JP2007281956A - Resolution evaluation device, resolution evaluation method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate resolution of an image forming apparatus in a short time by a simplified apparatus construction, without being influenced by characteristics of the image forming apparatus and an image reading apparatus. <P>SOLUTION: Image input means 13 inputs read image data obtained, by optically reading an image to be evaluated formed on a recording medium, based on original image data. Displacement calculation means 15 estimates displacement of distribution of pixel values of an image represented by the read image data, with respect to an image represented by the original image data. First correction means 16 corrects the read image data so as to eliminate the displacement. Evaluation value calculation means 17 estimates the evaluation value of the resolution of the image represented by the corrected read image data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for evaluating the resolving power of an image forming apparatus.

  As a method for evaluating the resolving power of the image forming apparatus, for example, a sample image having a sine wave pattern is formed on a recording medium such as paper by the image forming apparatus, and the sample image is read by an image reading apparatus (for example, a scanner). There is known a method for evaluating the resolving power by generating data and analyzing the MTF (Modulation Transfer Function) characteristic of the image represented by the image data. Also known is a method for evaluating the resolving power by analyzing CTF (Contrast Transfer Function) characteristics of a sample image of a rectangular wave pattern.

  However, the above-described prior art has a problem that the sample image is deteriorated due to interference between the sine wave or rectangular wave pattern and the screen of the image forming apparatus, and as a result, accurate evaluation cannot be performed. In order to avoid interference, a pattern having a cycle that is an integral multiple of the screen cycle may be used. In this way, since the interference between the pattern and the screen does not occur, accurate evaluation can be performed. However, in order to compare image forming apparatuses having different screen cycles, it is necessary to create a pattern in accordance with each screen cycle. Therefore, there is a problem that evaluation under the same conditions cannot be performed.

  In order to solve this problem, Patent Document 1 proposes a method for calculating the MTF characteristics of an image forming apparatus using sample images having different shades in a one-dimensional direction at random. According to this method, the resolving power can be evaluated without being affected by the screen period. However, the calculation results are actually affected by the screen and the image forming method for the following reasons.

FIG. 4 is an example of a sample image used in the technique of Patent Document 1. This image is an image in which the density in the x direction is randomly changed. A density distribution in the x direction of this image is obtained, and an evaluation value of resolving power is obtained based on this density distribution. This method is based on the premise that pixels having the same pixel value are output in the y direction perpendicular to the x direction. However, in the screening process performed by a normal image forming apparatus, the pixel values in the y direction vary. Since this variation is superimposed as noise, the high-frequency component in the density distribution in the x direction increases, and as a result, there is a problem that the evaluation value of the resolving power is calculated higher than the actual value. Further, the variation varies greatly depending on the image forming method. For example, when comparing an image of a small-diameter dot error diffusion screen used in an ink-jet printer with a density gradation image of a silver halide photographic printer, the ink-jet printer has a larger variation in pixel values in the y direction.
As a means for solving this problem, it is conceivable to use a sample image of a two-dimensional random pattern. However, when the method of Patent Document 1 is extended to two dimensions, there is a problem that the amount of calculation increases dramatically.

Furthermore, there is a problem caused by the image reading apparatus. That is, the image data generated by the image reading device is affected by characteristics inherent to the image reading device, for example, the resolution of the image reading device, so even if the same sample image is read, it is generated if the image reading device is different. Different image data will be used. With the technique of Patent Document 1, when the image reading apparatus is changed, evaluation under the same conditions as before the change cannot be performed.
Further, in the technique of Patent Document 1, since it is necessary to measure the density distribution of a two-dimensional random pattern with a high resolving power, an expensive measuring machine must be used as the image reading apparatus.
Japanese Patent Laid-Open No. 2001-074602

  The present invention has been made under the background described above, and evaluates the resolving power of an image forming apparatus in a short time with a simple apparatus configuration without being affected by the characteristics of the image forming apparatus and the image reading apparatus. The purpose is to provide technology that can be used.

  In order to solve the above-described problem, the present invention provides an image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data; A deviation calculating means for obtaining a deviation of a distribution of pixel values of an image represented by the read image data input by the image input means with respect to an image represented by the original image data, and a deviation obtained by the deviation calculating means. First correction means for correcting the read image data so as to eliminate, and evaluation value calculation means for obtaining an evaluation value of the resolving power of the image represented by the read image data corrected by the first correction means. A resolving power evaluation apparatus is provided.

  According to another aspect of the present invention, there is provided an image input step of inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data, and the image input step. A deviation calculating step for obtaining a deviation of a distribution of pixel values of an image represented by the read image data with respect to an image represented by the original image data, and the read image so as to eliminate the deviation obtained in the deviation calculating step. Resolving power evaluation comprising: a first correcting step for correcting data; and an evaluation value calculating step for obtaining an evaluation value of the resolving power of an image represented by the read image data corrected in the first correcting step. Also provided as a method.

  Further, the present invention provides an image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data, and the image input means. A deviation calculating means for obtaining a deviation of a distribution of pixel values of an image represented by inputted read image data with respect to an image represented by the original image data, and a deviation obtained by the deviation calculating means are eliminated. As a program for functioning as first correction means for correcting the read image data and evaluation value calculation means for obtaining an evaluation value of the resolution of the image represented by the read image data corrected by the first correction means. Is also provided.

  According to the image forming apparatus, the image forming method, or the program described above, the read image data is corrected so as to eliminate the deviation of the distribution of pixel values of the image represented by the read image data from the image represented by the original image data. Then, the evaluation value of the resolving power of the image represented by the corrected read image data is obtained.

  Further, the present invention provides an image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data, and input by the image input means. Evaluation value calculation means for obtaining an evaluation value of the resolving power of the image represented by the read image data, and an evaluation value obtained by the resolving power evaluation means as an evaluation value of the resolving power when the image to be evaluated is optically read. And a third correction unit for removing the resolution.

  According to another aspect of the present invention, there is provided an image input step of inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data, and the image input step. An evaluation value calculation step for obtaining an evaluation value of the resolving power of the image represented by the read image data, and an evaluation value obtained by the resolving power evaluation means is an evaluation value of the resolving power when the image to be evaluated is optically read. And a third correction step. The method is also provided as a resolving power evaluation method.

  Further, the present invention provides an image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data, and the image input means. Evaluation value calculation means for obtaining an evaluation value of the resolution of the image represented by the input read image data, and an evaluation value obtained by the resolution evaluation means for the resolution when the image to be evaluated is optically read. It is also provided as a program for functioning as third correcting means for dividing by the evaluation value.

  According to the above image forming apparatus, image forming method, or program, a value obtained by dividing the evaluation value of the resolution of the image represented by the read image data by the evaluation value of the resolution when the image to be evaluated is optically read is obtained. Desired.

  According to the present invention, the resolving power of an image forming apparatus can be evaluated in a short time with a simple apparatus configuration without being affected by the characteristics of the image forming apparatus and the image reading apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a hardware configuration of a resolving power evaluation apparatus 10 according to the present invention.
The storage unit 4 is a nonvolatile memory such as a hard disk device, and stores a program such as an OS (Operating System) and also stores data input from the outside. A CPU (Central Processing Unit) 1 controls the operation of each part of the resolving power evaluation apparatus 10 by executing a program stored in the storage unit 4. A ROM (Read Only Memory) 2 stores an IPL (Initial Program Loader). A RAM (Random Access Memory) 3 is used as a work area when the CPU 1 executes a program.

A communication interface (hereinafter referred to as communication I / F) 5 is connected to an external device via a communication line, and mediates communication between the resolution evaluation device 10 and the external device. In the present embodiment, the resolving power evaluation apparatus 10 is connected to the image forming apparatus 30 and the image reading apparatus 50.
The instruction input unit 6 includes a keyboard and a pointing device (for example, a mouse), and a user can input an instruction to the resolving power evaluation apparatus 10. The input instruction is sent to the CPU 1, and the CPU 1 controls the resolving power evaluation apparatus 10 according to the received instruction.
The display unit 7 is a liquid crystal panel, for example, and displays an image based on the image data.

FIG. 2 is a diagram illustrating functional blocks of the resolving power evaluation apparatus 10. It should be noted that the operation subject of each functional block of the resolution evaluation apparatus 10 is the CPU 1.
Specifically, the image storage unit 11 is the storage unit 4 and stores image data (hereinafter referred to as “original image data”) 12 representing an original image.
FIG. 3 is a diagram illustrating an example of an original image. The original image is composed of a resolution evaluation pattern 121 whose density changes randomly in a two-dimensional direction, and position recognition patterns 122 and 123 for recognizing an image position.

The image forming apparatus 30 is a target for resolution evaluation in the present embodiment. The image forming apparatus 30 is, for example, an electrophotographic printer. Based on the original image data transmitted from the resolving power evaluation apparatus 10, for example, cyan (C), magenta (M), yellow (Y), black (K 4), the evaluated image 40 is formed on the recording medium for each color. The image forming method of the image forming apparatus 30 is not limited to the electrophotographic method, and any method may be used.
The image reading device 50 is, for example, a flat bed scanner, irradiates light on a document placed on a platen glass, receives reflected light, and converts it into an electrical signal.

  Here, the image reading device 50 reads the image to be evaluated 40 by using complementary color filters for cyan, magenta, and yellow in order to improve the S / N ratio of the read result. That is, when the evaluated image 40 is a cyan image, it passes through a red filter. Similarly, when it is magenta, it passes through a green filter, and when it is yellow, it passes through a blue filter. The evaluated image 40 is read. In the case of black, the evaluated image 40 is read through a green filter having the highest correlation with the human visual sensitivity. Then, the image reading device 50 converts an electrical signal obtained by reading the image to be evaluated 40 into image data (hereinafter referred to as “read image data”). The generated read image data is transmitted to the resolution evaluation apparatus 10.

This read image data is affected by the characteristics of the image forming apparatus 30 and the image reading apparatus 50. As a result, the image quality of the image represented by the read image data (hereinafter referred to as “read image”) is deteriorated with respect to the original image.
Specifically, the degradation of image quality is caused by the following causes. For example, when the image is formed by the image forming apparatus 30, the read image may be formed so as to be shifted in the vertical direction or the horizontal direction with respect to the origin. Alternatively, the read image may be formed by being slightly reduced or enlarged with respect to the original image. Similar deterioration may occur when the image reading apparatus 50 reads the image. In addition, when the resolution of the image reading device 50 is inferior to the resolution of the image forming device 30, the read image is deteriorated with respect to the original image.
Such image degradation appears as a shift of the pixel value distribution of the read image from the original image. The resolving power evaluation apparatus 10 according to the present invention is configured to calculate the evaluation value of the resolving power after quantifying the shift of the distribution of pixel values by a method described later and correcting the shift. In the present embodiment, reflectance is used as the pixel value.

  The image input unit 13 inputs the read image data transmitted from the image reading device 50. Specifically, the read image data transmitted from the image reading device 50 is received via the communication I / F 5. The received read image data is stored in the storage unit 4.

The conversion unit 14 converts the original image data and the read image data into reflectance data. A conversion table is used for conversion. This conversion table is created in advance by the following method and stored in the storage unit 4.
First, patch data is input to the image forming apparatus 30 and an image (hereinafter referred to as “patch image”) is formed on a recording medium based on the patch data. This patch data is, for example, an image having a uniform density created for each of the 256 gradations. In the case of an image having a uniform density, it is considered virtually impossible that the formed image is deteriorated due to the influence of the characteristics of the image forming apparatus 30.

Next, the reflectance of the patch image is measured using a measuring instrument, and a conversion table is created by associating the obtained reflectance with the patch data for each gradation.
The conversion unit 14 converts the original image data 12 into two-dimensional reflectance data A (x, y) using the conversion table thus obtained. In other words, the reflectance data A (x, y) represents the reflectance obtained when the evaluated image 40 is formed and read without being affected by the characteristics of the image forming apparatus 30 and the image reading apparatus 50. Represents.
The conversion unit 14 converts the read image data into two-dimensional reflectance data B (x, y). Also in this conversion, the above conversion table is used.

The deviation calculation unit 15 obtains a deviation in the distribution of pixel values between the original image and the read image. In this embodiment, the reflectance is used as the pixel value, and the deviation of the reflectance distribution is obtained by the following procedure.
First, since the sizes of the original image and the read image may be different, trimming is performed so that both are the same size. Specifically, the read image is enlarged or reduced so that the position recognition patterns 122 or 123 shown in FIG.

C_POC(x,y)：位相限定相関法による２次元相関係数
ρ：２次元フーリエ変換
ρ^−１：２次元フーリエ逆変換
A(x,y)：原画像の反射率データ
B(x,y)：読取画像の反射率データ
となる。求められた２次元相関係数のピーク位置が原画像と読取画像との反射率分布のずれを表し、ピークの高さが２つの画像の類似度を表す。
位相限定相関法を用いて画像のずれを算出する利点は、算出されるピークが鋭いので、ノイズがあってもピーク位置を正確に求めることができ、さらに、画像の明るさの変化や、画像のぼけに対してロバストであるという点である。 Next, the deviation of the reflectance distribution between the original image and the read image is calculated using a known phase-only correlation method. The phase only correlation method is a method in which two images to be compared are developed in a two-dimensional Fourier space, and a correlation coefficient is obtained using phase spectrum information of each image. The correlation coefficient can be obtained by normalizing two Fourier transform images for each spectrum and then combining them and performing inverse Fourier transform. That is,

C _POC (x, y): Two-dimensional correlation coefficient ρ: Two-dimensional Fourier transform ρ ⁻¹ : Two-dimensional inverse Fourier transform
A (x, y): Reflectance data of the original image
B (x, y): Reflected image reflectance data. The obtained peak position of the two-dimensional correlation coefficient represents the difference in reflectance distribution between the original image and the read image, and the peak height represents the similarity between the two images.
The advantage of calculating the image shift using the phase-only correlation method is that the calculated peak is sharp, so that the peak position can be obtained accurately even if there is noise, and further, the change in the brightness of the image, Robust against blur.

  The first correction unit 16 corrects the deviation of the read image from the original image. Specifically, the read image is trimmed so as to eliminate the deviation of the reflectance distribution obtained by the deviation calculating means 15.

MTF(λ,δ)：読取画像の空間周波数特性
λ：ｘ方向の周波数
δ：ｙ方向の周波数
ρ：２次元フーリエ変換
A（x,y）原画像の反射率データ
B'（x,y）：ずれ補正後の読取画像の反射率データ
である。
ここで、原画像のフーリエ変換画像は、ずれ算出手段１５で既に求められているので新たに算出する必要はなく、全体の演算時間を短縮できる。 The evaluation value calculation unit 17 obtains a two-dimensional spatial frequency characteristic of the read image as a resolution evaluation value of the image forming apparatus 30. Specifically, Fourier transformation is performed on the read image whose deviation is corrected, and an energy ratio with the original image is obtained. That is,

MTF (λ, δ): Spatial frequency characteristics of the read image λ: Frequency in the x direction δ: Frequency in the y direction ρ: Two-dimensional Fourier transform
A (x, y) original image reflectance data
B ′ (x, y): Reflectance data of the read image after deviation correction.
Here, since the Fourier transform image of the original image has already been obtained by the deviation calculating means 15, it is not necessary to newly calculate it, and the entire calculation time can be shortened.

The second correction unit 18 corrects the evaluation value obtained by the evaluation value calculation unit 17 using the resolution evaluation value of the image reading device 50. The resolving power evaluation value of the image reading device 50 is obtained in advance as a two-dimensional spatial frequency characteristic for each color channel, and is stored in the reading resolving power storage unit 19, that is, the storage unit 4.
Here, an example of a method for calculating the resolution evaluation value of the image reading apparatus 50 will be described. In this method, first, a highly accurate measurement sample of the above-described two-dimensional random pattern is prepared. In order to create this measurement sample, there is a method using a highly accurate image forming apparatus. In this case, the image forming apparatus is preferably an apparatus capable of reproducing not only the fine spatial resolution capability that can be reproduced but also high density.

  Moreover, as a method for creating a highly accurate measurement sample, it was prepared by etching treatment (after depositing a metal thin film such as chromium on the glass substrate, and then forming a desired pattern by photolithography and etching). A sample may be used. Moreover, you may use what formed the image in the photosensitive material for photosetting using an image setter as a sample for a measurement.

MTF_{IIT_N}(λ,δ)：画像読取装置５０のＮ色センサの空間周波数特性、ＮはＲ，Ｇ，Ｂのいずれか
λ：ｘ方向の周波数
δ：ｙ方向の周波数
ρ：２次元フーリエ変換
Rf(x,y)：測定用サンプルの画像データ
Rf_N'(x,y)：測定用サンプルをＮ色センサで読み取った画像データ（位置補正後）
となる。
上記の手順は、既に説明した変換手段１４、ずれ算出手段１５、第１の補正手段１６、評価値算出手段１７による一連の処理と同様であるから、効率的に処理を行うことができる。 The measurement sample created as described above is read by each of the R, G, and B channels of the image reading device 50, converted into reflectance, and developed into a frequency space. Also, the image data of the measurement sample is converted into reflectance and developed in the frequency space. Then, a shift between the two images is obtained by the phase-only correlation method, and the shift is corrected. Then, the energy ratio on the frequency space is obtained. In this manner, the spatial frequency characteristic that is a two-dimensional resolution evaluation value of the image reading apparatus 50 can be obtained. That is,

MTF _{IIT_N} (λ, δ): Spatial frequency characteristics of the N color sensor of the image reading device 50, N is one of R, G, and B λ: frequency in the x direction δ: frequency in the y direction ρ: two-dimensional Fourier transform
Rf (x, y): Image data of measurement sample
Rf _N '(x, y): Image data obtained by reading a measurement sample with an N-color sensor (after position correction)
It becomes.
The above-described procedure is the same as the series of processes performed by the conversion unit 14, the deviation calculation unit 15, the first correction unit 16, and the evaluation value calculation unit 17 described above, so that the process can be performed efficiently.

  Using the resolution evaluation value of the image reading device 50 obtained as described above, the second correction unit 18 corrects the resolution evaluation value obtained by the evaluation value calculation unit 17. The read image is an image obtained by forming the evaluation image 40 based on the original image data by the image forming apparatus 30 and reading the evaluation image 40 by the image reading apparatus 50. Therefore, the spatial frequency characteristic of the read image is the product of the spatial frequency characteristic of the image forming apparatus 30 and the spatial frequency characteristic of the image reading apparatus 50. Therefore, in order to obtain the spatial frequency characteristics of the image forming apparatus 30, the spatial frequency characteristics of the read image may be divided by the spatial frequency characteristics of the image reading apparatus 50.

MTF_IOT(λ,δ)：画像形成装置３０の空間周波数特性
MTF(λ,δ)：読取画像の空間周波数特性
MTF_{IIT_N}(λ,δ)：画像読取装置５０のＮ色センサの空間周波数特性、ＮはＲ，Ｇ，Ｂのいずれか
λ：ｘ方向の周波数
δ：ｙ方向の周波数 Therefore, the second correcting unit 18 reads the spatial frequency characteristic of the image reading device 50 from the storage unit 4 and divides the spatial frequency characteristic obtained by the evaluation value calculating unit 17 by the spatial frequency characteristic of the image reading device 50. That is,

MTF _IOT (λ, δ): Spatial frequency characteristics of the image forming apparatus 30
MTF (λ, δ): Spatial frequency characteristics of scanned image
MTF _{IIT_N} (λ, δ): Spatial frequency characteristics of the N color sensor of the image reading apparatus 50, N is one of R, G, and B λ: Frequency in the x direction δ: Frequency in the y direction

Heretofore, the functional blocks of the resolution evaluation device 10 have been described.
According to the present invention, the resolving power of the image forming apparatus 30 can be accurately evaluated without being affected by the image shift due to the characteristics of the image forming apparatus 30 or the resolving power of the image reading apparatus 50. In addition, since the increase in the amount of calculation can be suppressed as compared with the case where the conventional technique is extended to two dimensions, the evaluation value can be obtained in a short time. Further, since the influence of the image reading device 50 is corrected, it is not necessary to use an expensive image reading device, and the resolution can be evaluated with a simple device configuration.

<Modification>
The present invention is not limited to the form described above, and can be implemented in various forms. For example, the embodiment described above can be modified as follows.

  In the above-described embodiment, the MTF that is the spatial frequency characteristic for the sine wave pattern is used as the evaluation value of the resolving power. However, the CTF that is the spatial frequency characteristic for the rectangular wave pattern may be used.

In the above-described embodiment, the image forming apparatus 30 and the image reading apparatus 50 are separated, but the present invention is not limited to this. For example, when the present invention is applied to a copying machine, the same processing can be performed using a scanner incorporated in the copying machine as an image reading apparatus.
Further, the resolution evaluation device 10 and the image reading device 50 may be integrated.
The image reading device 30 may be a scanning densitometer, a CCD (Charge Coupled Device) camera, or the like. A color sensor may be incorporated in the image forming apparatus and used as the image reading apparatus 30.

As a method for calculating the evaluation value in the evaluation value calculation unit 17, the following method may be used. For example, the MTF obtained by the method shown in the above-described embodiment is converted into a complex format, and then inverse Fourier transform is performed to obtain a line spread function LSF (Line Spread Function) of the read image, which is approximated to obtain a resolution. It is also possible to obtain the pixel size as the evaluation value. This makes it possible to obtain an evaluation value of resolving power that is in good agreement with the subjective evaluation.
It is also possible to calculate the evaluation value of the resolving power by calculating the frequency λ at which MTF = 0.5 using the MTF obtained by the method shown in the above-described embodiment. This makes it possible to obtain an evaluation value of resolving power that is in good agreement with the subjective evaluation.

  In the above-described embodiment, the original image data and the read image data are converted into reflectance, and the deviation is calculated using the reflectance. However, the present invention is not limited to the reflectance. For example, it may be converted into density, brightness, brightness, and the like.

It is a figure which shows the hardware constitutions of the resolution evaluation apparatus 10 which concerns on this invention. FIG. 3 is a diagram showing functional blocks of the resolution evaluation device 10. It is a figure which shows the example of the original image used for resolution evaluation. It is an example of the sample image used with the technique of patent document 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Resolving power evaluation apparatus, 1 ... CPU, 2 ... ROM, 3 ... RAM, 4 ... Memory | storage part, 5 ... Communication interface, 6 ... Instruction input part, 7 ... Display part, 30 ... Image forming apparatus, 40 ... Evaluated image , 50 ... image reading device, 11 ... image storage means, 12 ... original image data, 13 ... image input means, 14 ... conversion means, 15 ... deviation calculation means, 16 ... first correction means, 17 ... evaluation value calculation means , 18 ... second correcting means, 19 ... reading resolution storing means.

Claims (10)

Image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
A deviation calculating means for obtaining a deviation in distribution of pixel values of an image represented by the read image data input by the image input means with respect to an image represented by the original image data;
First correction means for correcting the read image data so as to eliminate the deviation obtained by the deviation calculation means;
An evaluation value calculating means for obtaining an evaluation value of the resolution of an image represented by the read image data corrected by the first correction means.   2. The correction unit according to claim 1, further comprising a second correction unit that divides the evaluation value obtained by the evaluation value evaluation unit by an evaluation value of resolving power when the image to be evaluated is optically read. Resolution evaluation device. Image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
Evaluation value calculation means for obtaining an evaluation value of the resolving power of the image represented by the read image data input by the image input means;
And a third correction unit that divides the evaluation value obtained by the resolution evaluation unit by the evaluation value of the resolution when the image to be evaluated is optically read. The evaluation value obtained by the evaluation value calculating means is a spatial frequency characteristic of the resolving power of the image represented by the read image data input by the image input means,
The resolution evaluation apparatus according to claim 1, wherein the evaluation value of the resolution when the image to be evaluated is optically read is a spatial frequency characteristic.   The resolution evaluation apparatus according to claim 1, wherein the original image data represents an image having a two-dimensional random density distribution.   The resolving power evaluation apparatus according to claim 5, wherein the deviation calculating unit obtains a deviation by a phase-only correlation method. An image input step of inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
A deviation calculating step for obtaining a deviation in distribution of pixel values of an image represented by the read image data input in the image input step with respect to an image represented by the original image data;
A first correction step of correcting the read image data so as to eliminate the shift obtained in the shift calculation step;
An evaluation value calculating step for obtaining an evaluation value of the resolution of an image represented by the read image data corrected in the first correction step. An image input step of inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
An evaluation value calculating step for obtaining an evaluation value of the resolving power of the image represented by the read image data input in the image input step;
And a third correction step of dividing the evaluation value obtained by the resolution evaluation means by the evaluation value of the resolution when the image to be evaluated is optically read. Computer
Image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
A deviation calculating means for obtaining a deviation of a distribution of pixel values of an image represented by the read image data input by the image input means with respect to an image represented by the original image data;
First correction means for correcting the read image data so as to eliminate the deviation obtained by the deviation calculation means;
A program for functioning as an evaluation value calculation means for obtaining an evaluation value of a resolution of an image represented by read image data corrected by the first correction means. Computer
Image input means for inputting read image data obtained by optically reading an image to be evaluated formed on a recording medium based on original image data;
Evaluation value calculation means for obtaining an evaluation value of the resolving power of the image represented by the read image data input by the image input means;
A program for causing the evaluation value obtained by the resolution evaluation means to function as third correction means for dividing the evaluation value by the resolution evaluation value when the image to be evaluated is optically read.

Images