JP6742178B2 - MTF measuring device and its program - Google Patents

Description

The present invention relates to an MTF measuring device for measuring an MTF (Modulation Transfer Function) indicating a spatial frequency characteristic of a camera and its program.

Conventionally, as a method for quantitatively measuring the resolution characteristic of a camera, there is a method using an inmega cycle chart and a method for measuring a spatial frequency characteristic such as a slanted edge method (slanted edge method).
The method using the inmegacycle chart is a test chart provided by the Institute of Image Information and Television Engineers (ITE) as a test chart (ITE high-definition inmegacycle chart: (See FIG. 10), a CTF (Contrast Transfer Function) is measured as a spatial frequency characteristic from an image obtained by capturing the chart with a camera.
As shown in FIG. 10, the inmegacycle chart is a rectangle in which black and white vertical stripes corresponding to video frequencies of 1 MHz to 36 MHz are arranged, and 800 TVL/ph (27.7 MHz) vertical stripes are arranged at the center of the chart and four corners. Has a wave pattern.

In the slanted-edge method, a black-and-white pattern in which a boundary inclined by several degrees from a vertical (or horizontal) direction with respect to an image sensor is a straight line is captured by a camera, and a predetermined region (ROI: Region Of Interest ]) (ROI image) is used to measure the frequency characteristic in the horizontal direction or the frequency characteristic (MTF) in the vertical direction (see Patent Documents 1 to 3 and Non-Patent Document 1).
FIG. 11A shows a ROI image (vertical edge image) of a black-and-white pattern in which a boundary inclined several degrees from the vertical direction is a straight line, and a boundary inclined several degrees from the horizontal direction is a straight line in FIG. 11B. The ROI image (horizontal edge image) having the black and white pattern is shown.

For example, in the case of obtaining the horizontal frequency characteristic as the MTF from the ROI image (vertical edge image) of FIG. 11A, first, the slanted-edge method, as shown in FIG. The pixels of the edge image are projected on the horizontal axis (x axis) at the same angle as θe.
Then, as shown in FIG. 12B, the slanted-edge method averages the pixel values of the pixels projected on the horizontal axis (x-axis) for each sub-pixel unit, thereby indicating an edge characteristic. Generate a profile.
Then, the slanted-edge method obtains a line spread function (LSF) by differentiating the edge profile, and Fourier transforms the LSF to obtain the MTF.

When obtaining the frequency characteristic in the vertical direction as the MTF from the ROI image (horizontal edge image) of FIG. 11B, the Slanted-edge method uses the vertical axis as the axis onto which the pixels of the edge image are projected. The MTF is obtained by the same method as the ROI image (vertical edge image) of FIG.
Alternatively, in the slanted-edge method, the ROI image (horizontal edge image) of FIG. 11B is rotated by 90°, and the pixels of the edge image are processed in the same manner as the ROI image (vertical edge image) of FIG. Is projected on the horizontal axis (x axis) to obtain the MTF.

JP, 2010-197201, A JP, 2010-237177, A JP, 2005-94701, A

ISO 12233:2014, “Photography-Electronic still picture imaging-Resolution and spatial frequency responses”

In the method using the above-mentioned Inmega cycle chart, since the chart corresponds to only 14 kinds of frequencies, the measurable frequencies are limited. In addition, this method has a problem that the higher the definition of the camera whose characteristics are to be measured, the more susceptible it is to aliasing distortion depending on the sampling frequency of the image sensor of the camera.

On the other hand, the slanted-edge method is less susceptible to aliasing distortion within the Nyquist frequency of the image sensor due to the effect of oversampling that averages pixel values in subpixel units when generating an edge profile.
Therefore, in order to measure the spatial frequency characteristic of the camera more accurately, it can be said that it is preferable to use the slanted-edge method.

However, the spatial frequency characteristic changes greatly with a slight focus shift. Therefore, when actually measuring the spatial frequency characteristic, it is necessary to move the focus position of the camera little by little and repeat the process of performing the measurement each time to obtain the measurement result at the focus position having the best frequency characteristic.
In particular, the slanted-edge method has a problem in that it takes time to obtain an accurate frequency characteristic because a process accompanied by a calculation cost, such as obtaining an edge inclination, occurs when measuring the MTF. ..

The present invention is made in view of such a problem, and when measuring MTF by the Slanted-edge method, the MTF measuring device and its program which can measure exact MTF by one operation. The challenge is to provide.

In order to solve the above-mentioned problems, the MTF measuring apparatus according to the present invention captures a black-and-white pattern in which a boundary, which is inclined at a predetermined angle (several degrees) from a vertical direction or a horizontal direction with respect to an image sensor of the camera, is a straight line, and the camera It is an MTF measuring device for measuring the MTF representing the spatial frequency characteristic of, and is configured to include edge spread amount measuring means, frame selecting means, and MTF calculating means.

In such a configuration, the MTF measuring device has a predetermined area (ROI) including an edge between a bright portion and a dark portion in a plurality of frames in which the focus position is moved by the edge spread amount measuring means and the camera captures a black-and-white pattern. The number of pixels having the brightness of is measured as the edge spread amount. That is, the edge spread amount measuring means measures the number of pixels imaged in gray between the brightness of white and black as the edge spread amount. When the focus is out of focus, a sharp edge is not captured due to the blur of the focus, and the number of gray pixels increases, so that the edge spread amount can be used as a reference for whether or not the focus is in focus.

Then, in the MTF measuring device, the frame selecting unit selects the frame having the minimum edge spread amount measured by the edge spread amount measuring unit from the plurality of frames. Thereby, the frame imaged in the focused state is selected.
Then, the MTF measuring device calculates the MTF of the predetermined area (ROI) in the frame selected by the frame selecting means by the MTF calculating means by using the slanted-edge method.
As a result, the MTF measuring device can accurately measure the MTF from the focused image by calculating the MTF once.

In order to solve the above-mentioned problems, the MTF measuring device according to the present invention images a black-and-white pattern in which a boundary inclined by a predetermined angle (several degrees) from a vertical direction or a horizontal direction with respect to an image sensor of a camera is a straight line. An MTF measuring device that measures an MTF representing a spatial frequency characteristic of a camera may be configured to include an edge spread amount measuring unit, a focus position selecting unit, and an MTF calculating unit.

In such a configuration, the MTF measuring device has a predetermined area (ROI) including an edge between a bright portion and a dark portion in a plurality of frames in which the focus position is moved by the edge spread amount measuring means and the camera captures a black-and-white pattern. The number of pixels having the brightness of is measured as the edge spread amount.

Then, the MTF measuring device selects, by the focus position selecting means, the focus position where the frame having the smallest edge spread amount measured by the edge spread amount measuring means is imaged among the plurality of frames imaged by moving the focus position. .. As a result, the focus position when the best focus is achieved is selected.
Then, the MTF measuring device inputs a frame captured by fixing the focus position of the camera to the focus position selected by the focus position selecting means, and the MTF calculating means uses the slanted-edge method in the frame, The MTF of the predetermined area (ROI) is calculated.
As a result, the MTF measuring device can accurately measure the MTF by calculating the MTF once from an image captured with the focus position completely fixed without any motion blur associated with the movement of the focus position. it can.

The MTF measuring device can be operated by the MTF measuring program that causes the computer to function as the above-described edge spread amount measuring means, frame selecting means, and MTF calculating means. Further, the MTF measuring device can operate the computer with an MTF measuring program for causing the computer to function as the above-described edge spread amount measuring means, focus position selecting means, and MTF calculating means.

The present invention has the following excellent effects.
According to the present invention, the MTF can be calculated after determining the image or the focus position in which the focus is optimum for the calculation of the MTF by measuring the edge spread amount.
Therefore, the present invention can significantly reduce the time required for focus adjustment, as compared with the method of measuring the MTF by repeating the adjustment of the focus position and the calculation of the MTF as in the conventional slanted-edge method. The MTF can be measured at high speed and accurately.

It is a block configuration diagram showing a configuration of an MTF measuring device according to a first embodiment of the present invention. It is a figure for demonstrating ROI in a picked-up image, (a) is a vertical ROI (vertical edge image), (b) is a horizontal ROI (horizontal edge image). It is explanatory drawing for demonstrating the spread of an edge. It is an explanatory view for explaining the method of specifying the MTF measurement object frame from the amount of edge spread. It is a flow chart which shows operation of the MTF measuring device concerning a 1st embodiment of the present invention. It is a block block diagram which shows the structure of the MTF measuring device which concerns on 2nd Embodiment of this invention. It is a flow chart which shows operation of the MTF measuring device concerning a 2nd embodiment of the present invention. It is a block block diagram which shows the structure of the modification of the MTF measuring device which concerns on 1st Embodiment of this invention. It is a block block diagram which shows the structure of the modification of the MTF measuring device which concerns on 2nd Embodiment of this invention. It is an Inmega cycle chart which is an example of the conventional test chart. An edge image used in a conventional slanted-edge method, where (a) is an image (vertical edge image) for obtaining a horizontal frequency characteristic as an MTF, and (b) is an image for obtaining a vertical frequency characteristic as an MTF. It is an image (horizontal edge image). 9A and 9B are diagrams for explaining a conventional procedure for generating an edge profile of the slanted-edge method, in which FIG. It is a figure which shows the process which averages the pixel value of the projected pixel and produces|generates an edge profile.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
«First embodiment»
[Configuration of MTF measuring device]
First, the configuration of the MTF measuring device 1 according to the first embodiment of the present invention will be described with reference to FIG.

The MTF measuring device 1 measures the MTF representing the spatial frequency characteristic of the camera 2. Here, the MTF measuring device 1 is connected to the camera 2 to be measured.

The camera 2 is a general camera (imaging system) that is an MTF measurement target. The camera 2 is a video camera having at least a focus adjustment function (here, the focus lens 20 and its drive unit 21). The drive unit 21 drives and controls the position (focus position) of the focus lens 20 by operating a focus ring (not shown) or the like. Here, the operator operates a focus ring (not shown) or the like to move the focus position from the front to the back or from the back to the front, so that the camera 2 captures an image of the test chart C at the focus position ( The moving image) is output to the MTF measuring device 1.

The test chart (MTF measurement chart) C is a chart used in the Slanted-edge method having a black-and-white pattern in which a boundary inclined by a predetermined angle from a vertical direction or a horizontal direction with respect to an image sensor (not shown) of the camera 2 is a straight line. is there. The camera 2 captures an image with the black and white boundary line of the test chart C tilted at a predetermined angle (about 1 to 5 degrees). Here, when measuring the frequency characteristic in the horizontal direction, the camera 2 captures an image of the test chart C in a state where the boundary line is in a diagonally vertical direction as shown in FIG. Then, the operator designates the ROI from the video image of the test chart C as shown in FIG. In this case, the ROI identifies vertical edge images having different brightness (reference white level, reference black level) in the horizontal direction.
Further, when measuring the frequency characteristic in the vertical direction, the camera 2 captures an image of the test chart C with the boundary line being in the diagonally horizontal direction as shown in FIG. Then, the operator designates the ROI from the video image of the test chart C as shown in FIG. In this case, the ROI identifies horizontal edge images having different brightness (reference white level, reference black level) in the vertical direction.

Hereinafter, the configuration of the MTF measuring device 1 that measures the MTF of the camera 2 using the image captured by the camera 2 will be described in detail.
The MTF measuring device 1 includes a video input unit 10, an ROI specifying unit 11, an ROI cutout unit 12, an edge spread amount measuring unit 13, a frame selecting unit 14, and an MTF calculating unit 15.

The image input means 10 is for inputting an image of the test chart C captured from the camera 2. The video input means 10 outputs the input video to the ROI cutout means 12 in frame units.
At this time, the video input unit 10 outputs the frame to the ROI cutout unit 12 in association with a number (frame number) that identifies the frame. When the video signal in which the time code is recorded is input from the camera 2, the time code may be used as the number for identifying the frame.
Here, the image input means 10 is instructed by the operator to input and end the image, and inputs the image while moving the focus.

The ROI specifying means 11 is for inputting information for specifying the ROI (ROI specifying information). This ROI identification information is, for example, the coordinates of the diagonal points of the ROI. The ROI identification means 11 outputs the input ROI identification information to the ROI cutout means 12.

The ROI cutout unit 12 cuts out the ROI region specified by the ROI specifying information input from the ROI specifying unit 11 from the video input by the video input unit 10 in frame units. In the ROI cutout unit 12, the ROI region is cut out in association with the frame number and the frame (image).

The edge spread amount measuring unit 13 measures, for each frame, the edge spread amount indicating the degree of edge spread in the ROI region cut out by the ROI cutout unit 12. The edge spread amount measuring means 13 outputs the measured edge spread amount to the frame selecting means 14 in association with the frame number of the measured frame.
Note that the edge spread amount measuring means 13 may measure the edge spread amount each time a frame is input to the ROI cutout means 12, or the ROI cutout image in a state where the focus is moved to the ROI cutout means 12. It is also possible to measure the edge spread amount in each frame after storing all in the storage means (not shown).

Here, the spread of the edge refers to a range in which a pixel having a brightness between the reference white and the reference black exists between the pixels of the reference white (bright portion) and the reference black (dark portion) that form the ROI. In the ROI imaged in a focused state, the number of pixels of the brightness of the reference white and the reference black is small at the edge portion. However, when the focus is out of focus, the number of pixels of the brightness between the reference white and the reference black is large in the edge portion.
That is, the spread of the edge serves as a reference for determining whether or not the focus is achieved.
Therefore, the edge spread amount measuring unit 13 uses the edge spread amount indicating the degree of the edge spread as a reference for determining whether or not the frame is in focus in the ROI region cut out by the ROI cutout unit 12. To measure.

Here, the measurement of the edge spread amount performed by the edge spread amount measuring unit 13 will be specifically described with reference to FIG. 3 (see FIG. 1 as appropriate).
Here, an example will be described in which a vertical edge image is used as the image specified by the ROI, and the horizontal edge spread amount is measured.

As shown in FIG. 3, the edge spread amount measuring means 13 causes the signal level (brightness) of adjacent pixels from the left end of the ROI to exceed a predetermined brightness difference along the horizontal row (line L) on the ROI. Up to the horizontal position is determined as the signal level of one reference (reference white W: bright part here), and the horizontal position is set as the left end of the edge spread. In addition, the edge spread amount measuring unit 13 specifies the left end of the edge spread, and then, along the horizontal row (line L) on the ROI, the signal level of the adjacent pixel falls within a predetermined brightness difference. The position is the right end of the edge spread. The signal level of the pixels continuing to the right of the right end of the spread of the edge becomes the signal level of the other reference (here, reference black B: dark portion).
Here, an example in which the left reference signal level is W and the right reference signal level is B is shown, but an edge image in which the left reference signal level is B and the right reference signal level is W is shown. Even if it is used, it can be measured by the same method.

At the right end of the edge spread, the edge spread amount measuring means 13 has a signal level (brightness) exceeding a predetermined brightness difference from the right end of the ROI along the horizontal row (line L) on the ROI. It is also possible to determine up to the horizontal position as the signal level of the reference (here, the reference black B) and to determine the horizontal position as the right end of the spread of the edge.
Thereby, the edge spread amount measuring unit 13 can specify the range of different brightness between the reference white W and the reference black B as the edge spread (the number of pixels).
Here, the edge spread amount measuring means 13 may determine the edge spread in all lines of the ROI (vertical edge image) and obtain the sum or average thereof to obtain the edge spread amount. The edge spread amount may be the spread of edges measured on at least one line, but it is preferable to use a statistic (sum of edge spreads, average) in consideration of the influence of noise and the like.

Further, here, an example in which the horizontal edge spread amount is measured from the vertical edge image has been described. However, when a horizontal edge image is used as the image specified by the ROI, vertical lines (columns) are used instead of lines. The edge spread amount may be measured with.
Whether the image specified by the ROI is the vertical edge image (FIG. 2A) or the horizontal vertical edge image (FIG. 2B) may be set in advance from the outside. The edge spread amount measuring unit 13 may make the determination based on the number of horizontal pixels and the number of vertical pixels of the ROI.
Returning to FIG. 1, the description of the configuration of the MTF measuring device 1 will be continued.

The frame selection unit 14 selects a frame corresponding to the ROI having the smallest edge spread amount from the captured frames. Here, the frame selection unit 14 selects the frame corresponding to the frame number having the smallest edge spread amount associated with the frame number measured by the edge spread amount measurement unit 13 as the MTF measurement target frame. The frame selection means 14 outputs the ROI image associated with the selected frame number to the MTF calculation means 15.

For example, as shown in FIG. 4, the frame selection means 14 sets the frame having the frame number of the ROI for which the edge spread amount, which is sequentially input in the frame number order, becomes the minimum value as the MTF measurement target frame. In this case, the frame selection unit 14 stores the images specified by the ROIs of at least several frames before and after the frame having the minimum edge expansion amount in order to specify the frame having the minimum edge expansion amount (not shown). ) Hold.

The MTF calculation means 15 calculates the MTF from the ROI in the MTF measurement target frame. Here, the MTF calculation unit 15 calculates the MTF for the image of the ROI region specified by the frame number selected by the frame selection unit 14.
The MTF calculating means 15 calculates the MTF from the ROI (edge image) using a general slanted-edge method. That is, the MTF calculating means 15 generates an edge profile showing the characteristics of an edge from the edge image, differentiates the edge profile to obtain the line spread function (LSF), and Fourier transforms the LSF to obtain the MTF.

By configuring the MTF measuring device 1 as described above, the MTF measuring device 1 can measure the MTF with the ROI of the MTF measurement target frame imaged in a focused state. At this time, the MTF measuring apparatus 1 may perform the MTF calculation once with the ROI of the in-focus MTF measurement target frame without repeating the adjustment of the focus position and the calculation of the MTF. It can be carried out.
The MTF measuring device 1 can operate a computer (not shown) with a program (MTF measuring program) that functions as each of the above-described means.

[Operation of MTF measuring device]
Next, the operation of the MTF measuring device 1 according to the first embodiment of the present invention will be described with reference to FIG. 5 (for the configuration, refer to FIG. 1 as appropriate).
First, the MTF measuring device 1 inputs the ROI specifying information for specifying the MTF measuring area by the ROI specifying means 11 (step S1). Here, the MTF measurement device 1 inputs ROI identification information (for example, coordinates of diagonal points) that identifies a rectangular area (ROI) designated on the captured image of the test chart C captured by the camera 2.

Then, the MTF measuring device 1 inputs the image captured by the operator by moving the focus position of the camera 2 by the image input means 10 (step S2).
Then, the MTF measuring device 1 cuts out the ROI region specified by the ROI specifying information input in step S1 from the input video by the ROI cutting means 12 in frame units (step S3).
As a result, the frames (ROI regions) having different focus positions are sequentially cut out by the ROI cutout means 12.

Then, the MTF measuring device 1 measures the edge spread amount of the ROI cut out by the ROI cutout unit 12 by the edge spread amount measuring unit 13 (step S4). Here, if the image specified by the ROI is a vertical edge image (FIG. 2A), the edge spread amount measuring unit 13 determines the reference black and the reference black for each line in the image area of the ROI in frame units. The number of pixels of brightness between white and white is measured, and the sum or average of the total number of lines of the number of pixels is taken as the edge spread amount. If the image specified by the ROI is a horizontal edge image (FIG. 2B), the edge spread amount measuring unit 13 causes the reference black and the reference white for each column in the image area of the ROI in units of frames. The number of pixels of lightness between and is measured, and the sum or average of the total number of columns of the number of pixels is taken as the edge spread amount.

Then, the MTF measuring apparatus 1 selects, as the MTF measurement target frame, the frame corresponding to the ROI having the minimum edge spread amount measured in step S4 by the frame selecting means 14 (step S5). Here, the frame selection unit 14 selects the frame number of the frame with the smallest edge spread amount, and outputs the image specified by the ROI of the selected frame number to the MTF calculation unit 15.

After that, in the MTF measuring device 1, the MTF calculating means 15 calculates the MTF with the ROI corresponding to the frame number selected in step S5 (step S6).
That is, the MTF calculation unit 15 calculates the MTF from the image specified by the ROI of the frame number selected in step S5, which is output from the frame selection unit 14.

With the above operation, the MTF measuring device 1 can measure the MTF having the best frequency characteristic by only performing the MTF calculation once for the ROI of the in-focus MTF measurement target frame.

«Second embodiment»
[Configuration of MTF measuring device]
Next, the configuration of the MTF measuring device 1B according to the second embodiment of the present invention will be described with reference to FIG.
The MTF measuring device 1B measures the MTF representing the spatial frequency characteristic of the camera 2B. Similar to the MTF measuring device 1 (see FIG. 1), the MTF measuring device 1B specifies the focus position by the edge spread amount of the edge image, and measures the MTF by the ROI imaged at the focus position. However, the MTF measuring device 1B has a function of designating the focus position of the camera 2B.
Here, the MTF measuring device 1B is connected to the camera 2B to be measured.

The camera 2B is an image pickup system of the measured object of the MTF. Like the camera 2 (see FIG. 1), the camera 2B is a video camera having at least a focus adjustment function (here, the focus lens 20 and its drive unit 21), and further outputs the focus position to the outside. It also has a function of focusing on a designated focus position.
The test chart C is the same as that described with reference to FIG.

Hereinafter, the configuration of the MTF measuring device 1B will be described in detail.
The MTF measuring device 1B includes a video input unit 10B, an ROI specifying unit 11, an ROI cutout unit 12, an edge spread amount measuring unit 13B, an MTF calculating unit 15B, a focus position selecting unit 16, and a focus position specifying unit 17. And
The ROI identification means 11 and the ROI cutout means 12 have the same configurations as the MTF measuring device 1 described in FIG. Hereinafter, the image input means 10B, the edge spread amount measuring means 13B, the focus position selecting means 16, the focus position designating means 17, and the MTF calculating means 15B will be described in this order.

The image input means 10B is for inputting an image of the test chart C and a focus position from the camera 2B. The video input means 10B outputs the input video to the ROI cutout means 12 in frame units.
At this time, the video input unit 10B outputs the frame to the ROI cutout unit 12 in association with the focus position.

The edge spread amount measuring unit 13B measures, for each frame, the edge spread amount indicating the degree of the edge spread in the ROI region cut out by the ROI cutout unit 12, and the edge spread amount measuring unit 13 (see FIG. 1)). The edge spread amount measuring unit 13B outputs the edge spread amount measured for each frame and the focus position associated with the frame to the focus position selecting unit 16.

The focus position selecting means 16 selects the focus position of the frame having the smallest edge spread amount. Here, the focus position selection unit 16 selects, as the MTF measurement focus position, the focus position where the edge spread amount is the minimum in the edge spread amount and the focus position input from the edge spread amount measuring unit 13B for each frame. The focus position selecting means 16 outputs the selected focus position (MTF measurement focus position) to the focus position designating means 17.
It should be noted that the focus position selecting unit 16 is operated after the movement of the focus position by the operator is completed. For example, the focus position selection unit 16 operates by being instructed by the operator from outside after the focus position is moved by the operator.

The focus position designating means 17 is for instructing the focus position to the camera 2B so that it becomes the focus position selected by the focus position selecting means 16. As a result, the image is input to the image input unit 10B in the in-focus state after the focus adjustment, and the in-focus frame is input to the ROI cutout unit 12.

The MTF calculating means 15B calculates the MTF from the ROI in the MTF measurement target frame. Here, the MTF calculation unit 15B calculates the MTF of the image of the ROI region specified by the ROI specification unit 11 that is cut out by the ROI cutout unit 12.
As the MTF calculating method in the MTF calculating means 15B, a general slanted-edge method may be used as in the MTF calculating means 15 (see FIG. 1).
Here, after the focus adjustment to the focus position designated by the focus position designating means 17, there is no change in the edge spread amount in the state where the focus is not moved. Therefore, the MTF calculating means 15B selects one of the frames after the focus adjustment. This is the MTF measurement target frame.

By configuring the MTF measuring device 1B as described above, the MTF measuring device 1B can measure the MTF by using the ROI of the MTF measurement target frame imaged in a focused state. At this time, the MTF measuring device 1B may calculate the MTF once with the ROI of the in-focus MTF measurement target frame without repeating the adjustment of the focus position and the calculation of the MTF. It can be carried out.
Further, since the MTF measuring device 1B measures the MTF by fixing the focus position in a focused state, the motion blur caused by the movement of the focus ring within one frame period depending on the frame rate of the moving image. Therefore, the MTF can be accurately measured.
The MTF measuring apparatus 1B can operate a computer (not shown) with a program (MTF measuring program) that causes each of the above-described units to function.

[Operation of MTF measuring device]
Next, the operation of the MTF measuring apparatus 1B according to the second embodiment of the present invention will be described with reference to FIG. 7 (for the configuration, see FIG. 6 as appropriate).
First, the MTF measuring device 1B inputs the ROI specifying information for specifying the MTF measuring region by the ROI specifying means 11 (step S10).

Then, in the MTF measuring device 1B, the image input means 10B inputs the image captured by the operator by moving the focus position of the camera 2 together with the focus position (step S11).
Then, the MTF measuring device 1B cuts out the ROI region specified by the ROI specifying information input in step S10 from the input video by the ROI cutting means 12 in frame units (step S12).
As a result, the frames (ROI regions) having different focus positions are sequentially cut out by the ROI cutout means 12.

Then, the MTF measuring device 1B measures the edge spread amount of the ROI cut out by the ROI cutout unit 12 by the edge spread amount measuring unit 13B (step S13).

Then, in the MTF measuring device 1B, the focus position selecting means 16 selects the focus position with the minimum edge spread amount measured in step S12 as the MTF measuring focus position (step S14).

After that, the MTF measuring device 1B drives the drive unit 21 of the camera 2B to specify the focus position of the focus lens 20 by specifying the MTF measurement focus position selected in step S14 by the focus position specifying means 17. It is moved to the designated position (step S15).

Further, the MTF measuring device 1B inputs the image whose focus is fixed at the MTF measurement focus position by the video input means 10B (step S16).
Then, the MTF measuring device 1B cuts out the ROI region specified by the ROI specifying information input in step S10 in frame units from the input video by the ROI cutting means 12 (step S17).

Then, the MTF measuring device 1B calculates the MTF by the MTF calculating means 15B by the ROI in the image captured at the MTF measurement focus position cut out by the ROI cutout means 12 in step S17 (step S18).

With the above operation, the MTF measuring apparatus 1B can measure the MTF having the best frequency characteristic by only performing the MTF calculation once for the ROI of the focused MTF measurement target frame.
Although the configuration and operation of the MTF measuring devices 1 and 1B according to the embodiment of the present invention have been described above, the present invention is not limited to this embodiment.

«Modification 1»
Here, the MTF measuring apparatuses 1 and 1B input the image (moving image) of the test chart C captured by the cameras 2 and 2B by moving the focus. However, the target for moving the focus position may be the test chart C. For example, an X stage may be used in which a metal plate, a glass plate, or the like on which the test chart C is printed or affixed is vertically fixed and moved in the optical axis direction of the cameras 2 and 2B. In this case, the camera 2B does not need to have the function of outputting the focus position or the function of focusing on the focus position, and the X stage has the function. As a result, the focus position can be adjusted more finely than the focus rings of the cameras 2 and 2B.

«Modification 2»
In addition, here, as the test chart C, a chart having a unidirectional edge for measuring frequency characteristics in the vertical or horizontal direction was used. However, as the test chart C, for example, a multidirectional MTF measurement chart having edges (straight lines) in a plurality of directions as described in JP 2010-237177 A may be used.
In that case, the ROI specifying unit 11 specifies a plurality of ROIs from an image obtained by capturing the multidirectional MTF measurement chart. Then, the edge spread amount measuring means 13 and 13B measure the edge spread amount for each of the plurality of ROIs. When the ROI is set to be tilted depending on the direction of the edge, the edge spread amount measuring means 13 and 13B may rotate the image of the ROI according to the tilt and then measure the edge spread amount. ..

At this time, in the case of the MTF measuring device 1 (see FIG. 1), the frame selecting unit 14 selects a frame having the smallest edge spread amount for each ROI, and the MTF calculating unit 15 individually selects the edge spread for each ROI. The frame with the smallest amount is read out and the MTF of the ROI is calculated.

Further, in the case of the MTF measuring device 1B (see FIG. 6), the focus position selecting unit 16 selects the focus position that minimizes the edge spread amount for each ROI, and the focus position specifying unit 17 selects the focus position for each ROI. Switch. Then, the MTF measuring device 1B sequentially outputs the images captured at the optimum focus position for each ROI to the ROI cutout unit 12 by the video input unit 10B, and the MTF calculation unit 15B reads out the frame for each ROI to output the MTF. To calculate.
As a result, even when the multidirectional MTF measurement chart to be imaged is tilted with respect to the optical axes of the cameras 2 and 2B, the MTF can be accurately calculated using the frame of the optimum focus position for each ROI. can do.

«Modification 3»
Although the ROI cutout unit 12 sequentially cuts out ROIs here, it is also possible to store consecutive frames including the ROIs as they are and measure the MTF in the ROI region within the frames.

For example, as shown in FIG. 8, it may be configured as an MTF measuring device 1C including a frame storage means 18 for storing a frame instead of the ROI cutout means 12 of FIG. In this case, the ROI specifying means 11 outputs the ROI specifying information to the edge spread amount measuring means 13 and the MTF calculating means 15. Then, the edge spread amount measuring unit 13 measures the edge spread amount with the ROI specified by the ROI specifying information within the frame, and the MTF calculating unit 15 calculates the MTF with the ROI specified by the ROI specifying information within the frame. do it.

Further, for example, as shown in FIG. 9, instead of the ROI cutout unit 12 of FIG. 6, it may be configured as an MTF measuring device 1D including a frame storage unit 18 that stores a frame. In this case, the ROI specifying means 11 outputs the ROI specifying information to the edge spread amount measuring means 13B and the MTF calculating means 15B. Then, the edge spread amount measuring means 13B measures the edge spread amount with the ROI specified by the ROI specifying information within the frame, and the MTF calculating means 15B calculates the MTF with the ROI specified by the ROI specifying information within the frame. do it.

«Modification 4»
Further, here, the measured MTF is output to the outside as it is. However, the MTF measuring devices 1 and 1B may be configured to include the graph generating means in the subsequent stage of the MTF calculating means 15 and 15B.
This graph generating means generates a graph that can be visualized by plotting the MTF for each spatial frequency calculated by the MTF calculating means 15 and 15B on the coordinate where the horizontal axis is the frequency and the vertical axis is the MTF. To do. The graph generation means outputs the generated graph to the display device so that the operator can visually recognize the MTF analysis result of the cameras 2 and 2B.

«Modification 5»
In addition, here, the edge spread amount measuring means 13 and 13B determines the brightness of a pixel in which the brightness difference between adjacent pixels exceeds a predetermined brightness difference as the brightness between the bright portion and the dark portion, and determines the edge spread. It was decided to measure the amount.
However, even if the amount of edge spread is measured by counting the number of pixels having the brightness in a predetermined range between the signal level W of the brightness and the signal level B of the dark part among the pixels included in the ROI. Good. In this case, the signal level W of the bright part and the signal level B of the dark part may be obtained from the average value of the signal levels of the pixels in which the brightness difference between the adjacent pixels does not exceed the predetermined brightness difference, or the video signal level in advance. It may be measured from and set manually.

DESCRIPTION OF SYMBOLS 1 MTF measuring device 10 Image input means 11 ROI specifying means 12 ROI cutting means 13 Edge spread amount measuring means 14 Frame selecting means 15 MTF calculating means 16 Focus position selecting means 17 Focus position specifying means 18 Frame storing means 2 Camera 20 Focus lens 21 Driver C test chart (MTF measurement chart)

Claims (6)

An MTF measuring device for measuring a MTF representing a spatial frequency characteristic of the camera by imaging a black-and-white pattern in which a boundary inclined by a predetermined angle from a vertical direction or a horizontal direction with respect to an image pickup element of the camera is a straight line,
In a plurality of frames in which the camera captures the black-and-white pattern by moving the focus position, in a predetermined area including edges, the number of pixels having the lightness between the bright part and the dark part is measured as the edge spread amount measurement. Means and
In the plurality of frames, a frame selection unit that selects a frame whose edge spread amount measured by the edge spread amount measuring unit is the smallest,
MTF calculating means for calculating the MTF of the predetermined area in the frame selected by the frame selecting means,
An MTF measuring device comprising: An MTF measuring device for measuring a MTF representing a spatial frequency characteristic of the camera by imaging a black-and-white pattern in which a boundary inclined by a predetermined angle from a vertical direction or a horizontal direction with respect to an image pickup element of the camera is a straight line,
In a plurality of frames in which the camera captures the black-and-white pattern by moving the focus position, in a predetermined area including edges, the number of pixels having the lightness between the bright part and the dark part is measured as the edge spread amount measurement. Means and
In the plurality of frames, a focus position selecting unit that selects a focus position in which a frame in which the edge spread amount measured by the edge spread amount measuring unit is imaged is selected,
An MTF calculating unit that inputs a frame captured by fixing the focus position of the camera to the focus position selected by the focus position selecting unit and calculates the MTF of the predetermined area in the frame.
An MTF measuring device comprising: The edge spread amount measuring means,
When the image of the predetermined area is an edge image having different brightness in the horizontal direction, the sum or average of the number of pixels having the brightness between the bright portion and the dark portion for all lines of the predetermined area is defined as the edge spread. Measured as a quantity,
When the image of the predetermined area is an edge image with different brightness in the vertical direction, the sum or average of the number of pixels having the brightness between the light portion and the dark portion for all columns of the predetermined area is defined as the edge spread. It measures as a quantity, The MTF measuring device of Claim 1 or Claim 2 characterized by the above-mentioned. The edge spread amount measuring means measures the edge spread amount by determining the brightness of a pixel in which the brightness difference between adjacent pixels exceeds a predetermined brightness difference as the brightness between the bright portion and the dark portion. The MTF measuring device according to any one of claims 1 to 3, characterized in that. 2. The edge spread amount measuring means measures, as the edge spread amount, a total number of pixels having brightness in a predetermined range between the light portion and the dark portion in the predetermined area. 5. The MTF measuring device according to claim 4. An MTF measurement program for causing a computer to function as each unit of the MTF measurement device according to any one of claims 1 to 5.