KR20140058373A - Test chart and method for using thereof - Google Patents

Abstract

Provided is a test chart capable of determining a spatial resolution of an imaging device in a large portion in a visual field of the imaging device. The test chart (100) comprises at least one chart (110, 120, 140, 160, and 180). Each chart includes a plurality of rings (111) arranged in a concentric circle structure, wherein the rings (111) have a spatial frequency which increases in a direction from the periphery towards the center. In addition, each chart includes at least one pair of marks 112 and 114 or 113 and 115 disposed outside of the rings (111), wherein the one pair of marks is disposed in the horizontal direction or the vertical direction passing through the center of the rings.

Description

[0001] TEST CHART AND METHOD FOR USING THEREOF [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a test chart for an imaging device such as a camera and a method of using the same.

Conventionally, it is known to use a circular zone plate (CZP) to evaluate the spatial frequency of a camera. When the known CZP chart is photographed with a video camera and the video signal of the video camera is evaluated by a measuring device such as a waveform monitor, it is determined whether the change in the observation waveform of the measuring device is caused by the characteristics of the lens of the video camera, There is a problem in that it can not be discriminated whether it is due to the characteristics of the camera body. To cope with this problem, Japanese Patent Application Laid-Open No. 2011-101100 discloses a test chart prepared by using the CZP chart of this publication. As the disclosed test chart, there are two charts for evaluating the horizontal resolution of a camera and the like and for evaluating the vertical resolution. A test chart for horizontal resolution evaluation (see Fig. 2 of the above publication) is prepared by cutting a known CZP chart into vertical lines bisecting right and left from the center, joining the left side of the cut left side and the right side of the other side , So that the spatial frequency characteristic is the highest at the central portion and lowered toward the peripheral portion in the horizontal direction. On the other hand, a test chart for vertical resolution evaluation (see Fig. 3 of the above publication) is obtained by cutting a CZP chart from a central portion to a horizontal line bisecting the upper and lower halves by using a known CZP chart, And is formed by joining the lower side of the other side. As a result, the spatial frequency characteristic is highest at the center portion and lowered toward the peripheral portion in the vertical direction. These test charts for horizontal resolution evaluation and vertical resolution evaluation show that the spatial frequency is highest at the center and lowered toward the peripheral portion in the horizontal direction or the peripheral portion in the vertical direction, It is easy to discriminate between the lens and the main body.

However, in the test chart disclosed in Japanese Patent Application Laid-Open No. 2011-101100, the spatial resolution is evaluated only in two lines, that is, a line extending in the horizontal direction from the center of the test chart and a line extending in the vertical direction from the center I can not.

It is therefore an object of the present invention to provide a test chart capable of determining the spatial resolution of the imaging apparatus in a larger portion of the visual field of the imaging apparatus.

It is also an object of the present invention to provide a measurement method for measuring the spatial resolution of an image sensing apparatus using the test chart.

Yet another object of the present invention is to provide a computer-readable storage medium and a computer program for carrying out the above-mentioned measuring method.

A test chart provided in accordance with an embodiment of the present invention is a test chart including at least one chart, wherein the chart is a plurality of rings arranged in a concentric circle shape, A plurality of rings having a spatial frequency that increases in a direction in which the plurality of rings face each other and at least one pair of marks disposed outside the plurality of rings, And at least one pair of marks arranged in the longitudinal direction.

Further, a measurement method provided according to another embodiment of the present invention includes the steps of: a) receiving a digital image pickup signal of the test chart according to any one of claims 1 to 5 from an image pickup apparatus to be measured; b) determining a measurement area at an angle of the one chart by detecting the pair of marks of one of the at least one chart of the test chart from the digital image pickup signal; c) Determining a plurality of measurement lines from a low spatial frequency to a high spatial frequency in the measurement area; d) determining, from each of the measurement lines, a series of digital data along the measurement line Based on at least one of a period and an amplitude of a waveform determined by the series of digital data, And between a plurality of the measuring line and the phase, e) to obtain a resolution using a plurality of spatial resolution obtained respectively, and a, obtaining a spatial resolution in the measurement area of the image pickup apparatus of the to-be-measured.

Further, according to another embodiment of the present invention, various more specific features regarding the test chart and measurement method are provided.

1 is a plan view showing the entirety of a test chart 100 according to an embodiment of the present invention.
Fig. 2 (A) is an enlarged view of the upper half of the center chart in the test chart of Fig. 1, Fig. 2 (B) is a view in which a part of the central chart is further enlarged, 2B is a diagram showing the waveform of the luminance defined by the enlarged portion of Fig. 2B. Fig.
3 is a diagram showing a measurement system for evaluating spatial resolution of an imaging apparatus using a test chart according to an embodiment of the present invention.
Fig. 4 is a flowchart showing a measurement flow for evaluating the spatial resolution of the image pickup apparatus, which is executed by the measurement apparatus of Fig. 3;
Fig. 5 is a flowchart showing the measurement process of one embodiment showing in detail the spatial resolution measurement step in the measurement flow of Fig. 4. Fig.
Fig. 6A shows images on a plurality of measurement lines in a still image, and Fig. 6B shows waveforms of brightness determined by images of two other measurement lines among the plurality of measurement lines.
Fig. 7 is a diagram showing the waveform diagram of Fig. 6 in more detail.
Fig. 8A shows values of digital data in certain measurement lines obtained in the measurement processing of Fig. 5, and Fig. 8B is a diagram showing values of some digital data in this measurement line in more detail to be.
Figs. 9A and 9B are diagrams showing display examples of measurement results when the specified angle interval is 5 degrees, which is displayed by the result display step of the measurement flow in Fig.
Figs. 10 (A) and 10 (B) are views showing still another measurement result display example in the case where the specified angle interval is 5 degrees. Fig.
Figs. 11A and 11B are diagrams showing an example of display of measurement results identical to Figs. 9A and 9B when the specified angular interval is 1 degree.
Figs. 12 (A) and 12 (B) are diagrams showing examples of display of measurement results identical to Figs. 10 (A) and 10 (B) when the specified angular interval is 1 degree.
Fig. 13 is a flowchart showing a measurement process of another embodiment of the resolution measuring step of Fig. 4; Fig.
Fig. 14 is a waveform diagram for explaining the period used in the measurement process of Fig. 13. Fig.
15 is a flowchart showing a measurement process of another embodiment of the resolution measurement step of Fig.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the drawings.

1 is a plan view showing the entirety of a test chart 100 according to an embodiment of the present invention. As shown, the test chart 100 has a rectangular shape and has a 16: 9 aspect ratio (for HDTV). It is also possible to use other aspect ratios in accordance with the aspect ratio of the imaging device to be measured. As shown in the figure, the test chart 100 includes a central chart 110 arranged at the center of the rectangular frame 102, four peripheral charts 120-180 arranged at four corners of the rectangular frame 102, Lt; / RTI > Compared with the vertical size of the rectangular frame 102, the center chart 110 has a size of about 1/3, and each of the surrounding charts 120 to 180 has a size of about 1/5.

2, which is an enlarged view of the upper half of the central chart 110, the central chart 110 includes a plurality of concentric rings 111 arranged at the center, Four position detection marks 112, 113, 114 and 115 arranged around the ring, and a central circular area 116 in the center of the ring 111. [ The plurality of concentric rings 111 define a concentric circle shape in which the spatial frequency increases from the periphery to the center by continuously varying the brightness between black and white. The spatial frequency changes from 350TV lines (outside) to 1150TV lines (center side), and the rate of change is 10TV lines / cycle. The TV pattern is a unit that indicates how many vertical lines of black and white are separated and classified within a horizontal width equal to the vertical height of the screen. At this time, the vertical lines of white and black are counted as one each. In one scan line, the vertical lines of black and white correspond to one cycle of a square wave (or sinusoidal wave) of the luminance signal. Since the floor of the luminance signal is represented by white and the bone is represented by black, one cycle corresponds to a period of two television sets. In Fig. 2 (B), rings for two cycles are shown in more detail. In Fig. 2 (B), although the gray scale is shown as changing step by step, in practice, gray scales changing continuously are used. 2 (C) shows the luminance generated by the ring for two cycles, normalized to a value of 0 to 1, and the luminance continuously changes with the function sin ² x.

The position detection marks 112, 113, 114, and 115 included in the central chart 110 are used to automatically determine the position and direction of the chart. The marks 112 and 114 indicate the horizontal direction passing through the center of the chart (indicating an angle of 0 degrees and 180 degrees), and the marks 113 and 115 indicate the vertical direction passing through the center of the chart (indicating 90 degrees and 270 degrees). In addition, as shown in Fig. 2 (A), the central chart 110 includes a black central circular area 116 to define a central band-shaped part 118 having a width of 2d. 2d is made smaller than the diameter of the circular region 116, the end portion on the center side can be made to be a line relatively close to a straight line, thereby avoiding the arrangement of the ring at the center portion, . From the region of the strip-shaped portion 118, a plurality of lines to be used as a measurement line for measuring spatial resolution is selected. The reason why a plurality of lines are used as the measurement lines is to reduce the influence thereof because the measurement results of the spatial resolution for each line are uneven.

The peripheral charts 120 to 180 have the same configuration as each other and have the same configuration as the central chart 110. [ The difference between the surrounding charts and the central chart is that the overall size of the surrounding chart is small and the plurality of rings arranged at the center are small. A plurality of rings of each surrounding chart (for example, a plurality of rings 122 of the surrounding chart 120) have spatial frequencies of 350TV lines (outside) to 1150TV lines (center side) the same as the central chart, Is 50TVB / cycle, and the rate of change per cycle is higher than that of the central chart.

In the test chart 100 described above, the center may be black-and-white arrangement, or the arrangement may be reversed.

In the above description, the test chart is described as constituting a shape in which grayscale, that is, gray scale, changes between black and white charts, that is, between two colors of black of the first color and white of the second color. In the black and white chart, the values of the components of red (R), green (G), and blue (B) become the same value, As the luminance data. In addition, other colors other than black and white may be used for the test chart. For example, any two colors other than black and white can be used as the first and second colors. The following table shows each value (8-bit representation) of a representative 8-color RGB channel when each color is expressed.

R G B White 255 255 255 Yellow 255 255 0 Cyan 0 255 255 Green 0 255 0 Magenta 255 0 255 Red 255 0 0 Blue 0 0 255 Black 0 0 0

In addition, Table 1 shows only the representative eight colors, and it is also possible to use other colors as arbitrary two colors other than black and white.

When using any two colors other than black and white, the gradation of the color is changed between the two colors between the positive and negative peaks. This makes it possible to analyze the change in the distribution of the resolution due to color. Also, the gradation change can change the values of three channels of the RGB channel simultaneously, change two of the three channels simultaneously, or change only one channel. As a method of changing the gradation, for example, gradation is possible. In addition to changing the three channels of the RGB channels to the same phase, they may be shifted from each other in phase (for example, 90 degrees). By providing the phase difference to the change of the gradation, the measurement accuracy of the spatial resolution can be improved.

According to the test chart 100 described above, the plurality of charts 110 and 120 to 180 are arranged in the rectangular frame 102, so that the spatial resolution of other areas in the visual field can be evaluated independently of each other. In addition, each of the charts includes a ring of concentric circles, so that spatial resolution in a plurality of different directions can be evaluated in each of the regions. This allows the spatial resolution of any desired number of regions in the field of view to be evaluated in all directions from 0 degrees to 360 degrees.

Next, with reference to FIG. 3, a measurement system 300 for evaluating the spatial resolution of the image sensing apparatus using the test chart 100 will be described in detail. As shown in the figure, the measurement system 300 includes an imaging device 310 to be measured, which captures the test chart 100 shown in Fig. 1, and a measurement device 310, which receives an imaging output signal from the imaging device 310 Device 320 as shown in FIG. Examples of the imaging device 310 to be measured include a digital camera, a video camera, a device having any other camera mechanism, for example, a smart phone, a cellular phone, or a module of such a camera mechanism. The measurement apparatus 320 may be constituted by a device dedicated for measurement, or may be realized by a general-purpose apparatus such as a computer. In the following description, it is assumed that the measurement apparatus is implemented by a personal computer (PC). The PC includes a known element such as a processor, an input device, a storage device storing a computer program, and an output device such as a display. In addition, the computer program may be stored in a computer-readable storage medium.

4, a measurement flow performed by a computer program executed by the measurement apparatus 320 for evaluating the spatial resolution of the image sensing apparatus 310 will be described. First, in the first step 400, an output signal of a result of photographing the test chart 100 from the image capturing apparatus 310 is received and placed in a buffer in the PC. This output signal is, for example, a still image file of a camera image, and can be an arbitrary format such as JPEG, BITMAP, PNG, or TIFF. In addition to receiving the still picture file directly from the image pickup apparatus 310, the already received still picture file may be received from a storage medium such as a network (e.g., the Internet), a capture board, and a USB . Next, in step 402, a measurement range of the spatial frequency in the received still image is determined. That is, for example, the central chart 110 among five charts 110 and 120 to 180 is selected, and the direction in which the spatial resolution of the selected central chart 110 is measured is designated as an angle. For example, an angle of 0 degrees indicating the right horizontal direction from the center of the chart is designated as the measurement start angle, and an angular interval to be measured is specified within the range of 0.01 to 90 degrees. Further, in the present embodiment, measurements are simultaneously made in four directions. Therefore, when 0 degree is designated as the measurement start angle, measurements at 90 degrees, 180 degrees, and 270 degrees are also specified.

Next, in step 404, a measurement area of spatial resolution is detected. Concretely, the coordinates of the white square marks 112 to 115 are determined by scanning the square surrounding the four position detection marks 112 to 115 for each line from left to right. Next, the measurement area in the vertical direction is determined by the coordinates of the upper white rectangle, that is, the upper left and right corners of the mark 113 and the lower white rectangle, i.e., the coordinates of the lower left and right corners of the mark 115. Similarly, the measurement area in the horizontal direction is determined by the coordinates of the upper left corner and the upper right corner of the white square, i.e., the mark 114, and the coordinates of the upper right corner and the lower right corner of the mark 112, Next, the peak of the first ring is obtained. Further, for more accurate measurement of the spatial resolution, the measurement area is defined to include a plurality of measurement lines. Also, which measurement line in the measurement area is to be used.

Next, in step 406, the spatial resolution is measured in the determined measurement line, and the measurement result is stored. Details of this measurement will be described later with reference to Fig. Next, in step 408, it is determined whether the measurement in the measurement area has been completed. If not, in step 410, the next measurement area is selected. Details of the processing in step 410 will be described later. Next, the spatial resolution measurement of step 406 is resumed. If it is determined in step 408 that the measurement is complete, in step 412, the stored measurement result is displayed and the flow ends.

Next, with reference to Fig. 5, the details of the measurement process of the embodiment of spatial resolution measurement step 406 will be described. In the measurement process of Fig. 5, an abnormality in the generation of the positive and negative peaks in the waveform is used. First, in step 500, the measurement buffer is initialized to initialize measurement parameters (line counter, inspection data, pointer, result recording buffer, and the like). Next, in step 502, measurement lines within each measurement area in four directions are selected. Basically, the measurement lines in the measurement area are selected from the left side to the right side and from the top side to the bottom side, and are recorded in the line counter. Within each measurement area, 40 lines are selected and their average value is taken as a measurement value. Next, in step 504, the high frequency noise among the data of the selected measurement line is removed by using, for example, a Gauss filter. Specifically, when the measured image is HD (1920 x 1080), since one cycle of the highest resolution is 2 dots (the frequency is half of 74.25 MHz), the frequency components of one period 2 dots or less are regarded as noise and removed.

Fig. 6 shows the image thus obtained (Fig. 6 (A)) and the waveform of the image data (Fig. 6 (B)). In this drawing, a plurality of lines of images including the horizontal line 535 and the horizontal line 540 are shown, while the waveforms of the lower side show normalized luminance variations of the horizontal line 535 and the horizontal line 540 in the range of 0 to 1 . Fig. 7 is an enlarged view of the waveform diagram of Fig. 6, and it can be seen that the horizontal line 535 and the horizontal line 540 are slightly shifted from the sampling point. For this reason, as described above, in one embodiment of the present invention, the spatial resolution is measured by a plurality of measurement lines in each measurement area.

Next, in step 506, by performing the previous processing of the image data, data having only floor and valley peaks are obtained. Specifically, it specifies (1) peaks of floor and valleys in all cycles of the waveform of the image data, (2) in each cycle, data among the two peaks of the floor and the valley, The data between the peak of the bone at the start of the elevation and the peak of the next floor are all converted into the data value of the peak of the peak at the start of the rise and (3) the two peaks of the floor and the valley The data during the descent, that is, the data between the peak of the floor at the start of descent and the peak of the next valley, is converted into the data value of the floor at the start of descent. Next, in step 508, an average value of the preprocessed data is obtained, and this average value is set as a threshold value for determining a floor and a peak of a bone, and this threshold value is also referred to as a "slider" value.

Fig. 8 shows data obtained by the processing of steps 506 and 508. Fig. 8 (A) shows digital values of luminance data (1 to 560) in one line including two measurement lines of 0 degree and 180 degrees, for example. Fig. 8 (B) 8 (A), the brightness data 157 to 177 enclosed in a square are enlarged and shown. Further, in the drawings, for the sake of understanding of the present invention, a slider having a value obtained as described above is shown. As can be seen from the figure, data other than the vicinity of the peak of the floor and the valley are not included.

Next, in step 510, an inspection data pointer pointing to the inspection target data in the measurement line is initialized to indicate the first data to be inspected. Concretely, the data at the right end of the measurement line at 0 degrees, the upper end at 90 degrees, the left end at 180 degrees, and the lower end at 270 degrees. For example, in the example of FIG. 8A, the inspection data pointer points to the digital data 560 when the 0-degree measurement line is selected and to the digital data 1 when the 180-degree measurement line is selected .

Next, in step 512, it is determined whether or not the inspection data pointer reaches the center of the chart, that is, the side opposite to the inspection start position of the selected measurement line. This determination is made by detecting whether the black data continues for a predetermined number or more. It is determined that the inspection on the selected measurement line is completed, and the process advances to step 520. When it is judged that it has not arrived, the process goes to step 514.

In step 514, it is determined whether or not the data indicated by the pointer corresponds to the falling portion of the waveform. The determination of the falling portion is made by determining whether or not the value of the descending portion is smaller than the value of the data immediately before the inspection. (Data 800 or 801 in the example of FIG. 8 (B)), the process goes to step 516 to set the inspection data pointer in the center direction to 1 And the process returns to step 512. On the other hand, if it is determined in step 514 that it is a descending part (data 802 or 804 in the example of FIG. 8B), then in step 517, whether the value of the data under examination is above the slider . (Data 804 in the example of FIG. 8 (B)), it is determined that the upper limit of the spatial resolution is exceeded from the point in which a score exceeding the slider does not appear (black and white are distorted and can not be discriminated) (The data 801 in the example of FIG. 8 (B)) is determined as the upper limit value, and the value of the pointer of the immediately preceding inspection data is recorded.

If YES in step 517, the determined spatial resolution is determined as the measurement result on the measurement line under inspection. Specifically, the value of the pointer is converted into the position on the chart, and the number of TV bones corresponding to the converted chart position is calculated. The calculated TV picture shows the spatial resolution. Next, in step 522, the measurement result is stored in the designated buffer.

In the present embodiment, the combination of the descent detection in step 514 and the determination as to whether or not the slider is above the slider in step 517 is used, but other methods are possible. For example, in step 514, the rising is detected, and in step 517, it is judged whether or not it is below the slider.

Next, in step 524, it is determined whether or not the measurement has been completed for all four measurement lines (0 degree, 90 degrees, 180 degrees, 270 degrees). If not, the next measurement line is selected And then steps 512 to 522 are repeated. On the other hand, when the measurement is completed with respect to all of the four measurement lines, it is determined in step 526 whether measurement on all the measurement lines in each of the four measurement areas has been completed. If not completed, Each of the next measurement lines in the measurement area is selected. For example, when the measurement on measurement line 535 of FIG. 6 is completed but the measurement on line 540 is not being performed, measurement line 540 is selected. Then, the above-described steps 504 to 524 are repeated. When the measurement on all of the measurement lines in each measurement area is completed, in step 528, the average value of the measurement results in the plurality of measurement areas in each measurement area is obtained, and the TV value, which is the average value, The final spatial resolution is determined and stored in the result buffer. As a result, the final spatial resolution in four directions is obtained.

Next, proceeding to step 408 of FIG. 4, and when the measurement in all the measurement areas has not been completed, the next measurement area is selected in step 410. That is, for example, when the measurement in the measurement areas of 0 degree, 90 degrees, 180 degrees, and 270 degrees is completed, the measurement area is selected at the following four angles separated by the specified angular interval. For example, when the specified angular interval is 5 degrees, a measurement area of 5 degrees, 95 degrees, 185 degrees, and 275 degrees is selected. When the specified angular interval is 1 degree, measurement areas of 1 degree, 91 degrees, 181 degrees, and 271 degrees are selected. Here, at the time of selecting the next measurement area, coordinates for defining a spatial area corresponding to the measurement area are spatially rotated by a specified angular interval with the center of the chart as an axis, and as a result, Is obtained by determining the next measurement area. The spatial rotation of the coordinates is also possible in a well known manner, for example by using the following equation.

Here, F (x, y) is a source coordinate, F '(x', y ') is a target coordinate, and? Is a rotation angle. Since the origin of F and F 'overlap, F (0, 0) = F' (0, 0).

Next, in step 408, if the measurement is completed in all the measurement areas, proceed to step 412 to display the measurement results stored in the result buffer. An example of the measurement result (specified angle interval = 5 degrees) is shown in the following table (intermediate values are omitted).

  Angle x coordinate y coordinate resolution (TV view) 0 421 356 830
5 427 349 820
10 423 344 810
15 420 338 800
20 418 333 800
25 420 325 810
30 411 324 830
- - - -
- - - -
- - - -
320 415 406 810
325 428 406 790
330 442 406 750
335 452 400 730
340 455 392 730
345 450 381 750
350 427 368 790

The x-coordinate is an x-axis (horizontal axis) coordinate indicating a position on the chart indicating the upper limit position of the spatial resolution, and the y-coordinate is a y-axis (vertical axis) coordinate of the position. As a result of measurement, in addition to the method of displaying the result in the above-mentioned tabular expression, measurement results can be displayed in various other formats described below.

Fig. 9 (A) is a diagram showing the values of the TV model in which the horizontal axis indicates the angle of the measurement area and the vertical axis indicates the spatial resolution. 9 (B), the abscissa is the x-coordinate and the ordinate is the y-coordinate. Therefore, the result display in Fig. 9 (B) spatially corresponds to the chart as a source.

10 (A) is a display in polar coordinate format, and the result display of Fig. 9 (B) is displayed as a plot of " x " overlaid on a test chart. Respectively. Thus, spatial resolution over 360 degrees can be grasped in relation to the chart. Fig. 10B is a display in polar coordinate format, and the value of the TV pattern at an angle is represented by the distance from the pole at that angle. Thus, the length of the line from the pole represents the size of the spatial resolution, and the center is 0TV base, and the circumference (edge) of the white circle is 1150TVB. This display format may also require a distribution of spatial resolution over 360 degrees.

Figs. 11 (A), 11 (B), 12 (A) and 12 (B) The same figure shows the result when the specified angular interval is smaller than 1.

Next, with reference to Fig. 13, a measurement process which is another embodiment of the resolution measurement step 406 of Fig. 4 will be described. In this embodiment, the length of the period in the waveform is used to determine the spatial resolution. As shown in the figure, the measurement processing in Fig. 13 is similar to the measurement processing in Fig. 5, and the other includes a binarization step 1301, and instead of steps 506 and 512 to 520 in Fig. 5, Step 1300 and steps 1302-1310.

In detail, in step 1300, in addition to the preprocessing in step 506 of FIG. 5, the floor data is referred to as "floor data" from the peak of the floor to the peak of the next floor, and the floor data from the peak of the floor to the next floor are referred to as floor data. Alternatively, from the peak of the floor to the peak of the next valley, it is called "floor data", and from the peak of the floor to the peak of the next floor may be called "floor data". Either way, the waveform data is divided into two pieces: the floor data and the goal data. Next, in step 1301, this preprocessed data is binarized by slicing it with the value of the slider, thereby generating a binarized waveform as shown in Fig. The dotted line portion is a one-period portion of the waveform.

After such processing, in step 1302, it is determined whether or not one period is detected. For example, when "bone data" is detected for the first time, since it is not one cycle, the process proceeds to step 1304, in which the inspection data pointer is shifted one by one towards the center side, and the process returns to step 1302. Here, it is determined whether or not one cycle is again detected. For example, when "floor data" has been detected for the present time, it is determined that one period has been detected because "previous data" has been previously detected. At this time, the process proceeds to step 1306, where it is determined whether or not the detection of one period is the first time. In the case of the first time, the cycle length of one period is recorded in the buffer in step 1308, and then, the process proceeds to step 1304. On the other hand, when it is determined in step 1306 that it is not the first time, it is determined in step 1310 whether or not it is longer than the one cycle detected so far, i.e., the cycle length stored in the buffer. If it is not long, that is, if the length is short or equal, the cycle length detected this time is recorded in the buffer to update the cycle length, and then the process proceeds to step 1304 to move to the next test. On the other hand, when it is determined to be long in step 1310, it is determined that the black-and-white detection period has become black and white and that the discrimination can not be made. . Then, proceeding to the same step as that after step 522 of FIG. 5, the final measurement value can be generated.

Referring to Fig. 15, a measurement process which is still another embodiment of the resolution measurement step 406 of Fig. 4 will be described. In this embodiment, the amplitude in the waveform is used to determine the spatial resolution. As shown in the figure, the measurement process of Fig. 15 is similar to the measurement process of Fig. 5, and the other is that there is no step 508 of Fig. 5, and instead of step 506 and steps 512 to 520 of Fig. And steps 1502 to 1506 are included.

More specifically, in step 1500, in addition to the preprocessing in step 506 in Fig. 5, the same as the processing in Fig. 13, from the peak of the floor to the peak of the next valley is referred to as "valley data", and from the peak of the valley to the peak of the next valley Quot; floor data ". Alternatively, from the peak of the floor to the peak of the next valley, it is called "floor data", and from the peak of the floor to the peak of the next floor may be called "floor data". Either way, the waveform data is divided into two pieces: the floor data and the goal data. After such processing, in step 1502, it is determined whether or not one period is detected. For example, when "bone data" is detected for the first time, since it is not one cycle, the process proceeds to step 1504, in which the inspection data pointer is shifted one by one towards the center side, and the process returns to step 1502. Here, it is determined whether or not one cycle is again detected. For example, when " floor data " has been detected for the present time, " goal data " has been detected last time, it is determined that one period has been detected. At this time, the process proceeds to step 1506, where it is determined whether or not the detected amplitude of one cycle is smaller than a predetermined threshold value. If it is not smaller than the threshold value, it is determined that black and white have not been distorted, and the process proceeds to step 1504 to move to the next data check. On the other hand, if it is smaller than the threshold value, it is determined that the black and white image is distorted, and the coordinates on the chart and the value of the TV image at the position of this coordinate are obtained from the value of the previous inspection data pointer. Then, proceeding to the same step as that after step 522 of FIG. 5, the final measurement value can be generated.

Using the test chart of the present invention explained in detail above, it is possible to evaluate the spatial resolution in spatially different view areas in different directions within 360 degrees in each area, thereby enabling a detailed evaluation compared with the conventional one . Further, according to the measuring method of the present invention, the spatial resolution can be accurately evaluated by using the test chart, and the evaluation result can be displayed in a format easy for the user to understand.

Claims (19)

In a test chart comprising at least one chart,
In the chart,
A plurality of rings arranged in a concentric circle shape, the plurality of rings having a plurality of rings having a spatial frequency increasing in a direction from the periphery toward the center,
At least one pair of marks disposed outside of the plurality of rings and the pair of marks include at least one pair of marks arranged in the transverse direction or the longitudinal direction passing through the centers of the plurality of rings Include, test chart. The method according to claim 1,
Wherein each pair of the at least one pair of marks defines a measurement area to be used for measurement of the spatial resolution and the width of the measurement area is determined by the width of the corresponding pair of marks. 3. The method of claim 2,
Wherein the chart includes the black circular area at the center of the plurality of rings,
Wherein the circular area has a diameter that is related to the width of the mark in a direction perpendicular to the transverse direction or the longitudinal direction in which the mark is disposed. The method according to claim 1,
Wherein each of the plurality of rings has a first color at one of the peaks of the waveform defining the spatial frequency and a second color at the other of the peaks defining the spatial frequency, Wherein the color changes between the first color and the second color. The method according to claim 1,
Wherein the test chart has a rectangular shape and includes a plurality of the charts,
The plurality of charts may include:
A center chart arranged at the center of the rectangle of the test chart,
And four surrounding charts disposed at each of the four corners of the rectangle. a) receiving a digital image pickup signal of the test chart according to any one of claims 1 to 5 from an image pickup apparatus to be measured,
b) determining a measurement area at an angle of the one chart by detecting, from the digital image pickup signal, the pair of marks of one of the at least one chart of the test chart;
c) determining a plurality of measurement lines in the measurement area from a low spatial frequency to a high spatial frequency;
d) acquiring, from each of the measurement lines, a series of digital data along the measurement line from the digital image pickup signal, and based on at least one of the period and the amplitude of the waveform determined by the series of digital data Obtaining a spatial resolution in each of the measurement lines;
and e) obtaining a spatial resolution in the measurement area of the imaging device of the measurement object, using a plurality of spatial resolutions respectively obtained from the plurality of measurement lines. The method according to claim 6,
Wherein the step of obtaining the spatial resolution in each of the measurement lines comprises:
Starting a detection of a peak of the waveform from the low spatial frequency,
Detecting a peak of one polarity not exceeding an average value of the waveform among the detected peaks;
Determining a spatial resolution in each of the measurement lines based on the spatial frequency corresponding to a waveform position having a polarity peak of one polarity exceeding the average value immediately before a polarity peak of one polarity not exceeding the average value . 8. The method of claim 7,
Wherein the spatial resolution of the measurement area is determined by an average value of the plurality of spatial resolutions obtained from the plurality of measurement lines. The method according to claim 6,
Wherein the step of obtaining the spatial resolution in each of the measurement lines comprises:
Starting the detection of the period of the waveform from the low spatial frequency,
Determining whether the detected period is longer than the immediately preceding detected period;
And determining the spatial resolution in each of the measurement lines based on the spatial frequency corresponding to the waveform position having the detected period when the detected period is longer than the immediately preceding detected period Way. The method according to claim 6,
Wherein the step of obtaining the spatial resolution in each of the measurement lines comprises:
Starting the detection of the amplitude of the waveform from the low spatial frequency,
Determining whether the detected amplitude is less than a threshold value;
Determining a spatial resolution in each of the measurement lines based on the spatial frequency corresponding to a waveform position having an amplitude detected immediately before the detected amplitude when the detected amplitude is smaller than the threshold value , How to measure. The method according to claim 6,
Generating a measurement area after rotation by rotating the measurement area at an angle around the center of the one chart;
Further comprising the step of performing steps c), d) and e) with respect to the post-rotation measuring area. The method according to claim 6,
Further comprising the step of displaying a value representing the spatial resolution obtained in the measurement area in association with an angle of the measurement area. 13. The method of claim 12,
Wherein a value indicating the spatial resolution and an angle of the measurement area are displayed in polar coordinates. 14. The method of claim 13,
Wherein the distance from the poles in the polar coordinates is related to the distance between the centers of the plurality of rings and the plurality of ring shaped positions of the chart having spatial frequencies represented by the distances. 15. The method of claim 14,
Wherein the distance from the poles in the polar coordinates is related to the spatial resolution. 16. The method of claim 15,
Wherein the distance from the center in the polar coordinates represents a value representing the spatial resolution. 13. The method of claim 12,
Wherein a value indicating the spatial resolution and an angle of the measurement area are expressed in Cartesian coordinates. A computer program for causing a computer to execute the method according to any one of claims 6 to 17. 17. A computer-readable storage medium storing computer-readable instructions for causing a computer to execute the method according to any one of claims 6 to 17.

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