Method and device for correcting image data

Abstract

The invention relates to a method for correcting image data, in which image data from a plurality of image locations (7) are acquired in order to generate a resulting image from a number of image elements represented by the image data. The image data from selected image locations (7) are corrected by means of a correction value each in order to compensate for known imaging errors. According to the invention, a correction is made to the image data of each of the selected image locations (7) during the acquisition of the image data in order to compensate for the known imaging errors. The invention further relates to a device for carrying out the method according to the invention.

Description

[0001] The invention relates to a method and a device for correcting image data.

[0002] In optical imaging techniques, such as microscopy and photography, aberrations such as a drop in light intensity toward the edge of the image (peripheral light falloff, vignetting) or uneven light output across the image area occur independently of the sample. These can at least be reduced with various technical measures. However, all additional image enhancement measures also involve additional costs and technical effort.

[0003] Shading (vignetting) refers to an effect that occurs independently of the specific sample being imaged, in which areas of the image—be it a captured image (camera image) and / or an image in an eyepiece—are darker than others. The light output achieved, for example, by a detector is not uniform across the detector's sensor surface. Shadowing often becomes increasingly apparent toward the edges of an image (so-called peripheral light falloff).

[0004] These variations in light output are caused, for example, by the optical conditions of a detection beam path and the optical elements contained therein in interaction with physical laws.

[0005] The lower intensities of the light to be detected (detection radiation) recorded in the shaded areas also mean that the signal-to-noise ratio (SNR), i.e. the information content of the obtained image areas, is lower there than in the other areas.

[0006] Current practice is to perform digital correction of the captured and stored image data after image acquisition. This correction consists of pixel-by-pixel multiplication by a pre-determined correction value, with each pixel assigned an individual correction value.

[0007] While this approach can significantly improve the resulting images for the viewer, it does have drawbacks. While multiplying the correction value changes the intensity value and thus the brightness perceived by the viewer, it does not increase the SNR. Thus, the information content of the pixels and image areas corrected in this way remains at the original level.

[0008] However, a consistently high SNR across the image is essential for many subsequent analyses. Such analyses include, for example, the resolution and precise localization of individual fluorescent proteins or the determination of sample topographies.

[0009] A further disadvantage is that the correction must be applied to all images. Image stacks (z-stacks), time series, and the acquisition and simultaneous display of different image planes (“tiles”), in particular, require enormous computing power. This computing power may also mean that it is not possible to provide a corrected display in real time for fast acquisitions.

[0010] The invention is based on the object of proposing a method by which the disadvantages of the prior art are reduced. Furthermore, the invention aims to provide a device by means of which such a method can be carried out.

[0011] The problem is solved by the subject matter of the independent claim and the subject matter of the subordinate claim. Advantageous developments of the invention are specified in the dependent claims.

[0012] This problem is solved with a method for correcting image data, in which image data from a plurality of image locations is acquired to generate a resulting image from a number of image elements (pixels) represented by the image data. The image data from selected image locations are each modified (corrected) using a correction value to compensate for known aberrations. The correction is performed, for example, by multiplying the value of the image data acquired at an image location by a correction value assigned to that image location.

[0013] According to the invention, the method is characterized in that a correction is made for the image data of each of the selected image locations during the acquisition of the image data in order to compensate for the known imaging errors.

[0014] For the purposes of this description, a picture element or pixel is understood to be the smallest unit from which an image is composed. For example, a pixel corresponds to a detector element of a detector with a plurality of detector elements. The image locations lie, for example, in an object plane, and detection radiation emanating from there is correspondingly imaged and captured in an image plane that coincides, for example, with a detector plane of a detector.

[0015] Since not all image data of all image locations necessarily have to be corrected, those image locations or the corresponding pixels are selected for which a correction is to be carried out using the method according to the invention.

[0016] If, instead of a detector with multiple detector elements, a detector with only one detector element is used, onto which image data from different image locations are imaged sequentially and acquired by the detector element, then one pixel corresponds to the image data acquired at one time for each image location. This applies, for example, to scanning imaging using a scanning microscope, in particular a laser scanning microscope (LSM), and the use of a single detector (e.g., a secondary electron amplifier; photomultiplier tube; PMT).

[0017] The basic idea of ​​the invention is not to carry out the correction of occurring shading effects in a subsequent process step on the already acquired and stored image data or to optimize the (detection) optics at great expense, but to integrate the correction into the process of acquiring the image data.

[0018] As in the known prior art methods, the method according to the invention also requires correction values ​​for each pixel to be corrected and keeps them readily available. As before, the correction values ​​can be determined for the individual pixels as part of a system calibration.

[0019] To implement the method according to the invention, the correction values ​​must be readily available in order to correct the respective pixel values ​​during the image data acquisition process. The correction can be performed by using at least one of the parameters explained in more detail below. These parameters include, in particular, the exposure time, the acquisition time, the gain, and the threshold value for detecting a gray value, known as the offset. These options for implementing the method according to the invention can be combined with one another.

[0020] Accordingly, in one embodiment of the method according to the invention, the selected image locations can be illuminated with an individually defined exposure duration. Since each image location is assigned to a pixel, i.e., the detection radiation originating from an image location represents the image data of a respective pixel, a correction is made for the selected pixels in this way. Adjusting the exposure duration advantageously changes both the brightness and the SNR. This not only results in more uniform brightness but also in a consistent SNR across the entire image.

[0021] In a further embodiment, the selected image locations can be illuminated with an individually defined exposure intensity. For example, an AOM (acousto-optic modulator) driver can be used to set the predetermined exposure intensity for each pixel individually or for a group of selected pixels.

[0022] In a further embodiment of the method, the image data representing a selected image location is acquired over an individually defined period of time (acquisition time). This means that while the exposure time remains constant, the readout time of the individual detector elements (pixels) is also varied. This changes the SNR on the detection side.

[0023] It is also possible to use the conventional process step of converting the image data captured as analog image data from each selected image location into digital image data for correction. During this process, the image data is modified using appropriate correction values ​​during the so-called A / D conversion. To implement this correction variant, internal A / D converters can be individually, i.e., pixel-precisely, supplied with different conversion factors as correction values. As a result, the SNR is improved, for example, at shadowed edge areas through correction before conversion to digital image data, and the amplification of unwanted noise resulting from digitization is reduced. This beneficial effect is particularly evident with low-light signals.

[0024] In a further embodiment, an adapted threshold for the acquisition of image data can be defined as a gray value as a correction value for each selected image location and applied during the acquisition of the image data for the selected image location. Such an application of a threshold can be carried out using an analog-to-digital converter (A / D converter), which is in particular arranged directly downstream of the detector, whereby the acquired image data is corrected before storage. By shifting the minimum voltage threshold, above which a gray value is acquired, a moderate increase in the SNR can be achieved across the entire image. This shift of the minimum voltage threshold occurs for each pixel. Groups of pixels can be selected to which a common correction value is assigned, which leads to a more efficient application of this correction variant.

[0025] If a scanning microscope is used instead of a detector with multiple detector elements, the parameters listed above can also be used for correction. In addition, the speed of an existing scanner must be adjusted depending on the location. Here, too, it is possible to make individual corrections for different lenses and / or illumination types in order to achieve a high and consistent SNR right up to the edges of the resulting image.

[0026] In a further development of the method according to the invention, image data from several image locations can be modified jointly. For example, a correction value can be assigned to several pixels that, for example, capture an entire section of the image. Such a section can, for example, be a number of pixels that represent an edge region of the image to be captured (image edge). Additionally or alternatively, several selected pixels, or their respective image data, can be modified with one and the same correction value, even if they are not directly adjacent to one another and jointly capture a section of the image.

[0027] The method according to the invention can be configured differently in that the correction of the image data is performed completely or incompletely for each image location. Complete correction means that after the correction, a high and uniform SNR and illumination are present across the entire image, whereby the SNR may only fluctuate within predefined narrow limits across the image. The fluctuation range is, for example, less than 10%, in particular less than 5%, and preferably at most 2.5% of the arithmetic mean of the SNR values.

[0028] If a method design with an incomplete correction is selected, the image data of the selected pixels are subjected to the specified correction values, but this does not necessarily achieve the above-mentioned narrow limits of the permissible fluctuation range of the SNR across the image.

[0029] In one embodiment, an incomplete correction can be combined with a correction of the acquired and stored image data known from the prior art. This allows a sufficient improvement in the SNR to be achieved, and the qualitatively improved image data can optionally be post-processed using known routines. In another embodiment of the method, the incompletely corrected data in this sense is used without further correction. In this case, computing power and storage space can be saved.

[0030] The method according to the invention can be carried out uniformly, regardless of the currently used lens and / or illumination mode. In further embodiments, the correction values ​​to be used and / or the selected image locations can be determined or pre-determined and stored in a retrievable manner depending on the currently used lens and / or illumination mode.

[0031] The selection of image locations and / or correction values ​​can optionally be performed by the user. Furthermore, in other process configurations, it is possible for the user to perform calibration.

[0032] To carry out the method according to the invention, a device can be used that comprises a detection beam path for guiding detection radiation emanating from image locations and to be detected; a detection unit arranged in the detection beam path for detecting image data from a plurality of image locations (in order to generate a resulting image from a number of image locations represented by the image data); and a correction unit. This unit is configured to modify / correct image data from selected image locations using a correction value in order to compensate for known aberrations.

[0033] A device according to the invention is characterized in that the correction unit generates control commands by means of which image data of selected image locations are changed / corrected during the respective acquisition.

[0034] The correction unit can, for example, be a computer in which correction values ​​assigned to selected image locations are stored and can be retrieved from an external storage medium using the correction unit. Captured image data from a selected image location is corrected using the respective correction value and made available as corrected image data for further data processing. The control commands can be used, for example, to control or regulate the detector, a scanning device (see below), and / or an AOM driver.

[0035] It is important for the device according to the invention that correction values ​​can be assigned to image data from each selected image location or to image data from image locations of an image section. The device can be, for example, an optical arrangement with a camera or a microscope, in particular a laser scanning microscope. Optionally, a computer unit, for example a computer (PC), can be provided, enabling additional correction according to the prior art.

[0036] In one embodiment, the device according to the invention can comprise a scanning device for controlled exposure of the image locations, for example, for an individual exposure duration each, and / or for controlled steering of the detection radiation in the detection beam path. The scanning device can advantageously be controlled by means of control commands from the correction unit, for example, to expose each selected image location with an individual exposure duration.

[0037] The invention also relates to a camera or a microscope, for example an LSM, with a device according to the invention.

[0038] Advantages of the invention lie in particular in the immediate correction of the acquired image data, which simultaneously advantageously increases the SNR across the entire image. Provided that the correction values ​​are appropriately set for each selected image location, a homogeneous SNR is also achieved across the entire image. The technical effort required to implement the correction in the camera or microscope, for example, in an LSM, is only necessary once and is justified by the achievable advantages.

[0039] The invention is explained in more detail below using exemplary embodiments. Fig. 1 shows a first embodiment of a device according to the invention in the form of a camera; and Fig. 2 a second embodiment of a device according to the invention in the form of a microscope with a scanning device.

[0040] In the Fig. 1 shows a device according to the invention as a component of a camera 1, wherein the essential technical elements are a detection beam path 2 (symbolized as an optical axis), a detection optics 3, a detector 4 and a correction unit 5.

[0041] From a sample 6, detection radiation 8 emanates from an image location 7, which is collected by the detection optics 3 and directed onto detector elements 4.n of the detector 4. As an example, the detection radiation 8 collected from a single image location 7 of the sample 6 is shown with a simplified beam path. The detection radiation 8 emanating from the image location 7 is detected by a detector element 4.1 (pixel 4.n), which is shown here in black for illustrative purposes. The acquired image data from the image location 7 are fed to the correction unit 5, where they are modified using a correction value assigned to the respective detector element 4.1. The image data corrected in this way are then fed to an image memory 9 and stored there for later evaluation and processing.

[0042] In a second embodiment, the device according to the invention is part of a microscope 10, in particular a laser scanning microscope. An excitation radiation (not shown) introduced by means of a beam splitter 11 into an excitation beam path 13, which here partially coincides with the detection beam path 2, is directed by means of a scanning device 12 onto the sample 6 in each case into an image location 7, and the sample 6 is scanned. The detection radiation 8 produced in the respective image location 7 is detected by the detection optics 3, converted (“descanned”) into a stationary beam by the action of the scanning device 12, and passes through the color splitter 11 onto the detector element 4.n of the detector 4. Depending on the current position of the scanning device 11, the associated position of the respectively acquired image data is known. These are Fig. 1 explains the correction unit 5, corrected there and then transferred to the image memory 9. Reference symbol 1 camera 2 Detection beam path 3 Detection optics 4 Detector 4.n detector element / pixel 5 Correction unit 6 Sample 7 Image location 8 Detection radiation 9 image memory 10 Microscope 11 color dividers 12 scanning device 13 Excitation beam path

Claims

[1] Method for adjusting a detected amount of light, in which Image data of a plurality of image locations (7) are recorded in order to generate a resulting image from a number of image elements represented by the image data; and the image data of selected image locations (7) are corrected by means of a correction value in order to compensate for known imaging errors, characterized by , that a correction is made for the image data of each of the selected image locations (7) during the acquisition of the image data in order to compensate for the known imaging errors. [2] Method according to claim 1, characterized by that the selected image locations (7) are illuminated with an individually defined exposure time. [3] Method according to claim 1 or 2, characterized by that the selected image locations (7) are illuminated with an individually defined exposure intensity. [4] Method according to one of the preceding claims, characterized by that the image data representing a selected image location (7) are recorded over an individually defined recording period. [5] Method according to one of the preceding claims, characterized by that image data of each selected image location (7) are captured as analog image data and converted into digital image data, wherein the image data are corrected during the conversion by means of respective correction values. [6] Method according to claim 1, characterized by that for each selected image location (7) an adapted threshold value for the acquisition of image data is set as a gray value as a correction value and is applied during the acquisition of the image data for the selected image location (7). [7] Method according to one of the preceding claims, characterized by that image data from several image locations (7) are corrected together. [8] Device for carrying out a method according to one of claims 1 to 7, comprising a detection beam path (2) for guiding a detection radiation (8) emanating from image locations (7) and to be detected; a detection unit (4) arranged in the detection beam path (2) for capturing image data of a plurality of image locations (7); and a correction unit (5) configured to correct image data of selected image locations (7) by means of a correction value in order to compensate for known imaging errors, characterized by , that the correction unit (5) generates control commands by means of which image data of selected image locations (7) are corrected during the respective acquisition. [9] Device according to claim 8, characterized bythat a scanning device (11) for the controlled exposure of the image locations (7) and / or for the controlled steering of the detection radiation (8) is present in the detection beam path (2) and / or in an excitation beam path (13) and can be controlled by means of control commands of the correction unit (5). [10] Camera (1) or microscope (10) with a device according to one of claims 8 and 9.

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