JP7169110B2 - Magnification chromatic aberration measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chromatic aberration of magnification measuring device, and more particularly to a chromatic aberration of magnification measuring device for simply measuring the chromatic aberration of magnification caused by a lens when subtracting the chromatic aberration of magnification from captured image information.

In general, an imaging device (camera) separates an image of a subject obtained through a lens into R (red), G (green), and B (blue) images, and captures a color image. At this time, since the light contained in each image has a different wavelength range, it is coupled to the imaging device at different magnifications due to the chromatic aberration of magnification of the lens. As a result, color shift (or color blurring) occurs in a color image obtained from the imaging device. This color misregistration significantly degrades the image quality especially in the peripheral portion of the image (video) screen, so it is desirable to correct it. In recent years, with the increase in the number of pixels in image pickup devices and the increase in the screen size of display devices, the influence of image quality deterioration due to color misregistration has become more pronounced, and correction with higher accuracy is required. As means for correcting this color shift, a technique is disclosed in which the amount of color shift of each image is measured in advance and the color shift is corrected by image processing (see Patent Documents 1 and 2 below).

By the way, to measure the amount of color shift, a black and white checkered grid pattern, striped pattern, or the like is imaged over the entire angle of view to create an aberration measurement chart. is generally used (see Patent Documents 3 and 4 below). For example, as shown in FIG. 12, the aberration measurement chart 15 is irradiated with the illumination light from the illumination 16, and the subject light from the aberration measurement chart 15 is imaged by the imaging lens 10 and the imaging element section 11A of the imaging device 11. Then, the photographed object image is separated into B, G, and R color signals, which are sent to the chromatic aberration measuring unit 12 to measure the chromatic aberration of magnification of the imaging lens 10 . The chromatic aberration measurement unit 12 outputs the color shift amount obtained by the measurement.
The image sensor section 11A may be composed of a three-color separation prism and a three-plate image sensor corresponding to each color light of B, G, and R, or may be composed of a three-color color filter array and a single-plate image sensor. , it is also possible to use either one.

By the way, since the magnitude of the color shift depends on the lens parameters such as the focal length and focus position of the lens, it is necessary to measure each lens parameter and obtain each correction value in advance. The magnitude of color shift depends on the spectral distribution of the light source used for measurement and the spectral reflectance of the aberration measurement chart. Therefore, when measuring the amount of color misregistration, the same chart for aberration measurement is used and the illumination conditions are kept constant.

JP-A-2000-3437 JP 2011-182071 A JP-A-2006-135805 JP-A-3-169190

However, when performing a large number of measurements while changing lens parameters, it is not easy to use the same chart for aberration measurement and perform these large numbers of measurements under constant illumination conditions. For example, assuming that the focus position is changed in the range of 1m to 30m and the measurement is performed, the amount of color shift is measured while actually moving the distance between the measurement chart and the camera in the range of 1m to 30m. However, it is not easy to keep lighting conditions constant over such a long distance. Also, for example, when trying to measure by setting a measurement chart at a position 30m from the camera, it is necessary to place the measurement chart in a range that can cover the entire angle of view, and furthermore, it is necessary to keep the lighting conditions constant in that range. However, in view of the space required and the time and effort required to adjust the lighting equipment, accurate measurement is actually difficult. That is, according to the conventional technology, it is difficult to make the illumination conditions and the spectral characteristics of the chart used constant for each lens parameter, and therefore it is difficult to accurately measure the amount of color shift due to chromatic aberration of magnification.

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a magnification chromatic aberration measuring apparatus capable of easily performing accurate measurement.

The magnification chromatic aberration measuring device of the present invention is
a light source, an aberration measurement chart as a subject irradiated with illumination light from the light source, an imaging lens for forming an image of the subject light from the aberration measurement chart at a predetermined position, and an image formed by the imaging lens An imaging device that converts the image of the aberration measurement chart into B, G, and R signals related to a color image and outputs them, and an imaging device that outputs the amount of color shift based on the chromatic aberration of magnification of the imaging lens. a chromatic aberration measuring unit obtained by calculating a correlation value of each image of B, G, and R and obtaining a maximum value; and a color filter arranged between the imaging lens and the imaging element,
The color filter is characterized by having spectral characteristics that transmit only a predetermined width of wavelength regions centered on the peak values of the respective B, G, and R wavelength regions in the spectral characteristics of the imaging device.

In this case, it is preferable that the predetermined width of the wavelength region is 40 nm or less.
Further, it is more preferable that the wavelength region of the predetermined width is 20 nm or less.
It is also preferable that the wavelength region of the predetermined width has a width of 10 nm or more and 20 nm or less.

According to the magnification chromatic aberration measuring device of the present invention, the following effects are obtained.
That is, the B, G, and R light beams output from the color filters are restricted to narrow band ranges centered on the peak wavelengths of the respective color light regions. Misalignment (image blurring) can be reduced, so even if the spectral characteristics of the light source used for measurement or the spectral reflectance characteristics of the measurement chart change, the resulting change in the amount of color misalignment is small compared to conventional technology. .

Therefore, it is possible to have a degree of freedom in the selection of illumination and measurement charts used for measurement, and it is not necessary to use the same light source conditions and measurement charts for each measurement when measuring with different lens parameters. In addition, since it is not always necessary to use a black and white pattern as a measurement chart, it is possible to measure natural objects and buildings as long as they have a regular pattern of light and shade, such as the walls of a room or the walls of a building. It can be used as a chart for

As described above, according to the magnification chromatic aberration measuring apparatus of the present invention, since B, G, and R images with small blurring and clear boundary portions can be obtained, it is possible to improve the measurement accuracy of the deviation amount. In addition, it is possible to save a lot of time and effort for adjusting the lighting and the measurement chart, and it is possible to perform the measurement more easily and accurately than in the prior art.

4 is a graph showing the relationship between the spectral transmission characteristics of a color filter used in the chromatic aberration of magnification measuring device according to the embodiment of the present invention and the spectral transmission characteristics of an imaging element of a camera. 1 is a schematic diagram showing a chromatic aberration of magnification measuring device according to Embodiment 1. FIG. 10 shows the result of comparing the amount of color misregistration between the case of using the conventional technology (B) and the case of using the technology of the present embodiment (C) with respect to the predetermined imaging pattern (A). 4 is a graph showing respective spectral distributions of illumination A and illumination B used in the simulation; 7 is a graph showing color misregistration states of the conventional technology (A) and the technology of the present embodiment (B) that occur under mutually different illumination conditions. 5 is a graph showing an example of spectral transmission characteristics of each optical filter when combining optical filters to form a color filter used in the chromatic aberration of magnification measuring apparatus according to the present embodiment. FIG. 5 is a schematic diagram showing a chromatic aberration of magnification measuring device according to Embodiment 2; FIG. 11 is a schematic diagram showing a chromatic aberration of magnification measuring device according to Embodiment 3; 4 is a graph for explaining the spectral transmission characteristics of a color filter used in the chromatic aberration of magnification measuring apparatus according to the present embodiment and a method for measuring the amount of color shift of this color filter. 10 is graphs ((A) to (F)) showing simulation results (w=10 nm to 32 nm) when using the color filter shown in FIG. 9; 10 is graphs ((G) to (L)) showing simulation results (w=40 nm to 90 nm) when using the color filter shown in FIG. 9; FIG. 2 is a schematic diagram showing an example of the configuration of a conventional device used to measure the amount of color shift due to chromatic aberration of magnification;

A magnification chromatic aberration measuring apparatus according to Embodiment 1 of the present invention will be described below with reference to the drawings.
First, the outline of the chromatic aberration of magnification measuring apparatus according to the first embodiment will be described with reference to FIG. 2, and then the configuration of the color filter used in the chromatic aberration of magnification measuring apparatus according to the present embodiment will be described with reference to FIG.

As shown in FIG. 2, an aberration measurement chart 55 is irradiated with illumination light from an illumination 56, and subject light from the aberration measurement chart 55 is imaged on a single-plate color image sensor section 51 by an imaging lens 50. do. The subject image picked up by this is converted into B, G, and R signals from the image sensor section 51 and output. At this time, a color filter 53 is arranged between the imaging lens 50 and the imaging element section 51 . The amount of color shift based on the chromatic aberration of magnification of the imaging lens 50 is calculated by the chromatic aberration measuring section 52 based on the B, G, and R signals output from the imaging element section 51 .
For calculating the amount of color misregistration, for example, a method of finding a value that maximizes the correlation value of each image, or the like is used.

FIG. 1 shows the spectral transmission characteristics of color filters used in the chromatic aberration of magnification measuring apparatus according to this embodiment. This color filter is, for example, formed by depositing a dielectric multilayer film (for example, alternate layers of TiO ₂ and SiO ₂ ) on a transparent plate such as glass using a vapor deposition method or the like.

In addition, the peak values of the spectral characteristics of the B, G, and R colored lights in the image sensor unit 51 are around 450 nm, around 540 nm, and around 600 nm, respectively. For example, it is configured to have a transmission characteristic to transmit only a wavelength band of 10 nm. Therefore, as shown in FIG. 1, an ordinary image pickup device is configured to be able to receive light of each color of B, G, and R over a wide wavelength range. , and R are only narrow-band colored lights with predetermined widths centered on respective peak values of approximately 450 nm, approximately 540 nm, and approximately 600 nm.

According to the color filter 53 used in the magnification chromatic aberration measuring apparatus of the present embodiment, only the wavelength regions near the respective peak positions of the B, G, and R light beams are transmitted, and the imaging element unit 51 is irradiated with the light beams. As a result, it is possible to greatly save the trouble of adjusting the illumination and the measurement chart, and it is possible to perform the measurement more easily and accurately than the conventional technique.

The effects of this color filter will be described in detail below.
FIG. 3A shows an example of an imaging pattern used for measuring the chromatic aberration of magnification, and FIG. , and shows the color shift state measured by the conventional technique (simulation), and FIG. (simulation) shows the color misregistration.

Here, it is assumed that the color shift occurs in the horizontal direction of the image, and that the imaging magnification of the image formed on the surface of the imaging element is proportional to the wavelength λ. Further, in the imaging pattern shown in FIG. 3A, the area on the left side of the drawing has a spectral reflectance that equally reflects light of all wavelengths, and the area on the right side of the drawing has a spectral reflectance that absorbs light of all wavelengths. shall have Illumination used for imaging at this time has a spectral distribution (solid line) indicated by illumination A and a spectral distribution (broken line) indicated by illumination B in FIG.

In the prior art shown in FIG. 12, the color lights having the spectral distributions of the illumination A and the illumination B are directly applied to the imaging element section 11A. , light corresponding to the spectral characteristics of the image sensor unit 11A having a broad wavelength range. Therefore, the color shift output from the chromatic aberration measuring unit 12 includes not only the color shift between the B, G, and R images, but also the color shift (image blurring) in each individual image. be

On the other hand, the B, G, and R images obtained by using the chromatic aberration of magnification measuring apparatus of this embodiment are restricted to a predetermined wavelength range centered on each peak position by the action of the color filter 53. The blurring of the image caused by the chromatic aberration of magnification occurring in the image is much smaller than the blurring of the image caused by the chromatic aberration of magnification when using the conventional technique, and the contour line becomes clearer.

As a method for detecting the amount of color misregistration, for example, a method of calculating the correlation value of each of the B, G, and R images and finding the maximum value to detect the amount of color misregistration is usually used.

As described above, by using the chromatic aberration of magnification measuring apparatus of the present embodiment, B, G, and R images with small blurring and clear boundary portions can be obtained, so that the accuracy of measuring the deviation amount can be improved.

FIGS. 5A and 5B compare the amount of color shift of the B, G, and R subject images obtained under different lighting conditions between the conventional technique and the present embodiment obtained by simulation.
Illumination used for imaging at this time has a spectral distribution (solid line) indicated by illumination A and a spectral distribution (broken line) indicated by illumination B in FIG.

As shown in FIG. 5A, the curves of the color shifts of illumination A (solid line) and illumination B (broken line) in the case of using the conventional technology hardly overlap each other, and the difference in the amount of color shift is large.
On the other hand, as shown in FIG. 5B, the curves of the color shifts of illumination A (solid line) and illumination B (broken line) when the technique of the present embodiment is used substantially overlap in a region where the signal value changes greatly. , the difference in the amount of color shift is small.

As described above, when comparing FIGS. 5A and 5B, it is clear that the color shift in the conventional technique shifts significantly to the left and right. Since it is clear that the amount of color shift that occurs changes greatly when the illumination conditions change, it is necessary to change the lighting conditions for each measurement in order to achieve accurate measurement of the amount of color shift using the conventional technique. It is clear that they must be aligned identically.

On the other hand, when the chromatic aberration of magnification measuring apparatus of this embodiment is used, the amount of color shift caused by illumination A (solid line) and the amount of color shift caused by illumination B (broken line) match. This indicates that the same amount of color shift occurs in the apparatus using the chromatic aberration of magnification measurement apparatus of the present embodiment even if the illumination conditions such as the illumination light used are changed. are not necessarily aligned identically.

Next, a method for manufacturing the color filter 53 will be described with reference to FIG.
That is, FIG. 6 illustrates an example in which optical filters are combined to realize the characteristics of the color filter 53 according to the magnification chromatic aberration device of the present invention, using the spectral transmission characteristics of each filter. In this example, the peak positions (maximum signal values) of the spectral characteristics of B, G, and R output from the imaging device 51 are approximately 450 nm, approximately 540 nm, and approximately 600 nm, respectively.

The optical filter (1) shown in FIG. 6A is a bandpass filter that transmits wavelengths of 445 nm to 605 nm. The optical filter (2) shown in FIG. 6B is a notch filter that cuts wavelengths of 455 nm to 540 nm. The optical filter (3) shown in FIG. 6C is a notch filter that cuts wavelengths of 545 nm to 595 nm. By combining the optical filter (1), the optical filter (2), and the optical filter (3), a wavelength band with a width of 10 nm centered on the peak position of the spectral characteristic of each of the B, G, and R colors of the image sensor 51 is obtained. A spectral transmittance characteristic that transmits only light can be realized. In practice, for example, the color filter 53 is formed by laminating the dielectric multilayer films constituting these three optical filters (1) to (3) on a substrate in order.

The narrower the width of the transmitted wavelength band, the smaller the change in the amount of color shift with respect to the change in illumination conditions, and the above-mentioned effect that it is not necessary to set the same illumination conditions for each measurement can be achieved more satisfactorily. On the other hand, the narrower the width of the transmitted wavelength range, the less the amount of light incident on the imaging device 51, and the sensitivity of the imaging device decreases.
Therefore, it is important to prepare multiple filters with different widths of transmitted wavelength bands, and to select an appropriate filter according to the brightness of the lighting that can be achieved and the required measurement accuracy. be.

As the magnification chromatic aberration measuring apparatus of the present invention, it is possible to adopt the apparatus of Embodiment 2 or Embodiment 3 shown below instead of the apparatus of Embodiment 1 described above.
In the apparatus for measuring chromatic aberration of magnification of Embodiment 2 shown in FIG. An image is formed on the color imaging element portion 61 of the plate. The image of the subject thus picked up is converted into B, G, and R signals from the image sensor section 61 and output. The configuration described above is the same as that of the chromatic aberration of magnification measuring apparatus of the first embodiment. However, in Embodiment 2, a color filter 63 that functions in the same manner as the color filter 53 is arranged between the measurement chart 65 and the imaging lens 60, more specifically, in the front stage portion close to the imaging lens 60. ing.
Even if the color filter 63 is arranged between the measurement chart 65 and the imaging lens 60, the case where the color filter 53 is arranged between the imaging lens 50 and the imaging element unit 51 as in the first embodiment The same effect can be obtained.

Further, for example, in the magnification chromatic aberration measuring apparatus of Embodiment 3 of FIG. 8, the illumination light from the illumination 76 is applied to the aberration measurement chart 75, and the subject light from the aberration measurement chart 75 is applied to the imaging lens of the imaging device. 70 forms an image on a single-plate color image pickup device 71 . The image of the subject thus picked up is converted into B, G, and R signals from the image sensor section 71 and output. The above configuration is the same as that of the magnification chromatic aberration measuring apparatus of the first and second embodiments. However, in Embodiment 3, a color filter 73 that functions in the same manner as the color filter 53 is arranged between the illumination 76 and the measurement chart 75, more specifically, in the latter part close to the illumination 76. . In other words, the color filter 73 functions as a light control filter for the lighting 76 .

Even if the color filter 73 is arranged between the illumination 76 and the measurement chart 75, it is different from the case where the color filter 53 is arranged between the imaging lens 50 and the imaging element unit 51 as in the first embodiment. Similar effects can be obtained.

In addition, various modes can be adopted as the magnification chromatic aberration measuring device of the present invention.
For example, the color filter may be composed of three filters for obtaining the R image, the G image, and the B image. In this case, each of the three filters for acquiring the R image, the G image, and the B image is configured to transmit only near the peak wavelength region of the spectral characteristics of the corresponding imaging device. During measurement, three images are obtained by switching three color filters, and B, G, and R signals are extracted from each image. In this method, when switching between the three filters, it is necessary to accurately match the illumination conditions and the positions of the measurement charts. Incidentally, the three color filters may be mounted on one turret or the like arranged in the optical path.
Also, in the above embodiment, the color filters are of the transmissive type, but they can also be of the reflective type.

The apparatus for measuring chromatic aberration of magnification according to the present invention will be further described below with reference to examples.

FIG. 9 shows the spectral characteristics of the color filters of the chromatic aberration of magnification measuring apparatus according to this embodiment.
This color filter is basically configured in the same manner as the color filter shown in FIG. That is, a dielectric multilayer film (for example, alternating layers of TiO ₂ and SiO ₂ are repeatedly laminated) is formed on a transparent plate such as glass by using a vapor deposition method or the like. A plurality of color filter samples having different spectral transmission characteristics were formed by varying the thickness. Specifically, the peak positions of the imaging characteristics for each color light in the image sensor are set to 448 nm (B light), 539 nm (G light), and 602 nm (R light), respectively, and a predetermined width is set around each of these peak positions. A configuration was made using a simulation so as to have spectral transmission characteristics that transmit only a narrow band (hereinafter referred to as a narrow band width W).

The samples were prepared with the narrow bandwidth W set to 10 nm, 14 nm, 18 nm, 22 nm, 28 nm, 32 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm and 90 nm. For each of these samples, changes in the amount of color shift based on the difference in the measurement light source (light source A and light source B having spectral distributions referred to as light source A and light source B in FIG. 4) were measured and shown in FIGS. F) and graphs of FIGS. 11(G)-(L).

That is, FIG. 10A shows the state of color shift when the narrow bandwidth W is 10 nm, and FIG. 10B shows the state of color shift when the narrow bandwidth W is 14 nm. FIG. 10(C) shows the state of color shift when the narrow bandwidth W is 18 nm, and FIG. 10(D) shows the state of color shift when the narrow bandwidth W is 22 nm. FIG. 10(E) shows the state of color shift when the narrow bandwidth W is 28 nm, and FIG. 10(F) shows the state of color shift when the narrow bandwidth W is 32 nm. FIG. 11G shows the state of color shift when the narrow bandwidth W is 40 nm, and FIG. 11H shows the state of color shift when the narrow bandwidth W is 50 nm. FIG. 11(I) shows the state of color shift when the narrow bandwidth W is 60 nm, and FIG. 11(J) shows the state of color shift when the narrow bandwidth W is 70 nm. 11(K) shows the state of color shift when the narrow bandwidth W is 80 nm, and FIG. 11(L) shows the state of color shift when the narrow bandwidth W is 90 nm. be.

As is clear from the simulation results of FIGS. 10 and 11, the greater the value of W, the greater the difference in the amount of color shift caused by the difference in light source (illumination conditions). That is, as the value of W increases, the effect of the color filter in the magnification chromatic aberration measuring apparatus of this embodiment decreases.

Also, the state of color shift when W=90 nm is almost the same as the simulation result (see FIG. 5A) in the case of the prior art without color filters. That is, when W=90 nm, the effect of the color filter according to the magnification chromatic aberration measuring apparatus of this embodiment is small.

When W is 40 nm or less, compared with the simulation results of the prior art without color filters, the change in color misregistration is suppressed to some extent, and a corresponding effect can be expected.
Furthermore, if W=20 nm or less, good accuracy can be secured. On the other hand, as the value of W is decreased, the amount of light incident on the camera decreases, which may hinder measurement in terms of S/N reduction and the like. For this reason, in order to suppress the change in color misregistration and ensure good accuracy, and to suppress the decrease in S/N to the extent that it does not interfere with the measurement, the value of W is set to For example, it is preferable to set the thickness in the range of 10 nm or more and 20 nm or less.
However, there is a trade-off relationship between securing the measurement accuracy (≈ W) associated with the suppression of color misregistration and S/N. It is important to appropriately select the optimum range, such as intentionally lowering (widening W) to secure the S/N ratio.

In addition, the state of color misregistration when W=10 nm is considered to be substantially the best in normal use (even if W<10 nm, the state of color misregistration is almost the same as when W=10 nm). Therefore, it is preferable to select W=10 nm if the reduction in S/N at this time is acceptable.
However, even in this case, since the above trade-off relationship is established, it is important to appropriately select the optimum value of W according to the situation.

Reference Signs List 10, 50, 60, 70 imaging lens 11 imaging device 11A, 51, 61, 71 imaging device section 12, 52, 62, 72 chromatic aberration measurement section 53, 63, 73 color filter 15, 55, 65, 75 chart for measurement 16 , 56, 66, 76 Illumination

Claims (4)

a light source, an aberration measurement chart as a subject irradiated with illumination light from the light source, an imaging lens for forming an image of the subject light from the aberration measurement chart at a predetermined position, and an image formed by the imaging lens An imaging device that converts the image of the aberration measurement chart into B, G, and R signals related to a color image and outputs them, and an imaging device that outputs the amount of color shift based on the chromatic aberration of magnification of the imaging lens. a chromatic aberration measuring unit obtained by calculating a correlation value of each image of B, G, and R and obtaining a maximum value; and a color filter arranged between the imaging lens and the imaging element,
The chromatic aberration of magnification measuring apparatus , wherein the color filter has a spectral characteristic of transmitting only a wavelength region of a predetermined width around a peak value of each of the B, G, and R wavelength regions in the spectral characteristics of the imaging device. . 2. A magnification chromatic aberration measuring apparatus according to claim 1, wherein said wavelength region of said predetermined width has a width of 40 nm or less. 2. A lateral chromatic aberration measuring apparatus according to claim 1, wherein said wavelength region of said predetermined width has a width of 20 nm or less. 2. A lateral chromatic aberration measuring apparatus according to claim 1, wherein said predetermined wavelength range has a width of 10 nm or more and 20 nm or less.

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