Correction device and correction method for correcting image data of an image sensor

Abstract

The invention relates to a correction device (100) for correcting image data of an image sensor (1) having a row- and column-wise arrangement of pixels for generating pixel values, wherein rows (2) or columns (3) of the image sensor each comprise a bright pixel region (4) with a plurality of bright pixels (5) and a dark pixel region (7) covered by a mask (6) with a plurality of dark pixels (8). The correction device comprises a function adaptation unit (102) adapted to adapt a function with multiple parameters to the pixel values ​​of the plurality of dark pixels of a row or column, a correction value determination unit (102) adapted to determine a correction value for the row or column based on the adapted function, and a correction unit (103) adapted to correct the pixel values ​​of the plurality of bright pixels of the row based on the correction value for the row or column.

Description

[0001] The invention relates to a correction device for correcting image data from an image sensor having a row- and column-wise arrangement of pixels for generating pixel values, wherein rows or columns of the image sensor each comprise a bright pixel region with a plurality of bright pixels and a dark pixel region covered by a mask with a plurality of dark pixels. The invention further relates to an electronic camera comprising such an image sensor and the correction device, a corresponding correction method, as well as a computer device and a computer program product. BACKGROUND OF THE INVENTION

[0002] Image sensors are often designed with the goal of being as sensitive as possible. However, this means that the image sensors are sensitive not only to an incoming light signal, but also to electrical interference. In line and area sensors (which are generally read line by line), such electrical interference can manifest itself, for example, as a line-by-line fluctuation in image brightness.

[0003] To compensate for this behavior, the majority of electronic cameras in use today include image sensors that, in addition to a region of defined light-sensitive pixels, so-called bright pixels, include on at least one side a region of relatively light-insensitive pixels, so-called dark pixels. For example, the dark pixels are covered with a mask, so that the incidence of a light signal on the dark pixels is blocked by the mask.

[0004] The signal from the bright pixels, the so-called bright signal, is approximately composed of two components: a first, exposure-dependent component caused by the incident light signal, and a second, exposure-independent component, the so-called dark signal. The dark signal is the signal that is already present in darkness and is caused by the electrical interference described above. In contrast to the first, exposure-dependent component, the dark signal is undesirable and should be removed from the image data. STATE OF THE ART

[0005] When capturing images with bright image content, initially no information is available about the dark signal of the bright pixels. Therefore, the assumption is used that the dark signal of the bright pixels, i.e. the signal of the bright pixels in the dark, approximately corresponds to the signal of the dark pixels. To compensate for the dark signal and to reduce the line-by-line fluctuation in image brightness, it is then customary to determine a correction value assigned to this line by averaging the pixel values ​​of the dark pixels in this image line and to subtract this correction value from the assigned signal of the bright pixels. Such a method for correcting image data from an image sensor is described, for example, in US 2004 / 0189839 A1.

[0006] In practice, however, the coverage of dark pixels is not perfect. If a bright light signal hits the image sensor near or in the area of ​​the dark pixels, stray light can enter the dark pixels due to residual light transmittance of the mask and, above all, due to multiple reflections in the layers between the mask and the silicon of the dark pixels, causing light from the bright pixels to reach the dark pixels from the side. In such a case, the average-based dark pixel correction described above leads to overcorrection and thus dark stripes in the image data.

[0007] DE 10 2008 016 393 A1 discloses that, in a method for correcting image errors in electronic cameras with image sensors that, in addition to at least one area with light-sensitive bright pixels, also have at least one area with relatively light-insensitive dark pixels, wherein the image errors are caused by parasitic exposure of dark pixels, a dark pixel value associated with this line is determined from the dark pixels of at least one image line. A difference is formed between the signal of the associated bright pixels and the dark pixel value, whereby image errors can be caused by the parasitic exposure of dark pixels.In this case, at least one first image area limited in the vertical direction or image area limited in the temporal direction is defined in which no overexposure can occur, and at least one second image area limited in the vertical direction or image area limited in time in which overexposure can occur and which does not overlap with the first image areas, and a difference is formed between the signal of the assigned bright pixels of the second image areas and dark pixel values ​​of the first image areas.

[0008] US 2004 / 0150729 A1 aims to provide an imaging device that can reliably correct dark current components that occur locally in an imaging sensor, such as those caused by an FDA.The imaging device comprises: a storage unit that prestores information representing a relationship between one of the dark current components and an output signal of an optical black pixel arranged in a predetermined optical black area on an imaging sensor, the dark current components being respectively superimposed on pixel signals of effective pixels arranged in a predetermined effective pixel area on the imaging sensor; a dark current extraction unit that extracts dark current components based on both the information stored in the storage unit and the output signal of the optical black pixel; and a correction unit that corrects the dark current components extracted by the dark current extraction unit according to the pixel signals.

[0009] US 2013 / 0271628 A1 describes examples of systems and methods that provide dark current estimates for pixels of a photosensor as a function of the temperature of the sensor and the gain applied to the photosensor. In various implementations, the dark current estimated for each pixel may depend at least in part on a global scale factor and bias that depend on temperature and gain, as well as a temperature-independent and gain-independent offset value for each pixel. The scale, bias, and offsets may be determined from multiple dark-field images acquired by the sensor over a range of operating temperatures. In some cases, the scale and bias may be determined from a subset of fewer than all of the image pixels.The scale and bias derived for a particular sensor can be used to calibrate different sensors. SUMMARY OF THE INVENTION

[0010] The invention is based on the object of providing a correction device for correcting image data of an image sensor with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows or columns of the image sensor each comprise a bright pixel area with a plurality of bright pixels and a dark pixel area covered with a mask with a plurality of dark pixels, wherein the correction device makes it possible to avoid an overcorrection of the image data, as can arise in the mean-based dark pixel correction known from the prior art, or at least to reduce such an overcorrection.

[0011] According to a first aspect of the invention, a correction device is provided for correcting image data of an image sensor having a row- and column-wise arrangement of pixels for generating pixel values, wherein rows or columns of the image sensor each comprise a bright pixel area with a plurality of bright pixels and a dark pixel area covered with a mask with a plurality of dark pixels, wherein the correction device comprises: - a function adaptation unit adapted to adapt a multi-parameter function to the pixel values ​​of the plurality of dark pixels of a row or column; - a correction value determination unit adapted to determine a correction value for the row or column based on the adjusted function; and - a correction unit adapted to correct the pixel values ​​of the plurality of bright pixels of the row or column based on the correction value for the row or column.

[0012] The invention is based on the inventor's finding that the pixel values ​​of the plurality of dark pixels in a row or column into which scattered light is incident have a characteristic that can be approximately described by a function with multiple parameters. By adapting such a function to the pixel values ​​of the plurality of dark pixels in a row or column and determining a correction value for the row or column based on the adapted function, it is possible to completely or at least partially subtract the proportion of scattered light when determining the correction value for the row or column, so that the correction value is essentially determined only by the dark signal component.If the pixel values ​​of the plurality of bright pixels of the row or column are then corrected based on the correction value for the row or column, it is possible to avoid or at least reduce overcorrection of the image data, as can occur with the mean-based dark pixel correction known from the prior art.

[0013] The invention can be used, for example, in an image sensor in which rows of the image sensor each comprise a bright pixel region with a plurality of bright pixels and a dark pixel region covered by a mask with a plurality of dark pixels, in order to correct row-by-row fluctuations in image brightness, in particular due to electrical interference. However, the invention can also be used in an image sensor in which columns of the image sensor each comprise a bright pixel region with a plurality of bright pixels and a dark pixel region covered by a mask with a plurality of dark pixels, in order to correct column-by-column fluctuations in image brightness. Such column-by-column fluctuations in image brightness can arise, for example, from differences in the analog-to-digital converters (ADCs), which are arranged column-by-column in some architectures.Of course, it is also possible to use the invention in an image sensor in which both rows and columns of the image sensor each comprise a bright pixel region with a plurality of bright pixels and a dark pixel region covered by a mask with a plurality of dark pixels. In this case, fluctuations in image brightness can be corrected both row-by-row and column-by-column. The "or" between the terms "row" and "column" in the claims is therefore not to be understood as an "exclusive or."

[0014] According to an advantageous development of the invention, the function has larger values ​​for dark pixels positioned closer to the bright pixel region than for dark pixels positioned farther away from the bright pixel region. This is based on the inventor's finding that the proportion of scattered light in the pixel values ​​of the majority of dark pixels in the row or column decreases with increasing distance of the dark pixels from the bright pixel region.

[0015] According to an advantageous development of the invention, the function is a non-linear function, preferably a power function. According to the inventor's knowledge, the decrease in the proportion of scattered light in the pixel values ​​of the majority of dark pixels in the row or column with increasing distance of the dark pixels from the bright pixel region often occurs such that the proportion decreases from one dark pixel to the next by a fixed percentage of the proportion of scattered light in the pixel value of the dark pixel. The fixed percentage depends on the brightness of the overexposure and its position in the image data; however, it is relatively constant within a row or column from one dark pixel to the next. This results in a non-linear function for the decrease in scattered light, which, according to the inventor's knowledge, can be described with good accuracy by a power function, for example, an exponential function.

[0016] According to an advantageous development of the invention, the correction device further comprises: - a pre-filtering unit adapted to pre-filter the plurality of dark pixels of the row or column before adapting the function to the pixel values ​​of the plurality of dark pixels of the row or column.

[0017] This is advantageous because saturated or defective dark pixels may occur in the majority of dark pixels in the row or column, which can negatively influence the correction value. The function is then adapted to the pixel values ​​of the majority of dark pixels in the row or column based on the pre-filtered majority of dark pixels.

[0018] The pre-filtering may, for example, comprise median filtering, or it may comprise the exclusion of dark pixels whose pixel value is greater than a threshold, or of dark pixels that were previously determined to be defective. Determining defective dark pixels may, for example, occur during the manufacture of the image sensor or in a subsequent step, such as a quality assurance step. The defective dark pixels may, for example, be stored in a memory of the correction device.

[0019] Dark pixels with pixel values ​​greater than the threshold, or dark pixels previously identified as defective, are not used when adapting the function to the pixel values ​​of the majority of dark pixels in the row or column. The function is then adapted only based on the pixel values ​​of a portion of the majority of dark pixels—not including the excluded dark pixels—in the row or column. If median filtering is used as pre-filtering, the function can be adapted to the pixel values ​​of the majority of dark pixels in the row or column based on the pixel values ​​of all dark pixels in the majority of dark pixels.Furthermore, it is also possible to interpolate the pixel values ​​of dark pixels whose pixel value is greater than the threshold, or of dark pixels previously determined to be defective, from the pixel values ​​of directly or indirectly neighboring dark pixels, for example, using a median function, a linear function, a quadratic function, a cubic function, or spline interpolation. The interpolated pixel values ​​can then also be used to adapt the function to the pixel values ​​of the majority of dark pixels in the row or column.

[0020] According to an advantageous development of the invention, the function adaptation unit is adapted to adapt the function to the pixel values ​​of the plurality of dark pixels in the row or column based on scaled positions of the plurality of dark pixels in the row or column. In this way, it is possible to use a function that can be easily and very efficiently adapted in software or hardware to the pixel values ​​of the plurality of dark pixels in the row or column. The software can, for example, be adapted to be executed on a central processor (CPU), a graphics processor (GPU), or a microprocessor (MCU). The hardware could be a computing unit, for example a field programmable gate array (FPGA) or an image signal processor (ISP) - for example as part of an integrated CPU (IC).embedded CPU) - can be used.

[0021] The function can be understood as a chained function in which the scaled positions of the majority of dark pixels of the row or column depend on the positions of the majority of dark pixels of the row or column and the values ​​of the function depend on the scaled positions of the majority of dark pixels of the row or column.

[0022] According to an advantageous development of the invention, the scaled positions of the plurality of dark pixels in the row or column result from the positions of the plurality of dark pixels in the row or column via a scaling function, wherein the scaling function comprises a hyperbola. According to the inventor's insight, the use of a scaling function comprising a hyperbola allows the characteristics of the pixel values ​​of the plurality of dark pixels in the row or column to be deformed non-linearly such that the adaptation of the function to the pixel values ​​of the plurality of dark pixels in the row or column can be carried out using a function particularly suitable for implementation in software or hardware.

[0023] For example, in digital circuits, it is comparatively simple, resource-efficient, and cost-effective to perform additions, subtractions, and multiplications. In an FPGA, for example, additions and subtractions can be performed using logic elements. Dedicated multipliers are also available for multiplications. The adaptation of the function to the pixel values ​​of the majority of dark pixels in the row or column can then be performed preferentially using such hardware-friendly operations.

[0024] According to an advantageous development of the invention, the hyperbola has the form p s = k / (k + p), where p is the position of a dark pixel in the dark pixel area, p sis the scaled position of the dark pixel, and k is a predetermined constant. The predetermined constant k is, in particular, a value that depends on the design of the image sensor and can be determined in advance. The scaled positions of the plurality of dark pixels in the row or column can, for example, be in a range from 0.0 to 1.0.

[0025] According to an advantageous development of the invention, the scaled positions of the plurality of dark pixels in the row or column are predetermined and stored in a memory of the correction device. In this way, the adaptation of the function to the pixel values ​​of the plurality of dark pixels in the row or column can be divided into a runtime-independent part, namely the determination of the scaled positions of the plurality of dark pixels in the row or column, and a runtime-dependent part, namely the adaptation of the function to the pixel values ​​of the plurality of dark pixels in the row or column based on the scaled positions of the plurality of dark pixels in the row or column. As explained above, according to the inventor's knowledge, the runtime-dependent part can be implemented simply and very efficiently in software or hardware.The storage of the predetermined scaled positions of the plurality of dark pixels of the row or column can be done, for example, in the form of a lookup table.

[0026] According to an advantageous development of the invention, the function is a polynomial of at least second order, preferably a parabola, wherein the correction value determining unit is adapted to determine the correction value for the row or column based on the limit value, for example the minimum or maximum, of the fitted polynomial.

[0027] Since the proportion of scattered light in the pixel values ​​of the majority of dark pixels of the row or column decreases with increasing distance of the dark pixels from the light pixel area, the limit value of the fitted polynomial, according to the inventor's finding, essentially corresponds to the dark signal sought.

[0028] According to an advantageous development of the invention, the function is preferably a polynomial of at least second order, preferably a parabola, wherein the correction value determining unit is adapted to determine the correction value for the row or column based on the value of the fitted function at a position of the dark pixel region which lies in a range extending from the position of the dark pixel positioned furthest from the bright pixel region toward the bright pixel region and whose width is 20%, preferably 10%, more preferably 5% of the width of the dark pixel region.

[0029] According to the inventor's discovery, the desired dark signal can be determined simply and very robustly by using, for example, the value of the fitted function at a predetermined location, e.g., at the end of the dark pixel region, i.e., in a region as far away as possible from the light pixel region, as the correction value for the row or column. The width of the region and the width of the dark pixel region can be determined, for example, based on the positions of the majority of dark pixels in the row or column or based on the scaled positions of the majority of dark pixels in the row or column.

[0030] According to an advantageous development of the invention, the function adaptation unit is adapted to adapt the function to the pixel values ​​of the plurality of dark pixels in the row or column using a least-squares method. This is more efficient than, for example, the use of iterative methods that approximate the solution in a number of iterative steps. When using a least-squares method, the adaptation of the function to the pixel values ​​of the plurality of dark pixels in the row or column can be implemented very efficiently in software or hardware, for example. This is particularly efficient if the function is a polynomial of at least second order, in particular a parabola.

[0031] According to an advantageous development of the invention, the functionality of the pre-filtering unit and / or the function adaptation unit and / or the correction value determination unit and / or the correction unit in the correction device is implemented in hardware logic. The hardware logic can, for example, comprise an FPGA or an ISP—for example, as part of an integrated CPU.

[0032] According to a further aspect of the invention, an electronic camera is provided, the electronic camera comprising: - an image sensor with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows or columns of the image sensor each comprise a light pixel area with a plurality of light pixels and a dark pixel area covered by a mask with a plurality of dark pixels; and - the correction device according to one of claims 1 to 12 for correcting the image data of the image sensor.

[0033] According to a further aspect of the invention, a correction method is provided for correcting image data of an image sensor having a row- and column-wise arrangement of pixels for generating pixel values, wherein rows or columns of the image sensor each comprise a bright pixel area having a plurality of bright pixels and a dark pixel area covered by a mask having a plurality of dark pixels, the correction method comprising: - Adapting a multi-parameter function to the pixel values ​​of the majority of dark pixels in a row or column; - Determining a correction value for the row or column based on the fitted function; and - Correcting the pixel values ​​of the plurality of bright pixels of the row or column based on the correction value for the row or column.

[0034] According to a further aspect of the invention, a computer device is provided, wherein the computer device comprises a computing unit configured to carry out the correction method according to claim 14.

[0035] According to a further aspect of the invention, a computer program product is provided, the computer program product comprising code means for causing a computer device to execute the correction method according to claim 14 when the computer program product is executed on the computer device.

[0036] It is understood that the correction device according to claim 1, the electronic camera according to claim 13, the correction method according to claim 14, the computer device according to claim 15 and the computer program product according to claim 16 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0037] It is understood that a preferred embodiment of the invention may also be any combination of the dependent claims with the corresponding independent claim. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Preferred embodiments of the invention are described in more detail below with reference to the accompanying figures, wherein Fig. 1 schematically and exemplarily shows an image sensor with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows of the image sensor each comprise a bright pixel area with a plurality of bright pixels and a dark pixel area covered by a mask with a plurality of dark pixels, Fig. 2 schematic and exemplary image data of the Fig. 1 shown image sensor, which were corrected with a mean-based dark pixel correction known from the prior art, Fig. 3 schematically and exemplarily shows an embodiment of a correction device for correcting image data of an image sensor with a row and column arrangement of pixels for generating pixel values, Fig. 4 shows schematically and exemplarily a possibility of determining the predetermined constant k in advance, Fig. 5 schematically and exemplarily shows an image sensor with a row- and column-wise arrangement of pixels for generating pixel values, wherein columns of the image sensor each comprise a bright pixel area with a plurality of bright pixels and a dark pixel area covered by a mask with a plurality of dark pixels, Fig. 6 schematic and exemplary image data of the Fig. 5 shown image sensor, which were corrected with a mean-based dark pixel correction known from the prior art, Fig. 7 shows a flowchart illustrating an example embodiment of a correction method for correcting image data of an image sensor having a row and column arrangement of pixels for generating pixel values, and Fig. 8 schematically and exemplarily shows an embodiment of an electronic camera with an image sensor and a correction device for correcting the image data of the image sensor.

[0039] In the figures, identical or corresponding elements or units are provided with identical or corresponding reference symbols. If an element or unit has already been described in connection with one figure, a detailed description may be omitted in connection with another figure.

[0040] Fig. Figure 1 schematically shows an example of an image sensor 1 with a row- and column-wise arrangement of pixels for generating pixel values. The rows 2 of the image sensor 1 each have a bright pixel region 4 with a plurality of bright pixels 5 and a dark pixel region 7 covered by a mask 6 with a plurality of dark pixels 8.

[0041] Fig. 2 shows schematically and exemplarily image data 10 of the Fig. 1, which were corrected using a mean-based dark pixel correction known from the prior art. The image data 10 show an outdoor scene whose light is incident on the image sensor 1. A bright light signal 11, in this case from the particularly bright sun, is incident on the image sensor 1 near or in the area of ​​the dark pixels 8. Due to residual light transmittance of the mask 6 and, above all, due to the fact that light from the bright pixels 5 reaches the dark pixels 8 from the side due to multiple reflections in the layers between the mask 6 and the silicon of the dark pixels 8, stray light can then enter the dark pixels 8. In such a case, the mean-based dark pixel correction known from the prior art leads to overcorrection and thus dark stripes 12 in the image data 10.This is because the correction values ​​determined by averaging in the lines 2 of the image sensor 1 assigned to the overexposure 11 are increased compared to the actual dark signal due to the scattered light incident on the dark pixels 8. The difference between the bright signal and the increased correction value creates the dark stripes 12 in the image data 10. In extreme cases, the stripes 12 could even be completely black.

[0042] Fig. Figure 3 schematically and exemplarily shows an embodiment of a correction device 100 for correcting image data 10 of an image sensor 1 with a row- and column-wise arrangement of pixels for generating pixel values. The correction device 100 comprises a pre-filtering unit 101, a function adaptation unit 102, a correction value determination unit 103, and a correction unit 104. The correction device 100 makes it possible to avoid, or at least reduce, overcorrection of the image data 10, as can arise with the mean-based dark pixel correction known from the prior art.

[0043] The function adaptation unit 102 is adapted to adapt a function with multiple parameters to the pixel values ​​of the plurality of dark pixels 8 of a row 2. The function has larger values ​​for dark pixels 8 that are positioned closer to the light pixel region 4 than for dark pixels 8 that are positioned further away from the light pixel region 4.

[0044] The pre-filtering unit 101 is adapted to pre-filter the plurality of dark pixels 8 of row 2 before adapting the function to the pixel values ​​of the plurality of dark pixels 8 of row 2. In this embodiment, the pre-filtering comprises excluding dark pixels 8 whose pixel value is greater than a threshold. For example, the largest possible unsaturated pixel value can be used as the threshold to thus exclude saturated dark pixels 8.

[0045] The function adaptation unit 102 is adapted here to perform the adaptation of the function to the pixel values ​​of the plurality of dark pixels 8 of row 2 or column 3 based on scaled positions of the plurality of dark pixels 8 of row 2. In this embodiment, the scaled positions of the plurality of dark pixels 8 of row 2 result from the positions of the plurality of dark pixels 8 of row 2 via a scaling function, wherein the scaling function comprises a hyperbola. In particular, the hyperbola here has the form p s = k / (k + p), where p is the position of a dark pixel 8 in the dark pixel area 7, p s is the scaled position of the dark pixel 8, and k is a predetermined constant. The predetermined constant k is a value that depends on the design of the image sensor and can be determined in advance (see also Fig. 4). The scaled positions of the majority of dark pixels 8 of row 2 lie in a range from 0.0 to 1.0.

[0046] In this embodiment, the scaled positions of the plurality of dark pixels 8 of row 2 are predetermined and stored in a memory (not shown in the figure) of the correction device 100. In other embodiments, however, it is also possible for the scaled positions of the plurality of dark pixels 8 of row 2 to be determined only at runtime.

[0047] In this embodiment, the adaptation of the function to the pixel values ​​of the plurality of dark pixels 8 of row 2 is thus carried out based on the pre-filtered plurality of dark pixels 8 and the scaled positions of the plurality of dark pixels 8. In this embodiment, the function adaptation unit 102 is adapted to adapt the function to the pixel values ​​of the plurality of dark pixels 8 of row 2 by means of a least squares method.

[0048] The correction value determination unit 103 is adapted to determine a correction value for row 2 based on the fitted function. In this embodiment, the function is at least a second-order polynomial, here a parabola, and the correction value determination unit 103 is adapted to determine the correction value for row 2 based on a limit value of the fitted polynomial.

[0049] The correction unit 104 is adapted to correct the pixel values ​​of the plurality of bright pixels 5 of the row 2 based on the correction value for the row 2.

[0050] The functionality of the pre-filtering unit 101, the function adaptation unit 102, the correction value determination unit 103, and the correction unit 104 is implemented in the correction device 100 in hardware logic (not shown in the figure).

[0051] In this embodiment, the correction device 100 for correcting image data 10 of an image sensor 1 is provided with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows 2 of the image sensor 1 each comprise a bright pixel region 4 with a plurality of bright pixels 5 and a dark pixel region 7 covered by a mask 6 with a plurality of dark pixels 8. In other embodiments, the correction device 100 for correcting image data 10 of an image sensor 1 can be provided with a row- and column-wise arrangement of pixels for generating pixel values, wherein columns 3 of the image sensor 1 each comprise a bright pixel region 4 with a plurality of bright pixels 5 and a dark pixel region 7 covered by a mask 6 with a plurality of dark pixels 8 (see also the Fig. 5 and Fig. 6). The described operations of the pre-filtering unit 101, the function adaptation unit 102, the correction value determination unit 103, and the correction unit 104 are then each carried out for a column 3 instead of for a row 2. In yet other embodiments, the correction device 100 can be provided for correcting image data 10 of an image sensor 1 with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows 2 and columns 3 of the image sensor 1 each comprise a bright pixel region 4 with a plurality of bright pixels 5 and a dark pixel region 7 covered by a mask 6 with a plurality of dark pixels 8.

[0052] One possibility to determine the predetermined constant k in advance is shown schematically and exemplarily in the Fig. 4 shown. Fig. Figure 4 (a) shows the characteristics of the pixel values ​​of the plurality of dark pixels 8 of a row 2 into which stray light is incident, for exemplary measurements on an image sensor 1 with 94 dark pixels 8 per row 2 for different bright light signals, i.e., row 2 is affected by different amounts of stray light. In this figure, the horizontal axis shows the unscaled positions (0 to 94) of the dark pixels 8, and the vertical axis shows the pixel values ​​of the dark pixels 8 (here in logarithmic representation). As can be seen, the dark pixels 8 that are positioned closer to the bright pixel area 4 (in the figure this would be on the left) have larger values ​​than dark pixels 8 that are positioned further away from the bright pixel area 4. Fig. 4 (b) shows the result of the joint fitting of the function with several parameters, here a parabola of the form a p s 2 + b p s+ c, where a, b, and c are the parameters of the parabola, and the constant k to the measured pixel values ​​of the plurality of dark pixels 8 of row 2 for the different brightness light signals. In this figure, the horizontal axis shows the scaled positions (0.0 to 1.0) of the dark pixels 8 resulting from scaling with the hyperbola as the scaling function, and the vertical axis shows the values ​​of the fitted parabola. The predetermined constant k can thus be determined as the value k for which the fitting of the parabola to the measured pixel values ​​of the plurality of dark pixels 8 of row 2 for the different brightness light signals produces the smallest error.

[0053] According to the inventor's discovery, it is also possible to set the linear parameter b of the parabola to 0 before jointly fitting the function with several parameters and the constant k to the measured pixel values ​​of the majority of dark pixels 8 of row 2 for the different bright light signals. In this case, the parabola has the form a p s 2 + c and fitting the parabola to the measured pixel values ​​of the majority of dark pixels 8 of row 2 for the different bright light signals produces a similarly small error. The use of a parabola of the form a p s 2 + c further simplifies implementation in software or hardware.

[0054] In the following, an embodiment of a correction method for correcting image data of an image sensor with a row and column arrangement of pixels for generating pixel values ​​is described with reference to the method described in the Fig. The correction procedure can be described using the flowchart shown in Figure 7. Fig. 3 or the further described embodiments of the correction device.

[0055] In step S101, the plurality of dark pixels 7 of row 2 or column 3 are pre-filtered before adapting the function to the pixel values ​​of the plurality of dark pixels 8 of row 2 or column 3. In step S102, a function with multiple parameters is adapted to the pixel values ​​of the plurality of dark pixels 8 of row 2 or column 3. In particular, in this embodiment, the adaptation of the function to the pixel values ​​of the plurality of dark pixels 8 of row 2 or column 3 is performed based on the pre-filtered plurality of dark pixels 8 and scaled positions of the plurality of dark pixels 8 of row 2 or column 3. In step S103, a correction value for row 2 or column 3 is determined based on the adapted function. In step S104, the pixel values ​​of the plurality of bright pixels 5 of row 2 or column 3 are corrected based on the correction value for row 2 or column 3.

[0056] In the embodiments described above, the correction unit 100 comprises the pre-filtering unit 101. In other embodiments, the correction unit 100 may not comprise the pre-filtering unit 101. In this case, it is possible for the function adaptation unit 102 to be adapted to adapt the function with multiple parameters to the non-pre-filtered pixel values ​​of the plurality of dark pixels 8 of a row 2 or column 3.

[0057] Fig.8 schematically and exemplarily shows an electronic camera 200. The electronic camera comprises an image sensor 1 with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows 2 or columns 3 of the image sensor 1 each comprise a bright pixel region 4 with a plurality of bright pixels 5 and a dark pixel region 7 covered by a mask 6 with a plurality of dark pixels 8, and the correction device 100 for correcting the image data 10 of the image sensor 1.

[0058] In the embodiments described above, the pre-filtering comprises the exclusion of dark pixels 8 whose pixel value is greater than a threshold value. In other embodiments, the pre-filtering may also comprise median filtering, or it may comprise the exclusion of dark pixels 8 that were previously determined to be defective. Furthermore, it is also possible to interpolate the pixel values ​​of the dark pixels 8 whose pixel value is greater than the threshold value, or of the dark pixels 8 that were previously determined to be defective, from the pixel values ​​of directly or indirectly neighboring dark pixels 8, for example using a median function, a linear function, a quadratic function, a cubic function, or spline interpolation. The interpolated pixel values ​​can then also be used in adapting the function to the pixel values ​​of the plurality of dark pixels 8 of row 2.In still other embodiments, the correction device 100 may not include the pre-filtering unit 101 at all.

[0059] In the embodiments described above, the function adaptation unit 102 is adapted to perform the adaptation of the multi-parameter function to the pixel values ​​of the plurality of dark pixels 8 of row 2 or column 3 based on the scaled positions of the plurality of dark pixels 8 of row 2 or column 3. In other embodiments, the function adaptation unit 102 may also be adapted to adapt the multi-parameter function based on the unscaled positions of the plurality of dark pixels 8 of a row 2 or column 3.

[0060] In the embodiments described above, the function is a parabola, and the correction value determining unit 103 is adapted to determine the correction value for row 2 or column 3 based on a limit value of the fitted polynomial. In other embodiments, the correction value determining unit 103 may also be adapted to determine the correction value for row 2 or column 3 based on the value of the fitted function at a position of the dark pixel region 7 that lies in a range extending from the position of the dark pixel 8, which is positioned furthest away from the bright pixel region 4, toward the bright pixel region 4, and whose width is 20%, preferably 10%, more preferably 5% of the width of the dark pixel region 7.

[0061] As described, the correction device 100 may be integrated into an electronic camera 200. However, the correction device 100 may also comprise a separate device, for example, a computer, a laptop, a tablet, a mobile phone, a dedicated external processing unit, a frame grabber card, or the like.

[0062] Further variations of the disclosed embodiments may be understood and practiced by one skilled in the art practicing the claimed invention from a consideration of the drawings, the specification, and the appended claims.

[0063] In the claims, the words “comprising” and “including” do not exclude other elements or steps, and the indefinite article “a” does not exclude a plurality.

[0064] A single unit or device may perform the functions of multiple elements recited in the claims. The fact that individual functions and / or elements are recited in different dependent claims does not mean that a combination of these functions and / or elements could not also be advantageously used.

[0065] The reference signs in the claims are not to be understood in such a way that the subject matter and the scope of protection of the claims are restricted by these reference signs.

[0066] In summary, a correction device for correcting image data of an image sensor with a row- and column-wise arrangement of pixels for generating pixel values ​​has been described, wherein rows or columns of the image sensor each comprise a bright pixel region with a plurality of bright pixels and a dark pixel region covered by a mask with a plurality of dark pixels. The correction device comprises a function adaptation unit adapted to adapt a function with multiple parameters to the pixel values ​​of the plurality of dark pixels of a row or column, a correction value determination unit adapted to determine a correction value for the row or column based on the adapted function, and a correction unit adapted to correct the pixel values ​​of the plurality of bright pixels of the row or column based on the correction value for the row or column.

Claims

[1] Correction device (100) for correcting image data (10) of an image sensor (1) with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows (2) or columns (3) of the image sensor (1) each comprise a bright pixel area (4) with a plurality of bright pixels (5) and a dark pixel area (7) covered by a mask (6) with a plurality of dark pixels (8), wherein the correction device (100) comprises: - a function adaptation unit (102) adapted to adapt a function having a plurality of parameters to the pixel values ​​of the plurality of dark pixels (8) of a row (2) or column (3); - a correction value determination unit (103) adapted to determine a correction value for the row (2) or column (3) based on the adjusted function; and - a correction unit (104) adapted to correct the pixel values ​​of the plurality of bright pixels (5) of the row (2) or column (3) based on the correction value for the row (2) or column (3). [2] Correction device (100) according to claim 1, wherein the function has larger values ​​for dark pixels (8) positioned closer to the bright pixel region (4) than for dark pixels (8) positioned further away from the bright pixel region (4). [3] Correction device (100) according to claim 1 or 2, wherein the function is a non-linear function, preferably a power function. [4] Correction device (100) according to one of claims 1 to 3, wherein the correction device (100) further comprises: - a pre-filtering unit (101) adapted to pre-filter the plurality of dark pixels (7) of the row (2) or column (3) before adapting the function to the pixel values ​​of the plurality of dark pixels (8) of the row (2) or column (3). [5] Correction device (100) according to one of claims 1 to 4, wherein the function adaptation unit (102) is adapted to perform the adaptation of the function to the pixel values ​​of the plurality of dark pixels (8) of the row (2) or column (3) based on scaled positions of the plurality of dark pixels (8) of the row (2) or column (3). [6] Correction device (100) according to claim 5, wherein the scaled positions of the plurality of dark pixels (8) of the row (2) or column (3) result from the positions of the plurality of dark pixels (8) of the row (2) or column (3) via a scaling function, wherein the scaling function comprises a hyperbola. [7] Correction device (100) according to claim 6, wherein the hyperbola has the form p s = k / (k + p), where p is the position of a dark pixel (8) in the dark pixel area (7), p s is the scaled position of the dark pixel (8), and k is a predetermined constant. [8] Correction device (100) according to one of claims 5 to 7, wherein the scaled positions of the plurality of dark pixels (8) of the row (2) or column (3) are predetermined and stored in a memory of the correction device (100). [9] Correction device (100) according to one of claims 1 to 8, wherein the function is a polynomial of at least second order, preferably a parabola, wherein the correction value determination unit (103) is adapted to determine the correction value for the row (2) or column (3) based on a limit value, for example the minimum or maximum, of the adapted polynomial. [10] Correction device (100) according to one of claims 1 to 9, wherein the function is preferably a polynomial of at least second order, preferably a parabola, wherein the correction value determination unit (103) is adapted to determine the correction value for the row (2) or column (3) based on the value of the adapted function at a position of the dark pixel region (7) which lies in a range extending from the position of the dark pixel (8) which is positioned furthest away from the light pixel region (4) in the direction of the light pixel region (4) and whose width is 20%, preferably 10%, more preferably 5% of the width of the dark pixel region (7). [11] Correction device (100) according to one of claims 1 to 10, wherein the function adaptation unit (102) is adapted to adapt the function to the pixel values ​​of the plurality of dark pixels (8) of the row (2) or column (3) by means of a least squares method. [12] Correction device (100) according to one of claims 1 to 11, wherein the functionality of the pre-filtering unit (101) and / or the scaling unit (102) and / or the function adaptation unit (102) and / or the correction value determination unit (103) and / or the correction unit (104) is implemented in hardware logic in the correction device. [13] Electronic camera (200), comprising: - an image sensor (1) with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows (2) or columns (3) of the image sensor (1) each comprise a bright pixel region (4) with a plurality of bright pixels (5) and a dark pixel region (7) covered by a mask (6) with a plurality of dark pixels (8); and - the correction device (100) according to one of claims 1 to 12 for correcting the image data (10) of the image sensor (1). [14] Correction method for correcting image data (10) of an image sensor (1) with a row- and column-wise arrangement of pixels for generating pixel values, wherein rows (2) or columns (3) of the image sensor (1) each comprise a bright pixel area (4) with a plurality of bright pixels (5) and a dark pixel area (7) covered with a mask (6) with a plurality of dark pixels (8), wherein the correction method comprises: - adapting (S102) a function with several parameters to the pixel values ​​of the plurality of dark pixels (8) of a row (2) or column (3); - determining (S103) a correction value for the row (2) or column (3) based on the adjusted function; and - Correcting (S104) the pixel values ​​of the plurality of bright pixels (5) of the row (2) based on the correction value for the row (2) or column (3). [15] Computer device comprising a computing unit configured to carry out the correction method according to claim 14. [16] A computer program product comprising code means for causing a computer device to carry out the correction method according to claim 14 when the computer program product is executed on the computer device.

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