivity, the target sensitivity and / or the exposure correction value from the input device, and based on receiving the recording sensitivity, the target sensitivity and / or the exposure correction value from the input device, the control device may control the camera to record, may determine the noise correction and may generate the corrected image data.

[0056] According to an advantageous embodiment, the camera further comprises a memory in which a noise characteristic of the image sensor is stored. Wherein the control device is configured to read out the noise characteristic from the memory and to determine the noise correction based on the read-out noise characteristic. In this respect, the fact that the noise characteristic is stored in the memory may mean that at least data related to the noise characteristic of the image sensor are stored in the memory.

[0057] The camera can be further configured in one of the above-described ways in connection with the method according to the invention. The embodiments and advantages of the embodiments described for the method also apply to the camera accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will now be further explained, by way of example only, with reference to the accompanying drawings.

[0059] Figure 1 An embodiment of a camera according to the invention is shown in a simplified schematic diagram; and

[0060] Figure 2 The sequence of an exemplary embodiment of the method according to the invention is shown schematically. Specific embodiments

[0061] Figure 1 The camera 11 shown is a movie camera, comprising a camera housing 13 and a lens 17. An image sensor 15 of the camera 11 is arranged in the camera housing 13. The lens 17 is connected to the camera housing 13. The lens 17 is configured to image light of a scene (not shown) to be recorded onto the image sensor 15.

[0062] The image sensor 15 comprises a plurality of light-sensitive detector elements arranged in rows and columns, and is configured to generate a respective charge as a function of the intensity of light which, during a respective single exposure, passes through the lens 17 and impinges on a respective one of the detector elements. In this respect, the image sensor 15 has an adjustable sensitivity, and is configured to amplify the respective charge as a function of the set sensitivity and to convert the respective charge into a respective image signal value. The image signal values ​​generated in this way during the respective single exposure then together form a respective single image. As a movie camera, the camera 11 is configured to record a sequence of a plurality of single images at a constant, preferably settable, frame rate by means of a plurality of single exposures in rapid succession. In this respect, the camera 11 is configured such that the recorded image data is formed by these single images.

[0063] The camera 11 further comprises an aperture 19, which can generally be integrated into the lens 17 or can also be independent of the lens 17. The aperture 19 has an adjustable aperture, which limits the cross section of the light beam incident through the lens 17 and can thereby influence the amount of light incident on the image sensor 15 during a single exposure. In addition, the camera 11 comprises a shutter 21 schematically shown by a dotted line. The shutter 21 has an adjustable shutter speed, by which the duration of the respective single exposure of light incident on the image sensor 15 is determined. The shutter 21 can be implemented by a mechanical element or an electronic shutter. For example, the shutter 21 can be configured in the form of a rotating aperture.

[0064] Furthermore, the camera 11 comprises a control device 23, a memory 25 and an input device 27. Noise characteristics are stored in the memory 25, the noise characteristics are determined empirically in particular for the corresponding image sensor 15 and can be read out by the control device 23. The control device 23 can receive user input via the input device 27. The control device 21 is configured to set the sensitivity of the image sensor 15, the aperture of the aperture 19 and the shutter speed of the shutter 21, and is configured to generally control the camera 11 to record image data according to the settings made. The control device 21 is specifically configured to control the image sensor 15 according to the settings made. Figure 2 The illustrated method 29 controls the camera 11 to record image data.

[0065] As method step 31, method 29 comprises predefining a recording sensitivity and a target sensitivity, wherein the deviation of the recording sensitivity from the target sensitivity is an exposure correction value. The recording sensitivity, the target sensitivity and / or the exposure correction value can in particular be input via input device 27. However, this is not absolutely necessary, as they can also be predefined in other ways. For example, as part of method 29 (as will be explained further below), the target sensitivity can be predefined and the exposure correction value can be predetermined, and these two values ​​are then predefined in method step 31.

[0066] As method step 33, method 29 further comprises recording image data by means of camera 11, while setting the sensitivity of image sensor 15 to the recording sensitivity. A sequence of individual images can be recorded in particular, since a plurality of individual exposures occur in rapid succession and in each individual exposure an amount of light depending on the aperture of light mirror 19 and the shutter speed of shutter 21 is incident on the detector element of image sensor 15 and is converted into image signal values ​​by means of the charge thus generated, which then form the corresponding individual image.

[0067] In a further method step 35, the recording sensitivity is compared with the target sensitivity (or the sign of the exposure correction value is evaluated). If the recording sensitivity is lower than the target sensitivity (negative exposure correction value), the method continues with method step 37; otherwise, the method continues with method step 39. In both method steps 37, 39, a noise correction is determined as a function of the target sensitivity and / or the exposure correction value, respectively, wherein this in each case comprises reading out the noise characteristic from the memory 25 and determining the noise correction based on the read noise characteristic. For example, the noise characteristic can be stored at least partially in the memory 25 in the form of a lookup table, which includes different data for the noise correction for different combinations of target sensitivity and exposure correction value (or recording sensitivity and exposure correction value, or recording sensitivity and target sensitivity).

[0068] In method step 37, the corresponding model parameters can be read out, for example, from a lookup table, with which the noise model of image sensor 15, which is also covered by the noise characteristic, can then be parameterized. Using this model, a corresponding noise value can then be calculated (also in method step 37) for each image signal value of the recorded image data and added to the corresponding image signal value in order to obtain corrected image data in this way.

[0069] In method step 39, corresponding filter parameters can be read out, for example, from a lookup table, with which a noise filter which is also covered by the noise characteristic is parameterized and determined in this way. The recorded image data (also in method step 39) can then be filtered using this noise filter in order to obtain corrected image data in this way.

[0070] In both cases, the corrected image data are ultimately adapted to the predefined target sensitivity and its difference from the recording sensitivity with respect to the noise contained therein. Such an adaptation is particularly meaningful if the recorded image data are to be "matched" with image data which were previously recorded under other exposure conditions and are referred to below for differentiation purposes as reference image data, since image data and reference image data recorded under different exposure conditions are not to be recognizable.

[0071] In this respect, the method 29 may also comprise recording reference image data, i.e., if the method 29 comprises the further method steps 41, 43 (referred to as Figure 2 In method step 41, reference image data are recorded by means of camera 11 under given exposure conditions (i.e. under exposure conditions which are present at the respective time of the recording due to external conditions and / or respective settings), wherein the sensitivity of image sensor 15 for the recording is set to a target sensitivity which can be selected approximately freely depending on the respective creative intention at this time.

[0072] After a change in the exposure conditions, which may occur due to external circumstances or (undesirable) side effects of an adjustment of settings, which may occur, for example, for creative reasons, an exposure correction value is then determined in method step 43 as a function of this change in the exposure conditions. In this respect, the exposure correction value is expediently determined such that it indicates how much the exposure must be changed, in particular by adjusting the sensitivity of the image sensor 15, so that the image data recorded under the changed exposure conditions have approximately the same brightness as the reference image data.

[0073] The recording sensitivity for the further recording of the image data can then be determined as a function of the target sensitivity and the exposure correction value, and the recording sensitivity can be predefined together with the target sensitivity for further method steps 33-39 in method step 31. In this respect, the recording sensitivity does not have to be determined and predefined explicitly, since it can also be predefined only indirectly, i.e. in method step 31, the target sensitivity and the determined exposure correction value are predefined.

[0074] Reference numerals

[0075] 11 Camera

[0076] 13 Camera Housing

[0077] 15 Image Sensor

[0078] 17 lenses

[0079] 19-stop

[0080] 21 Shutter

[0081] 23 Control device

[0082] 25 Memory

[0083] 27 Input Devices

[0084] 29 Methods

[0085] 31-43 Method steps

Claims

1. A method for recording image data by means of a camera (11), in, The camera (11) comprises an image sensor (15) with adjustable sensitivity, the image sensor (15) comprising a plurality of light-sensitive detector elements arranged in rows and columns, and the image sensor (15) is configured to: generate respective charges according to the intensity of light incident on respective detector elements during respective single exposures; amplifying the corresponding charge according to a set sensitivity; and converting the corresponding charges into corresponding image signal values, Wherein, the method (29) comprises: - predefine (31) a recording sensitivity and a target sensitivity, wherein a deviation between the recording sensitivity and the target sensitivity is an exposure correction value; - recording (33) image data by means of the camera (11) while setting the sensitivity of the image sensor (15) to the recording sensitivity; - determining (35) a noise correction based on said target sensitivity and / or said exposure correction value; and - generating (37, 39) corrected image data by modifying the recorded image data based on said noise correction.

2. The method according to claim 1, wherein: If the recording sensitivity is lower than the target sensitivity, a corresponding noise value is determined as the noise correction for each image signal value of the recorded image data, and the corrected image data is generated (37) by adding the corresponding noise value to each image signal value.

3. The method according to claim 1 or 2, wherein: If the recorded sensitivity is higher than the target sensitivity, a noise filter is determined as the noise correction, and the corrected image data is generated (39) by filtering the recorded image data with the aid of the noise filter.

4. The method according to claim 1, wherein: The noise correction is determined based on noise characteristics of the image sensor (15).

5. The method according to claim 4, wherein: The noise characteristic comprises a theoretical model for the noise of the image sensor (15), and the determination of the noise correction comprises calculating data for the noise correction with the aid of the model.

6. The method according to claim 4, wherein: The noise characteristic comprises a lookup table, and the determining of the noise correction comprises reading data of the noise correction from the lookup table.

7. The method according to claim 1, wherein: The recording sensitivity and the target sensitivity are predefined directly or indirectly by a user of the camera (11).

8. The method according to claim 1, wherein: The generation of the corrected image data takes place in the camera (11).

9. The method according to claim 1, wherein: The method (29) further comprises: - firstly recording (41) reference image data under given exposure conditions by means of the camera (11) while setting the sensitivity of the image sensor (15) to the target sensitivity; and - after said exposure condition is changed, determining (43) said exposure correction value according to said change of said exposure condition.

10. A camera (11), comprising: - an image sensor (15) with adjustable sensitivity, the image sensor (15) comprising a plurality of light-sensitive detector elements arranged in rows and columns and configured to generate respective charges according to the intensity of light incident on respective detector elements during respective single exposures; amplifying the corresponding charges according to a set sensitivity; and converting the corresponding charges into corresponding image signal values; and - a control device (23) configured to control the camera (11) to record image data according to the method (29) according to claim 1.

11. The camera according to claim 10, wherein: The camera (11) further comprises: - a memory (25) in which the noise characteristics of the image sensor (15) are stored; and Therein, the control device (23) is configured to read out the noise characteristic from the memory (25) and determine the noise correction based on the read noise characteristic.

12. The camera according to claim 10, wherein: The camera (11) further comprises: An input device (27) by which the recording sensitivity, the target sensitivity and / or the exposure correction value can be predefined.

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