Display modulation degree measuring device and program

Abstract

To provide a display modulation degree measurement device that measures the modulation degree of a display.SOLUTION: A display modulation degree measurement device 1 includes an image input unit 11 that captures a sine wave pattern image displayed on a display 2 at various phases from a camera 3 directly facing the display 2 and inputs the captured images as images, an ROI image extraction unit 14 that extracts an ROI image for measuring the degree of modulation from the captured image, a projection information generation unit 15 that generates projection information by associating the position of each pixel of the ROI image along an inclination of a predetermined angle with a projection axis of bins at subpixel intervals parallel to the modulation direction of the sine wave pattern, a sine wave profile generation unit 17 that generates a sine wave profile by averaging pixel values of the ROI image for each bin associated with the projection information, and a modulation degree calculation unit 18 that calculates a modulation degree on the basis of the sine wave pattern of the sine wave profile and the white level and black level.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a display modulation degree measuring device and a program therefor for measuring the modulation degree of a display. [Background technology]

[0002] In recent years, display technology has diversified, with RGB subpixels no longer arranged in stripes, but instead using patterns such as PenTile or RGBW arrays, or incorporating film-like devices such as diffusers and touch sensors on the display surface, all of which are affecting the resolution characteristics of displays.

[0003] Therefore, conventionally, in order to measure the resolution characteristics of a display, there is a method of measuring the modulation degree by displaying a square wave (Non-Patent Document 1) or a sine wave (Non-Patent Document 2) on the display (see Non-Patent Document 1). Conventional methods for measuring the modulation depth of a display involve displaying a black and white rectangular wave pattern horizontally or vertically on the display and capturing it at high magnification with a camera. Then, the conventional method obtains an oversampled one-dimensional luminance profile from the average value of the vertical or horizontal luminance of the image captured by the camera, applies a smoothing filter the width of one pixel of the display, and measures the contrast from the peaks and valleys of the profile. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] “IDMS(Information Display Measurements Standard)”, SID(Society of Information Display), ICDM(International Committee for Display Metrology), version1.03, pp.109-138, June 1, 2012. [Non-Patent Document 2] Triantaphillidou, S. and Jacobson, RE, “Measurements of the modulation transfer function of image displays”, Journal of Imaging Science and Technology. 48 (1), pp.58-65, 2004. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Conventional methods measure at high magnification to ignore the effects of the camera's MTF (Modulation Transfer Function). IDMS recommends that there be 30 or more camera pixels for every 1 pixel width of the display. However, conventional methods have a problem in that they analyze a wide area of ​​the camera image, making it difficult to accurately measure the modulation degree due to influences such as lens shading and differences in resolution characteristics (MTF) between the optical axis center and periphery. Therefore, the object of the present invention is to provide a display modulation degree measuring device and program that can measure the modulation degree of a display with high accuracy using only the central portion of an image captured by a camera. [Means for solving the problem]

[0006] To solve the aforementioned problems, the display modulation degree measuring device according to the present invention measures the modulation degree of a display from an image captured by a camera in which an image sensor, in which pixels are arranged in a square array with the optical axis of the camera facing the display as the axis of rotation, is tilted by a predetermined angle, and the device comprises an image input unit, an ROI (Region of Interest) image extraction unit, a projection information generation unit, a sine wave profile generation unit, and a modulation degree calculation unit.

[0007] In such a configuration, the display modulation degree measuring device inputs a captured image from a camera through an image input unit. At this time, since the captured image is tilted at a predetermined angle with respect to the modulation direction of the sine wave pattern, sine waves are captured in the captured image at various phases with respect to the modulation direction of the pattern. Then, the display modulation degree measuring device extracts an ROI image of a region of interest set as an object for measuring the modulation degree from the captured image through an ROI image extraction unit.

[0008] Then, the display modulation degree measuring device, through a projection information generation unit, ROI image generates projection information by associating the positions of each pixel of the ROI image along the inclination of a predetermined angle with a projection axis of a bin having a sub-pixel interval and parallel to the modulation direction of the sine wave pattern. Furthermore, the display modulation degree measuring device generates a sine wave profile by averaging the pixel values of each pixel of the ROI image for each bin of the projection axis associated with the projection information through a sine wave profile generation unit. As a result, a sine wave profile in which the pixel values of the sine wave pattern in an oversampled state are projected onto the projection axis is generated.

[0009] Then, the display modulation degree measuring device calculates the modulation degree based on the sine wave pattern of the sine wave profile and the white level of the white image and the black level of the black image previously captured by the camera through a modulation degree calculation unit. At this time, the modulation depth calculation unit detects the phase of the sine wave pattern in the sine wave profile by using the value of the inverse tangent function of the correlation ratio between each of the cosine waves and sine waves with amplitude 1, sampled at a spatial frequency obtained by dividing the spatial frequency of the sine wave pattern in the sine wave pattern image by the pixel ratio, which is the spatial frequency of the display relative to the spatial frequency of the camera, and the oversampling ratio, which is the number of subpixels corresponding to one pixel on the projection axis, and the sine wave in the sine wave profile. The unit then calculates the amplitude of the sine wave that minimizes the sum of the values ​​obtained by multiplying the difference between the sine wave pattern in the sine wave profile and the phase sine wave by a window function, and calculates the modulation depth by the ratio of the amplitude to the difference between the white level and the black level. Note that the display modulation degree measuring device can be operated by a display modulation degree measurement program for causing a computer to function as each of the above-described units.

Advantages of the Invention

[0010] According to the present invention, since the sine wave pattern is tilted at a predetermined angle and oversampled to measure the modulation degree, even in a relatively small region of interest, a uniformly shifted distribution with respect to the sampling position of the display can be obtained, and the modulation degree can be accurately measured.

Brief Description of the Drawings

[0011] [Figure 1] It is a block diagram showing the configuration of a display modulation degree measurement device according to an embodiment of the present invention. [Figure 2] It is a diagram showing an example of a sine wave pattern image to be displayed on a display. [Figure 3] It is an enlarged view of a part of the sine wave pattern image in FIG. 2. [Figure 4] It is an explanatory diagram for explaining an example of setting an ROI on a photographed image. [Figure 5] It is a diagram showing an example of an ROI image. [Figure 6] (a) to (j) are diagrams showing examples of ROI images extracted from sine wave pattern images with different spatial frequencies. [Figure 7] It is an explanatory diagram for explaining the inclination of an ROI image. [Figure 8] It is an explanatory diagram for explaining the correspondence relationship between the position of a pixel in an ROI image and the position of a bin on a projection axis. [Figure 9] (a) is a diagram showing a state where pixel values of an ROI image are assigned to bins on a projection axis, and (b) is a diagram showing an example of a sine wave profile obtained by averaging pixel values of each bin. [Figure 10] (a) shows an ROI image, and (b) is a diagram showing an example of a sine wave profile and a sine wave pattern corresponding to the ROI image. [Figure 11] It is a diagram showing an example of a chart of MTF. [Figure 12] It is a flowchart showing the operation of a display modulation degree measurement device according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Configuration of Display Modulation Degree Measurement Device] First, with reference to Figure 1, the configuration of the display modulation degree measuring device 1 according to an embodiment of the present invention will be described.

[0013] The display modulation degree measuring device 1 measures the modulation degree of the display 2. The display modulation degree measuring device 1 measures the modulation degree of the display 2 from an image captured by a camera tilted at a predetermined angle with respect to the modulation direction of the sine wave pattern displayed on the display 2.

[0014] Display 2 is the display device to be measured for modulation depth. Display 2 can be any device that displays images, such as a UHDTV, smartphone, tablet device, or projector. Furthermore, the pixel structure of Display 2 is not limited to RGB stripes; any pixel structure is acceptable, such as a PenTile arrangement or an RGBW arrangement. The display modulation degree measuring device 1 operates by connecting the display 2, camera 3, and display device 4.

[0015] Camera 3 (luminance measurement camera) is a camera used to measure the brightness of the screen displayed by Display 2. Camera 3 captures the screen of Display 2 with a pixel ratio of 1 or greater. Here, the pixel ratio is the number of pixels in the camera output signal that corresponds to one pixel width of the input signal format of Display 2 captured by Camera 3. This pixel ratio is not particularly limited, but it is, for example, around 1.5 to 2.5 times.

[0016] Furthermore, camera 3 is positioned to face display 2 directly, and the image captured by camera 3 is positioned at a predetermined angle of inclination with respect to the image displayed on display 2, using the camera's optical axis as the axis of rotation. This angle is such that the phase of the sine wave pattern in the sine wave pattern image displayed on display 2 is uniformly captured at the sampling position of the image sensor of camera 3, and is approximately a few degrees (for example, 3 degrees).

[0017] The display device 4 provides a user interface for operating the display modulation degree measuring device 1 and displays images captured by the camera 3, modulation degree measurement results, etc. For example, the display device 4 may be a liquid crystal display, an organic EL display, etc. The configuration of the display modulation degree measuring device 1 will be described in detail below.

[0018] As shown in Figure 1, the display modulation degree measuring device 1 comprises a measurement image display unit 10, an image input unit 11, a tilt detection unit 12, an ROI setting unit 13, an ROI image extraction unit 14, a projection information generation unit 15, a projection information storage unit 16, a sine wave profile generation unit 17, a modulation degree calculation unit 18, and an MTF display unit 19.

[0019] The measurement image display unit 10 displays an image (measurement image) for measuring the modulation degree of the display 2. The measurement image display unit 10 displays an image with a sine wave pattern drawn on it (sine wave pattern image) as the measurement image on the display 2. The measurement image display unit 10 displays sine wave pattern images, which are drawn with sine wave patterns of different spatial frequencies, either by external specification or in a predetermined order.

[0020] For example, the measurement image display unit 10 prepares sine wave pattern images G, as shown in Figure 2, for different spatial frequencies in advance, or draws them as appropriate, and displays the specified sine wave pattern image G on the display 2. Figure 3 is a sine wave pattern image GX, which is an enlarged portion of the sine wave pattern image G in Figure 2. The sine wave pattern image G may be an image with inverted brightness (phase inversion). The input signal values ​​(pixel values) of the sine wave pattern image G are corrected to be the inverse of the grayscale characteristics of display 2, so that the brightness displayed on display 2 during measurement is sinusoidal.

[0021] The spatial frequency of the sine wave pattern in the sine wave pattern image G is, for example, 0.05 (cycles / pixel). DISP) to 0.5 (cycles / pixel) DISP The increments are 0.001 up to 0.01, etc. The horizontally modulated sine wave pattern image G is represented by a linearly corrected signal A sin(2πfx) / 2+B. Here, x is an integer and represents the horizontal pixel position of display 2, with the sampling position of a pixel close to the center of the ROI as the origin, and pixel DISP This indicates the pixel spacing of display 2. In the case of full range, A is the maximum value of the signal, and B is A / 2. Note that the sine wave pattern image G is an image used to measure the horizontal modulation depth of display 2. When measuring the vertical modulation depth, a sine wave pattern image obtained by rotating the sine wave pattern image G by 90° can be used.

[0022] Here, before the measurement step to measure the modulation degree, the measurement image display unit 10, as an initial step, detects the tilt of the optical axis of the camera 3 by displaying a line image on the display 2, which is a line drawn horizontally or vertically to the modulation direction of the sine wave pattern image G to be measured. Also, as an initial step, the measurement image display unit 10 displays a white image on the display 2 for measuring the white level and a black image for measuring the black level. These images can be switched by external instructions.

[0023] The image input unit 11 receives images (captured images) taken by the camera 3. Furthermore, if the camera 3 is a video camera, it is preferable for the image input unit 11 to add and average the sequentially input captured images (frames) at predetermined intervals. The image input unit 11 stores the input captured image in a memory (not shown in the diagram). The captured images input by the image input unit 11 and stored in memory are output to the display device 4 via an image output unit (not shown in the figure) and are also read out by the ROI image extraction unit 14.

[0024] In the initial stage before measuring the modulation depth, the image input unit 11 captures a white image displayed by the display 2 with the camera 3, stores the pixel values ​​of the white level in a memory (not shown), and captures a black image displayed by the display 2 with the camera 3, stores the pixel values ​​of the black level in a memory (not shown). These white and black level pixel values ​​are used by the modulation depth calculation unit 18. Furthermore, the image input unit 11 outputs the line image displayed on the display 2 to the tilt detection unit 12 in the initial stage before the modulation degree is measured.

[0025] The tilt detection unit 12 detects the tilt angle of the axis perpendicular to the modulation direction of the sine wave relative to a predetermined reference axis (here, the y-axis) in a coordinate system (xy coordinate system) with two axes, horizontal and vertical, in the line image input by the image input unit 11. This tilt angle can be determined using a general method. For example, in a line image, the tilt detection unit 12 detects edges using Sobel edge detection and detects the tilt angle of the edges using Hough transform. This allows the tilt detection unit 12 to detect the rotation angle of the optical axis of the camera 3 as the tilt angle. The tilt detection unit 12 outputs the detected tilt angle to the projection information generation unit 15.

[0026] The ROI setting unit 13 sets the region within the captured image taken by the camera 3 as the ROI (Region of Interest) where the modulation degree of the display 2 is to be measured. For example, within the captured image displayed by the display device 4, the ROI setting unit 13 sets information that identifies the ROI (position and shape, mask data of the closed region, etc.) as ROI information when a closed region (circle, ellipse, rectangle, arbitrary shape, etc.) is specified by a pointing device (not shown) operated by the measurer.

[0027] For example, the ROI setting unit 13 sets ROI information by having the operator specify the ROI using a rectangle in the captured image D, as shown in Figure 4. This ROI then identifies an ROI image R containing a sine wave pattern, as shown in Figure 5. Figure 5 shows the ROI size for a 100(W)×200(H) camera pixel that can be used in actual measurements, with a pixel ratio of 1.8.

[0028] Furthermore, when the measurement image display unit 10 draws sine wave patterns with different spatial frequencies, the ROI setting unit 13 will set the sine wave pattern images with different spatial frequencies as ROIs, as shown in the examples in Figures 6(a) to (j). Figures 6(a) to (e) show values ​​of 0.05, 0.20, 0.45, 0.49, and 0.50 (cycles / pixel), respectively. DISP The example shows a spatial frequency of ), a pixel ratio (sampling interval of the display input signal / sampling interval of the camera output signal) of 1.8, and a size of 200 vertical pixels and 100 horizontal pixels (note that these pixels are from camera 3). Figures 6(f) to (j) are the sine waves of Figures 6(a) to (e) with the phase shifted by 90°, respectively.

[0029] The ROI setting unit 13 only needs to be set once if there is no need to change the ROI. The ROI setting unit 13 outputs ROI information that identifies the set ROI to the ROI image extraction unit 14.

[0030] The ROI image extraction unit 14 extracts images of ROIs indicated by the ROI information set in the ROI setting unit 13 as targets for measuring modulation degree, from the captured images input by the image input unit 11, and uses these images as ROI images. The ROI image extraction unit 14 outputs the extracted ROI image to the projection information generation unit 15. Furthermore, after the projection information generation in the projection information generation unit 15 is completed, the ROI image extraction unit 14 outputs the ROI image to the sine wave profile generation unit 17. Here, the ROI image extraction unit 14 outputs the ROI image to the projection information generation unit 15, and after receiving a notification from the projection information generation unit 15 that the generation of projection information is complete, it outputs the ROI image to the sine wave profile generation unit 17.

[0031] The projection information generation unit 15 generates projection information by associating the position of each pixel in the ROI image with the projection axis of bins that are parallel to the modulation direction of the sinusoidal wave pattern in the ROI image and have sub-pixel spacing, along a predetermined angle of inclination. Furthermore, if camera 3 is a video camera and continuously captures images, the projection information generation unit 15 assumes that the tilt angle between display 2 and camera 3 is constant, generates projection information only once initially, and omits the generation of projection information until the ROI is reset. This makes it possible to measure the modulation degree in real time, even with moving images, by reusing the projection information generated initially.

[0032] The projection information generation unit 15 associates each pixel of the ROI image with the projection axis of a bin parallel to the modulation direction of the sine wave in the ROI image and spaced at subpixel intervals, using the tilt angle detected by the tilt detection unit 12. The projection axis has a subpixel spacing smaller than that of the pixels in the ROI image, for example, 1 / 4 or 1 / 8 of a single pixel. Furthermore, if camera 3 is a video camera and continuously captures images, the projection information generation unit 15 assumes that the tilt angle between display 2 and camera 3 is constant, generates projection information only once initially, and omits the generation of projection information until the ROI is reset. This makes it possible to measure the modulation degree in real time, even with moving images, by reusing the projection information generated initially.

[0033] Specifically, as shown in Figure 7, the axis e perpendicular to the modulation direction of the sine wave is assumed to be rotated with respect to the reference axis (in this case, the y-axis) by the tilt angle θe detected by the tilt detection unit 12. Note that Figure 7 is an enlarged portion of Figure 5. In this case, as shown in Figure 8, the projection information generation unit 15 rotates each pixel position (x,y) of the ROI image R by a predetermined rotation center (for example, the average value of the xy coordinates of the pixels in the ROI image) by an angle of inclination (-θe) in the opposite direction to the rotation direction of the inclination angle θe detected by the inclination detection unit 12. The projection information generation unit 15 then generates projection information by associating the position (x,y) of each pixel before rotation of the ROI image R with the position of bins that are divided by the subpixel width of the projection axis on a subpixel unit onto which the pixels are projected. The projection information generation unit 15 stores the generated projection information in the projection information storage unit 16. The projection information generation unit 15 stores the projection information in the projection information storage unit 16, and then outputs a notification to the ROI image extraction unit 14 indicating that the generation of the projection information is complete.

[0034] The projection information storage unit 16 stores the projection information generated by the projection information generation unit 15. This projection information storage unit 16 is, for example, a general storage device such as a semiconductor memory. The projection information stored in the projection information storage unit 16 is referenced by the sine wave profile generation unit 17.

[0035] The sine wave profile generation unit 17 generates a sine wave profile by averaging the pixel values ​​of each pixel in the ROI image extracted by the ROI image extraction unit 14 for each bin of the projection axis associated with the projection information generated by the projection information generation unit 15. The sine wave profile is information that shows the shape of the pixel distribution of a sine wave. Specifically, the sinusoidal profile generation unit 17 projects pixel values ​​from the ROI image extracted by the ROI image extraction unit 14 to the same bin on the projection axis, based on the projection information stored in the projection information storage unit 16, as shown in Figure 9(a). Then, the sinusoidal profile generation unit 17 averages the pixel values ​​for each bin to generate a sinusoidal profile P, which associates the subpixel positions on the projection axis with the pixel values, as shown in Figure 9(b).

[0036] The sinusoidal wave profile P does not represent an exact sine wave, but rather discrete information shown by dots in Figure 10(b) for an ROI image R of 200 vertical pixels and 100 horizontal pixels (where the pixels are those of camera 3) as shown in Figure 10(a). The sinusoidal wave S shown in Figure 10(b) will be determined by the modulation depth calculation unit 18, which will be described later. In Figure 10(b), the horizontal axis represents the coordinate position of the projection axis in subpixel units, and the vertical axis represents the relative brightness. As a result, the sine wave profile generation unit 17 can generate a sine wave profile in which pixels are uniformly distributed at subpixel positions along the projection axis. The sine wave profile generation unit 17 outputs the generated sine wave profile to the modulation depth calculation unit 18.

[0037] The modulation depth calculation unit 18 calculates the modulation depth of the display 2 using the sine wave pattern of the sine wave profile generated by the sine wave profile generation unit 17, the white level of the white image previously captured by the camera 3, and the black level of the black image.

[0038] Specifically, the modulation depth calculation unit 18 calculates the modulation depth by the following calculation. Hereinafter, the sine wave pattern identified by the sine wave pattern image displayed on the display 2 is called the displayed sine wave, and the sine wave pattern identified by the sine wave profile generated by the sine wave profile generation unit 17 is called the oversampled sine wave. First, the modulation depth calculation unit 18 detects the phase of the oversampled sine wave. Here, the modulation depth calculation unit 18 calculates the spatial frequency f of the oversampled sine wave and the displayed sine wave using the pixel ratio m and the oversampling ratio N. bin The spatial frequency (f / m / N) obtained by dividing by the given value. bin A sine wave with amplitude 1 sampled using (sin(2πfx / m / N)) bin )) and cosine wave (cos(2πfx / m / N) bin The correlations a and b with ) are determined, and the phase φ is detected by the value of the arctangent function (arctan) of b / a. Here, x is the one-dimensional position with respect to the pixels of the display as the unit.

[0039] Here, the spatial frequency f is the number of cycles per pixel of the display 2, and is the known spatial frequency (cycles / pixel DISP ) of the displayed sine wave. That is, the spatial frequency f is the spatial frequency of the sine wave of the sine wave pattern image displayed on the measurement image display unit 10. DISP Also, the pixel ratio (spatial frequency ratio) m is a known ratio, which is the sampling interval (pixel DISP ) of the display input signal / the sampling interval (pixel CAM ) of the output signal of the camera. Also, the oversampling ratio N bin is a known ratio, which is the number of bins per pixel (pixel CAM ) of the camera 3 on the projection axis.

[0040] Next, the modulation degree calculation unit 18 searches for the amplitude a (a>0) and the offset d such that the difference between the sine wave a sin(2πfx / m / N bin +φ)+d and the oversampled sine wave is minimized. For example, the modulation degree calculation unit 18 calculates the sum (sum of squares) of the values obtained by multiplying the difference between the sine wave a sin(2πfx / m / N bin +φ)+d and the oversampled sine wave by a window function (for example, a Hann window), and calculates the parameter values (a, d) that minimize that value. As a result, the shape of the oversampled sine wave is specified.

[0041] Then, the modulation degree calculation unit 18 uses the amplitude a, the white level W and the black level K of the display 2 photographed by the same camera 3 that previously measures the modulation degree, and calculates M sin =2×a / (W-K) as the ratio of the amplitude to the difference between the white level W and the black level K, thereby calculating the modulation degree M sin . Similarly, the modulation degree calculation unit 18 uses the amplitude a (a>0) and the offset d as parameters for the cosine wave a cos(2πfx / m / N binThe amplitude a that minimizes the difference between (+φ)+d and the oversampled sine wave is given by M as the ratio of the amplitude to the difference between the white level W and the black level K. cos The modulation index M is calculated by calculating =2 × a / (WK). cos Calculate.

[0042] Then, the modulation degree calculation unit 18 calculates the modulation degree M sin and modulation degree M cos The average value of ((M sin +M cos The modulation index M at spatial frequency f is calculated as () / 2). The modulation depth calculation unit 18 outputs the modulation depth corresponding to the calculated spatial frequency to the MTF display unit 19.

[0043] The MTF display unit 19 displays the modulation depth for each spatial frequency calculated by the modulation depth calculation unit 18 as an MTF chart on the display 2. The MTF display unit 19 generates an MTF chart of the modulation indices for different spatial frequencies calculated by the modulation indices calculation unit 18 and displays it on the display device 4. For example, as shown in Figure 11, the MTF display unit 19 has the horizontal axis representing spatial frequency (cycles / pixel). DISP ), plot the modulation index corresponding to each spatial frequency on a chart with the vertical axis representing MTF (modulation factor), and generate an MTF chart by linear interpolation. For reference, Figure 11 shows the modulation degree M calculated by the modulation degree calculation unit 18 using a sine wave. sin The dotted line indicates the modulation depth M, which is determined by the cosine wave. cos This is indicated by a dashed line.

[0044] As explained above, the display modulation depth measuring device 1 tilts the sine wave pattern at a predetermined angle and measures the modulation depth from the oversampled sine wave pattern. Therefore, even in a small area, it can obtain a distribution that is uniformly shifted relative to the sampling position of the display. As a result, the display modulation depth measuring device 1 can accurately measure the modulation depth of the display 2. Furthermore, the display modulation degree measuring device 1 can be operated using a display modulation degree measuring program that causes a computer (not shown in the figure) to function as one of the aforementioned components.

[0045] [Operation of the display modulation degree measuring device] Next, referring to Figure 12 (and Figure 1 for the configuration), the operation of the display modulation degree measuring device 1 according to an embodiment of the present invention will be described. It is assumed that the display modulation depth measuring device 1 has already acquired the white and black levels of the display 2 via the image input unit 11. Furthermore, it is assumed that the tilt angle of the axis perpendicular to the modulation direction of the sine wave has been detected by the tilt detection unit 12.

[0046] In step S1, the measurement image display unit 10 displays an image on the display 2 (sine wave pattern image) in which a sine wave pattern is drawn horizontally or vertically on the display surface of the display 2, as an image (measurement image) for measuring the modulation degree of the display 2. In step S2, the image input unit 11 captures the sine wave pattern image displayed in step S1 with the camera 3, which is tilted a few degrees relative to the display 2, and inputs it as the captured image. In step S3, the ROI setting unit 13 sets the region of interest (ROI) within the captured image input in step S2, where the modulation degree of the display 2 is to be measured (see Figure 4). In step S4, the ROI image extraction unit 14 extracts an image of the ROI set in step S3 (ROI image) from the captured image input in step S2.

[0047] In step S5, the projection information generation unit 15 generates projection information by associating each pixel of the ROI image extracted in step S4 with the position obtained by projecting the pixel along the tilt angle onto an axis (projection axis) parallel to the modulation direction of the sine wave in the ROI image (see Figure 8). At this time, the projection axis is set to a sub-pixel unit smaller than the pixel unit of the ROI image. In step S6, the projection information generation unit 15 stores the projection information generated in step S5 in the projection information storage unit 16.

[0048] In step S7, the sine wave profile generation unit 17 generates a sine wave pattern from the ROI image extracted in step S4 and the projection information stored in the projection information storage unit 16. Here, the sine wave profile generation unit 17 generates a sine wave profile that associates the subpixel positions on the projection axis with the pixel values ​​by projecting the pixel values ​​from the ROI image to the same bin on the projection axis based on the projection information and averaging them (see Figure 9).

[0049] In step S8, the modulation depth calculation unit 18 calculates the modulation depth of the display 2 using the sine wave profile generated in step S7 and the white level of the white image and the black level of the black image previously captured by the camera 3. In step S9, the MTF display unit 19 displays an MTF chart on the display device 4, which plots the modulation depth corresponding to the spatial frequency calculated in step S8.

[0050] In step S10, the measurement image display unit 10 determines whether or not there are still measurement images with different spatial frequencies. If measurement images of different spatial frequencies exist (Yes in step S10), the display modulation depth measuring device 1 returns to step S1 and continues its operation. On the other hand, if all measurement images are displayed (No in step S10), the display modulation degree measuring device 1 terminates its operation.

[0051] Through the above operation, the display modulation depth measuring device 1 measures the modulation depth from an oversampled sine wave pattern, allowing it to acquire a uniformly shifted distribution relative to the sampling position of the display, even in a small area, and thus accurately measure the modulation depth of the display 2.

[0052] Although embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Here, the modulation degree calculation unit 18 calculates the sine wave a sin(2πfx / m / N) bin +φ)+d and the cosine wave a cos(2πfx / m / N) bin The modulation index was calculated from (+φ)+d, and the average value was taken as the modulation index at spatial frequency f. However, the spatial frequency is the Nyquist frequency (0.5 cycles / pixel). DISP ) Neighborhood, for example, 0.45~0.5 cycles / pixel DISP If this is not the case, the modulation index calculated using either a sine wave or a cosine wave can be approximated as the modulation index at spatial frequency f (see Figure 11).

[0053] Furthermore, although this configuration includes an MTF display unit 19 for displaying an MTF chart, if only the modulation index at a desired spatial frequency needs to be measured, the MTF display unit 19 may be omitted. [Explanation of Symbols]

[0054] 1. Display Modulation Degree Measurement Device 10 Display unit for measurement image 11 Image Input Section 12 Tilt detection unit 13 ROI setting section 14 ROI Image Extraction Unit 15 Projection information generation section 16 Projection information storage section 17. Sine wave profile generation unit 18 Modulation degree calculation unit 19 MTF display section 2 displays 3 cameras 4 Display device

Claims

1. A display modulation degree measuring device that measures the modulation degree of a display from an image captured by tilting a horizontally or vertically modulated sine wave pattern image displayed on a display by a predetermined angle around the optical axis of a camera positioned directly in front of it, the device comprising: An image input unit that receives the captured image from the camera, An ROI image extraction unit extracts an ROI image of the region of interest set as the target for measuring the modulation degree from the captured image, A projection information generation unit generates projection information by associating the position of each pixel in the ROI image with the projection axis of bins with sub-pixel spacing that are parallel to the modulation direction of the sinusoidal wave pattern in the ROI image, along the predetermined angle of inclination. A sinusoidal profile generation unit generates a sinusoidal profile by averaging the pixel values ​​of each pixel in the ROI image for each bin of the projection axis associated with the projection information, The system includes a modulation degree calculation unit that calculates the modulation degree based on the sine wave pattern of the sine wave profile and the white level of a white image and the black level of a black image previously captured by the camera, The modulation degree calculation unit, The phase of the sine wave pattern in the sine wave profile is detected by the value of the inverse tangent function of the correlation ratio between each of the cosine waves and sine waves with amplitude 1, sampled at a spatial frequency obtained by dividing the spatial frequency of the sine wave pattern in the sine wave pattern image by the pixel ratio, which is the spatial frequency of the display relative to the spatial frequency of the camera, and the oversampling ratio, which is the number of subpixels corresponding to one pixel on the projection axis, and the sine wave pattern in the sine wave profile. The amplitude of the sine wave is calculated such that the sum of the values ​​obtained by multiplying the difference between the sine wave pattern of the sine wave profile and the phase sine wave by a window function is minimized. A display modulation degree measuring device characterized by calculating the modulation degree based on the ratio of the amplitude to the difference between the white level and the black level.

2. The display modulation depth measuring device according to claim 1, further comprising an MTF display unit that displays the modulation depth for each spatial frequency calculated by the modulation depth calculation unit as an MTF chart using sinusoidal pattern images of different spatial frequencies.

3. When using a video camera that inputs images sequentially as the aforementioned camera, The display modulation degree measuring device according to claim 1, characterized in that the projection information generation unit generates the projection information only once in the ROI image in which the region of interest is set.

4. A display modulation degree measurement program for causing a computer to function as a display modulation degree measurement device according to claim 1.

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