JP2012247743A - Chart for checking resolution and method for checking resolution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chart for checking resolution by which the checking accuracy of one and the same image height position is improved, while suppressing the influence of illumination as much as possible and to provide a method for checking resolution.SOLUTION: A horizontal striped pattern 22 and a vertical striped pattern 23 are adjacently provided and a black reference part 24 is arranged therebetween, so that the horizontal striped pattern 22, the vertical striped pattern 23, and the black reference part 24 can be imaged under the same illumination environment. Therefore, the variation of check data is suppressed to accurately check vertical resolution and horizontal resolution for instance.

Description

  The present invention relates to a resolution inspection chart and a resolution inspection method for inspecting the resolution of an image captured by an imaging apparatus including at least an imaging lens and an imaging element.

  Conventionally, a small and thin imaging device has been mounted on a portable terminal which is a small and thin electronic device such as a mobile phone or a PDA (Personal Digital Assistant), thereby enabling not only audio information but also images to a remote place. Information can also be transmitted between each other.

  Such an imaging apparatus is manufactured as a single unit, and it is common to perform various inspections on the imaging apparatus before being mounted on a portable terminal. Among them, an important inspection is a resolution inspection.

  Various resolution inspection charts are used for resolution inspection. In a certain resolution inspection chart, a large number of black and white lines having the same line width and pitch are provided, and the contrast ratio of the image is determined and inspected by imaging these lines. Specifically, a stripe pattern in which a plurality of black lines and white lines are alternately arranged is arranged at an image height to be inspected such as the center of the resolution inspection chart and the four peripheral areas, and further, By arranging the stripe patterns whose directions are different from each other by 90 degrees, the resolution characteristics in different directions can be inspected. However, in this case, a reference gradation level is required when determining the contrast of the stripe pattern, and for this purpose, a black reference pattern having a predetermined area and a white reference pattern are arranged in the vicinity of the stripe pattern. The luminance data of the black reference pattern and the white reference pattern of the captured image is used as the reference value.

  Here, there is a possibility that the position of the optical axis of the image pickup lens varies with respect to the image pickup device due to a manufacturing error or an assembly error. On the other hand, since the resolution inspection is performed at a predetermined position (image height) of a captured image, the above-described contrast is determined by an imaging device in which the position of the optical axis of the imaging lens varies with respect to the imaging device. When the resolution inspection chart is imaged, the resolution inspection chart may be shifted in position on the captured image. In such a case, even if the contrast of the fringe pattern picked up at a predetermined peripheral position on the image is determined, the corresponding position on the fringe pattern of the resolution inspection chart will be different.

  In addition, the resolution inspection chart is illuminated by a light source at the time of imaging. However, it is difficult to actually illuminate uniformly, and it is often illuminated with a partially different brightness in the stripe pattern. For this reason, since the gradation level of white is lowered in a dark part of the stripe pattern, the image signal value obtained from the image sensor may change depending on the location even in the same white. Therefore, even if the gradation level of the reference pattern is constant, the detection position of the fringe pattern differs depending on the variation of the individual imaging devices, and the contrast ratio differs between the bright and dark portions of the illumination. There is a fear. For this reason, depending on which part of the fringe pattern is detected, even a non-defective imaging device may be determined as a defective product, and the reliability of inspection becomes a problem.

  On the other hand, the present inventor, as shown in Patent Document 1, from a stripe pattern in which a plurality of black lines and white lines are alternately arranged, from a black thick line adjacent to one side of the stripe pattern And a resolution inspection chart having an inspection pattern in which a plurality of reference patterns consisting of white thick lines adjacent to the other side of the stripe pattern are arranged adjacent to each other in the width direction of each line. .

JP 2009-53019 A

  According to the technique of Patent Document 1, since the imaging apparatus is inspected using the inspection pattern in which the reference pattern is adjacent to the fringe pattern, the position of the optical axis of the imaging lens is individually shifted with respect to the imaging element, Even if there is uneven illumination on the resolution inspection chart, the influence thereof is small, and it is possible to accurately determine the quality of the imaging apparatus.

  However, even in the resolution inspection chart of Patent Document 1, since the vertical stripe pattern and the horizontal stripe pattern must be created at different positions, the vertical resolution inspection position by vertical stripe pattern imaging and the horizontal resolution inspection position by horizontal stripe pattern imaging are required. Therefore, there is a problem that the correlation between the two cannot be obtained and the resolution inspection at the same image height position (especially on the optical axis) of the lens cannot be performed. Also, when the lens is moved in the optical axis direction for focusing, if the inspection position is shifted due to the change in the angle of view, the continuity of the inspection data is lost, and the resolution inspection at the same image height position of the lens cannot be performed. There is also a fear.

  The present invention has been made in view of such problems, and it is an object of the present invention to provide a resolution inspection chart and a resolution inspection method in which the influence of illumination is suppressed as much as possible and inspection accuracy at the same image height position is improved. To do.

The resolution inspection chart according to claim 1 is taken by an imaging device to be inspected, and used for inspecting the resolution based on an image signal from the imaging device.
A first pattern including a plurality of black lines arranged at a first pitch so as to extend in a first direction;
A second pattern provided adjacent to the first pattern and including a plurality of black lines arranged at a second pitch so as to extend in a second direction intersecting the first direction; ,
At least a black reference portion provided between the first pattern and the second pattern;
A white reference part,
It is characterized by having.

  According to the present invention, the first pattern and the second pattern are provided adjacent to each other, and the black reference portion is disposed between the first pattern, the second pattern, and the black reference. Therefore, it is possible to accurately inspect the vertical resolution and the horizontal resolution, for example.

  Further, in the conventional resolution inspection chart, as shown in FIG. 17A, the vertical resolution inspection pattern 22 ′ and the horizontal resolution inspection pattern 23 ′ are arranged at different positions with respect to the chart center O. There has been a problem that the resolution near the optical axis to be truly measured cannot be inspected. On the other hand, according to the present invention, as shown in 17 (b), the first pattern 22 corresponding to the vertical resolution inspection pattern and the second pattern 23 corresponding to the horizontal resolution inspection pattern are arranged adjacent to each other. Therefore, for example, by arranging the black reference portion 24 on the optical axis, the pattern can be arranged as close as possible to the chart center O, and the resolution near the optical axis to be truly measured can be inspected.

  A resolution inspection chart according to a second aspect of the present invention is the resolution inspection chart according to the first aspect, wherein the black reference portion is a frame surrounding the first pattern and the second pattern. Thus, by enclosing the first pattern and the second pattern at the black reference portion, the first pattern and the second pattern can be blocked, and the block can be placed at an arbitrary position. By arranging, even if the angle of view changes due to the focusing operation of the imaging device to be inspected, the same block can be tracked, and inspection data discontinuity due to change in inspection position is eliminated it can.

  A resolution inspection chart according to a third aspect is the invention according to the first or second aspect, wherein the first pattern is a horizontal stripe, and the second pattern is a vertical stripe. However, vertical stripes used for horizontal resolution inspection are tilted within 20 degrees with respect to the vertical direction, and horizontal stripes used for vertical resolution inspection are tilted within 20 degrees with respect to the horizontal direction, such as moire stripes. Can be avoided.

  The resolution inspection chart according to claim 4 is the invention according to claim 3, wherein the white reference portion includes a first white reference portion and a second white reference portion, and is adjacent to the first pattern. The black reference portion and the first pattern are separated from each other in the vertical direction by a distance larger than the first pitch, and the first white reference portion is provided between the black reference portion and the second pattern. The reference portion and the second pattern are separated from each other by a distance larger than the second pitch in the lateral direction, and the second white reference portion is provided therebetween. Thereby, the white reference | standard which is not influenced by illumination environment is securable.

  According to a fifth aspect of the present invention, in the resolution inspection chart according to any one of the first to fourth aspects, the first pattern and the second pattern are repeatedly formed. As a result, in the imaging apparatus to be inspected, it is possible to inspect a predetermined image height position even if the optical axis of the lens is inclined.

  The chart for resolution inspection according to claim 6 is arranged in rows or columns in the invention according to claim 5 so that one of the first pattern and the second pattern is sandwiched between the other. It is characterized by. Thereby, the inspection can be performed at any image height position.

  According to a seventh aspect of the present invention, in the resolution inspection chart according to the fifth aspect, the first pattern and the second pattern are arranged in a staggered pattern. Since the vicinity of the center of the resolution inspection chart is not affected by the image height, it is easy to detect the vertical and horizontal stripe patterns.

  The resolution inspection chart according to claim 8 is the invention according to any one of claims 1 to 7, wherein the first pattern and the second pattern have the same shape, and the first direction and the It is characterized by being orthogonal to the second direction. Thereby, the difference of the image signal which image | photographed each pattern becomes clear.

  The resolution inspection chart according to claim 9 is the invention according to any one of claims 1 to 8, wherein the black reference portion, the first pattern, and the second pattern are arranged at a center and a periphery. It is characterized by that. Thereby, inspection corresponding to the optical axis of the lens and a predetermined image height can be performed.

  The chart for resolution inspection according to claim 10 is characterized in that, in the invention according to any one of claims 1 to 8, the black reference portion, the first pattern, and the second pattern are formed on the entire surface. And Thereby, inspection corresponding to an arbitrary image height can be performed.

  The chart for resolution inspection according to claim 11 is the invention according to any one of claims 1 to 10, wherein the number of black lines of the first pattern and the second pattern is any of 4 to 8. It is characterized by that. When the number of the black lines is too small, the accuracy of the inspection is lowered, and there is a possibility that erroneous detection is caused in a state where the focus is not achieved. On the other hand, when the number of black lines is too large, the area of the pattern increases and the size of the chart for resolution inspection increases, so the position where the imaging device is placed may be far away, and there is a risk that accurate measurement cannot be performed. . Such a fear can be avoided by setting the number of black lines to 4 to 8.

The resolution inspection method according to claim 12 is a resolution inspection method using the resolution inspection chart according to claims 1 to 11,
Disposing the imaging device with respect to the resolution inspection chart so that any one of the first pattern and the second pattern is at a predetermined image height position with respect to the optical axis of the imaging lens of the imaging device; ,
Capturing the resolution inspection chart by the imaging device, scanning the image signal output from the imaging device, and analyzing the obtained image signal to store the coordinates of the predetermined image height position; ,
Performing focus adjustment of the imaging device;
The resolution inspection chart is imaged by the imaging device, the image signal output from the imaging device is scanned, and the image signal only within a predetermined range with respect to the coordinates of the predetermined image height position is used. Inspecting the resolution at a predetermined image height position.

  In general, when a resolution inspection chart is taken, in order to find a pattern to be inspected, it is necessary to analyze an image signal over a wide range each time. On the other hand, according to the present invention, since the pattern composed of the first pattern, the second pattern, and the black reference portion is unique, the entire resolution inspection chart is first scanned to obtain an image signal. By performing the entire analysis and storing coordinates (specific pixels of the image sensor) corresponding to an arbitrary image height position (including the optical axis position of the lens), after a focus adjustment, a predetermined range including the image height position The inspection can be performed by focusing only on the image signal, thereby greatly reducing the inspection time. Note that “scan” refers to obtaining an image signal from the pixels of the image sensor, and “analysis” refers to, for example, comparing values of the obtained image signal.

  According to the present invention, it is possible to provide a resolution inspection chart and a resolution inspection method in which the influence of illumination is suppressed as much as possible and the inspection accuracy at the same image height position is improved.

It is sectional drawing which shows an example of the imaging device used as the inspection object of resolution. It is a front view of the resolution inspection chart concerning this Embodiment. It is a figure which expands and shows the pattern part. It is a figure which cuts out and shows one horizontal stripe pattern 22 and the vertical stripe pattern 23 with the surrounding black reference | standard part 24 from the pattern part 21. FIG. It is a schematic diagram of a resolution inspection apparatus. It is a figure which shows the correlation of a pattern and an image signal. It is a figure which shows the correlation of a pattern and an image signal. It is a figure which shows the correlation of a pattern and an image signal. It is a figure which shows the correlation of a pattern and an image signal. It is a figure which expands and shows another pattern part. It is a front view of the resolution inspection chart concerning a modification. It is a flowchart of the inspection method of the resolution concerning this embodiment. It is a schematic diagram of a resolution inspection chart used in the resolution inspection method. It is a figure which cuts out and shows a part of pattern. It is a figure which cuts out and shows a part of pattern. It is a figure which shows the state at the time of a view angle change. It is a figure which compares and shows a prior art example and this invention.

  Embodiments relating to a resolution inspection chart and a resolution inspection method according to the present invention will be described. FIG. 1 is a cross-sectional view illustrating an example of an imaging apparatus to be inspected for resolution. In FIG. 1, the image sensor 12 is a CCD (Charge Coupled Device) type image sensor, a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor, or the like. The image sensor 12 is mounted on the substrate 13. The imaging lens 11 that forms an image of the subject on the imaging element 12 is supported so as to be movable in the optical axis direction with respect to the lens frame 15. Specifically, the imaging lens 11 is supported while being biased to the image side by the coil spring 17 and is driven to an arbitrary position in the optical axis direction against the biasing force of the coil spring 17 by the actuator 18. ing. Further, the lens frame 15 is bonded to the substrate 13 with an adhesive S. An infrared cut filter 16 and a diaphragm plate 14 are disposed on the subject side of the imaging lens 11. In addition to the image sensor 12, a plurality of electronic components 19 such as capacitors are also mounted on the substrate 13.

  FIG. 2 is a front view of the resolution inspection chart according to the present embodiment. In FIG. 2, the resolution inspection chart 20 has five pattern portions 21 having the same shape arranged at the center and four locations around the periphery, and these consist of only black and white of the same color. FIG. 3 is an enlarged view showing the pattern portion 21. The pattern portion 21 in FIG. 3 is formed by arranging a plurality of horizontal stripe patterns (first patterns) 22 and vertical stripe patterns (second patterns) 23 adjacent to each other in a staggered pattern (that is, a checkered pattern). Between the adjacent horizontal stripe pattern 22 and vertical stripe pattern 23 and in the periphery, a black reference portion 24 extending linearly is disposed. In other words, each horizontal stripe pattern 22 and each vertical stripe pattern 23 are surrounded by the black reference portion 24.

  FIG. 4 is a diagram showing one horizontal stripe pattern 22 and vertical stripe pattern 23 cut out from the pattern portion 21 together with the surrounding black reference portion 24. This is called a pair pattern. The number of pair patterns in the pattern part 21 is arbitrary. In one pair pattern, the black reference portion 24 includes three equal-width W column portions 24a, 24b, and 24c that extend in the vertical direction with an equal interval Δ, and upper and lower ends of the column portions 24a, 24b, and 24c. Are connected to each other at equal intervals Δ so as to extend horizontally and have equal width W beam portions 24d and 24e.

  In a square space sandwiched between the pillars 24a and 24b and the beam parts 24d and 24e, it is inclined at about 10 degrees with respect to the horizontal direction (that is, in the first direction) at a regular interval δ. A horizontal stripe pattern 22 composed of eight black lines 22a of equal width T extending is formed. That is, the pitch (first pitch) of the black lines 22a is equal and is (δ + T). On the other hand, in a square space sandwiched between the column parts 24b and 24c and the beam parts 24e and 24d, it is inclined at about 10 degrees with respect to the vertical direction (that is, in the second direction) at equal intervals δ. A horizontal stripe pattern 23 composed of eight black lines 23a of equal width T extending straight is formed. That is, the pitch (second pitch) of the black lines 23a is equal to (δ + T). It is preferable that the black line 22a and the black line 23a extend in directions orthogonal to each other.

  The minimum distance D between the beam portion 24d and the black line 22a closest thereto is larger than the interval δ of the black line 22a, and the first white reference portion 25 is provided here. On the other hand, the minimum distance D between the column part 24b and the black line 23a closest thereto is larger than the distance δ of the black line 23a, and the second white reference part 26 is provided here. In one pair pattern, the beam portion 24d, the horizontal stripe pattern 22, and the beam portion 24e are blocks used for the vertical resolution inspection, and the column portion 24b, the vertical stripe pattern 23, and the column portion 24c are blocks used for the horizontal resolution inspection. is there.

  The line width W of the column portions 24a, 24b, 24c and the beam portions 24e, 24d is preferably 2 to 6 times the line width T of the black lines 22a, 23a. This is undesirable because it leads to an increase in the size of the chart. The width of the black lines 22a and 23a is preferably 3 or more in terms of the number of pixels of the image sensor. Furthermore, if the line width of the black reference portion 24 is too narrow, the white line and the black line may be close to gray when the focus adjustment of the imaging lens with respect to the image sensor is not appropriate, and may not be a criterion for discrimination. On the other hand, if the line width of the black reference portion 24 is too thick, the pattern portion 21 becomes large, and as a result, the resolution inspection chart 20 may become large. Therefore, the above range is desirable.

  FIG. 5 is a schematic diagram of the resolution inspection apparatus. An outline of the inspection of the imaging apparatus will be described. Set on an inspection table (not shown) so that the imaging lens 11 of the imaging device 1 to be inspected connected to the image processing device 4 faces the center of the resolution inspection chart 20 attached to the chart attaching plate 5. To do. In this state, the resolution inspection chart 20 is illuminated as uniformly as possible by the plurality of illumination devices 3 arranged around the resolution inspection chart 20, and the resolution inspection chart 20 is imaged by the imaging device 1. The lighting device 3 is preferably a fluorescent lamp, but may be an LED or the like.

  The optical image of the resolution inspection chart 20 is photoelectrically converted by the imaging device of the imaging device 1 and output to the image processing device 4 as an image signal. In the image processing device 4, predetermined image processing is performed on the image signal to generate an image signal. Further, the image signal of the resolution inspection chart 20 is subjected to image processing by the image processing device 4 to inspect the resolution. Note that the image processing device 4 can drive and control the actuator 18 of the imaging device 1.

  Here, when performing a resolution inspection, the image sensor 12 of the image capturing apparatus 1 scans from the upper left pixel toward the right toward the image sensor 12, and when the first line scan is completed, 2 is continued. The entire image signal is obtained by scanning from the left end of the line to the right. The obtained image signal is analyzed to check the resolution.

  Here, in the image signal obtained as described above, the image signal corresponding to the pair pattern shown in FIG. 6A is analyzed. First, when the image signal is generated by the image processing apparatus 4, the image signal at the position indicated by the arrow in FIG. 6A is analyzed, and the relationship between the pixel output and the position is shown in FIG. 6B. A waveform is obtained. That is, the luminance is low in the region A corresponding to the pillar portion 24a of the black reference portion 24, and thereafter the luminance is high in a wide region B (wider than the region A) corresponding to the first white reference portion 25, and In the area C corresponding to the column part 24b, the gradation is lowered again, and thereafter, the brightness is increased in the narrow area D corresponding to the second white reference part 26 (similar to the areas B and C), and the vertical stripe pattern 23 is further increased. In the region E corresponding to, after the luminance changes in a short cycle, the luminance again decreases in the region F corresponding to the column part 24c. Here, since the luminance of the regions A, C, and F that are substantially equally spaced corresponds to the black reference, and the luminance of the region D corresponds to the white reference, this interval α is the maximum luminance difference. Since the width of the region B is wider than the width of the region D, the region B can be distinguished from the region D, but here it is not used as a white reference. On the other hand, the position where the fluctuation width β of the region E is the largest is the focus position, and the resolution (β / α) can be inspected using the maximum value.

  On the other hand, the waveform shown in FIG. 7B is obtained by analyzing the image signal at the position indicated by the arrow in the pair pattern shown in FIG. 7A (the same as in FIG. 6A). That is, the luminance is low in the region A ′ corresponding to the column portion 24a of the black reference portion 24, and thereafter, the luminance is intermediate in the wide region B ′ corresponding to the horizontal stripe pattern 22, and further, the region C corresponding to the column portion 24b. In ', the luminance decreases again, and then the luminance increases in the narrow region D' corresponding to the second white reference portion 26, and further, in the region E 'corresponding to the vertical stripe pattern 23, the luminance changes in a short cycle, In the region F ′ corresponding to the column part 24c, the gradation is lowered again. Similarly, since the gradations of the regions A ′, C ′, and F ′ that are substantially equally spaced correspond to the black reference, and the gradation of the region D ′ corresponds to the white reference, the space α is the maximum luminance difference. On the other hand, the position where the fluctuation width β of the region E is the largest is the focus position, and the resolution (β / α) can be inspected using the maximum value. Therefore, the resolution inspection can be performed using either the image signal at the arrow position in FIG. 6 or the image signal at the arrow position in FIG.

  Here, when the waveform of FIG. 6B is compared with the waveform of FIG. 7B, the waveforms of the regions B and B ′ are clearly different. That is, whether the pattern analysis is at the arrow position in FIG. 6A or the arrow position in FIG. 7A can be determined by analyzing the waveforms in the regions B and B ′. As is clear, when the beam portions 24d and 24e are analyzed, the gradation is lowered in the entire region. That is, by counting the number of waveforms in FIG. 6B or FIG. 7B, it is possible to pinpoint which position of the resolution inspection chart 20 is being analyzed.

  In a specific resolution inspection, an approximate focus position is obtained from an output difference (tone difference) between the white reference and the black reference. The reference detection can be realized by analyzing an image signal having a pattern that matches the number of pixels corresponding to the width of the black reference portion or the white reference portion. In other words, it is calculated in advance whether the width of the black reference portion or the white reference portion corresponds to the number of pixels of the imaging device of the imaging device to be inspected, and the error of the pixel that is determined as the black reference portion or the white reference portion is determined. It is necessary to keep it. If the width of the black reference part or white reference part in calculation is 20 pixels, the detection pixel width is determined so that, for example, the 15-22 pixel range is recognized as the black reference part or white reference part. Is preferred.

  When the luminance difference between the black reference portion and the white reference portion exceeds a certain level, detection of whether the pattern is a vertical stripe or a horizontal stripe is started. The value of the luminance difference between the black reference portion and the white reference portion where the vertical stripe and horizontal stripe pattern detection is started varies depending on the imaging device to be inspected.

  Focus so that the brightness difference between the vertical and horizontal stripe patterns is the largest. It is desirable to confirm that the number of stripes detected at that time matches the number of stripes on the chart. Since there may be a case where a pseudo peak that matches the focus is detected even in a state where the focus is not in focus, it is possible to prevent erroneous detection by checking the number.

  FIG. 8A shows a state in which the pattern is photographed in a state of being out of focus. In such a case, since the vertical stripe pattern 23 is blurred, as shown in FIG. 8B, the region E of the output image signal is shown. The shake width β is smaller than the reference luminance difference α. On the other hand, FIG. 9A shows a state in which the pattern is photographed in a focused state. In such a case, the outline of the vertical stripe pattern 23 is sharp, and as shown in FIG. The width β increases with respect to the reference mechanical difference α. When a position where the shake width β is the largest with respect to the reference luminance difference α is searched for while moving the imaging lens 11 in the optical axis direction by the actuator 18 of the imaging apparatus 1, the position becomes a focused position.

  In this state of focus, the resolution is inspected. On the other hand, when the vertical resolution inspection is performed, the resolution inspection chart 20 can be similarly analyzed by analyzing the image signal vertically.

  The number of the black lines 22a and 23a of the horizontal stripe pattern 22 and the vertical stripe pattern 23 whose resolution is to be measured can be changed by the imaging apparatus 1 as the inspection target, but theoretically three lines are provided for the following reason. The above is desirable. Actually, four or more are desirable, and the optimum is about six to eight. However, it can be said that even if the number is increased beyond eight, the inspection accuracy is not improved and the chart becomes large, which is not desirable.

  FIG. 10 is a diagram showing a pattern portion 21 ′ according to a modification. In the pattern portion 21 shown in FIG. 3, the horizontal stripe pattern 22 and the vertical stripe pattern 23 are arranged in a zigzag pattern. In this modification, the rows where the horizontal stripe pattern 22 is arranged and the rows where the vertical stripe pattern 23 is arranged are alternately arranged. Are lined up. The horizontal stripe pattern 22 and the vertical stripe pattern 23 are the same as those in the above-described embodiment.

  FIG. 11 is a diagram showing a resolution inspection chart 20 'according to a modification. In the resolution inspection chart 20 shown in FIG. 2, the pattern portion 21 is formed only at the center and the periphery. However, in this modification, the pattern portion 21 ′ in which the horizontal stripe pattern 22 and the vertical stripe pattern 23 are alternately formed on the entire chart surface. Have In this modification, the horizontal stripe pattern 22 and the vertical stripe pattern 23 may be arranged in a staggered pattern, or each may be arranged in rows or columns.

Next, a resolution inspection method according to the present embodiment will be described. As a premise of inspection,
(1) The resolution method uses a contrast method.
(2) The hill-climbing method is used to detect the in-focus position.

  In general, when detecting the focal position, the position where the resolution is highest is determined by repeating photographing, data acquisition, resolution inspection, and lens movement. As a method for obtaining the highest resolution, there is a mountain climbing method. This is named because the resolution value obtained by performing the above-described resolution inspection is shaped like a mountain. When this method is used, the amount of data change near the peak of the mountain (where the resolving power is highest) is reduced, so the lens must be moved slightly. Have problems. For this reason, it is considered effective to first inspect the approximate shape of the mountain by moving the lens greatly, and inspecting by moving the lens slightly only in the vicinity that seems to be the focal position. However, in order to find the chart to be inspected from the charts that are usually taken, it is necessary to analyze the image signal of a large area. In the resolution inspection chart of this embodiment, the stripe pattern, which is the basic configuration, is surrounded by a rectangular black frame. By remembering, the position of the target basic pattern can be predicted at the next inspection, and the basic pattern can be detected by analyzing only the image signal of a small area around the target basic pattern. I can do it. As a result, the time required for analyzing the basic pattern can be shortened, and as a result, the entire inspection time can be shortened.

  Hereinafter, the horizontal resolution inspection will be specifically described as an example. FIG. 12 is a flowchart of the resolution inspection method according to the present embodiment. In step S101 in FIG. 12, as shown in FIG. 5, the imaging apparatus 1 in FIG. 1 images the resolution inspection chart 20 schematically shown in FIG. The pattern part 21 is the same as that of the above-described embodiment. Thereby, the image processing apparatus 4 inputs the image signal output from each pixel of the image sensor of the imaging apparatus 1.

  Next, in step S102, the image processing device 4 obtains an image signal by scanning. The image signal analysis is performed in the direction indicated by the arrow in order from the upper left to the right in the pixel corresponding to the resolution inspection chart 20 in FIG. It is assumed that the desired resolution inspection position is the S image height position in the upper left pattern portion 21.

  Further, in step S103, the image processing apparatus 4 detects a pattern in the inspection direction closest to the resolution inspection desired position. This is called a basic pattern. Specifically, it is assumed that the resolution inspection desired position S is a basic stripe pattern 23 that appears after passing through M black reference portions in the Nth column of the pixel arrangement.

  Next, in step S104, the image processing apparatus 4 inspects the resolution using the contrast method. Further, in step S105, the image processing apparatus 4 stores the center coordinates S (x, y) of the basic pattern (see FIG. 14). The central coordinate S (x, y) indicates the y-th pixel in the x-th column when counted from the upper left pixel of the image sensor.

  Thereafter, if the image processing apparatus 4 determines that the inspection value is the highest in step S106, the image processing apparatus 4 ends the inspection. If it is determined that the inspection value is not the highest, the image processing apparatus 4 proceeds to step S107, Focusing operation is performed by driving in the axial direction. After focusing, the imaging apparatus 1 again captures the resolution inspection chart 20 and outputs an image signal in step S108.

  In step S109, the image processing apparatus 4 further multiplies the number of pixels corresponding to the vertical and horizontal dimensions X and Y of the vertical stripe pattern by the coefficient 1.5 with respect to the stored center coordinates S (x, y) of the basic pattern. The image signal from the position of coordinates (x-1.5X, y-1.5Y) subtracted from the numerical values up to the coordinates (x + 1.5X, y + 1.5Y) is cut out and stored in a temporary memory (not shown) ( (See FIG. 15). Thereby, since the basic pattern is always included in the cut-out image signal, the resolution inspection can be performed in a short time even in an imaging apparatus using an imaging device having a large number of pixels.

  Thereafter, the flow returns to step S104, and the image processing apparatus 4 can perform the resolution inspection by executing the process starting from step S104 as described above.

  By the way, the size of the area from which the image signal is cut out can be dealt with by changing it according to the characteristics of the lens to be inspected and the amount of movement of the lens. This area needs to be made somewhat larger than the basic pattern. The reason is that in the case of a lens having a focus function, the coordinates of the basic chart may deviate from the previous inspection position because the angle of view slightly changes when the focus is moved. If the lens is close to the focal position, inspection is performed with a small amount of lens movement, so the amount of change in the angle of view is also small. It will be a thing.

  Hereinafter, a method for setting a cutout area of an image signal when the angle of view moves will be described with reference to the drawings. FIG. 16 shows the area around the resolution inspection portion in the upper left part of the resolution inspection chart, and the vertical and horizontal lines are frames serving as black reference portions. Here, when the angle of view changes due to the lens movement, the chart moves on the captured image as shown in FIGS. Specifically, the inspection position (S) does not change in the image, but the chart itself moves to the upper left. Therefore, as described above, the position of the coordinates obtained by subtracting the numerical value obtained by further multiplying the coefficient corresponding to the number of pixels corresponding to the vertical and horizontal dimensions of the stripe pattern with respect to the center coordinates of the basic pattern is set as the cutout start position of the image signal. It is possible to follow the basic pattern to be inspected regardless of the change in the angle of view.

  In this way, when the amount of movement according to the change in the angle of view is known to some extent, the position of the basic pattern can be predicted, so by starting to cut out the chart image signal from the expected position, all charts The basic pattern can be detected quickly without analyzing the image signal. The greatest advantage of this method of tracking the basic pattern is that the same basic pattern is always inspected, so that there is no discontinuity in the inspection value. In the case of a system that does not track a basic pattern different from the present invention, if the variation in the angle of view is large, there is a risk of measuring the adjacent pattern, which may result in discontinuous inspection data.

  According to the present embodiment described above, by using the unique pattern portion 21, the vertical resolution area and the horizontal resolution area can be arranged adjacent to each other, and the black reference can be obtained in an almost equal environment. An accurate correlation between the resolution and the horizontal resolution can be obtained. Further, since the pattern portion 21 has a block shape, the block to be inspected can be selected intentionally, so that the same block can be tracked even when the angle of view changes due to focusing of the imaging lens. It is possible to eliminate the discontinuity of the inspection data due to the change of the inspection area. Note that the thickness of the black line or the black reference line can be the same as in the prior art. Moreover, it can utilize also for detecting a physical chart position by using the black reference | standard part as a frame.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the pitch of the first pattern may be changed from the pitch of the second pattern.

DESCRIPTION OF SYMBOLS 1 Imaging device 11 Imaging lens 12 Imaging element 20 Resolution inspection chart 21 Pattern part 22, 23 Stripe pattern 3 Illumination device 4 Image processing device

Claims (12)

In a resolution inspection chart that is taken by an imaging device to be inspected and used to inspect the resolution based on an image signal from the imaging device,
A first pattern including a plurality of black lines arranged at a first pitch so as to extend in a first direction;
A second pattern provided adjacent to the first pattern and including a plurality of black lines arranged at a second pitch so as to extend in a second direction intersecting the first direction; ,
At least a black reference portion provided between the first pattern and the second pattern;
A white reference part,
A resolution inspection chart characterized by comprising:   The resolution inspection chart according to claim 1, wherein the black reference portion is a frame surrounding the first pattern and the second pattern.   The resolution inspection chart according to claim 1, wherein the first pattern is a horizontal stripe, and the second pattern is a vertical stripe. The white reference part includes a first white reference part and a second white reference part,
The black reference portion adjacent to the first pattern and the first pattern are separated from each other by a distance larger than the first pitch in the vertical direction, and the first white reference portion is provided therebetween, The reference portion adjacent to the second pattern and the second pattern are separated from each other by a distance larger than the second pitch in the lateral direction, and the second white reference portion is provided therebetween. The resolution inspection chart according to claim 3.   The chart for resolution inspection according to claim 1, wherein the first pattern and the second pattern are repeatedly formed.   6. The resolution inspection chart according to claim 5, wherein one of the first pattern and the second pattern is arranged in a row or a column so as to be sandwiched between the other.   The resolution inspection chart according to claim 5, wherein the first pattern and the second pattern are arranged in a staggered pattern.   The resolution inspection according to claim 1, wherein the first pattern and the second pattern have the same shape, and the first direction and the second direction are orthogonal to each other. For charts.   The chart for resolution inspection according to claim 1, wherein the black reference portion, the first pattern, and the second pattern are arranged at the center and the periphery.   The chart for resolution inspection according to claim 1, wherein the black reference portion, the first pattern, and the second pattern are formed on the entire surface.   The number of black lines of said 1st pattern and said 2nd pattern is either 4-8, The chart for resolution inspection in any one of Claims 1-10 characterized by the above-mentioned. A resolution inspection method using the resolution inspection chart according to claim 1,
Disposing the imaging device with respect to the resolution inspection chart so that any one of the first pattern and the second pattern is at a predetermined image height position with respect to the optical axis of the imaging lens of the imaging device; ,
Capturing the resolution inspection chart by the imaging device, scanning the image signal output from the imaging device, and analyzing the obtained image signal to store the coordinates of the predetermined image height position; ,
Performing focus adjustment of the imaging device;
The resolution inspection chart is imaged by the imaging device, the image signal output from the imaging device is scanned, and the image signal only within a predetermined range with respect to the coordinates of the predetermined image height position is used. And a step of inspecting a resolution at a predetermined image height position.