Correction apparatus and correction method for correcting image data of image sensor

Abstract

The invention relates to a correction device (100) for correcting image data of an image sensor (1) having pixels arranged in rows and in columns for generating pixel values, wherein the rows (2) or columns (3) of image sensors each comprise a bright pixel region (4) having a plurality of bright pixels (5) and a dark pixel region (7) covered with a mask (6) and having a plurality of dark pixels (8). A correction device includes: a function matching unit (102) that matches a function having a plurality of parameters to pixel values of a plurality of dark pixels of a row or a column; a correction value determination unit (103) adapted to determine a correction value for the row or column on the basis of the adapted function; and a correction unit (104) adapted to correct the pixel values of the plurality of bright pixels of the row on the basis of the correction value for the row or the column.

Description

Technical Field

[0001] The present invention relates to a correction device for correcting image data of an image sensor, the image sensor having row - arranged and column - arranged pixels for generating pixel values, wherein a row or a column of the image sensor respectively includes a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask. The present invention also relates to an electronic camera including such an image sensor and a correction device, a corresponding correction method, a computer device, and a computer program product. Background Art

[0002] Image sensors are generally improved with the goal of being as sensitive as possible. However, this means that the image sensor is sensitive not only to incident light signals but also to electrical interference. In line sensors and area sensors (the area sensors are usually read row by row), this electrical interference can be indicated by, for example, the row - by - row fluctuations of the image brightness.

[0003] To compensate for this manifestation, most of the currently used electronic cameras include an image sensor that, in addition to a region of pixels with defined photosensitivity, so - called bright pixels, also includes, at least on one side, a region of pixels that are relatively insensitive to light, so - called dark pixels. For example, the dark pixels are covered with a mask such that the incidence of light signals onto the dark pixels is blocked by the mask.

[0004] The signal of the bright pixels, i.e., the so - called bright signal, is approximately composed of two parts, namely a first part related to the illumination caused by the incident light signal and a second part independent of the illumination, the so - called dark signal. The dark signal is a signal that already exists in the dark and is caused by the above - mentioned electrical interference. Contrary to the first part related to the illumination, the dark signal is undesirable and should be removed from the image data.

[0005] When recording an image with a bright image content, initially there is no information about the dark signal of the bright pixels. Therefore, the following assumption is used: 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 row - by - row fluctuations of the image brightness, it is common to determine a correction value associated with the row by taking the median of the pixel values of the dark pixels of the image row and subtracting this correction value from the associated signal of the bright pixels. For example, such a method for correcting image data of an image sensor is described in US 2004 / 0189839 A1.

[0006] However, in reality, the coverage of the dark pixels is not perfect. If a bright light signal impinges on the image sensor near or in the area of a dark pixel, then scattered light incidence into the dark pixel can be caused by residual light penetration of the mask and in particular by light reaching the dark pixel laterally from a bright pixel due to multiple reflections in the layer between the mask and the silicon of the dark pixel. The described median-based dark pixel correction causes overcorrection in this case, resulting in dark stripes in the image data. Summary of the Invention

[0007] The object on which the present invention is based is to provide a correction device for correcting the image data of an image sensor, which image sensor has row-wise and column-wise arranged pixels for generating pixel values, wherein a row or a column of the image sensor respectively includes a bright pixel region having a plurality of bright pixels and a dark pixel region covered with a mask and having a plurality of dark pixels, and wherein the correction device achieves: avoiding overcorrection of the image data, as can occur in median-based dark pixel correction known from the prior art, or at least reducing such overcorrection.

[0008] According to a first aspect of the present invention, there is provided a correction device for correcting the image data of an image sensor, which image sensor has row-wise and column-wise arranged pixels for generating pixel values, wherein a row or a column of the image sensor respectively includes a bright pixel region having a plurality of bright pixels and a dark pixel region covered with a mask and having dark pixels, and wherein the correction device comprises:

[0009] - a function matching unit, which is matched to match a function having a plurality of parameters to the pixel values of a plurality of dark pixels of a row or a column;

[0010] - a correction value determination unit, which is matched to determine a correction value for a row or a column based on the matched function; and

[0011] - a correction unit, which is matched to correct the pixel values of a plurality of bright pixels of a row or a column based on the correction value for the row or the column.

[0012] The present invention is based on the following recognition of the inventors: The pixel values of a plurality of dark pixels in a row or column into which scattered light is incident have characteristics that can be approximated by a function having a plurality of parameters. By matching such a function to the pixel values of a plurality of dark pixels in a row or column according to the present invention and determining a correction value for the row or column based on the matched function, the share of scattered light can be at least partially calculated therefrom when determining the correction value for the row or column, such that the correction value is substantially determined only by the dark signal component. Thus, if the pixel values of a plurality of bright pixels in a row or column are corrected based on the correction value for the row or column, it is possible to avoid overcorrection of the image data, as would occur with median-based dark pixel correction known from the prior art, or at least reduce such overcorrection.

[0013] The present invention can be used, for example, in the following image sensors: In the image sensor, the rows of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask, in order to correct, row by row, fluctuations in image brightness caused especially by electrical interference. However, the present invention can also be used in the following image sensors, in which the columns of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask, in order to correct, column by column, fluctuations in image brightness. Such column-by-column fluctuations in brightness may be generated, for example, by analog-to-digital converters (ADCs) of pixels arranged column by column in some architectures. Of course, it is also possible to use the present invention in the following image sensors, in which the rows and columns of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask. Thus, in this case, fluctuations in image brightness can be corrected row by row and column by column. That is, in this context, the "or" in the terms "row" and "column" is not understood as an "exclusive or".

[0014] According to an advantageous refinement of the present invention, the function for dark pixels located closer to the bright pixel region has a greater value compared to the function for dark pixels located farther from the bright pixel region. This is based on the following recognition of the inventors: The share of scattered light in the pixel values of a plurality of dark pixels in a row or column decreases as the distance of the dark pixels from the bright pixel region increases.

[0015] According to an advantageous refinement of the invention, the function is a non-linear function, preferably a power function. The share of scattered light in the pixel values of a plurality of dark pixels in a row or column decreases as the distance of the dark pixels from the bright pixel region increases. According to the inventor's understanding, this is achieved in many cases such that the decrease in the share from one dark pixel to the next takes place respectively by a fixed percentage of the share of scattered light in the pixel value of the dark pixel. Here, the fixed percentage is related to the brightness of the over-illumination and its orientation in the image data; however, the fixed percentage is relatively constant from one dark pixel to the next within the row or column. Thus, a non-linear function results for the decrease of the scattered light, which according to the inventor's understanding can be described with good accuracy by a power function, for example an exponential function.

[0016] According to an advantageous refinement of the invention, the correction device further comprises:

[0017] - a pre-filtering unit, which is adapted to pre-filter a plurality of dark pixels in a row or column before matching the function to the pixel values of the plurality of dark pixels in the row or column.

[0018] This is advantageous because saturated or defective dark pixels may occur among the plurality of dark pixels in a row or column, which would have an adverse effect on the correction value. The matching of the function to the pixel values of the plurality of dark pixels in the row or column is then based on the pre-filtered plurality of dark pixels.

[0019] The pre-filtering can for example comprise median filtering, or the pre-filtering can comprise excluding dark pixels with a pixel value greater than a threshold or dark pixels previously determined to be defective. The determination of defective dark pixels can for example be carried out during the manufacture of the image sensor or in a subsequent step, such as a quality assurance step. Defective dark pixels can for example be stored in the memory of the correction device.

[0020] Dark pixels with a pixel value greater than the threshold or dark pixels previously determined to be defective are not used when matching the function to the pixel values of the plurality of dark pixels in the row or column. The matching of the function is then carried out only based on the pixel values of a part of the plurality of dark pixels (in the case of non-excluded pixel values) in the row or column. If median filtering is carried out as pre-filtering, then it is optionally possible to carry out the matching of the function to the pixel values of the plurality of dark pixels in the row or column based on the pixel values of all the dark pixels of the plurality of dark pixels. In addition, it is also possible to interpolate the pixel value of a dark pixel with a pixel value greater than the threshold or a dark pixel previously determined to be defective by the pixel values of directly or indirectly adjacent dark pixels, for example by means of median functions, linear functions, quadratic functions, cubic functions or spline interpolation. The interpolated pixel value can then also be used when matching the function to the pixel values of the plurality of dark pixels in the row or column.

[0021] According to an advantageous refinement of the invention, the function matching unit is adapted to perform the matching of the function to the pixel values of a plurality of pixels of a row or column based on the scaled positions of a plurality of dark pixels of the row or column. In this way, it is possible to use a function which can be matched in a simple and very efficient manner to the pixel values of a plurality of dark pixels of a row or column in software or hardware. The software can for example be adapted to run on a central processing unit (CPU), a graphics processing unit (GPU) or a microcontroller unit (MCU). As hardware, a computing unit can be used, such as a field programmable gate array (FPGA) or an image signal processor (ISP) (for example as part of an embedded CPU).

[0022] The function can be understood as a chained function in which the scaled positions of a plurality of dark pixels of a row or column are related to the positions of a plurality of dark pixels of the row or column and the values of the function are related to the scaled positions of a plurality of dark pixels of the row or column.

[0023] According to an advantageous refinement of the invention, the scaled positions of a plurality of dark pixels of a row or column are obtained from the positions of a plurality of dark pixels of the row or column via a scaling function, wherein the scaling function includes a hyperbola. The use of a scaling function including a hyperbola allows, according to the inventor's knowledge, the characteristics of the pixel values of a plurality of dark pixels of a row or column to be non-linearly deformed such that the matching of the function to the pixel values of a plurality of dark pixels of a row or column can be performed by a function which is particularly suitable for implementation in software or hardware.

[0024] Thus, for example in a digital circuit, addition, subtraction and multiplication can be performed relatively simply, resource-savingly and at low cost. For example, in an FPGA, addition and subtraction can be performed by means of logic elements. Alternatively, a dedicated multiplier can also be used for multiplication. The matching of the function to the pixel values of a plurality of dark pixels of a row or column can then preferably be carried out using such hardware-friendly operations.

[0025] According to an advantageous refinement of the invention, the hyperbola has the form p s = k / (k + p), where p is the position of the dark pixel in the dark pixel region, p sis the scaled position of the dark pixels, and k is a predetermined constant. Here, the predetermined constant k is in particular a variable that is related to the structural form of the image sensor and can be determined in advance. The scaled positions of the dark pixels of a row or column can be in the range from 0.0 to 1.0, for example.

[0026] According to an advantageous refinement of the invention, the scaled positions of the dark pixels of a row or column are predetermined and stored in the memory of the correction device. In this way, the matching of the function to the pixel values of the dark pixels of a row or column can be divided into a part that is independent of the runtime, namely determining the scaled positions of the dark pixels of a row or column, and a part that is related to the runtime, namely matching the function to the pixel values of the dark pixels of a row or column based on the scaled positions of the dark pixels of a row or column. As explained above, the part related to the runtime can be carried out in a simple and particularly efficient manner in software or hardware based on the inventor's knowledge. The storage of the predetermined scaled positions of the dark pixels of a row or column can be carried out in the form of a look-up table, for example.

[0027] According to an advantageous refinement of the invention, the function is a polynomial of at least second order, preferably a parabola.

[0028] wherein the correction value determination unit is matched to determine a correction value for a row or column based on the extreme value, such as the minimum or maximum value, of the matched polynomial.

[0029] Since the share of scattered light in the pixel values of the dark pixels of a row or column decreases as the distance of the dark pixels from the bright pixel region increases, the extreme value of the matched polynomial basically corresponds to the sought dark signal according to the inventor's knowledge.

[0030] According to an advantageous refinement of the invention, the function is preferably a polynomial of at least second order, preferably a parabola.

[0031] wherein the correction value determination unit is matched to determine a correction value for a row or column based on the value of the matched function at a position in the dark pixel region that extends in the direction from the position of the dark pixel that is located furthest from the bright pixel region towards the bright pixel region and the width of which is 20%, preferably 10%, more preferably 5% of the width of the dark pixel region.

[0032] According to the inventor's understanding, the sought-after dark signal can be determined in a simple and very robust manner by using, as a correction value for a row or column, for example, the value of a function matched at a preset location, such as at the end of the dark pixel region, i.e., in a region as far as possible from the bright pixel region. The width of the region and the width of the dark pixel region can be determined, for example, based on the positions of a plurality of dark pixels in a row or column or based on the scaled positions of a plurality of dark pixels in a row or column.

[0033] According to an advantageous refinement of the invention, the function matching unit is matched such that the function is matched to the pixel values of a plurality of dark pixels in a row or column by means of the least squares method. This is more efficient compared to, for example, using an iterative method that approximates the solution through a plurality of iterative steps. When using the least squares method, the matching of the function to the pixel values of a plurality of dark pixels in a row or column can be implemented very efficiently in software or hardware. This can be implemented particularly efficiently when the function is a polynomial of at least second order, in particular a parabola.

[0034] According to an advantageous refinement of the invention, the functionality of the pre-filtering unit and / or the function matching unit and / or the correction value determination unit and / or the correction unit is implemented in hardware logic in the correction device. The hardware logic can include, for example, an FPGA or an ISP (e.g., as part of an integrated CPU).

[0035] According to another aspect of the invention, there is provided an electronic camera, wherein the electronic camera includes:

[0036] - an image sensor having row-wise and column-wise pixels for generating pixel values, wherein the rows and columns of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask; and - a correction device for correcting the image data of the image sensor according to the invention.

[0037] According to another aspect of the invention, there is provided a correction method for correcting the image data of an image sensor having row-wise and column-wise pixels for generating pixel values, wherein the rows or columns of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask, the correction method including:

[0038] - matching a function having a plurality of parameters to the pixel values of a plurality of dark pixels in a row or column;

[0039] - determining a correction value for a row or column based on the matched function; and

[0040] - correcting the pixel values of a plurality of bright pixels in a row or column based on the correction value for the row or column.

[0041] According to another aspect of the present invention, there is provided a computer device, wherein the computer device includes a computing unit, and the computing unit is designed to execute the calibration method according to the present invention.

[0042] According to another aspect of the present invention, there is provided a computer program product, wherein the computer program product includes a code mechanism, and the code mechanism is used to cause the computer device to implement the calibration method according to the present invention when the computer program product runs on the computer device.

[0043] It goes without saying that the calibration device according to the present invention, the electronic camera according to the present invention, the calibration method according to the present invention, the computer device according to the present invention, and the computer program product according to the present invention have similar and / or identical preferred embodiments, especially as defined herein.

[0044] It goes without saying that the preferred embodiments of the present invention can also be any combination of the features according to the present invention. Description of the Drawings

[0045] Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein

[0046] Figure 1 An image sensor having row - arranged and column - arranged pixels for generating pixel values is schematically and exemplarily shown, wherein the rows of the image sensor respectively include a bright pixel region having a plurality of bright pixels and a dark pixel region covered with a mask and having a plurality of dark pixels;

[0047] Figure 2 An image sensor shown schematically and exemplarily in Figure 1 is shown, and the image data has been corrected by means of median - based dark pixel correction known from the prior art;

[0048] Figure 3 An embodiment of a calibration device for correcting the image data of an image sensor having row - arranged and column - arranged pixels for generating pixel values is schematically and exemplarily shown;

[0049] Figure 4 The possibility of pre - determining a predetermined constant k is schematically and exemplarily shown;

[0050] Figure 5 An image sensor having row - arranged and column - arranged pixels for generating pixel values is schematically and exemplarily shown, wherein the columns of the image sensor respectively include a bright pixel region having a plurality of bright pixels and a dark pixel region covered with a mask and having a plurality of dark pixels;

[0051] Figure 6 shown schematically and by way of example Figure 5 the image data of the image sensor shown in FIG., the image data having been corrected by means of median-based dark pixel correction known from the prior art;

[0052] Figure 7 shows a flow chart which by way of example shows an embodiment of a correction method for correcting the image data of an image sensor, the image sensor having row-wise and column-wise arranged pixels for generating pixel values; and

[0053] Figure 8 shown schematically and by way of example is an embodiment of an electronic camera having an image sensor and a correction device for correcting the image data of the image sensor. DETAILED DESCRIPTION

[0054] In the figures, the same or corresponding elements or units are respectively provided with the same or corresponding reference signs. When an element or unit has been described in connection with one figure, it may not be described in detail in connection with another figure.

[0055] Figure 1 shown schematically and by way of example is an image sensor 1 having row-wise and column-wise arranged pixels for generating pixel values. The rows 2 of the image sensor 1 each have a bright pixel region 4 and a dark pixel region 7, the bright pixel region having a plurality of bright pixels 5, the dark pixel region being covered with a mask 6 and having a plurality of dark pixels 8.

[0056] Figure 2 shown schematically and by way of example in Figure 1The image data 10 of the image sensor 1 shown, which has been corrected by means of median-based dark pixel correction known from the prior art. The image data 10 shows an outdoor scene, the light of which is incident on the image sensor 1. Here, a bright light signal 11, in this case particularly bright sunlight, impinges on the image sensor 1 near or in the region of the dark pixel 8. Due to the residual light penetrability of the mask 6 and in particular due to the multiple reflections of light from the bright pixel 5 in the layer between the mask 6 and the silicon of the dark pixel 8, the subsequent incidence of scattered light into the dark pixel 8 may be caused. The median-based dark pixel correction known from the prior art causes overcorrection in this case, resulting in dark streaks 12 in the image data 10. Thus, this causes the correction value obtained by taking the median in row 2 of the image sensor 1 associated with the over-radiation 11 to be increased compared to the true dark signal due to the incidence of scattered light into the dark pixel 8. By taking the difference between the bright signal and the increased correction value, dark streaks 12 are generated in the image data 10. In extreme cases, the streaks 12 may even be completely black.

[0057] Figure 3 Schematically and by way of example, an embodiment of a correction device 100 for correcting the image data 10 of an image sensor 1 is shown, which image sensor has row-wise and column-wise arranged pixels for generating pixel values. The correction device 100 includes a pre-filtering unit 101, a function matching unit 102, a correction value determination unit 103, and a correction unit 104. The correction device 100 achieves: avoiding overcorrection of the image data 10, as may occur in median-based dark pixel correction known from the prior art, or at least reducing such overcorrection.

[0058] The function matching unit 102 is matched such that a function with a plurality of parameters is matched to the pixel values of the plurality of dark pixels 8 in row 2. Here, the function for the dark pixels 8 located closer to the bright pixel region 4 has a greater value compared to the dark pixels 8 located further away from the bright pixel region 4.

[0059] The pre-filtering unit 101 is matched to pre-filter the plurality of dark pixels 8 in row 2 before matching the function to the pixel values of the plurality of dark pixels 8 in row 2. In this embodiment, the pre-filtering includes excluding dark pixels 8 with pixel values greater than a threshold. As the threshold, for example, the maximum possible, non-saturated pixel value can be used to exclude such saturated dark pixels 8.

[0060] The function matching unit 102 is matched here to match the function to the pixel values of the plurality of dark pixels 8 in row 2 or column 3 based on the scaled positions of the plurality of dark pixels 8 in row 2. In the present embodiment, the scaled positions of the plurality of dark pixels 8 in row 2 are obtained via a scaling function based on the positions of the plurality of dark pixels 8 in row 2, where the scaling function includes a hyperbola. In particular, the hyperbola has the form p s = k / (k + p), where p is the position of the dark pixel 8 in the dark pixel region 7, p s is the scaled position of the dark pixel 8, and k is a predetermined constant. Here, the predetermined constant k is a variable related to the structural type of the image sensor and can be determined in advance (see also Figure 4 ). The scaled positions of the plurality of dark pixels 8 in row 2 are in the range of 0.0 to 1.0.

[0061] In the present embodiment, the scaled positions of the plurality of dark pixels 8 in row 2 are pre-determined and stored in a memory (not shown in the figure) of the correction device 100. However, in other embodiments, it is also possible that the scaled positions of the plurality of dark pixels 8 in row 2 are determined at runtime.

[0062] Thus, in the present embodiment, the function is matched to the pixel values of the plurality of dark pixels 8 in row 2 based on the pre-filtered plurality of dark pixels 8 and the scaled positions of the plurality of dark pixels 8. In the present embodiment, the function matching unit 102 is matched to match the function to the pixel values of the plurality of dark pixels 8 in row 2 by means of the least squares method.

[0063] The correction value determination unit 103 is matched to determine a correction value for row 2 based on the matched function. In the present embodiment, the function is a polynomial of at least the second order, here a parabola, and the correction value determination unit 103 is matched to determine a correction value for row 2 based on the limit value of the matched polynomial.

[0064] The correction unit 104 is matched to correct the pixel values of the plurality of bright pixels 5 in row 2 based on the correction value for row 2.

[0065] The functionality of the pre-filtering unit 101, the function matching unit 102, the correction value determination unit 103, and the correction unit 104 is implemented in hardware logic (not shown in the figure) in the correction device 100.

[0066] In the present embodiment, the calibration device 100 is provided for calibrating the image data 10 of the image sensor 1, which has pixels arranged in rows and columns for generating pixel values, wherein the rows 2 of the image sensor 1 each include a bright pixel region 4 having a plurality of bright pixels 5 and a dark pixel region 7 having a plurality of dark pixels 8 covered by a mask 6. In other embodiments, the calibration device 100 can be provided for calibrating the image data 10 of the image sensor 1, which has pixels arranged in rows and columns for generating pixel values, wherein the columns 3 of the image sensor 1 each include a bright pixel region 4 having a plurality of bright pixels 5 and a dark pixel region 7 having a plurality of dark pixels 8 covered by a mask 6 (see also Figure 5 and 6 ). The described operations of the pre-filtering unit 101, function matching unit 102, calibration value determination unit 103, and calibration unit 104 are then performed for the columns 3 respectively, and not for the rows 2. In a further embodiment, the calibration device 100 can be provided for calibrating the image data 10 of the image sensor 1, which has pixels arranged in rows and columns for generating pixel values, wherein the rows 2 and columns 3 of the image sensor 1 each include a bright pixel region 4 having a plurality of bright pixels 5 and a dark pixel region 7 having a plurality of dark pixels 8 covered by a mask 6.

[0067] The possibility of pre-determining a predetermined constant k is schematically and exemplarily shown in Figure 4 . Figure 4 (a) shows the characteristics of the pixel values of the plurality of dark pixels 8 in the row 2 into which scattered light is incident, for exemplary measurements at an image sensor 1 having 94 dark pixels 8 in each row 2 (i.e., each row 2 relates to a different amount of scattered light) for light signals of different brightnesses. In this figure, the horizontal axis shows the unscaled position of the dark pixels 8 (from 0 to 94) and the vertical axis shows the pixel values of the dark pixels 8 (here in a logarithmic plot). As can be seen, the dark pixels 8 located closer to the bright pixel region 4 (which is the left side in the figure) have larger values compared to the dark pixels 8 located farther from the bright pixel region 4. Figure 4 (b) shows the result of the common matching of a function having a plurality of parameters, here in the form a·p s 2 +b·p sA parabola of +c, where a, b, and c are parameters of the parabola, and the constant k matches the measured pixel values of the multiple dark pixels 8 in row 2 for light signals of different brightnesses. In this figure, the horizontal axis shows the scaled position (0.0 to 1.0) of the dark pixels 8 obtained by scaling according to a hyperbola as a scaling function, and the vertical axis shows the values of the matched parabola. The predetermined constant k can be determined in this way as the value k for which the matching of the parabola to the measured pixel values of the multiple dark pixels 8 in row 2 for light signals of different brightnesses results in the smallest error.

[0068] According to the inventors' understanding, it is also feasible that, before jointly matching a function with multiple parameters and the constant k to the measured pixel values of the multiple dark pixels 8 in row 2 for light signals of different brightnesses, the linear parameter b of the parabola is set equal to 0. In this case, the parabola has the form a·p s 2 +c, and the matching of the parabola to the measured pixel values of the multiple dark pixels 8 in row 2 for light signals of different brightnesses results in a similarly small error. The use of the parabola of the form a·p s 2 +c simplifies the execution in software or hardware once again.

[0069] Below, an embodiment of a correction method for correcting image data of an image sensor is described with reference to the flowchart shown in Figure 7 , the image sensor having pixels arranged in rows and columns for generating pixel values. The correction method can be performed, for example, by means of the correction device 100 shown in Figure 3 or other described embodiments of the correction device.

[0070] In step S101, before matching the function to the pixel values of the multiple dark pixels 8 in row 2 or column 3, the multiple dark pixels 7 in row 2 or column 3 are pre-filtered. In step S102, a function with multiple parameters is matched to the pixel values of the multiple dark pixels 8 in row 2 or column 3. In particular, in this embodiment, based on the pre-filtered multiple dark pixels 8 in row 2 or column 3 and the scaled positions of the multiple dark pixels 8 in row 2 or column 3, the matching of the function to the pixel values of the multiple dark pixels 8 in row 2 or column 3 is performed. In step S103, correction values for row 2 or column 3 are determined based on the matched function. In step S104, the pixel values of the multiple bright pixels 5 in row 2 or column 3 are corrected based on the correction values for row 2 or column 3.

[0071] In the above-described embodiment, the correction unit 100 includes a pre-filtering unit 101. In other embodiments, the correction unit 100 may also not include the pre-filtering unit 101. In this case, it is feasible that the function matching unit 102 is matched such that a function with a plurality of parameters is matched to the unpre-filtered pixel values of the plurality of dark pixels 8 in row 2 or column 3.

[0072] Figure 8 An electronic camera 200 is schematically and exemplarily shown. The electronic camera includes an image sensor 1 and a correction device 100 for correcting the image data 10 of the image sensor 1. The image sensor has pixels arranged in rows and columns for generating pixel values. Here, row 2 or column 3 of the image sensor 1 respectively includes a bright pixel region 4 having a plurality of bright pixels 5 and a dark pixel region 7 having a plurality of dark pixels 8 covered by a mask 6.

[0073] In the above-described embodiment, the pre-filtering includes excluding dark pixels 8 with pixel values greater than a threshold. In other embodiments, the pre-filtering may also include median filtering, or the pre-filtering may include excluding dark pixels 8 that have been previously determined to be defective. Additionally, it is also feasible to interpolate the pixel values of dark pixels 8 with pixel values greater than the threshold or dark pixels 8 that have been previously determined to be defective based on the pixel values of directly or indirectly adjacent dark pixels 8, for example, by means of median function, linear function, quadratic function, cubic function, or spline interpolation. The interpolated pixel values can then also be used when matching the function to the pixel values of the plurality of dark pixels 8 in row 2. In a further embodiment, the correction device 100 may also not include the pre-filtering unit 101 at all.

[0074] In the above-described embodiment, the function matching unit 102 is matched to perform the matching of a function with a plurality of parameters to the pixel values of the plurality of dark pixels 8 in row 2 or column 3 based on the scaled positions of the plurality of dark pixels 8 in row 2 or column 3. In other embodiments, the function matching unit 102 may also be matched to match a function with a plurality of parameters based on the unscaled positions of the plurality of dark pixels 8 in row 2 or column 3.

[0075] In the above-described embodiment, the function is a parabola, and the correction value determination unit 103 is matched to determine the correction value for row 2 or column 3 based on the limit value of the matched polynomial. In other embodiments, the correction value determination unit 103 may also be matched to determine the correction value for row 2 or column 3 based on the value of the matched function at positions in the dark pixel region 7 in a region that extends from the position of the dark pixel 8 that is furthest from the bright pixel region 4 towards the bright pixel region 4 and has a width of 20%, preferably 10%, more preferably 5% of the width of the dark pixel region 7.

[0076] As described, calibration device 100 can be integrated in electronic camera 200. However, calibration device 100 can also include a separate device, such as a computer, notebook, tablet, mobile phone, dedicated external processing unit, image acquisition card, etc.

[0077] For the purposes of the drawings and the description, other variants of the disclosed embodiments can be understood and implemented by those skilled in the art of the invention claimed.

[0078] In this document, the terms "having" and "including" do not exclude other elements or steps and the indefinite article "a" does not exclude a plurality.

[0079] A single unit or device can perform the functions of multiple elements described herein. The fact that the various functions and / or elements are implemented in different embodiments does not mean that combinations of these functions and / or elements cannot be used advantageously.

[0080] The reference signs in the embodiments should not be understood as limiting the subject matter and scope of protection of the embodiments by these reference signs.

[0081] In summary, a calibration device for calibrating image data of an image sensor is described, the image sensor having rows and columns of pixels arranged for generating pixel values, wherein the rows or columns of the image sensor each include a bright pixel region having a plurality of bright pixels and a dark pixel region having a plurality of dark pixels covered with a mask. The calibration device includes: a function matching unit configured to match a function having a plurality of parameters to the pixel values of the plurality of dark pixels of a row or column; a correction value determination unit configured to determine a correction value for a row or column based on the matched function; and a correction unit configured to correct the pixel values of the plurality of bright pixels of a row or column based on the correction value for the row or column.

Claims

1. A correction device (100) for correcting image data (10) of an image sensor (1), the image sensor having pixels arranged in rows and in columns for generating pixel values, wherein a row (2) or a column (3) of the image sensor (1) comprises a bright pixel region (4) having a plurality of bright pixels (5) and a dark pixel region (7) covered by a mask (6) and having a plurality of dark pixels (8), wherein the correction device (100) comprises: - a function matching unit (102), the function matching unit being matched to match a function having a plurality of parameters to the pixel values ​​of a plurality of dark pixels (8) in a row (2) or a column (3); a correction value determination unit (103) adapted to determine a correction value for the row (2) or column (3) based on the adapted function; and A correction unit (104) adapted to correct the pixel values ​​of a 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. A correction device (100) according to claim 1, wherein the function for dark pixels (8) located closer to the bright pixel area (4) has a larger value than that for dark pixels (8) located farther away from the bright pixel area (4).

3. The correction device (100) according to claim 1 or 2, wherein the function is a non-linear function, preferably a power function.

4. The calibration device (100) according to any one of claims 1 to 3, wherein the calibration 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. A correction device (100) according to any one of claims 1 to 4, wherein the function matching unit (102) is matched to perform matching of the function on the pixel values ​​of the multiple dark pixels (8) of the row (2) or column (3) based on the scaled positions of the multiple dark pixels (8) of the row (2) or column (3).

6. A correction device (100) according to claim 5, wherein the scaled positions of the multiple dark pixels (8) in the row (2) or column (3) are obtained via a scaling function based on the positions of the multiple dark pixels (8) in the row (2) or column (3), wherein the scaling function includes a hyperbola.

7. The correction device (100) according to claim 6, wherein the hyperbola has the form p s = k / (k+p), where p is the position of the 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. The correction device (100) according to any 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. The correction device (100) according to any one of claims 1 to 8, wherein the function is a polynomial of at least second order, preferably a parabola, 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, such as a minimum value or a maximum value, of the adapted polynomial.

10. Correction device (100) according to any one of claims 1 to 9, wherein the function is preferably a polynomial of at least second order, preferably a parabola, The correction value determination unit (103) is matched to determine the correction value for the row (2) or column (3) based on the value of the matched function at a position in the dark pixel region (7) located in the following area, wherein the area extends from the position of the dark pixel (8) located farthest from the bright pixel region (4) toward the bright pixel region (4) and the width of the area is 20%, preferably 10%, and more preferably 5% of the width of the dark pixel region (7).

11. The correction device (100) according to any one of claims 1 to 10, wherein the function matching unit (102) is matched to match the function to the pixel values ​​of multiple dark pixels (8) of the row (2) or column (3) by means of a least squares method.

12. A correction device (100) according to any 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 matching unit (102) and / or the correction value determination unit (103) and / or the correction unit (104) is implemented in the correction device in hardware logic.

13. An electronic camera (200), comprising: - an image sensor (1) having pixels arranged in rows and in columns for generating pixel values, wherein the rows (2) and columns (3) of the image sensor (1) respectively comprise a bright pixel region (4) having a plurality of bright pixels (5) and a dark pixel region (7) covered by a mask (6) and having a plurality of dark pixels (8); and - A correction device (100) for correcting image data (10) of the image sensor (1) according to any one of claims 1 to 12.

14. A correction method for correcting image data (10) of an image sensor (1), the image sensor having pixels arranged in rows and in columns for generating pixel values, wherein a row (2) or a column (3) of the image sensor (1) comprises a bright pixel region (4) having a plurality of bright pixels (5) and a dark pixel region (7) covered by a mask (6) and having a plurality of dark pixels (8), wherein the correction method comprises: - matching (S102) a function having a plurality of parameters to the pixel values ​​of a plurality of dark pixels (8) of a row (2) or a column (3); - determining (S103) a correction value for said row (2) or column (3) based on the matched function; as well as - Correcting (S104) the pixel values ​​of a plurality of bright pixels (5) of the row (2) based on the correction value for the row (2) or column (3). 15 . A computer device comprising a computing unit, which is designed to execute the correction method according to claim 14 . 16 . A computer program product, comprising code means for causing a computer device to carry out the calibration method according to claim 14 when the computer program product is run on the computer device.

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