A chart and method for camera sfr testing

Abstract

The application provides a chart for camera SFR test, which comprises a chart layer and a substrate layer for supporting the chart layer, wherein the chart layer comprises a focusing center and a plurality of layers of nested resolution bars, each layer of the resolution bars is centered on the focusing center and constitutes a closed shape. When the camera SFR test is performed based on the chart, for a small-FOV long-focus camera, the complete imaging of the inner layer of the resolution bars can be used to calculate the SFR, and for a large-FOV wide-angle camera, the complete imaging of the outer layer of the resolution bars can be used to calculate the SFR. Therefore, one chart can be used for the SFR test of cameras with different FOV specifications, and it is not necessary to replace the corresponding chart for different FOV specifications, which improves the compatibility of the chart and the efficiency of the SFR test of cameras with different FOV specifications.

Description

[0001] This application claims domestic priority for the invention patent filed on August 2, 2022, entitled "A Pattern Card for Camera SFR Testing" and with application number 202210920578.3. Technical Field

[0002] This application relates to the field of camera performance testing technology, and in particular to a test chart for camera SFR testing. Background Technology

[0003] With the rapid development of mobile internet, the Internet of Things, and autonomous driving technologies, the demand for cameras with different FOVs (Field of View) has increased dramatically in smart terminal devices, autonomous vehicles, and smart manufacturing plants. Camera resolution, also known as sharpness or sharpness, reflects a camera's ability to reproduce details of the scene being photographed. It is one of the important performance parameters reflecting camera quality; the higher the camera's resolution, the clearer the image. Therefore, camera resolution testing is a necessary step in camera development.

[0004] Currently, common methods for testing camera resolution include MTF (Modulation Transfer Function), SFR (Spatial Frequency Response), and CTF (Contrast Transfer Function). Regardless of the method used, a chart is required when testing camera resolution. A chart is a multi-layered structure consisting of layers with specific shapes and a base layer used as a backing layer. It is typically obtained by exposing, developing, fixing, washing, drying, and die-cutting multiple layers of photogravure film (usually silver halide film or photosensitive film) through processes such as exposure, imaging, development, fixing, washing, drying, and inspection. This type of chart has the most standard and regulated layer shapes. Alternatively, layers with specific shapes can be coated, pasted, or printed onto a base layer. A common chart used for camera SFR testing is... Figure 1 As shown, the central area of ​​the chart's layer includes a slanted square (or slanted rectangle) shape of a certain size. A single chart is only suitable for SFR testing of cameras within a specific FOV range. When used for SFR testing of cameras with FOVs outside the specific range, SFR calculation cannot be completed because a complete image cannot be obtained or the obtained image does not meet the minimum resolution requirement. For example, as... Figure 2As shown, when a chart suitable for testing the SFR of a large FOV camera is used to test the SFR of a small FOV camera, the shape 'a' in the captured image will be incomplete at the edge of the field of view (usually greater than 0.7F), making it impossible to obtain complete data for calculating the SFR; while... Figure 3 As shown, when a chart suitable for small FOVs is used to test the SFR of a camera with a large FOV, the shape 'a' in the captured image at zero field of view (i.e., the center of the field of view) is too small to meet the minimum resolution requirement, thus failing to obtain complete data for SFR calculation. Therefore, existing charts for camera SFR testing cannot be used for SFR testing of automotive forward-looking cameras that simultaneously possess the wide-angle performance of a large FOV and the telephoto performance of a small FOV, exhibiting poor compatibility. Summary of the Invention

[0005] The purpose of this application is to provide a chart and method for SFR testing of cameras, so as to at least partially solve the technical problem that existing charts are only applicable to SFR testing of cameras within a specific FOV range.

[0006] One embodiment of this application provides a pattern card for camera SFR testing, the pattern card including a layer and a substrate for supporting the layer, wherein the layer includes:

[0007] Focus center and multi-layered nested analytical force bars;

[0008] Each layer of resolving force strips forms a closed shape with the focusing center as the center.

[0009] Optionally, wherein each layer of resolving force strips forms a closed shape centered on the focus center, including:

[0010] Each layer of resolution bars includes several resolution bars, wherein the several resolution bars form a polygonal shape centered on the focus center.

[0011] Optionally, each resolution stripe satisfies the minimum resolution requirement of the camera.

[0012] Optionally, the difference in distance from the closed shape formed by the resolution strips of adjacent layers to the focus center satisfies a preset threshold.

[0013] Optionally, the layers of the chart for camera SFR testing further include:

[0014] A closed shape formed by multiple sets of nested analytical force bars of the same shape but different positions.

[0015] Optionally, another embodiment of this application also provides an apparatus for SFR testing of a camera, wherein the apparatus includes the pattern card and a glass plate, wherein the layers of the pattern card are flatly bonded to the glass plate.

[0016] Another embodiment of this application provides a method for SFR testing of a camera, wherein the method includes:

[0017] Obtain electronic imaging of the layers of the image card;

[0018] Determine the complete closed shape in the electron imaging;

[0019] Determine the center point of the complete closed shape, and calculate whether the included angle between the corresponding edge contours of the complete closed shape and the corresponding positive complete closed shape at the same center point meets a preset threshold. If it does, determine the center point of the ROI on each edge contour of the complete closed shape.

[0020] Based on the center point of the ROI on each edge contour and the preset ROI parameters, determine the ROI on each remote contour;

[0021] SFR is calculated based on the ROI on each edge contour.

[0022] In another embodiment of this application, a method for SFR testing of a camera is provided, wherein the method includes:

[0023] Electron imaging of the layers of the device;

[0024] Determine the complete closed shape in the electron imaging;

[0025] Determine the center point of the complete closed shape, and calculate whether the included angle between the corresponding edge contours of the complete closed shape and the corresponding positive complete closed shape at the same center point meets a preset threshold. If it does, determine the center point of the ROI on each edge contour of the complete closed shape.

[0026] Based on the center point of the ROI on each edge contour and the preset ROI parameters, determine the ROI on each remote contour;

[0027] SFR is calculated based on the ROI on each edge contour.

[0028] Compared with existing technologies, this application provides a chart and method for SFR testing of cameras. The chart includes layers and a base layer to support the layers. Each layer includes a focus center and multiple resolution bars, where each resolution bar forms a closed shape centered on the focus center. Optionally, each resolution bar layer includes a plurality of resolution bars, which form a polygonal shape centered on the focus center. When performing SFR testing based on this chart, for telephoto cameras with a small FOV, the SFR can be calculated using the complete image of the inner resolution bars; for wide-angle cameras with a large FOV, the SFR can be calculated using the complete image of the outer resolution bars. Therefore, a single chart can be used for SFR testing of cameras with different FOV specifications, eliminating the need to replace the chart with a different chart for different FOV specifications, thus improving chart compatibility and increasing the efficiency of SFR testing for cameras with different FOV specifications. Optionally, this application also provides an apparatus for SFR testing of a camera, wherein the apparatus includes the pattern card and a glass plate, wherein the layer of the pattern card is flatly bonded to the glass plate. This apparatus can ensure the flatness of the layer and guarantee the stability of SFR test results at different telephoto ranges when used for SFR testing of a camera with a small FOV and long focal length. Attached Figure Description

[0029] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 A schematic diagram of the structure of a chart for SFR testing of cameras in the prior art is shown;

[0031] Figure 2 This diagram illustrates the imaging process of testing the SFR of a small FOV camera using a chart suitable for testing the SFR of a large FOV camera in the prior art.

[0032] Figure 3 This diagram illustrates the imaging process of testing the SFR of a large FOV camera using a chart suitable for testing the SFR of a small FOV camera in the prior art.

[0033] Figure 4 This diagram illustrates the structure of a chart for SFR testing of a camera, according to an optional embodiment of this application.

[0034] Figure 5 This illustration shows an imaging schematic of a chart for camera SFR testing according to an optional embodiment of this application;

[0035] Figure 6This diagram illustrates the structure of a chart for SFR testing of a camera, according to another alternative embodiment of this application.

[0036] Figure 7 This diagram illustrates the ROI of yet another optional embodiment of this application;

[0037] In the accompanying drawings, the same or similar reference numerals represent the same or similar parts. For the sake of simplicity, the figures schematically illustrate the relevant parts of the invention and do not represent their actual structure as a product.

[0038] In addition, to make the drawings concise and easy to understand, some attached drawings may only schematically indicate one of the components that have the same structure or function. Detailed Implementation

[0039] In the field of camera performance testing technology, SFR (Single-Fold Rate) testing is a commonly used method for testing camera resolution performance. After the camera under test has focused, a pattern card is photographed, resulting in an image of a layer containing the pattern card of a certain shape. The image is then processed to calculate the SFR value. Existing pattern cards commonly used for camera SFR testing consist of a single shape layer of a certain size, such as a rhombus. This only covers a certain field of view (FOV) range for SFR testing: when the pattern card is at zero field of view (i.e., the center of the field of view), it can obtain an image that meets the minimum resolution requirement, but near the edge of the field of view, it may not be able to obtain a complete image of the shape; conversely, when it meets the edge of the field of view, it can obtain a complete image, but at zero field of view, the shape image may not meet the minimum resolution requirement. In either case, the SFR value cannot be calculated. Therefore, a commonly used pattern card with a single shape layer cannot simultaneously meet the SFR testing requirements of cameras with both small FOV telephoto lenses and large FOV wide-angle lenses.

[0040] This application provides a chart and method for SFR testing of a camera that can solve the above-mentioned technical problems.

[0041] To further illustrate the technical means adopted and the effects achieved in this application, the technical solution of this application will be clearly and completely described below in conjunction with the accompanying drawings and preferred embodiments.

[0042] This application claims a pattern card for SFR testing of a camera, the pattern card including layers and a substrate for supporting the layers, wherein the layers of the pattern card include:

[0043] Focus center and multi-layered nested analytical force bars;

[0044] Each layer of resolving force strips forms a closed shape with the focusing center as the center.

[0045] At the start of the test, the camera under test first focuses based on the focus center. For example, to test the SFR value of a vehicle-mounted forward-looking camera, the image card is placed at an appropriate position in a collimator. After focusing, the camera under test photographs the image card to obtain an image of the image card's layer shape. For different FOVs, the center point of the shape in the image (usually corresponding to the image of the focus center) and at least one complete closed shape contour can be determined. The tilt angle of the shape contour is calculated to see if it meets the requirements (usually the tilt angle is in the range of 5-8°; if the tilt angle is too large, it may cause a large deviation). If the tilt angle does not meet the requirements, the image card is rotated and adjusted around the focus center, and the image is re-imaged until the tilt angle meets the requirements. The center point of the ROI (Region of Interest) of each tilted edge of the contour (corresponding to the image of the resolution bar) is determined. Taking the center point of each ROI as the center, a pixel square ROI that meets the minimum resolution requirement of the camera under test is obtained. The SFR value can be calculated according to the SFR calculation method based on the tilted edge.

[0046] Optionally, wherein each layer of resolving force strips forms a closed shape centered on the focus center, including:

[0047] Each layer of resolution bars includes several resolution bars, wherein the several resolution bars form a polygonal shape centered on the focus center.

[0048] Within each resolution bar layer, the length of each resolution bar is not necessarily equal, nor is its size specifically limited. However, the multi-layered nested polygonal shapes formed by the resolution bars of each layer should cover all existing possible sizes of single-layer polygonal shapes of the same type applicable to various FOV specifications. For example, a chart containing two nested quadrilateral layers covers both the single-layer quadrilateral layer shapes applicable to charts with small FOV and telephoto lenses, and the single-layer quadrilateral layer shapes applicable to charts with large FOV and wide-angle lenses.

[0049] In SFR testing, for the image corresponding to the layer shape of the image card captured by the camera, the first step is to obtain the center point of the ROI including the image of the corresponding oblique resolution bar. Then, the corresponding ROI is obtained according to the minimum resolution requirement of the camera being tested. For example, the layer shape of the image card is usually made into a rectangle or square shape. For an image card containing multiple nested rectangular layer shapes, the multiple rectangles are oblique rectangles. If the sides of the rectangles in the layer shapes contained in the image card are parallel or perpendicular to the horizontal direction, then when using the image card for SFR testing, the image card can be directly rotated by a small angle (usually in the range of 5 to 8 degrees) so that the shape image in the image captured by the camera is a multi-layered nested oblique rectangle shape.

[0050] A schematic diagram of a chart for camera SFR testing, comprising two nested rectangular layers, is shown in one optional embodiment. Figure 4 As shown, the imaging diagram obtained during camera SFR testing is as follows: Figure 5 As shown. For a large FOV camera, shape b can meet the resolution requirements at the zero field of view position, and the SFR value can be calculated by processing each tilted edge of shape b; for a small FOV camera, shape a has a higher pixel resolution, and shape a is complete at the edge field of view position, so the SFR value can be calculated by processing each tilted edge of shape a.

[0051] Optionally, each resolution stripe satisfies the minimum resolution requirement of the camera.

[0052] In this multi-layered nested closed shape, each layer of the resolution strip should meet the minimum resolution requirement of the camera under test, so that clear imaging can be obtained whether it is the zero field of view of a large FOV camera or the edge field of view of a small FOV camera, so as to obtain the complete ROI for calculating the SFR value of the camera.

[0053] Optionally, the difference in distance from the closed shape formed by the resolution strips of adjacent layers to the focus center satisfies a preset threshold.

[0054] Specifically, the difference in distance from the closed shape formed by adjacent resolution bars to the focus center should meet a preset threshold, and should at least meet the corresponding distance difference of two existing image cards with single-layered similar shapes. For example, for an image card with a layer shape of two nested quadrilaterals, the difference in distance from the inner quadrilateral to the focus center and the distance from the outer quadrilateral to the focus center can be the same as the corresponding distance difference of an existing image card with a single-layered quadrilateral layer shape for small FOV telephoto and an image card with a single-layered quadrilateral layer shape for large FOV wide-angle, so that the image card can meet the SFR test for cameras that simultaneously have both small FOV telephoto and large FOV wide-angle capabilities.

[0055] Optionally, in the chart for camera SFR testing, the chart layer further includes:

[0056] A closed shape formed by multiple sets of nested analytical force bars of the same shape but different positions.

[0057] The layers of the chart can also include multiple sets of closed shapes with the same shape but different positions, which are composed of the same multi-layered nested resolution bars, to accommodate SFR testing of cameras with a larger FOV range.

[0058] The set of closed shapes in the middle includes a focus center used for focusing the camera being tested.

[0059] Another alternative embodiment shows a schematic diagram of a card structure comprising five sets of two-layered, nested oblique rectangular shapes, as shown below. Figure 6 As shown.

[0060] Another optional embodiment of this application provides an apparatus for camera SFR testing, wherein the apparatus includes:

[0061] The image and glass sheet as described in the foregoing embodiments or alternative embodiments, wherein the image layer is flatly bonded to the glass sheet.

[0062] In this device, the layer of the graphic card in the aforementioned embodiment or embodiment can be flattened and bonded to a glass sheet that meets the flatness requirements to ensure the flatness of the layer. When used for small FOV long-focal SFR testing, it can ensure the stability of SFR test results of the tested camera under different focal lengths.

[0063] Another optional embodiment of this application provides a method for SFR testing of a camera, wherein the method includes:

[0064] Obtain electronic imaging of the layers of the image card;

[0065] Determine the complete closed shape in the electron imaging;

[0066] Determine the center point of the complete closed shape, and calculate whether the included angle between the corresponding edge contours of the complete closed shape and the corresponding positive complete closed shape at the same center point meets a preset threshold. If it does, determine the center point of the ROI on each edge contour of the complete closed shape.

[0067] Based on the center point of the ROI on each edge contour and the preset ROI parameters, the ROI on each edge contour is determined;

[0068] SFR is calculated based on the ROI on each edge contour.

[0069] For example, the image card layer consists of two nested square shapes. To test the SFR value of the wide-angle (FOV) of the camera under test, a collimator can be used as the light source, with the image card embedded within it. After focusing and other adjustments, the camera under test first captures an image of the image card to obtain an electronic image of the layer. Next, a complete square shape corresponding to the large FOV in the electronic image is determined (usually, the complete square shape that best meets the resolution requirements is selected). Then, the center point of this complete square shape is determined, and the angles between corresponding sides of this square and a regular square with the same center point (where the sides of the regular square are parallel or perpendicular to the horizontal or vertical axis) are calculated to see if they meet a preset threshold, for example, whether they meet the range of 5-8°. If they do, the center point of the ROI on each side of the square is determined. If not, the image card can be rotated and fine-tuned, and the electronic image can be captured again, repeating the above steps until the angles meet the preset threshold. Wherein, for example... Figure 7 As shown, in the obtained complete square ABCD, the angles A(X) can be determined according to the following formulas. A Y A ), B(X B Y B ), C(X) C Y C ), D(X D Y D ), calculate the horizontal midpoint coordinates (X) of the left and right corner points A and D. A +(X D -X A ) / 2) and the coordinates of the vertical midpoints (Y and C) of the upper and lower corners B and C C +(Y B -Y C Let (x, y) / 2) be the horizontal and vertical coordinates of the center point of the square, respectively, to determine the center point of the square; the center points of the ROIs on the four sides can be determined based on the coordinates of the four corner points. For example, the horizontal coordinate of the center point of the ROI on side AC is (X, y) / 2). A +(X C -X A ) / 2), the vertical coordinate is (Y C +(Y A -Y C ) / 2), the horizontal coordinate of the center point of the ROI on side AB is (X A +(X B -X A ) / 2), the vertical coordinate is (Y A +(Y B -Y AThe center coordinates of the ROIs on edges BD and CD are similarly determined. Then, based on the determined center points of the ROIs on each edge and the preset ROI parameters, the ROIs on each edge can be determined. For example, if the preset ROI parameters determine the ROI as a 40*40 pixel square region (ROI parameters cannot be set too small; if the ROI parameters are set too small, the ROI sampling pixels will be too few, and the SFR calculation results may fluctuate significantly. Therefore, the selection of ROI parameters needs to ensure the consistency and stability of the SFR calculation results to avoid large fluctuations), then the size of the square ROI on each edge can be determined. Finally, based on the determined ROIs, the SFR value is calculated. The SFR value calculation process typically includes:

[0070] 1) Perform grayscale conversion on the ROI data;

[0071] 2) Linearized grayscale ROI data;

[0072] 3) Calculate the centroid to obtain the centroid data;

[0073] 4) Perform linear regression to obtain the corresponding marginal data, including slope, intercept, etc.

[0074] 5) Obtain the repositioned ROI data and get the ESF (Edge Spread Function);

[0075] 6) Oversample the ESF by 4 times and perform difference operations to obtain the LSF (Line Spread Function);

[0076] 7) Apply Hamming window to LSF;

[0077] 8) Perform DFT (Discrete Fourier Transform) operation and obtain SFR based on the result.

[0078] The above calculation process for SFR has been implemented in software code.

[0079] Another optional embodiment of this application provides a method for SFR testing of a camera, wherein the method includes:

[0080] Electron imaging of the layers of the device;

[0081] Determine the complete closed shape in the electron imaging;

[0082] Determine the center point of the complete closed shape, and calculate whether the included angle between the corresponding edge contours of the complete closed shape and the corresponding positive complete closed shape at the same center point meets a preset threshold. If it does, determine the center point of the ROI on each edge contour of the complete closed shape.

[0083] Based on the center point of the ROI on each edge contour and the preset ROI parameters, the ROI on each edge contour is determined;

[0084] SFR is calculated based on the ROI on each edge contour.

[0085] For example, the device's layers are two nested square shapes. To test the SFR value of a telephoto lens with a small FOV, a collimator can be used as the light source. The image card is built into the collimator. After focusing and other adjustments, the image card is first photographed using the camera under test to obtain an electronic image of the layers. Next, a complete square shape corresponding to the small FOV in the electronic image is determined (usually, the complete square shape that best meets the resolution requirements is selected). Then, the center point of this complete square shape is determined, and the angles between the square and a regular square with the same center point (where each side of the regular square is parallel or perpendicular to the horizontal or vertical axis) are calculated to see if they meet a preset threshold, for example, whether they meet the range of 5-8°. If they do, the center point of the ROI on each side of the square is determined. If not, the image card can be rotated and fine-tuned, and the electronic image re-photographed. The above steps are repeated until the angles meet the preset threshold. Within the resulting complete square, the horizontal midpoint coordinates of the sum of the left and right corner points and the vertical midpoint coordinates of the sum of the top and bottom corner points are calculated based on each corner point. These coordinates are then used as the horizontal and vertical coordinates of the square's center point, thus determining the center point of the square. The center points of the four ROIs on each of the four sides are determined based on the coordinates of the four corner points. Then, based on the determined center points of the ROIs on each side and the preset ROI parameters, the ROIs on each side are determined. Finally, the SFR value is calculated based on the determined ROIs.

[0086] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description; thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units or devices recited in the apparatus claims may also be implemented by a single unit or device through software and / or hardware. The terms "first," "second," etc., are used to indicate names and do not indicate any particular order.

Claims

1. A chart for testing camera resolution, the chart comprising a layer and a substrate for supporting the layer, characterized in that, The layer is adapted to be flatly bonded to the glass sheet, and the layer includes: Focus center and multi-layered nested analytical force bars; Each layer of resolution strips includes several resolution strips, wherein the several resolution strips form a polygonal shape centered on the focus center; The difference in distance from the closed shape formed by the adjacent layer resolution strips to the focus center satisfies a preset threshold, and at least satisfies the corresponding distance difference between two existing charts with single-layer similar shapes. The two single-layer similar shapes are single-layer quadrilateral layer shapes used for different FOVs. The layer also includes: multiple sets of closed shapes composed of nested resolution bars of the same shape but different positions, with different focus centers corresponding to different sets of closed shapes.

2. The drawing card according to claim 1, characterized in that, Each resolution bar meets the minimum resolution requirement of the camera.

3. An apparatus for SFR testing of a camera, characterized in that, The device includes: glass slides; and The image card for camera resolution testing as described in any one of claims 1 to 2, wherein the layer of the image card for camera resolution testing is flatly bonded to the glass plate.

4. A method for SFR testing of a camera, characterized in that, The method includes: Obtain an electronic image of the layers of a chart for camera resolution testing as described in any one of claims 1 to 2; Determine the complete closed shape in the electron imaging; Determine the center point of the complete closed shape, and calculate whether the included angle between the complete closed shape and the corresponding edge contour of the corresponding positive complete closed shape at the same center point satisfies a preset threshold. If it satisfies the threshold, then determine the center point of the ROI on each edge contour of the complete closed shape. Based on the center point of the ROI on each edge contour and the preset ROI parameters, the ROI on each edge contour is determined; SFR is calculated based on the ROI on each edge contour.

5. A method for SFR testing of a camera, characterized in that, The method includes: Obtaining electronic imaging of the layers of the apparatus as described in claim 3; Determine the complete closed shape in the electron imaging; Determine the center point of the complete closed shape, and calculate whether the included angle between the complete closed shape and the corresponding edge contour of the corresponding positive complete closed shape at the same center point satisfies a preset threshold. If it satisfies the threshold, then determine the center point of the ROI on each edge contour of the complete closed shape. Based on the center point of the ROI on each edge contour and the preset ROI parameters, the ROI on each edge contour is determined; SFR is calculated based on the ROI on each edge contour.

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