JP2018138904A - Chart for mtf measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chart for MTF measurement corresponding to an imaging system for an ultra high definition video image.SOLUTION: A chart for MTF measurement CH has a rectangular chart surface aspect ratio of 16:9, defines a predetermined position of a chart surface as a center position O, inclines a horizontal line Lpassing through the center position O and a vertical line Lby a predetermined inclination angle φ, forms radiation areas B-Bdividing a chart surface by each of the inclined horizontal line Land vertical line L, and a diagonal line Lof the chart surface, and colors an adjacent radiation area B using a color having different contrast.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an MTF measurement chart used in an MTF measurement apparatus that measures MTF representing spatial frequency characteristics of resolution of an imaging system.

  The biggest feature of high-resolution television is high spatial resolution, and the resolution characteristics of the camera are important. As a resolution measurement of the current high-definition camera, as shown in FIG. 14, a technique using an in-mega cycle chart in which rectangular waves having a plurality of spatial frequencies are spatially arranged is known.

  In the method using the inmega cycle chart, resolution measurement is performed by reading a CTF (Contrast Transfer Function) representing a spatial frequency characteristic of the modulation degree of a rectangular wave from a waveform monitor. The method using the inmegacycle chart is easy to read visually from the waveform monitor, but the waveform amplitude fluctuates due to the sampling phase and camera noise. In addition, the method using the inmegacycle chart often measures only the rectangular wave response at the center of the chart corresponding to 800 TVL / ph because the resolution characteristics of the camera are different between the center and the periphery of the lens. Furthermore, in the method using the inmega cycle chart, it is necessary to frame the imaging angle of view accurately to the chart size in order to obtain a desired spatial frequency, but a 4K / 8K camera often uses a wide-angle lens. Large Inmega chart is necessary and unrealistic.

  Therefore, a Slanted-edge method has been proposed instead of the Inmega cycle chart (Patent Documents 1 and 2, Non-Patent Documents 1 and 2). This Slanted-edge method is a technique that requires a relatively small chart size and does not require framing. It captures a slightly tilted edge image and expresses the spatial frequency characteristics of the modulation degree of the sine wave from the spread of the edge. MTF (Modulation Transfer Function) is calculated. The procedure of the Slanted-edge method is shown below.

First, in the Slanted-edge method, a rectangular region of interest (ROI: Region Of Interest, FIG. 15) including an edge is selected from a chart image obtained by imaging a chart. Next, in the Slanted-edge method, as shown in FIG. 16A, an algorithm based on ISO12233 (Non-Patent Document 2) or a more accurate algorithm (Patent Document 1, Non-Patent Document 1) is used. Then, an edge is detected from the region of interest. Next, in the Slanted-edge method, as shown in FIG. 16 (b), each pixel of the region of interest along the edge inclination theta _e, is projected on the horizontal axis is divided into equal intervals in the sub-pixel. Then, in the Slanted-edge method, as shown in FIG. 17, the average value of the pixel values of a plurality of pixels projected in each section is obtained, and the edge spread obtained by oversampling (in the case of ISO12233, four times oversampling) Find a function. Further, in the Slanted-edge method, a line spread function obtained by differentiating the edge spread function is calculated, and the line spread function is subjected to discrete Fourier transform to obtain an absolute value, thereby obtaining an MTF in a band exceeding the sampling frequency from the DC component. Ask for. An example of the MTF measurement result is shown in FIG.

  Thus, in the Slanted-edge method, the MTF in the vertical direction can be measured if the edge is inclined slightly from the horizontal. If measurement is performed with the edge positioned at the periphery of the image, the horizontal or vertical MTF of the periphery of the image can be measured. In general, when anisotropy of resolution characteristics is considered due to the pixel structure of the camera, image processing, or the like, multidirectional MTF measurement is required. ISO 12233's Slanted-edge method can measure only MTFs in two directions, the horizontal direction and the vertical direction, but can measure multi-directional MTFs using a starburst chart as shown in FIG. 19 (Patent Document 2). This chart is a binary image, in which an even number of edges are arranged at equally spaced angles. The ROI of each edge is an edge slightly rotated from the vertical direction by rotating by a known angle. Then, the image is projected in the horizontal direction as shown in FIG. 20 to obtain the oversampled edge spread function of each edge, and then the MTF is obtained in the same manner as the ISO 12233 Slanted-edge method. FIG. 21 shows a result example (radar chart).

Japanese Patent Laying-Open No. 2015-94701 JP 2010-237177 A (Patent No. 5193113)

K. Masaoka et al., "Modified slanted-edge method and multidirectional modulation transfer function estimation", Optics Express, 22 (5), 2014 ISO 12233: 2000, "Photography-Electronic Still-picture Cameras-Resolution Measurements"

  For example, in an ultra-high definition video lens such as HDTV (High Definition Television) and UHDTV (Ultra High Definition Television), the distance from the center to four vertices on a diagonal line is 40 on a chart with an aspect ratio of 16: 9. The MTF in the radial direction or the circumferential direction is often measured at a position of% or 80%. FIG. 22 shows a measurement result display screen when the MTF is measured at a position where the distance is 40%. Therefore, there is a demand for measuring the MTF of the imaging system (camera system) in order to compare the measurement results of the lens for ultra-high definition video and the MTF.

  Accordingly, an object of the present invention is to provide an MTF measurement chart corresponding to an imaging system for ultra-high definition video.

  In view of the above-described problems, the MTF measurement chart according to the present invention is an MTF measurement chart used in an MTF measurement apparatus that measures MTF representing spatial frequency characteristics of resolution of an imaging system, and is a rectangular chart. The aspect ratio of the surface is 16: 9, and is spaced from the center side to the outer peripheral side of the chart surface with a horizontal axis that is centered on a predetermined position of the chart surface and that is inclined by a predetermined inclination angle through the center. Is set in advance, the vertical position that is inclined by the inclination angle through the center and the diagonal position of the chart surface is set in advance the division position equidistant from the horizontal axis, Octagonal segmented regions connecting segmented lines orthogonal to each other at the segmented positions of the horizontal axis, the vertical axis, and the diagonal axis, and the segmented lines of the horizontal axis and the diagonal axis and the long sides of the chart surface And connected Square segmented regions are arranged concentrically with respect to the center, and the boundary between the center of the chart surface, the segmented region on the outermost periphery side and the segmented region adjacent to the segmented region is the long side of the chart surface A first end point that is in contact with each other, and a radiation region having a vertex at a second end point at a preset distance from the first end point on the long side of the chart surface is arranged point-symmetrically with respect to the center, and the adjacent sections A color having a different contrast is arranged in the region, and the radiation region is arranged in the same color as the outermost segmented region.

  According to this configuration, the MTF measurement chart has the same aspect ratio as that of the ultra high definition video, so that the MTF can be measured by the imaging system for the ultra high definition video. Furthermore, since the MTF measurement chart has a large segment area concentrically arranged on the outer periphery side of the chart surface, an ROI can be set in a desired segment area regardless of the angle of view of the imaging system. At this time, since the MTF measurement chart can set the ROI in the circumferential direction in the octagonal segmented region, the MTF in the radial direction can be measured. The aspect ratio represents the ratio between the width and height of the chart surface.

  Further, in view of the above-described problem, the MTF measurement chart according to the present invention has a rectangular chart surface with an aspect ratio of 16: 9, and a horizontal line passing through the center with a predetermined position on the chart surface as a center. And a plurality of radiating regions that separate the chart surface by each of the inclined horizontal line and the vertical line and a diagonal line of the chart surface, and the adjacent radiating regions In this configuration, colors having different contrasts are arranged.

  According to this configuration, the MTF measurement chart has the same aspect ratio as that of the ultra high definition video, so that the MTF can be measured by the imaging system for the ultra high definition video. Furthermore, since the MTF measurement chart can set the ROI in the radial direction, the MTF in the circumferential direction can be measured.

According to the present invention, the following excellent effects can be obtained.
Since the MTF measurement chart according to the present invention has the same aspect ratio as that of the ultra high definition video, the MTF can be measured by the imaging system for the ultra high definition video.

It is a pattern figure of the chart for MTF measurement concerning a 1st embodiment of the present invention. It is explanatory drawing explaining the inclination | tilt angle of the chart for MTF measurement of FIG. It is a pattern figure of the chart for MTF measurement concerning a 2nd embodiment of the present invention. It is explanatory drawing explaining the division area of the chart for MTF measurement of FIG. It is explanatory drawing explaining the inclination-angle of the chart for MTF measurement of FIG. It is explanatory drawing explaining the radiation | emission area | region when utilizing the whole MTF measurement chart of FIG. It is explanatory drawing explaining the radiation | emission area | region when utilizing the half of the chart for MTF measurement of FIG. It is a block diagram which shows the structure of the MTF measuring apparatus which concerns on 3rd Embodiment of this invention. In 3rd Embodiment, it is explanatory drawing explaining the method of setting ROI in the position of 40% in the chart image of FIG. In 3rd Embodiment, it is explanatory drawing explaining the method of setting ROI in the position of 40% in the chart image of FIG. In 3rd Embodiment, it is explanatory drawing explaining the method of setting ROI in the 80% position in the chart image of FIG. In 3rd Embodiment, it is explanatory drawing explaining the method of setting ROI in the 80% position in the chart image of FIG. It is a flowchart which shows operation | movement of the MTF measuring apparatus of FIG. It is explanatory drawing explaining the conventional in megacycle chart. It is explanatory drawing explaining ROI in the conventional Slanted-edge method. In the conventional Slanted-edge method, (a) is an explanatory diagram for explaining edge detection, and (b) is an explanatory diagram for explaining generation of an edge profile. It is explanatory drawing explaining the measurement of MTF in the conventional Slanted-edge method. It is a graph which shows the measurement result of MTF in the conventional Slanted-edge method. It is a pattern diagram of a conventional multi-directional MTF measurement chart. When a conventional multi-directional MTF measurement chart is used, (a) is an explanatory diagram for explaining the rotation of the ROI, and (b) is an explanatory diagram for explaining the generation of the edge profile. It is a radar chart showing the measurement result of MTF in the case of using a conventional multi-directional MTF measurement chart. It is a figure which shows an example of the measurement result display screen of the MTF in the lens for the conventional super high-definition images.

Each embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In each embodiment, the same member is denoted by the same reference numeral, and the description thereof is omitted.
First, MTF measurement charts will be described as first and second embodiments. Next, an MTF measuring apparatus using an MTF measurement chart will be described as a third embodiment.

(First embodiment)
<MTF measurement chart pattern>
The MTF measurement chart CH according to the first embodiment of the present invention will be described with reference to FIGS.
The MTF measurement chart CH is used in the MTF measurement apparatus 1 that measures MTF (see FIG. 8). That is, the imaging system 2 captures the MTF measurement chart CH, and the MTF measurement apparatus 1 measures the MTF using the captured image (chart image).

As shown in FIGS. 1 and 2, the MTF measurement chart CH has a rectangular chart surface aspect ratio (width W: height H) of 16: 9. Also, the chart for MTF measurement CH is a predetermined position of the chart surface and the center position O, tilting the horizontal line L _H and vertical line L _V by a predetermined inclination angle φ passing through the center position O. The chart for MTF measurement CH, respectively and is inclined horizontal line L _H and vertical line L _V, emission region B to form a plurality of partitioning a chart surface with a diagonal line L _D chart surface. Further, the MTF measurement chart CH arranges colors having different contrasts in the adjacent radiation regions B.

In the MTF measurement chart CH, a position at which the width W and the height H of the chart surface are halved is defined as a center position O. Also, the chart for MTF measurement CH has a horizontal line _{L H,} eight that are partitioned by the vertical line _{L V} and the diagonal _{L D} emission region _B 1 .about.B ₈ radiating from the center position O. The diagonal L _D has signed a apexes of the four corners of the chart surface, passing through the center position O of the chart surface. Further, the radiation area B reaches the inner edge of the rectangle of the chart surface, and has a shape like a right triangle with the center position O as a vertex.

In the MTF measurement chart CH, each radiation region B is colored in white or black so that the radiation regions B of the same color are not adjacent to each other. Specifically, the radiation areas B ₁ , B ₃ , B ₅ , and B ₇ are white. Further, the radiation areas B ₂ , B ₄ , B ₆ , and B ₈ are black. Therefore, in the MTF measurement chart CH, white and black appear alternately in the radiation regions B _{1 to} B ₈ .

The MTF measurement chart CH has the same number of boundaries as the radiation region B. That is, the MTF measurement chart CH has _eight boundaries such as a boundary between the radiation regions B ₈ and B _1, a boundary between the radiation regions B ₁ and B ₂ , and so on, and a boundary between the radiation regions B ₇ and B _8. . Each boundary is linear and extends radially from the center position O.

  In the Slanted-edge method, the inclination angle φ is set in advance so that various phases can be measured. In the Slanted-edge method, when measuring the MTF, the MTF measurement chart CH is inclined by the inclination angle φ. Here, the boundary of the MTF measurement chart CH is provided in the horizontal direction or the vertical direction, the MTF measurement chart CH is rotated by the inclination angle φ and attached to the wall surface, or the imaging system 2 is rotated by the inclination angle φ. Can be considered. However, when measuring the MTF, it is difficult and time-consuming to rotate the MTF measurement chart CH or the imaging system 2 accurately. Therefore, in the present embodiment, the pattern itself of the MTF measurement chart CH is inclined.

Chart for MTF measurement CH may be inclined by the inclination angle φ to a horizontal line _{L H} and vertical line _{L V} clockwise (Figure 2). This inclination angle φ may be several degrees (for example, 2 ° or more and 5 ° or less) in MTF measurement. As a result, in the MTF measurement chart CH, the boundaries of the radiation regions B ₂ and B _{3 and} the boundaries of the radiation regions B ₆ and B ₇ are also tilted by the tilt angle φ with respect to the horizontal direction. Further, in the MTF measurement chart CH, the boundaries of the radiation regions B ₈ and B _{1 and} the boundaries of the radiation regions B ₄ and B ₅ are also tilted by the tilt angle φ with respect to the vertical direction. In this manner, since the pattern itself is inclined by the inclination angle φ in the MTF measurement chart CH, edges that are inclined by the inclination angle φ are formed in the vertical direction and the horizontal direction. Therefore, the MTFs in the vertical direction and the horizontal direction are formed. Can be measured. Incidentally, the chart for MTF measurement CH does not have to incline the diagonal _{L D.}

  In FIG. 2, the color scheme of the MTF measurement chart CH is omitted for ease of explanation. In FIG. 2, the horizontal and vertical axis lines are indicated by alternate long and short dash lines, but it is not necessary to draw axis lines on the MTF measurement chart CH.

<Method for Producing MTF Measurement Chart>
Next, an example of a method for manufacturing the MTF measurement chart CH will be described.
The MTF measurement chart CH can be manufactured by arranging the pattern of FIG. 1 on a rectangular chart member. The chart member is not particularly limited, and is, for example, paper, film, glass, or metal.

When the chart member is paper, the pattern of FIG. 1 can be printed on the chart member to manufacture the MTF measurement chart CH. Further, when the chart member is a film, the MTF measurement chart CH can be manufactured by photography.
Moreover, what is necessary is just to vapor-deposit the pattern of FIG. 1 with chromium etc., when a chart member is glass. Further, when the chart member is made of metal, the white portion is cut with the pattern shown in FIG.
Thus, the chart member made of glass or metal makes it difficult for the MTF measurement chart CH to be bent during MTF measurement.

[Action / Effect]
As described above, since the MTF measurement chart CH has the same aspect ratio as that of the ultra high definition video, the MTF can be measured by the imaging system 2 for the ultra high definition video. Furthermore, since the MTF measurement chart CH can set the ROI in the radial direction (diagonal direction, horizontal direction and vertical direction), it is possible to measure the MTF in the circumferential direction (see FIG. 9).

(Second Embodiment)
<MTF measurement chart pattern>
3, with reference to FIG. 4, will be described MTF measuring chart CH ₂ according to a second embodiment of the present invention.
As shown in FIGS. 3 and 4, MTF measurement chart CH _2, the aspect ratio of a rectangular chart surface 16: 9. Further, the MTF measurement chart CH ₂ has a predetermined position on the chart surface as the center position O, and is spaced from the center side to the horizontal axis A _H that passes through the center position O and is inclined by the inclination angle φ from the center side to the outer periphery side of the chart surface. presetting a wide becomes such division position P _H. Further, in the MTF measurement chart CH ₂ , the division positions P _V and P _D are set in advance on the vertical axis _AV and the diagonal axis _AD on the chart surface that pass through the center position O and are inclined by the inclination angle φ.

Further, MTF measurement chart CH ₂ is divided position of the horizontal axis _{A H} and the vertical axis _{A V} and the diagonal axis _{A D P H, P V,} section lines _N H orthogonal with _{P D, N V,} N _D the division area C ₁ -C ₉ octagonal connected and arranged concentrically with reference to the center position O. Further, the MTF measurement chart CH ₂ includes octagonal segmented regions C ₁₀ and C _{11 in which} the segment lines N _H2 and N _D2 of the horizontal axis A _H and the diagonal axis _AD are connected to the long side L _{W of the} chart surface. Are arranged concentrically with the center position O as a reference.

Further, the MTF measurement chart CH ₂ forms a radiation region D having the center position O of the chart surface, the first end point T ₁ , and the second end point T ₂ as vertices with point symmetry with respect to the center position O (FIG. 6). Then, MTF measuring chart CH _2, together with the contrast color scheme different colors to adjacent partitioned regions C, and color in the most outer peripheral side of the partition areas C ₁₁ the same color as the emitting area D.

<< Division area >>
First, the segment area C will be described in detail. As shown in FIG. 4, the MTF measurement chart CH ₂ arranges ₁₁ divided regions C _{1 to} C ₁₁ with reference to the center position O of the chart surface. Here, since the divided regions C _{1 to} C ₉ have a diameter less than the height H of the chart surface, each side of the octagon fits on the chart surface. Therefore, the segment areas C _{1 to} C ₉ are arranged concentrically with the center position O as a reference. On the other hand, since the divided regions C ₁₀ and C ₁₁ have a diameter equal to or greater than the height H of the chart surface, the upper and lower sides of the octagon do not fit on the chart surface. For this reason, the segment areas C ₁₀ and C ₁₁ use the long side L _W of the chart surface as the upper and lower sides of the octagon. Further, the partitioned areas C ₁₀ and C ₁₁ are arranged with the center position O as a reference, like the partitioned areas C _{1 to} C ₉ .

To draw the segmented region C, MTF measurement chart CH ₂ is the diagonal axis _{A D} extending radially from the center position O of the chart surface, horizontal axis _{A H,} and sets the vertical axis _{A V.} As shown in FIG. 5, the horizontal axis A _H and the vertical axis A _V, the horizontal direction and the vertical direction, inclined by clockwise inclination angle phi. This inclination angle φ may be several degrees (for example, 2 ° or more and 5 ° or less) in MTF measurement. Then, MTF measuring chart CH ₂ is the diagonal axis _{A D,} the horizontal axis _{A H,} and divided positions on each of the vertical axis _{A V P D, P H,} sets the _{P V.}

Here, by adjusting the zoom magnification of the imaging system 2, it is possible to acquire a captured image having the same shape. Therefore, on the horizontal axis _AH , the outer peripheral side of the chart surface is adjacent to the adjacent segment position P. The interval between _{H 1} and P _H2 becomes wide. Specifically, the ratio of the distance from the center position O to the segment positions P _H and P _{H2 with} respect to the total length (= width W / 2) from the center position O to the outer periphery of the chart surface is represented by an arbitrary geometric series. Is done. In this embodiment, in order to measure the MTF in the radial direction and the circumferential direction at the positions of 40% and 80%, the ratio of the distance from the center position O to the segment positions P _H and P _{H2 is set} to √ with respect to the total length. A geometric series of 2. Accordingly, the segment positions P _H and P _H2 are 5√2%, 10 / √2%, 10%, 10√2%, 20 / √2%, 20%, 20√2%, 40 with respect to the total length. / √2%, 40%, 40√2%, 80%. In addition, when the MTF is measured at positions of 40% and 80%, the ratio of the distances described above may be a geometric series of 2 ^ (1 / n) (where n is a positive integer).

  Note that the geometric series and the MTF measurement position are not limited to those described above. For example, when the MTF is measured at the positions of 20% and 60%, the above-described distance ratio may be a geometric series of 3 ^ (1 / n).

Hereinafter, an example of a segmented region C _9. In this case, on a horizontal axis A _H, the distance from the center position O to 2 sets the section line N _H to the section position P _H to be 40%. Furthermore, on the vertical axis _{A V,} the distance from the center position O to 2 sets the dividing line _{N V} to the section position _{P V} which is 40%. Furthermore, as shown in FIG. 4, on the diagonal axis A _D, the distance from the center position O is at division positions P _D as the 40% set four normal as division line N _D. Thereafter, the dividing lines N _H , N _V , and N _D are extended so as to be connected to each other to form a dividing region C ₉ . Therefore, segmented region _{C 9} is a section line _{N H,} N V, sandwiched _{N D} region.

The divided areas C _{1 to} C ₈ can be formed in the same manner as the divided area C ₉ . Specifically, the divided areas C _{1 to} C ₈ can be formed by the same procedure as the divided area C _{9 at a} divided position (not shown in FIG. 4) where the distance from the center position O is a geometric series.

Next, an example of a segmented region _{C 11.} MTF measuring chart CH _2, since the height H of the chart surface is less than width W, it can not be set all wedges position the horizontal axis A _H and equidistant vertical axis A _V. Thus, partitioning position _{P H2, P D2} is set only in the horizontal axis _{A H} and the diagonal axis _{A D,} not set in the vertical axis _{A V.}

Section line _{N H2, N D2} is on a horizontal axis _{A H} and the diagonal axis _{A D,} the division position _{P H2, P D2} the distance from the center position O is 80%, marking lines _N H, and _{N D} The same procedure can be used. Further, division lines of the vertical axis A _V because unset utilizes long side L _W of the chart surface, instead of dividing line of the vertical axis A _V. That is, partitioned area _{C 11} is constituted by two section lines _{N H2,} 4 pieces of division lines _{N D2,} the two charts surface long side _{L W.} Therefore, segmented region _{C 11} is a dividing line _{N H2, N D2} and a region sandwiched between the long side _{L W} of the chart surface.

Incidentally, partitioned area _{C 10} can be formed similarly to the partitioned area _{C 11.} Specifically, partitioned area C _10, in the division position where the distance from the center position O is 40√2% (FIG. 4 not shown) can be formed in the same manner as segment regions C _11.

In FIG. 4, the color scheme of the MTF measurement chart CH ₂ is omitted for ease of explanation. Further, in FIG. 4, for easy explanation, a diagonal axis _AD , a horizontal axis A _H , and a vertical axis _AV and segment positions P _D , P _H , P _V , P _D2 , and P _H2 are shown. It illustrated, but there is no need of drawing them to the MTF measuring chart CH _2.

<< Radiation area >>
Next, the radiation region D will be described in detail.
As shown in FIG. 6, the MTF measurement chart CH ₂ has radiation areas D _{1 to} D ₄ with the center position O of the chart surface, the first end point T ₁ , and the second end point T ₂ as vertices. That is, the radiation region D, the center position O and the apex, the area of the triangle having the base first end point T ₁ and a line segment between the second terminal point T _2.

The first end point _{T 1} is that the boundary between the divided areas _{C 10} adjacent in the segment _{C 11} the outermost segmented region _{C 11} is in contact with a long side _{L W} of the chart surface.
The second end point T ₂ are, on the long side L _W of the chart surface, the center side in the width W direction from the first end point T _1, a point which is located a preset distance. The distance from the first end point T ₁ to the second endpoint T ₂ are, can be set at any value.

Here, the role of the radiation region D will be described. Since the radiation area D corresponds to the zoom-in and zoom-out of the imaging system 2, it has a role as a marker indicating the set position of the ROI. As described above, the first terminal point T ₁ of the emission region D represents the 40% position. Thus, we obtain a line segment _{L B} connecting the first terminal point _{T 1} of the upper and lower, may be set ROI (not shown) to the boundary of the segmented region C intersecting the line _{L B.}

As shown in FIG. 6, when the entire MTF measurement chart CH ₂ is used, an ROI is set at the boundary between the segment areas C ₉ and C ₁₀ intersecting the line segment L _B (see FIG. 10).
In FIG. 6, for ease of explanation, the partitioned regions C ₁₀ and C ₁₁ are illustrated by broken lines, and the other partitioned regions C and the color scheme of the MTF measurement chart CH ₂ are omitted. In addition, there is no need to draw a line segment L _B actually.

Furthermore, as shown in FIG. 7, a case where half of the MTF measurement chart CH ₂ is used is considered. At this time, the contact point of the end point T _1A of the long sides of the MTF measuring chart CH _2, a straight line from the center position O to the first end point T ₁ of the when the half width W and height H. In this case, a line segment L _B2 connecting the upper and lower end points T _1A is obtained, and an ROI (not shown) is set at the boundary between the segment areas C ₇ and C ₈ intersecting the line segment L _B2 .

In FIG. 7, the range used as the MTF measurement chart CH ₂ is shown by a solid line, and the other range is shown by a dotted line. Further, in FIG. 7, for easy explanation, the partitioned areas C ₇ and C 8 are illustrated by broken lines, and the other partitioned areas C and the color scheme of the MTF measurement chart CH ₂ are omitted. Further, it is not necessary to actually draw the line segment L _B2 .

Returning to FIG. 3, the description of the MTF measurement chart CH ₂ will be continued.
MTF measuring chart CH ₂ is the same color segmented region C so as not adjacent to color each segmented region C in white or black. Specifically, the segment areas C ₁ , C ₃ , C ₅ , C ₇ , C ₉ and C ₁₁ are black. Further, the segment areas C ₂ , C ₄ , C ₆ , C ₈ , and C ₁₀ are black. Therefore, in the MTF measurement chart CH, white and black appear alternately in the divided regions C _{1 to} C ₁₁ . Further, MTF measurement chart CH ₂ is color in the emission region _D 1 to D _4, the outermost segment areas _{C 11} of the same color in contact with the first terminal point _{T 1} (black).

The MTF measurement chart CH ₂ has boundaries between the segment areas C ₁ and C ₂ , boundaries between the segment areas C ₂ and C ₃ ,..., And boundaries between the segment areas C ₁₀ and C ₁₁ . Each boundary extends in the circumferential direction because the segmented region C has an octagonal shape. Further, MTF measurement chart CH ₂ has a boundary between the white segment regions _{C 2, C 4, C 6} , C 8, C 10 and the radiation region _D 1 to D _4.
Note that the manufacturing method of the MTF measurement chart CH ₂ is the same as that in the first embodiment, and thus the description thereof is omitted.

[Action / Effect]
As described above, since the MTF measurement chart CH ₂ has the same aspect ratio as that of the ultra high definition video, the MTF can be measured by the imaging system 2 for the ultra high definition video. Further, MTF measurement chart CH _2, since it sets the ROI in the circumferential direction, can be measured MTF of the radiation direction (see FIG. 10).

Further, MTF measurement chart CH _2, since a large segmented region C on the outer peripheral side of the chart surface is concentrically arranged, regardless of zoom in or zoom out of the imaging system 2 can be set an ROI in the desired segment region C . Further, MTF measurement chart CH ₂ refers to the position of the emission region D, it is possible to easily grasp the setting position of the ROI.

(Third embodiment)
[Configuration of MTF measuring device]
Hereinafter, with reference to FIG. 8, the structure of the MTF measuring apparatus 1 which concerns on 3rd Embodiment of this invention is demonstrated. The MTF measuring apparatus 1 measures MTF using an MTF measuring chart CH. That is, when the MTF measurement apparatus 1 measures the MTF with an image obtained by imaging the MTF measurement chart CH, the MTF measurement apparatus 1 measures the spatial frequency characteristics corresponding to the direction in the ROI straddling the radiation regions having different contrasts. Therefore, it is only necessary to determine which MTF measurement chart CH to use according to the direction in which the spatial frequency characteristic is desired to be measured. In the third embodiment, the MTF measurement chart CH of FIG. 1 is used.

  As shown in FIG. 8, the MTF measurement device 1 includes a chart image storage unit 10, an image position specifying unit 11, an image extraction unit 12, a calculation unit 13, and a graph generation unit 14. Here, it is assumed that the MTF measuring apparatus 1 is connected to an imaging system 2 for an ultra-high-definition video to be measured and a display device 3 that provides a user interface for operating the MTF measuring apparatus 1.

  The chart image storage means 10 stores an image (chart image) obtained by imaging the MTF measurement chart CH of FIG. 1 in the imaging system 2 to be measured, and is a general storage device such as a hard disk. .

  The image position specifying means 11 specifies the position of the ROI image for MTF measurement from the chart image obtained by imaging the MTF measurement chart CH. Here, the image position specifying unit 11 includes a chart center acquiring unit 111, a reference ROI region information acquiring unit 112, a relative position determining unit 113, and an angle-specific ROI region specifying unit 114.

  The chart center acquisition unit 111 acquires the center position O (FIG. 1) of the radial boundary in the chart image stored in the chart image storage unit 10. The chart center acquisition unit 111 displays a chart image on the display device 3, and acquires the center position O of the chart image by the operator specifying the center with a pointing device (input unit) such as the touch pen 31, for example. To do. The chart center obtaining unit 111 may extract a plurality of straight lines that are boundaries of the radiation region B by edge detection in the chart image, and obtain the center position O from the intersection of the straight lines.

Here, when the center position O is set, the chart center acquisition unit 111 sets the coordinate system so that the center position O becomes the center coordinates (0, 0) of the chart image, and each pixel of the chart image The coordinates of are to be shifted. When the center coordinates of the chart image are known, the coordinates for inputting another chart image are input so that the center becomes the center coordinates (0, 0). Acquisition of the center position O can also be omitted.
The chart center acquisition unit 111 outputs the acquired center position O to the relative position determination unit 113 and the angle-specific ROI region specifying unit 114.

  The reference ROI region information acquisition unit 112 specifies region information indicating the region of the reference ROI serving as a measurement reference by specifying a rectangular region straddling the radiation region B having different horizontal or vertical contrasts in the chart image. To get. At this time, the reference ROI region information acquisition unit 112 designates the reference ROI at a position where the distance from the center position O of the chart surface is 40%. That is, as shown in FIG. 9, the center of the reference ROI is located at a position where the distance from the center position O of the chart surface is 40%.

  Here, the reference ROI area information acquisition unit 112 is a chart image displayed on the display device 3. For example, when the operator designates a rectangular area with a pointing device such as the touch pen 31, the position and the size of the reference ROI are displayed. Is acquired as region information.

For example, as shown in FIG. 9, in the chart image IMG _CH , a region R ₁ near the vertical boundary where the radiation regions B ₈ and B ₁ are adjacent and above the center position O is designated as the reference ROI. . In FIG. 9, the vertical axis and the horizontal axis represent a coordinate system based on the center coordinates (0, 0).
In addition, the region R ₇ near the horizontal boundary where the radiation regions B ₆ and B ₇ are adjacent and to the left of the center position O may be designated as the reference ROI.
The reference ROI region information acquisition unit 112 outputs the region information (coordinate values) of the reference ROI to the relative position determination unit 113.

  The relative position determination unit 113 determines a relative position with respect to the center position of the reference ROI based on the region information of the reference ROI acquired by the reference ROI region information acquisition unit 112 and the center position O acquired by the chart center acquisition unit 111. To do. That is, the relative position determination unit 113 determines in which direction (up / down / left / right) the image is present with respect to the center position O. The relative position determining unit 113 outputs the determination result to the angle-specific ROI region specifying unit 114.

The angle-specific ROI region specifying unit 114 specifies the angle-specific ROI obtained by rotating the reference ROI by a predetermined angle with the center position O of the chart image as a reference.
This angle-specific ROI region specifying means 114 specifies the position and rotation direction (and its angle) of the angle-specific ROI based on the relative position determined by the relative position determination means 113. At this time, the angle-specific ROI region specifying unit 114 specifies the angle-specific ROI at a position where the distance from the center position O is 40%. That is, as shown in FIG. 9, the center of the angle-specific ROI is located at a position where the distance from the center position O is 40%.

For example, consider a case where the reference ROI (R ₁ ) is selected in the chart image IMG _CH as shown in FIG. In this case, the ROI area specifying unit 114 for each angle 114 sets the reference ROI (R ₁ ) in the clockwise direction with respect to the center position O as 60 °, 90 °, 120 °,. The ROI (R ₂ , R ₃ ,..., R ₈ ) by angle is specified at the position rotated by °. This angle-specific ROI is a rotation of the reference ROI, and therefore has the same size as the reference ROI, although there is a difference in direction.

As described above, the angle-specific ROI region specifying unit 114 rotates the reference ROI region by a predetermined angle to specify the region of the angle-specific ROI. Therefore, each angle-specific ROI has an edge with a different contrast in the region. Will be included.
The angle-specific ROI region specifying unit 114 outputs region information (coordinate values) of the specified angle-specific ROI (including the reference ROI) to the image extracting unit 12.

  The image extracting unit 12 extracts an ROI image for each angle specified by the image position specifying unit 11 from the chart image. Here, the image extraction means 12 includes ROI extraction means 121 and ROI rotation means 122.

  The ROI extraction unit 121 extracts and reads out the image of each ROI (including the reference ROI) specified by the image position specifying unit 11 from the chart image storage unit 10. The ROI extraction unit 121 stores the extracted image (angle-specific ROI) in a memory (not shown) and notifies the ROI rotation unit 122 of the extracted image.

The ROI rotation means 122 performs a coordinate conversion on the angle-specific ROI extracted by the ROI extraction means 121 with reference to the center position O according to the rotation angle from the reference ROI, thereby corresponding to the position of the reference ROI. The ROI for each rotation angle that is rotated in the direction is generated.
This ROI rotating means 122 converts the coordinate value of the pixel value of each angle ROI (this coordinate system may be arbitrary) into a polar coordinate system and rotates it according to the rotation angle, and then the Cartesian coordinate system ( (xy coordinate value), the pixel value corresponding to the coordinates after the rotation of each angle ROI can be obtained.

  As described above, the image extraction unit 12 can extract the ROI by angle for each predetermined direction from the chart image as the ROI by rotation angle having the same orientation and substantially the same shape as the reference ROI. it can. The ROI in each direction (ROI by angle, ROI by rotation angle) has substantially the same edge image although the pixel structure (the inclination thereof) is different. Further, the edge of each ROI has the same inclination angle if there is no distortion of the imaging system 2 and the center position O is correctly selected.

  The calculating means 13 calculates MTF from ROI (reference ROI, ROI classified by rotation angle). Here, the calculation unit 13 includes an edge profile generation unit 131, a trimming unit 132, and an MTF calculation unit 133.

  The edge profile generation unit 131 detects an edge inclination of each ROI and generates an edge profile according to the direction of the edge. For example, the edge profile generation unit 131 uses an XY coordinate value of a ROI (reference ROI, ROI by rotation angle) and its pixel in a coordinate system (xy coordinate system) having two horizontal and vertical axes in a chart image. The edge slope is obtained from the value. This edge inclination can be obtained by fitting with a normal cumulative density function or the like. Further, this fitting is performed only for obtaining the edge inclination, and it is not necessary to completely fit the image.

The edge profile generation means 131, when the reference ROI is an image including an edge in the vertical direction (i.e., when a reference ROI to _{R 1} in FIG. 9), each ROI (reference ROI, angle of rotation by ROI) Then, the pixel value is projected on the horizontal axis (x-axis) along the edge inclination and averaged to generate an edge profile. Note that the size of the bin of the axis to be averaged is smaller than the pixel. For example, a width of 1/4 or 1/8 of one pixel is set as a bin size. Then, the edge profile generation unit 131 outputs the generated ROI edge profile for each rotation angle to the trimming unit 132.

Here, in the case of the reference ROI (R ₁ ), the edge profile generation unit 131 detects the edge e in the reference ROI, and projects each pixel value of the reference ROI on the x axis along the edge inclination θe, The pixel values are averaged for each x coordinate bin (see FIG. 16).

On the other hand, in the case of other than the reference ROI (that is, the ROI by angle), the ROI rotation unit 122 rotates the ROI by angle to a position corresponding to the reference ROI, thereby generating the ROI by rotation angle in advance. Therefore, the edge profile generation unit 131 detects the edge e in the ROI for each rotation angle, projects each pixel value of the ROI for each rotation angle on the x axis along the edge inclination θe, and outputs each pixel value for each x coordinate bin. An average of the entered pixel values is obtained (see FIG. 20).
As a result, the edge profile generation unit 131 can generate an edge profile for an edge in a direction corresponding to an arbitrary angle other than the horizontal direction and the vertical direction.

  The trimming unit 132 trims each edge profile on the basis of the shortest edge profile so that the length of the edge profile of each ROI generated by the edge profile generation unit 131 is the same. For example, if the length is equal to or shorter than the length of the shortest edge profile, the MTF is calculated with the same spatial frequency step width for all ROIs.

  The MTF calculation means 133 calculates MTF for each rotation angle-specific ROI and reference ROI. The MTF calculating means 133 calculates the MTF from the edge profile using a general Slanted-edge method. That is, for each ROI, the MTF calculating unit 133 obtains the line broadening function (LSF) by sequentially differentiating the edge profile, and then obtains the MTF by performing discrete Fourier transform.

As a result, the MTF calculating means 133 in the ROI (R _{1 to} R ₈ ) in FIG. 9 has horizontal frequency components for R ₁ and R ₅ , vertical frequency components for R ₃ and R ₇ , and other ROIs. MTF corresponding to each direction can be obtained. The MTF calculating unit 133 outputs the calculated MTF to the graph generating unit 14.

  As described above, the calculation unit 13 calculates an MTF in an arbitrary direction from the measurement target image extracted from the chart image by the image extraction unit 12 according to the boundary direction in the radiation region B of the predetermined chart image. Can be calculated.

  The graph generation unit 14 graphs the MTF calculated by the MTF calculation unit 133. For example, the graph generation unit 14 plots the MTF calculated by the MTF calculation unit 133 on the coordinates with the frequency on the horizontal axis and the MTF on the vertical axis.

Further, the graph generation means 14 is calculated by the MTF calculation means 133 on the radial axis for each boundary direction of the radiation region B (for example, 0 °, 60 °, 90 °, 120 °,..., 300 °). A radar chart may be generated by plotting MTF values and connecting the plotted points on the axis.
The graph generated by the graph generation unit 14 is output to, for example, the display device 3 so that the operator can visually recognize the analysis result of the MTF of the imaging system 2.

  Thus, the MTF measuring apparatus 1 can measure the MTF in the circumferential direction from the chart image obtained by imaging the MTF measurement chart CH. In addition, since the MTF measuring apparatus 1 rotates and processes the ROI for each angle into an image corresponding to the reference ROI, it can accurately measure the MTF in the circumferential direction.

Incidentally, MTF measurement device 1, instead of the chart CH for MTF measurement of FIG. 1, by using the MTF measuring chart CH ₂ in FIG. 3, it is also possible to measure the MTF of the radiation direction. In this case, the MTF measuring apparatus 1 sets ROI (R _{1 to} R ₈ ) in the circumferential direction as shown in FIG.

Furthermore, as shown in FIGS. 11 and 12, the MTF measuring apparatus 1 has ROIs (R _{2 to} R ₄ , R) at positions where the distance from the center position O is 80% in each of the MTF measurement charts CH and CH ₂ . R _{6 to} R ₈ ) can also be set. Note that ROI (R ₁ , R ₅ ) is set at a position where the distance from the center position O is 40% because the height H of the chart surface is insufficient.

[Operation of MTF measuring device]
Next, the operation of the MTF measuring apparatus 1 will be described with reference to FIG. 13 (see FIG. 8 as appropriate).
First, the MTF measuring apparatus 1 images the MTF measurement chart CH by the imaging system 2, and stores the captured chart image in the chart image storage means 10 (step S1).
Then, the MTF measuring apparatus 1 displays the chart image on the display device 3 by the chart center acquisition unit 111 of the image position specifying unit 11 and designates the center by the operator, thereby determining the center position O of the chart image. Obtain (step S2).

  Further, the MTF measuring device 1 is configured such that the region of the reference ROI is specified by the operator specifying the region in the chart image displayed on the display device 3 by the reference ROI region information acquiring unit 112 of the image position specifying unit 11. Information (position and size) is acquired (step S3). In addition, you may perform operation | movement of this step S2, S3, changing the order.

  Then, the MTF measuring apparatus 1 uses the relative position determination unit 113 to determine the position of the reference ROI based on the center position O of the chart image acquired in step S2 and the region information of the reference ROI acquired in step S3. It is determined which of the upper, lower, left, and right positions (relative position) is designated with respect to the center position (step S4).

  Then, the MTF measuring apparatus 1 rotates the reference ROI by a predetermined angle around the center position acquired in step S2 based on the relative position determined in step S4 by the angle-specific ROI region specifying unit 114. The angle-specific ROI is specified (step S5).

  Thereafter, the MTF measuring apparatus 1 uses the ROI extraction unit 121 of the image extraction unit 12 to store the image of the angle-specific ROI (including the reference ROI) specified in step S5 in the chart image storage unit 10. Are extracted and read out (step S6).

  Further, the MTF measuring apparatus 1 uses the ROI rotation unit 122 of the image extraction unit 12 to convert the ROI for each angle read in step S6 according to the rotation angle from the reference ROI with reference to the center position O. A ROI for each rotation angle rotated to a position corresponding to the position is generated (step S7).

  Then, the MTF measuring apparatus 1 generates an edge profile by projecting the ROI pixel value onto the horizontal or vertical axis according to the edge inclination of each ROI by the edge profile generation unit 131 of the calculation unit 13 ( Step S8).

  Furthermore, the MTF measuring apparatus 1 trims each edge profile with the shortest edge profile as a reference so that the length of the edge profile of each ROI becomes the same by the trimming means 132 of the computing means 13 (step S9). .

Thereafter, the MTF measuring apparatus 1 obtains a line broadening function (LSF) for each edge profile of each ROI trimmed in step S9 by the MTF calculating means 133 of the calculating means 13, and then performs a discrete Fourier transform to obtain the MTF. Is calculated (step S10).
And the MTF measuring apparatus 1 produces | generates the graph which plotted MTF calculated by step S10 by the graph production | generation means 14, and outputs it to the display apparatus 3 (step S11).

  With the above operation, the MTF measuring apparatus 1 can measure the MTF in the circumferential direction from the chart image obtained by imaging the MTF measurement chart CH.

As mentioned above, although each embodiment of this invention was explained in full detail, this invention is not limited to above-described embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, the MTF measurement chart may be colored in reverse white and black. Further, the MTF measurement chart may be colored in a third color (for example, gray) instead of white or black.

  In the above-described embodiment, as illustrated in FIG. 2, the MTF measurement chart CH has been described as being inclined clockwise, but the present invention is not limited to this. That is, the MTF measurement chart CH may be inclined by the inclination angle φ counterclockwise with the inclination angle φ set to a negative value.

B, B _{1 to} B ₈ Radiation area C, C _{1 to} C ₁₁ Segment area CH, CH ₂ MTF measurement chart D, D _{1 to} D ₄ Radiation area A _D Diagonal axis A _H Horizontal axis A _V Vertical axis L _D Diagonal line L _H Horizontal line L _V Vertical line L _W Long side of chart surface N _D , N _H , N _V , N _D2 , N _H2 Dividing line O Center position (center)
P _D , P _H , P _V , P _D2 , P _H2 section position 1 MTF measuring device 10 Chart image storage means 11 Image position specifying means 12 Image extraction means 13 Calculation means 14 Graph generation means 111 Chart center acquisition means 112 Reference ROI region Information acquisition unit 113 Relative position determination unit 114 ROI region specifying unit for each angle 121 ROI extraction unit 122 ROI rotation unit 131 Edge profile generation unit 132 Trimming unit 133 MTF calculation unit

Claims (6)

An MTF measurement chart used in an MTF measurement device that measures MTF representing spatial frequency characteristics of resolution of an imaging system,
The aspect ratio of the rectangular chart surface is 16: 9,
A division position is set in advance on a horizontal axis that is centered on a predetermined position on the chart surface and passes through the center and is inclined by a predetermined inclination angle so that the interval is wider on the outer peripheral side of the chart surface than the center side. , Presetting the section position equidistant from the horizontal axis on the vertical axis and the diagonal axis of the chart surface passing through the center and inclined by the inclination angle;
Octagonal segmented regions connecting segmented lines orthogonal to each other at the segmented positions of the horizontal axis, the vertical axis, and the diagonal axis, and the segmented lines of the horizontal axis and the diagonal axis and the long sides of the chart surface Are arranged in a concentric circle with reference to the center,
The first end point at which the boundary between the center of the chart surface, the outermost segmented region and the segmented region adjacent to the segmented region touches the long side of the chart surface, and the first side on the long side of the chart surface A radiation region having a vertex at the second end point at a preset distance from the end point is arranged symmetrically with respect to the center,
A chart for MTF measurement, characterized in that a color having a different contrast is colored in the adjacent segmented region, and the radiation region is colored in the same color as the outermost segmented region.   The division position of the horizontal axis is preset at a position where a ratio of a distance from the center to the division position with respect to a total length from the center to the short side of the chart surface is represented by a geometric series. The MTF measurement chart according to claim 1.   3. The MTF measurement chart according to claim 1, wherein a white color, a black color, or a third color other than the white color and the black color is arranged in the divided area and the radiation area. An MTF measurement chart used in an MTF measurement device that measures MTF representing spatial frequency characteristics of resolution of an imaging system,
The aspect ratio of the rectangular chart surface is 16: 9,
Centering on a predetermined position of the chart surface, a horizontal line and a vertical line passing through the center are inclined by a predetermined inclination angle, and each of the inclined horizontal line and the vertical line and a diagonal line of the chart surface are used as the chart. Forming multiple radiation areas to separate the faces,
A chart for MTF measurement, characterized in that colors having different contrasts are arranged in adjacent radiation regions.   The MTF measurement chart according to claim 4, wherein white, black, or a third color other than white and black is arranged in the radiation region.   The MTF measurement chart according to any one of claims 1 to 5, wherein the inclination angle is not less than 2 degrees and not more than 5 degrees.