Evaluation system and evaluation method

An evaluation system includes an input unit that inputs a test chart image acquired by imaging a test chart including a plurality of characters, an evaluation unit that evaluates performance of an imaging unit using the test chart image, an image generation unit that generates an evaluation image representing an evaluation of the evaluation unit at each position on the test chart image with a color, and a display unit that displays the evaluation image along with the test chart image or in a superimposed manner on the test chart image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an evaluation system and an evaluation method for evaluating the performance of a lens and the like.

2. Description of the Related Art

An imaging device that images a subject using an imaging lens and an image sensor is widely used. In addition, a system that incorporates the imaging device, performs analysis and the like on an image imaged by the imaging device, and uses the result for its operation is widely used. The image acquired in such an imaging device or the system (hereinafter, referred to as the imaging device or the like) incorporating the imaging device is typically evaluated using an image (hereinafter, referred to as a test chart image) that is acquired by imaging a test chart (JP2015-082242A).

SUMMARY OF THE INVENTION

Resolution is one important image evaluation standard. However, in the method of evaluation using the test chart image in the related art, measurement locations are discrete in the image, and an arbitrary location cannot be evaluated. In addition, evaluation may only be performed in a specific direction such as the horizontal direction or the vertical direction of the image. Thus, the evaluation obtained using the method in the related art may not have a good correlation with the actual performance of the imaging device or the like.

For example, in the case of acquiring an image for display using the imaging device or the like, it is not unusual that there is a great difference between visual sensory evaluation and the evaluation obtained in the related art using the test chart image. In addition, in a case where the image acquired using the imaging device or the like is used in optical character recognition (hereinafter, referred to as OCR), the correlation between the evaluation obtained in the related art using the test chart image and the actual character recognition ratio is generally bad.

In addition, in the related art, in the case of presenting the evaluation, the presentation is typically provided in the format of a graph or the like in a specific direction of the evaluation of the resolution or the like. Thus, it is difficult to understand the correspondence between the test chart image and the graph representing the evaluation result, thereby posing a problem in that a comparison itself between the actual performance of the imaging device or the like and the evaluation obtained using the method in the related art is difficult.

An object of the present invention is to provide an evaluation system and an evaluation method that favorably represent the actual performance of an imaging device or the like and present an understandable evaluation result.

An evaluation system of the present invention comprises an input unit, an evaluation unit, and a display unit. The input unit inputs a test chart image acquired by imaging a test chart including a plurality of characters. The evaluation unit evaluates performance of an imaging unit using the test chart image. An image generation unit generates an evaluation image representing an evaluation of the evaluation unit at each position on the test chart image with a color. The display unit displays the evaluation image along with the test chart image or in a superimposed manner on the test chart image.

It is preferable that the evaluation unit evaluates the performance of the imaging unit using a character that has a constant line thickness among the characters included in the test chart image.

It is preferable that the evaluation unit evaluates the performance of the imaging unit in a case where the plurality of characters included in the test chart image are random.

It is preferable that the evaluation unit evaluates the performance of the imaging unit in a case where the test chart in the test chart image is in a gray scale.

It is preferable that the evaluation unit evaluates a resolution of the imaging unit.

It is preferable that the evaluation image shows a part having a higher resolution than a reference resolution or a part having a lower resolution than the reference resolution by representing a part having the reference resolution with a specific color and representing the part having the higher resolution than the reference resolution or the part having the lower resolution than the reference resolution with a color different from the specific color.

It is preferable that the image generation unit sets the reference resolution based on a character recognition ratio of optical character recognition software, and the evaluation image represents at least a part in which a character is recognizable, and a part in which a character is not recognizable with different colors in a case of recognizing the characters included in the test chart image using the optical character recognition software.

It is preferable that the evaluation unit evaluates chromatic performance of a lens included in the imaging unit.

It is preferable that the image generation unit generates the evaluation image in which color bleeding caused by a chromatic aberration at each position on the test chart image is represented as an image.

It is preferable that the image generation unit generates the evaluation image that represents magnitudes of an axial chromatic aberration and a lateral chromatic aberration with a color with respect to an image height.

It is preferable to further comprise an imaging unit that images the test chart image to be input to the input unit.

It is preferable to further comprise the test chart.

It is preferable that the characters included in the test chart have a constant line thickness.

It is preferable that the plurality of characters included in the test chart are random.

It is preferable that the color of the plurality of characters included in the test chart is a single color.

An evaluation method of the present invention comprises a step of inputting a test chart image acquired by imaging a test chart including a plurality of characters by an input unit, a step of evaluating performance of an imaging unit using the test chart image by an evaluation unit, a step of generating an evaluation image representing an evaluation of the evaluation unit at each position on the test chart image with a color by an image generation unit, and a step of displaying the evaluation image along with the test chart image or in a superimposed manner on the test chart image by a display unit.

The present invention can evaluate performance in any direction at any location by using a test chart including a plurality of characters and displays an evaluation image representing an evaluation with a color along with a test chart image or in other manners. Consequently, an evaluation result that favorably represents actual performance of an imaging device or the like can be presented in an understandable manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

As illustrated inFIG. 1, an evaluation system10comprises a test chart11, an imaging unit12, an analysis unit15, and a display unit20.

The test chart11includes at least a plurality of characters as a chart used for evaluation. In the present specification, the character is, for example, an alphabet, a number, hiragana, katakana, or kanji and is a symbol, a sign, or a figure configured with a combination of dots or lines. Therefore, the character includes a special symbol, sign, figure, or the like (for example, a symbol, a sign, or a figure that is used in only an expression) that does not have a meaning alone or in combination as a so-called word.

In the present embodiment, the test chart11is formed using a character string consisting of a plurality of alphabets as illustrated inFIG. 2. InFIG. 2, the character string constituting the test chart11is an arrangement of alphabets not having a linguistic meaning, but may be a sentence or the like having a linguistic meaning. In addition, inFIG. 2, the test chart11is configured using a plurality of types of characters. However, depending on the content of evaluation (such as whether or not the evaluation result affects the directivity or the density of the characters), the test chart11may be configured using a plurality of characters of one type.

As illustrated inFIG. 3, characters (for example, an Arial font or a boldface of other fonts) having an approximately constant point or line thickness D1is used in the plurality of characters constituting the test chart11. In the plurality of characters constituting the test chart11, the size of each character is an approximately constant size. That is, the test chart11is regarded as having a sufficiently insignificant effect on at least the evaluation result because an evaluation method that reduces the anisotropy of the character itself constituting the test chart11and, even in a case where anisotropy is present, averages the inside of a specific area SP (refer toFIG. 5) in the case of evaluating the imaging unit12is used.

Furthermore, the plurality of characters included in the test chart11are approximately random as a whole of the test chart11. The term “random” means that there is no deviation with respect to directivity (the directivity of the character itself and not the directivity of the character arrangement) and density, and consequently, the directivity and the density are regarded as being almost uniform. That is, while a different character or a combination of characters (a so-called word or the like) is used at each position in a case where the test chart11is locally seen, the whole of the test chart11is regarded as being uniform.

For example, in a case where there is a deviation such that “- (hyphen)” is densely located in a certain part of the test chart11, and “| (vertical line)” is densely located in another certain part, there may be a difference in evaluation result between evaluation of a resolution or the like using the part in which “- (hyphen) having horizontal directivity)” is densely located, and evaluation of the resolution or the like using the part in which “| (vertical line)” having vertical directivity is densely located. However, since characters having a constant thickness are approximately randomly arranged in the test chart11as a whole, and such a deviation is prevented, any part of the test chart11used for evaluation has a sufficiently insignificant effect on the evaluation result.

Besides, regarding the color of the test chart11, the color of the plurality of characters included in the test chart11is a single color. That is, the test chart11is monochrome, and the characters of the test chart11are configured in one color different from a background (a part in which a character is not present). For example, the background is in one color of white, and the characters are in one color of black. Therefore, since the test chart11is uniform as a whole with respect to color, any part of the test chart11used in the case of evaluation with respect to color (for example, in the case of evaluating chromatic performance such as a chromatic aberration) does not affect the result of evaluation.

The imaging unit12is a so-called digital camera that acquires a test chart image26(refer toFIG. 5) by imaging the test chart11, and includes an imaging lens13, an image sensor14, a control unit (not illustrated) controlling the imaging lens13, the image sensor14, and the like, and an image processing unit (not illustrated). The imaging lens13or the image sensor14included in the imaging unit12is a component constituting an evaluation target imaging device or the like or is the evaluation target imaging device or the like itself and can be individually replaced. Therefore, in the evaluation system10, the evaluation target imaging device or the like is changed by replacing the imaging lens13or the image sensor14.

The image processing unit included in the imaging unit12selectively performs, as necessary, one or a plurality of image processing such as a demosaicing process (referred to as a coloring process or demosaicing), an edge highlight process, a contrast highlight process, a noise reducing process, a light intensity correction process, a distortion correction process, or various aberration correction processes for a lateral chromatic aberration, an axial chromatic aberration, and the like on an image or a signal output by the image sensor14. In addition, the imaging unit12can turn OFF the various image processing. For example, in a case where only the imaging lens13is the evaluation target, a so-called RAW image is output as the test chart image26without performing the various image processing. In addition, in a case where parameters of the various image processing are adjusted using the imaging lens13and the image sensor14having known performance or the like, the evaluation system10can evaluate the performance of image processing of the imaging unit12(the performance of image processing with the adjusted parameters or a combination of the image processing with the adjusted parameters and other image processing).

The analysis unit15has an input unit16, an evaluation unit17, an image generation unit18, and a reference color setting unit19. For example, the analysis unit15is a so-called computer. Thus, for example, the input unit16, the evaluation unit17, the image generation unit18, and the reference color setting unit19are programs, operation devices such as central processing units (CPU), memories, and other electronic circuits.

The input unit16inputs the test chart image26, which is acquired by imaging the test chart11including the plurality of characters, into the evaluation unit17. The input unit16acquires the test chart image26from the imaging unit12. The test chart image26may consist of a plurality of images. For example, in a case where the image sensor14has a color filter of any of red, green, and blue (RGB) in each pixel, and the imaging unit12outputs a red image (R image), a green image (G image), and a blue image (B image) acquired by imaging the test chart11in pixels of each color, the input unit16may input the R image, the G image, the B image, or a combination of two or more of the R image, the G image, and the B image into the evaluation unit17as one test chart image26. Hereinafter, the test chart image26will be regarded as one image unless otherwise a particular description is needed.

The evaluation unit17evaluates the performance of the imaging unit12using the test chart image26. The performance of the imaging unit12is the imaging performance of the imaging lens13and the image sensor14, which are components (or the evaluation target imaging device or the like itself) constituting the evaluation target imaging device or the like or the imaging performance of the imaging lens13or the image sensor14and is, for example, the resolution, sharpness, or various aberrations such as a chromatic aberration. In the present embodiment, the evaluation unit17evaluates the resolution for each position on the test chart image26.

The evaluation unit17evaluates the performance of the imaging unit12using at least a character having a constant line thickness among the characters included in the test chart image26. In the present embodiment, characters having the approximately constant point or line thickness D1are used in the test chart11. Thus, the evaluation unit17can use all characters included in the test chart image26for evaluation of the performance of the imaging unit12.

In addition, the evaluation unit17evaluates the performance of the imaging unit12in a case where the plurality of characters included in the test chart image26are random. Therefore, in a case where a character in a part used in the case of evaluating the performance of the imaging unit12by the evaluation unit17is not random, error may be included in the evaluation of the performance of the imaging unit12. In the present embodiment, in the test chart11, the plurality of characters included in the test chart11are approximately random as a whole of the test chart11. Thus, the evaluation unit17can evaluate the performance of the imaging unit12using any part in the test chart image26.

In addition, the evaluation unit17can properly evaluate the performance of the imaging unit12particularly in a case where the test chart11(that is, the plurality of characters) in the test chart image26is in a gray scale. Therefore, in a case or the like where the test chart11in the test chart image26has a different color for each position, error may be included in the evaluation result in a case where the evaluation unit17evaluates the imaging unit12with respect to color. In the present embodiment, the background of the test chart11is in one color of white, and the characters are in one color of black. Thus, the test chart11in the test chart image26is in at least a gray scale. Thus, the evaluation unit17can evaluate the imaging unit12with respect to color using any part in the test chart image26.

The image generation unit18generates an evaluation image31(refer toFIG. 6) that represents the evaluation (for example, the value of the resolution) of the evaluation unit17at each position on the test chart image26with a color. In the present embodiment, since the evaluation unit17evaluates the resolution, the evaluation image31shows a part having a higher resolution than a reference resolution or a part having a lower resolution than the reference resolution by representing a part having the reference resolution with a specific color and representing the part having a higher resolution than the reference resolution or the part having a lower resolution than the reference resolution with a color different from the specific color. Specifically, the image generation unit18sets a color to be associated with the evaluation of the evaluation unit17in accordance with a setting of the reference color setting unit19.

The reference color setting unit19sets a color as a reference (hereinafter, referred to as a reference color) among colors to be associated with the evaluation (for example, the value of the resolution) of the evaluation unit17in a case where the image generation unit18generates the evaluation image31. In addition, the reference color setting unit19sets a color (hereinafter referred to as a first color) to be associated in a case where the evaluation exceeds the reference, and a color (hereinafter, referred to as a second color) in a case where the evaluation is below the reference as at least colors that may be distinguished from each other. Simply speaking, the reference color setting unit19sets a color scale32(refer toFIG. 6) of the evaluation image31by setting the reference color, the first color, and the second color.

For example, the reference color is yellow. In addition, in a case where the reference color is yellow, for example, the first color is a red-based color, and the second color is a blue-based color. The red-based color is a set of colors acquired by gradually increasing a red component and gradually decreasing a blue component based on the value of the evaluation from yellow, which is the reference color, to red. For example, orange and red are red-based colors. The blue-based color is a set of colors acquired by gradually increasing a blue component and gradually decreasing a red component based on the value of the evaluation from yellow, which is the reference color, to blue. For example, green and blue are blue-based colors.

The reference color setting unit19sets the correspondence between the reference color and the evaluation such that the actual performance of the imaging device or the like is favorably represented. Specifically, in the present embodiment, the direct and actual evaluation of the imaging unit12to be obtained by a user is not the resolution itself but whether or not characters can be recognized using specific OCR software. Thus, the reference color setting unit19sets the reference resolution and a color corresponding to the reference resolution based on the character recognition ratio of the specific OCR software. Specifically, a resolution at which the character recognition ratio in the case of performing character recognition using the specific OCR software is equal to a specific value (for example, 80%) is associated with the reference color. Accordingly, consequently, the image generation unit18sets the reference resolution and the color corresponding to the reference resolution based on the character recognition ratio of the specific OCR software, and the evaluation image31represents at least a part in which characters can be recognized, and a part in which characters cannot be recognized with different colors in the case of recognizing the characters included in the test chart image26using the specific OCR software. In the case of using other OCR software, the resolution at which the character recognition ratio is greater than or equal to the specific value changes depending on the performance of the OCR software. Thus, for example, the reference color setting unit19changes the resolution to be associated with the reference color for each OCR software.

The reference color setting unit19is a storage device such as a memory that temporarily or permanently stores the reference color, the first color, the second color, and the correspondence between each color and the value of the evaluation of the evaluation unit17, or is a user interface that appropriately inputs the reference color, the first color, the second color, and the correspondence between each color and the value of the evaluation of the evaluation unit17into the image generation unit18.

The display unit20displays the evaluation image31along with the test chart image26or in a superimposed manner on the test chart image26. The display unit20is a so-called monitor such as a liquid crystal display.

Hereinafter, an action of the evaluation system10will be described in accordance with a flowchart inFIG. 4. First, the imaging lens13or the like which is the evaluation target is attached to the imaging unit12, and the test chart11is imaged (S11). Accordingly, the imaging unit12acquires the test chart image26. In the case of imaging the test chart11, the imaging unit12is focused on the test chart11by adjusting its distance to the test chart11or using an auto focus function of the imaging lens13. While the imaging unit12images the test chart11with the center of the test chart11approximately in its front, precise positioning or the like is not needed. The reason is that the characters of the test chart11are random and are uniform with respect to color.

In a case where the imaging unit12acquires the test chart image26, the evaluation unit17evaluates the performance of the imaging unit12using the test chart image26(S12). Specifically, as illustrated inFIG. 5, from the test chart image26, the evaluation unit17cuts out the area SP that has a constant size and includes, at its center, a positional coordinate (hereinafter, referred to as an evaluation position) P0at which the resolution is calculated. The resolution at the evaluation position P0is calculated using the image of the area SP. Furthermore, for example, the evaluation unit17scans the position of the area SP on the test chart image26as illustrated by a broken arrow. Consequently, the resolution is calculated in almost the whole area of the test chart image26.

For example, a contrast method, a root mean square method, or a derivation method is known as a resolution calculation method. In the present embodiment, the evaluation unit17calculates the resolution using the contrast method. Specifically, first, an average value Aave of pixel values of the whole image of the cut area SP is calculated. Then, in the image of the area SP, an average value Wave of pixel values greater than or equal to the average value Aave is calculated. In addition, in the image of the area SP, an average value Bave of pixel values less than or equal to the average value Aave is calculated. A resolution Rpos at the evaluation position P0is calculated in accordance with Rpos=(Wave−Bave)/(Wave+Bave).

In a case where the evaluation unit17calculates the resolution which is the evaluation of the imaging unit12in the above manner, the image generation unit18generates the evaluation image31(S13). As illustrated inFIG. 6, the evaluation image31is an image in which a pixel at a position corresponding to each evaluation position P0of the test chart image26is set to have the resolution which is the evaluation of the evaluation unit17, and a color set in the color scale32set by the reference color setting unit19. In the present embodiment, as illustrated inFIG. 6andFIG. 7, a pixel at a position at which the character recognition ratio is equal to the specific value in the case of using the OCR software is yellow which is the reference color. In addition, a pixel at a position at which the character recognition ratio exceeds the specific value has the red-based color corresponding to the resolution at the position. In addition, a pixel at a position at which the character recognition ratio is below the specific value has the blue-based color corresponding to the resolution at the position. Therefore, in the evaluation image31, it is clearly seen that characters can be stably recognized by the OCR software in the area of yellow, which is the reference color, and the red-based color, and conversely, character recognition accuracy of the OCR software is low in the area of the blue-based color.

InFIG. 7, “example of characters” is an example of characters on the test chart image26, and “display color” is the color of display based on the color scale32in the evaluation image31. In addition, inFIG. 7, “OCR” is an evaluation representing a summary of the character recognition ratio in the case of using the OCR software and has three levels of “A”, “B”, and “C”. The evaluation “A” represents that the character recognition ratio of the OCR software exceeds the specific value, and almost all characters can be correctly recognized (read by the OCR software). The evaluation “B” represents that the character recognition ratio of the OCR software is approximately equal to the specific value, and while a part of characters may be erroneously recognized, or a part of characters may not be recognized as a character, most of the characters can be correctly recognized (almost read by the OCR software). The evaluation “C” represents that the character recognition ratio of the OCR software is below the specific value, and while a part of characters may be correctly recognized, many characters cannot be recognized, or many recognized characters are erroneously recognized (visually read but not read by the OCR software).

In a case where the image generation unit18generates the evaluation image31, the display unit20displays the evaluation image31on its display screen along with the test chart image26as illustrated inFIG. 8(S14).

As described above, the evaluation system10presents the evaluation result of the performance of the imaging unit12in the format of the evaluation image31. Thus, a comparison or the like between a visual sensory evaluation of the test chart image26and the evaluation of the evaluation system10can be more easily made than a case where the evaluation result is presented in the format of graph or the like as in the related art. In addition, the resolution at “any position” of the test chart image26can be easily found. From such points, the display of the evaluation result of the evaluation system10is more understandable than that in the related art.

In addition, for example, the user who tries to perform character recognition using the OCR software desires to find the evaluation such as the resolution of the imaging lens13or the like, but the evaluation is a so-called intermediate evaluation for finding whether or not characters can be eventually recognized using the OCR software. It is more favorable to find the evaluation as to whether or not characters can be recognized using the OCR software in a more direct form.

In the related art, in the case of presenting the graph of the resolution in a specific direction at any position, a determination as to whether or not a character at the position can be recognized by the OCR software has to be performed by considering graphs of the resolution in two directions. Therefore, the actual evaluation as to whether or not a character at a certain position on the test chart image26can be recognized is not directly acquired.

In the evaluation image31, the evaluation system10displays the evaluation of the resolution with a color in association with the character recognition ratio in the case of using the OCR software. Thus, the character recognition ratio in the case of using the OCR software can be more directly found than that in the related art.

Particularly, in the evaluation image31, the resolution at which characters can be recognized in the case of using the OCR software is set as the actual reference, and an area in which characters can be stably recognized (the area of the reference color and the red-based color), and an area in which the character recognition ratio is low (the area of the blue-based color) are displayed using a difference in color based on the reference. Thus, a determination as to whether or not characters can be recognized in the case of using the OCR software is particularly easily made.

For example, an evaluation image41illustrated inFIG. 9is an image in which the resolution calculated by the evaluation unit17is represented as a simple gray scale42corresponding to the numerical value of the resolution regardless of the character recognition ratio of the OCR software. In the evaluation image41, the resolution of the imaging unit12can also be found. In addition, in a case where the resolution at which characters can be stably recognized by the OCR software is known, a position on the test chart image26to which characters can be recognized can be more easily found than that in the related art by seeing the evaluation image41. However, a boundary between character recognizability and character unrecognizableness is still ambiguous.

Meanwhile, in the evaluation image31of the embodiment, the reference color is set based on the character recognition ratio of the OCR software. Thus, a determination as to whether or not characters can be recognized in the case of using the OCR software is particularly easily made. In addition, the first color representing the area in which characters can be stably recognized, and the second color representing the area in which the character recognition ratio is low are set to be easily distinguished from each other based on the reference color. Thus, a determination as to whether or not characters can be recognized in the case of using the OCR software is particularly easily made.

In the case of setting the evaluation image31as a gray scale, for example, a gray scale52in which the reference color (illustrated by a triangle mark (▴) inFIG. 10) is set for a resolution corresponding to a specific character recognition ratio of the OCR software is set like an evaluation image51illustrated inFIG. 10. In a case where noticeable differences in color (including light and shade) that can be identified from each other are set based on the reference color, a determination as to whether or not characters can be recognized in the case of using the OCR software can be easily made in the evaluation image51of the gray scale52in the same manner as the evaluation image31.

Besides, since the evaluation system10uses the uniform test chart11, there is an advantage such that precise positioning between the imaging unit12and the test chart11is not required. In the case of lining up and imaging a plurality of typical charts such as Siemens star charts and evaluating the imaging unit12using the image, positioning between the test chart11and the imaging unit12is basically needed. For example, in a case where an evaluation of the imaging center is to be obtained, the test chart needs to be imaged with the Siemens star chart or the like in the related art at its center. In a case where the position of the Siemens star chart or the like in the related art is shifted from the imaging center, the evaluation result is changed. Meanwhile, the evaluation system10simply needs to perform imaging with the test chart11approximately in its front. The reason is that the test chart11is uniform, and even evaluation can be performed even in a case where any part of the test chart11is imaged. Therefore, the evaluation system10can more easily evaluate the imaging unit12than an evaluation system in the related art.

In the first embodiment, the display unit20displays the test chart image26along with the evaluation image31. The display unit20may display a superimposition image36on which the test chart image26and the evaluation image31are superimposed as illustrated inFIG. 11. The superimposition image36is generated by the display unit20in the case of displaying the test chart image26and the evaluation image31. The superimposition image36may be generated in advance by the image generation unit18using the test chart image26and the evaluation image31.

In the first embodiment, the area SP cut out from the test chart image26by the evaluation unit17in order to calculate the resolution may have any shape and any size, but the area SP includes at least a plurality of characters. The reason is that the evaluation result (for example, the value of the resolution) is not to be affected by the unique directivity of each character, a combination of characters itself, and the like. Particularly, in a case where the plurality of characters included in the test chart11are a sentence or the like and are a collection of character strings written in one direction for each line, the area SP is set to include a plurality of characters in the horizontal direction and the vertical direction. The reason is that in a case where the number of characters included in the horizontal direction or the vertical direction is small, the evaluation result is easily affected by the directivity or the like of each character. Consequently, in the evaluation image31, the area of the reference color is scattered, and the distribution of the evaluation is not understandable.

For example, in a case where the test chart11is a collection of characters horizontally written for each line, and the area SP has an oblong shape, a length Lv in the vertical direction of the area SP is preferably a length including at least four lines or more (four characters or more in the vertical direction) of characters as illustrated inFIG. 12and is particularly preferably a length including eight lines or more (eight characters or more in the vertical direction) of characters. In addition, a length Lh in the horizontal direction of the area SP is preferably a length including at least four or more characters and is particularly preferably a length including eight or more characters. Furthermore, as illustrated inFIG. 13, in a case where a pitch Lvp for scanning the area SP in the vertical direction and a pitch Lhp for scanning the area SP in the horizontal direction are set in the test chart image26, it is preferable that Lvp≤Lv and Lhp≤Lh are satisfied. That is, it is preferable to scan the test chart image26with an overlap of at least a part of the area SP in the vertical direction and the horizontal direction. Furthermore, it is particularly preferable that Lvp≤Lv/2 and Lhp≤Lh/2 are satisfied. That is, it is particularly preferable to scan the test chart image26with an overlap of at least a part of ½ or more of the area SP in the vertical direction and the horizontal direction.

In addition, in the first embodiment, the evaluation unit17obtains the evaluation at the evaluation position P0by cutting out the area SP including the evaluation position P0at its center from the test chart image26. However, depending on the position of the evaluation position P0in the test chart image26, the whole area SP may not be filled with the test chart image26. For example, as illustrated inFIG. 14, in a case where a corner of the test chart image26is set as the evaluation position P0, the test chart image26is included in a lower right area of approximately ¼ of the area SP, but the test chart image26cannot be included in the upper right, upper left, and lower left areas of the area SP. In such a case, as illustrated inFIG. 15, for example, the evaluation unit17fills the upper right, upper left, and lower left areas of the area SP with an image acquired by performing a mirror process on a part of the test chart image26included in the lower right area of the area SP. By doing so, even in a case where the test chart image26can be included in only a part of the area SP, the evaluation unit17can evaluate the evaluation position P0with the same accuracy as that in a case where the test chart image26is included in the whole area SP. While the area SP is filled using the mirror process inFIG. 15, the upper right, upper left, and lower left areas of the area SP may be filled by copying a part of the test chart image26included in the lower right area of the area SP and tiling the copied part.

In the first embodiment, the evaluation unit17obtains the resolution as the evaluation of the imaging unit12using the contrast method. The resolution may be calculated using a method such as the root mean square method or the derivation method. Besides, in a case where the evaluation unit17obtains the resolution as the evaluation, the evaluation unit17can execute character recognition on the image of the area SP cut out from the test chart image26using the OCR software and can use the result (such as % of characters recognized in the image) as the “resolution”. In addition, in a case where the number of characters in the test chart image26is small in the case of obtaining the resolution using the contrast method, the resolution Rpos at the evaluation position P0can be obtained using the maximum value of the pixel values instead of the average value Wave of the pixel values greater than or equal to the average value Aave and using the minimum value of the pixel values instead of the average value Bave of the pixel values less than or equal to the average value Aave.

Second Embodiment

In the first embodiment, the evaluation unit17obtains the resolution as the evaluation of the imaging unit12. The evaluation unit17can also obtain an evaluation related to performance other than the resolution. For example, instead of the resolution or in addition to the resolution, the evaluation unit17can obtain the sharpness, the axial chromatic aberration, the lateral chromatic aberration, or the like as the evaluation of the imaging unit12. Hereinafter, an example in which the evaluation unit17evaluates, as the evaluation of the imaging unit12, the chromatic aberration (that is, at least any of the axial chromatic aberration or the lateral chromatic aberration) that is one chromatic performance of the imaging lens13included in the imaging unit12will be described.

In a case where the evaluation unit17evaluates the imaging unit12with respect to the chromatic aberration, the evaluation unit17cuts out an area Eij (for example, i=1 to 5 and j=1 to 5) from the test chart image26as illustrated inFIG. 16. Each area Eij is a part of the test chart image26. In addition, in the present embodiment, all areas Eij have the same shape and the same size. For example, the shape of the area Eij is a quadrangle, and the size of the area Eij is such that the characters of the test chart image26can be visually read. In addition, in the case of obtaining the axial chromatic aberration, the area Eij includes at least an area (hereinafter, referred to as a center area) that includes the center of the test chart image26. InFIG. 14, the area E33is the center area. In addition, the adjacent areas Eij are equidistant from each other in the vertical direction and are equidistant from each other in the horizontal direction in the test chart image26.

As illustrated inFIG. 17, the image generation unit18generates a second test chart image201by linking each image of the area Eij (hereinafter, referred to as an Eij image; the same applies in the case of using a specific number as the suffix i or the suffix j) cut out from the test chart image26in the above manner by the evaluation unit17without changing its positional order. The second test chart image201is an image in which bleeding of color (hereinafter, referred to as color bleeding) caused by the chromatic aberration is set to be visually recognized more easily than that in the test chart image26. In addition, since the second test chart image201is generated using the area Eij of a part of the test chart image26, the second test chart image201is also a “test chart image”.

The evaluation unit17obtains the evaluation related to the chromatic aberration in the area Eij using each Eij image. In a case where the imaging unit12has the chromatic aberration, for example, blue color bleeding δBin the rightward direction and red color bleeding δRin the leftward direction appear in the E35image as illustrated inFIG. 18. The evaluation unit17obtains the blue color bleeding δBand the red color bleeding δRusing the E35image and generates a color bleeding image Δ35(refer toFIG. 19) that represents the directions and the magnitudes of the blue color bleeding δBand the red color bleeding δRin the area E35. The same applies to other areas Eij. The evaluation unit17generates each color bleeding image Δij from each Eij image.

As illustrated inFIG. 19, by lining up and linking the color bleeding image Δij extracted by the evaluation unit17in the same manner as the arrangement of the area Eij, the image generation unit18generates an evaluation image202in which color bleeding caused by the chromatic aberration at each position on the test chart image26is represented as an image. The evaluation image202represents the blue color bleeding δBin blue and represents the red color bleeding δRin red. Accordingly, in the evaluation image202, the blue color bleeding δBand the red color bleeding ≢7Rcaused by the lateral chromatic aberration of each area Eij can be seen. In addition, approximately purple color bleeding caused by the axial chromatic aberration can be seen in the center part.

As illustrated inFIG. 20, the display unit20displays the second test chart image201along with the evaluation image202. Thus, in the evaluation system10, visual sensory evaluation can be performed using the second test chart image201, and the evaluation of the evaluation system10with respect to the chromatic aberration can be found using the evaluation image202. A comparison between the sensory evaluation and the evaluation of the evaluation system10is easily made. Particularly, each position on the evaluation image202corresponds to each position on the second test chart image, and the evaluation image202represents the extent and the direction of color bleeding caused by the chromatic aberration with the color of the color bleeding. Thus, the actual evaluation is directly perceived more easily than that in the case of comparing the graph (a so-called aberration diagram) in the related art with the test chart image26.

In the second embodiment, the evaluation image202is generated and displayed. Instead of the evaluation image202or in addition to the evaluation image202, an evaluation image212illustrated inFIG. 21may be generated and displayed. The evaluation image212represents the blue color bleeding δBand the red color bleeding δRat each image height with a horizontal axis denoting an image height (mm) and a vertical axis denoting the pixel count of the color bleeding δ (the blue color bleeding δBand the red color bleeding δR). That is, the evaluation image212is an image that represents the magnitudes of the axial chromatic aberration and the lateral chromatic aberration with respect to the image height with a color. In the evaluation image212, for example, the blue color bleeding δBat each image height is represented in blue, and the red color bleeding δRat each image height is represented in red.

For example, an “axial” part of the evaluation image212can be generated using data that is extracted in the diagonal direction (a so-called tangential direction) of the color bleeding image Δ33. In the same manner, the parts of other image heights can be generated using data that is extracted in the diagonal direction from the color bleeding image Δij. However, in the second embodiment, the area Eij is not set in the parts of 20 percent of the image height, 40 percent of the image height, 60 percent of the image height, 80 percent of the image height, and 90 percent of the image height. Thus, in the case of generating and displaying the evaluation image212, at least the area Eij that includes the part of the corresponding image height needs to be set in advance.

While the evaluation image212that represents the color bleeding in the tangential direction is generated and displayed, an evaluation image222in which the evaluation image212is displayed in complementary colors may be generated and displayed as illustrated inFIG. 22. The evaluation image222displays a red chromatic aberration ARand a blue chromatic aberration AB. Thus, in the case of generating and displaying the evaluation image222, the optical performance of the imaging lens13can be more directly displayed than that with the color bleeding.

In the second embodiment, the evaluation unit17evaluates the imaging unit12with respect to the chromatic aberration. Evaluation can also be performed for other aberrations. In this case, a specific generation method (an extraction method for data related to the aberration) for the evaluation image needs to be changed depending on the target aberration. The rest is the same as the second embodiment.

In the first embodiment and the second embodiment, in a case where the image sensor14used in the imaging unit12is a color sensor, the test chart image26has a red channel (R channel), a green channel (G channel), and a blue channel (B channel). Thus, the evaluation unit17can perform the evaluation in the first embodiment or the second embodiment for each color channel. In addition, the evaluation unit17can convert a signal of each color channel of the test chart image26into a brightness signal and then, can perform the evaluation in the first embodiment or the second embodiment using the brightness signal. That is, the evaluation unit17can convert the test chart image26into a monochrome image and use the monochrome image for evaluation. For example, the brightness signal is calculated in accordance with “brightness signal=0.2×R channel+0.7 G channel+0.1 B channel”.

In the first embodiment and the second embodiment, the plurality of characters included in the test chart11are random. The plurality of characters included in the test chart11may have regularity such as periodicity in a case where the test chart11as a whole can be regarded as being random. For example, the test chart11can be formed by repeatedly lining up a character string “ABC . . . XYZ” in which alphabets are arranged in the alphabetical order (refer toFIG. 2). In a case where the plurality of characters included in the test chart11have regularity, the randomness of the test chart11as a whole can be improved by phase shifting. For example, as illustrated inFIG. 23, in the case of repeating the character string “ABC . . . XYZ”, the randomness of the whole test chart11is improved by setting different characters to be lined up at the left end of the test chart11by shifting the phase of the repetition of the character string.

In the first embodiment and the second embodiment, in a case where a distortion of the imaging lens13or a distortion in the test chart image26caused by the inclination or the like of installation of the test chart11and the imaging unit12is known in advance, the distortion in the test chart image26can be reduced by adjusting the arrangement of the plurality of characters (including the adjustment of the directions and the sizes of the characters) included in the test chart11. For example, in a case where the imaging lens13is a fisheye lens or the like, and it is known that a distortion having a barrel shape occurs in the test chart image26in the case of imaging the test chart11in which the plurality of characters are horizontally lined up as illustrated inFIG. 24, the distortion in the test chart image26can be reduced using a test chart311in which the arrangement of the plurality of characters is modulated into a pincushion shape as illustrated inFIG. 25.

In the first embodiment, the second embodiment, and the modification example, a general reflective chart or a transmissive chart can be used as the test chart11. Besides, the test chart11may be an image that is projected to a display device such as a liquid crystal display. In addition, the test chart11may be an image that is projected to a screen using a projection device such as a projector. In the case of using the display device or the projection device, the plurality of characters included in the test chart11are easily changed or adjusted. That is, in the case of using the display device or the projection device, the font, the size, the color, the direction, or the arrangement of the plurality of characters included in the test chart11or a combination or the like of the characters can be easily changed or adjusted. For example, the test chart11can be easily set as the test chart311. In addition, as illustrated inFIG. 26, in the case of using the test chart11that is projected to a screen334using a projection device333, the evaluation unit17can evaluate the performance of a projection lens335mounted in the projection device333in a case where the imaging unit12having known performance or the like of its each unit is used. An evaluation method or the like is the same as that in the first embodiment or the second embodiment.

EXPLANATION OF REFERENCES

10: evaluation system11,311: test chart12: imaging unit13: imaging lens14: image sensor15: analysis unit16: input unit17: evaluation unit18: image generation unit19: reference color setting unit20: display unit26: test chart image31,41,51,202,212,222: evaluation image32: color scale36: superimposition image42,52: gray scale201: second test chart image333: projection device334: screen335: projection lensSP: area cut out for evaluationLv: length in vertical direction of area SPLh: length in horizontal direction of area SPLvp: scanning pitch in vertical direction of area SPLhp: scanning pitch in horizontal direction of area SPEij (E11to E55), SP: areaP0: evaluation positionΔij (Δ11to Δ55): color bleeding imageδB: blue color bleedingδR: red color bleedingAB: blue chromatic aberrationAR: red chromatic aberration