JP2003298861A - Method and device for image evaluation, image evaluating program, recording medium, screen arrangement, method and device for image processing, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for image evaluation and an image evaluating program, which automatically evaluate moire. <P>SOLUTION: In the image evaluation device which evaluates an image outputted from an image output device which reproduces an image by representing the gradation of each element color with a plurality of dots, a plurality spectrum data are generated for each element color by a spectrum generation part 104 and a spectrum operation part 106 on the basis of data caused by a density of input data, a screen angle, and positional relations between centroids of dots of respective screens. The plurality of spectrum data generated for each element color are composed by a convolution execution part 108, and a density constitution ratio of each element color or an image corresponding to the density itself is evaluated on the basis of the composed spectrum data by an evaluation value operation part 116. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image evaluation of color electrophotography in which an image is reproduced by using toners of a plurality of colors such as a color printer and a color copy, and more particularly, moire caused by a shift of halftone dots of a plurality of colors. The present invention relates to an image evaluation method, an image evaluation device, an image evaluation program, a recording medium recording the image evaluation program and a screen arrangement, an image processing method, a device, a program, and a recording medium for reducing stripes and reproducing a high-quality image.

[0002]

2. Description of the Related Art Color image output devices such as color printers and color copiers reproduce color images using cyan, magenta, yellow and black inks. In particular, a page printer that forms a latent image on a photosensitive drum by using a laser printer among color printers, develops the latent image with charged toner, and transfers the developed toner to a transfer sheet is irradiated with a laser beam. Regions can be variously changed within dots, and color image data with higher resolution and higher gradation can be reproduced even if the number of dots per unit area is small. In a color laser printer, as a binarization method for gradation reproduction of a grayscale image,
The dither method is widely used. According to this dither method, with respect to gradation data of each color which is an input signal, a conversion table called a dither matrix or a threshold matrix having correspondence between gradation data and image reproduction information is referred to The presence / absence (1,0) of the dot display is determined. Then, a halftone dot is formed depending on the presence or absence of display of a plurality of adjacent dots, and the halftone of the grayscale image is reproduced according to the size of the halftone dot.

An unavoidable problem in such a color laser printer is the displacement of the halftone dots of each color. Such positional displacement cannot be avoided even if an industrial printing apparatus is used, but in the case of a color image output apparatus, it mainly occurs in the sub-scanning direction due to uneven rotation (jitter) of the photosensitive drum, for example. Such a positional shift causes a change in brightness or, in the worst case, a color shift that deviates from a desired color. Therefore, in order to prevent such color misregistration, screen angles of halftone dots are dispersed for each color.

[0004]

However, if the screen angles of the halftone dots are shifted in order to prevent color misregistration as described above,
It is known that so-called moire fringes occur.
Currently, the evaluation of whether such moire is occurring is
A screen designer for a color laser printer sets the screen conditions by himself and then repeatedly prints a sample to evaluate the presence or absence of moire. However, such a work requires a considerable amount of work time for the screen designer and is a considerable burden.

The present invention has been made in order to solve the above problems, and suppresses the generation of moire, an image evaluation method, an image evaluation device, and an image evaluation program capable of automatically evaluating the presence or absence of moire. An object is to provide a screen layout, an image processing method, a device, a program, and a recording medium.

[0006]

In view of the above problems, the invention according to claim 1 reproduces an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots. An image evaluation method for evaluating an image output by a plurality of spectra based on the positional relationship between the data resulting from the density of input data, the screen angle, and the center of gravity of the halftone dots of each screen for each element color. A spectrum data generating step of generating data, a spectrum data combining step of combining a plurality of spectrum data generated for each element color, and an image corresponding to the density composition ratio of each element color based on the combined spectrum data And an image evaluation step for evaluating.

According to an image evaluation method for evaluating an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed by a plurality of dots configured as described above. For example, first, in the spectrum data generation step, a plurality of spectrum data is generated for each element color based on the data resulting from the density of the input data, the screen angle, and the positional relationship between the center of gravity of the halftone dots of each screen. . Then, the spectral data synthesizing step synthesizes a plurality of spectral data generated for each element color, and the image evaluation step evaluates the image corresponding to the density composition ratio of each element color based on the synthesized spectral data. To be done.

In view of the above-mentioned problems, the invention according to claim 2 provides an image output by an image output device which reproduces the image by expressing the gradation for each element color by the halftone dots formed by a plurality of dots. An image evaluation method for evaluation, which is, for each element color, spectral data for generating a plurality of spectral data based on the positional relationship between the data resulting from the density of input data, the screen angle and the center of gravity of the halftone dots of each screen. A generation step, a spectrum data combination step of combining a plurality of spectrum data generated for each element color, and an image evaluation step of evaluating an image corresponding to the density of each element color based on the combined spectrum data. Configured to have.

In view of the above problems, the invention described in claim 3 is the invention described in claim 1 or 2, wherein the center of gravity position of the halftone dot of the screen in the spectrum data generated in the spectrum data generating step is determined. It is configured to obtain the optimum position of the center of gravity of the halftone dots on the screen by changing the screen.

In view of the above problems, the invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the screen shape is based on the spectrum data generated in the spectrum data generating step. Is further configured to be deformed according to a predetermined rule.

In view of the above problems, the invention according to a fifth aspect provides an image output by an image output device that reproduces an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots. An image evaluation device for evaluating, for each element color, spectrum data for generating a plurality of spectrum data based on the data resulting from the density of input data, the screen angle and the positional relationship between the centers of gravity of the halftone dots of each screen Generating means, spectrum data synthesizing means for synthesizing a plurality of spectrum data generated for each element color, and image evaluation means for evaluating an image corresponding to a density composition ratio of each element color based on the synthesized spectrum data. And are provided.

In view of the above-mentioned problems, the invention according to claim 6 provides an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed by a plurality of dots. An image evaluation device for evaluating, for each element color, spectrum data for generating a plurality of spectrum data based on the data resulting from the density of input data, the screen angle and the positional relationship between the centers of gravity of the halftone dots of each screen The generating means, the spectrum data synthesizing means for synthesizing the plurality of spectrum data generated for each element color, and the image evaluation means for evaluating the image corresponding to the density of each element color based on the synthesized spectrum data. Configured to have.

In view of the above-mentioned problems, the invention according to claim 7 represents an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed by a plurality of dots. A program for causing a computer to perform image evaluation processing to be evaluated, for each element color,
Spectral data generation processing that generates multiple spectrum data based on the positional relationship between the data due to the density of the input data, the screen angle, and the center of gravity of the halftone dots on each screen, and the multiple spectra generated for each element color It is a program for causing a computer to execute a spectrum data combination process for combining data and an image evaluation process for evaluating an image corresponding to a density composition ratio of each element color based on the combined spectrum data.

In view of the above-mentioned problems, the invention according to claim 8 represents an image output by an image output device which reproduces an image by expressing a gradation for each element color by halftone dots formed by a plurality of dots. A program for causing a computer to perform image evaluation processing to be evaluated, for each element color,
Spectral data generation processing that generates multiple spectrum data based on the positional relationship between the data due to the density of the input data, the screen angle, and the center of gravity of the halftone dots on each screen, and the multiple spectra generated for each element color It is a program for causing a computer to execute a spectrum data combination process for combining data and an image evaluation process for evaluating an image corresponding to the density of each element color based on the combined spectrum data.

In view of the above problems, the invention described in claim 9 is a computer-readable recording medium in which the program according to claim 7 or 8 is recorded.

In view of the above-mentioned problems, the invention according to a tenth aspect is such that each element color of each element color obtained based on a combination of spectrum data of two or more screens arbitrarily selected from a plurality of screens. According to the evaluation value corresponding to the density composition ratio, the positional relationship of the centers of gravity of the halftone dots is the screen layout determined corresponding to the density composition ratio of each element color.

In view of the above problems, the invention according to claim 11 is one in which each element color of each element color obtained based on a combination of spectrum data of two or more screens arbitrarily selected from a plurality of screens is selected. According to the evaluation value corresponding to the density, the positional relationship of the center of gravity of the halftone dots is the screen layout determined corresponding to the density of each element color.

In view of the above problems, the invention according to claim 12 is the invention according to claim 10 or 11, wherein the positional relationship of the centers of gravity of the halftone dots is based on the position of the center of gravity of the halftone dots of a predetermined screen. It is configured such that the center of gravity of the halftone dots of another screen is located at a position moved by an integral multiple of 0.5 pixels in the scanning direction and an integral multiple of 1.0 pixels in the sub-scanning direction.

In view of the above-mentioned problems, the invention described in claim 13 is the invention described in claim 10 or 11, wherein the spectrum data has a circular halftone dot shape and a luminance value of 1.
0 and the luminance value of the halftone dot area is 0.0.

In view of the above problems, the invention of claim 14 is the invention of claim 10 or 11, wherein the evaluation value is 2 arbitrarily selected from a plurality of screens.
To combine the spectral data of the two screens,
It is configured to be obtained based on a product of the visual frequency characteristic functions that are not attenuated in the low frequency part.

In view of the above problems, the invention according to claim 15 is the invention according to claim 10 or 11, wherein the positional relationship of the centers of gravity of the halftone dots is determined so that the evaluation value is minimized. Is composed of.

In view of the above-mentioned problems, the invention described in claim 16 relates to the step of recording the screen arrangement according to claim 10 and the screen arrangement corresponding to the density composition ratio of each element color of the target pixel of the input image. And a step of selecting.

In view of the above problems, the invention according to claim 17 corresponds to the step of recording the screen arrangement according to claim 10 and the density composition ratio of each element color in the peripheral region of the target pixel of the input image. And a step of selecting a screen arrangement.

In view of the above problems, the invention described in claim 18 selects the screen layout according to the step of recording the screen layout described in claim 11 and the density of each element color of the target pixel of the input image. And a step of performing.

In view of the above problems, the invention described in claim 19 is the step of recording the screen arrangement according to claim 11, and the screen arrangement corresponding to the density of each element color in the target pixel peripheral region of the input image. And a step of selecting.

In view of the above-mentioned problems, the invention described in claim 20 is a means for recording the screen arrangement according to claim 10, and the screen arrangement corresponding to the density composition ratio of each element color of the target pixel of the input image. And means for selecting.

In view of the above problems, the invention according to claim 21 corresponds to the means for recording the screen arrangement according to claim 10 and the density composition ratio of each element color in the peripheral region of the target pixel of the input image. And means for selecting a screen arrangement.

In view of the above problems, the invention described in claim 22 selects the screen layout according to the means for recording the screen layout according to claim 11 and the density of each element color of the target pixel of the input image. And means for doing so.

In view of the above-mentioned problems, the invention described in claim 23 is a means for recording the screen arrangement according to claim 11, and the screen arrangement corresponding to the density of each element color in the peripheral region of the target pixel of the input image. And means for selecting.

In view of the above-mentioned problems, the invention described in claim 24 relates to the process of recording the screen arrangement according to claim 10 and the screen arrangement corresponding to the density composition ratio of each element color of the target pixel of the input image. Is a program for causing a computer to execute the process of selecting.

In view of the above problems, the invention described in claim 25 corresponds to the processing for recording the screen arrangement according to claim 10 and the density composition ratio of each element color in the peripheral region of the target pixel of the input image. It is a program for causing a computer to execute a process of selecting a screen layout.

In view of the above-mentioned problems, the invention described in claim 26 selects the screen layout according to the process of recording the screen layout described in claim 11 and the density of each element color of the pixel of interest of the input image. Is a program for causing a computer to execute the processing.

In view of the above problems, the invention according to claim 27 is such that the screen layout according to claim 11 is recorded and the screen layout is associated with the density of each element color in the peripheral region of the target pixel of the input image. Is a program for causing a computer to execute the process of selecting.

In view of the above problems, the invention according to claim 28 is a computer-readable recording medium in which the program according to any one of claims 24 to 27 is recorded.

[0035]

1 is a block diagram of an image output system according to a preferred embodiment of the present invention. In this example,
In the host computer 50, image data 56 consisting of RGB gradation data (8 bits for each, a total of 24 bits) is generated and given to an image output device 60 such as a page printer. The image output device 60 such as a page printer reproduces a color image based on the supplied image data 56. The image output device 60 includes a controller 62 that performs image processing and supplies laser driving data 69 to the engine 70, and an engine 70 that reproduces an image in accordance with the driving data 69.

The host computer 50 is an application program 5 such as a word processor and a graphic tool.
2, character data, graphic data, bitmap data, etc. are generated. The respective data generated by these application programs 52 are rasterized by the driver 54 for the image output device installed in the host computer 50, and the image data 56 consisting of gradation data of each RGB color for each pixel or dot. Is converted to.

The image output device 60 also includes a microprocessor (not shown), and the color conversion unit 64, according to the microprocessor and the installed control program.
A controller 62 including a halftone processing unit 66, a pulse width modulation unit 68, etc. is configured. Also, the engine 7
The laser driver 72 in 0 drives the laser diode 74 for image drawing based on the driving data 69.
The engine 70 includes a photosensitive drum, a transfer belt and the like, and a drive unit thereof, but they are omitted in FIG.

The color conversion section 64 in the controller 62 converts the supplied RGB gradation data 56 for each dot into gradation data 10 of C (cyan) M (magenta) Y (yellow) K (black). To do. CMYK gradation data 10
Is 8-bit gradation data for each color, and the maximum is 256.
Has gradation. Note that the color conversion unit 64 uses RGB for each dot.
The gradation data 56 is converted into the gradation data 10 for each dot of each plane of CMYK. Therefore, the halftone processing unit 66 is supplied with the gradation data 10 (see the input data 10 in FIG. 2) corresponding to the dots for each plane of each color.

The halftone processing unit 66 refers to the conversion table having the correspondence between the gradation data created in advance and the image reproduction information for the gradation data 10 for each dot,
Image reproduction data 30 for each dot is generated. The halftone processing unit 66 uses the dither method described below with reference to FIGS. 2 to 5 to generate the image reproduction data 30 representing halftone. For example, by using the conversion table including the threshold matrix 20 shown in FIG. 2, binary image reproduction data 30 can be generated for each dot.

FIG. 2 is a diagram for explaining a binarization method for tone reproduction of a grayscale image by the dither method. Image data is generated by an image generation program such as a host computer and supplied as input data to an image processing unit for image output. The input image data is, for example, gradation data 10 for each color dot. In FIG. 2, gradation data is written in each dot. According to the dither method, the conversion table 2 called a threshold matrix in which the threshold value of each dot is changed according to a predetermined rule is applied to the gradation data.
0 is used. More specifically, the gradation data of each dot is compared with the threshold value of the threshold matrix, and if the gradation data is equal to or more than the threshold value of the corresponding dot, the image reproduction data 30 with drawing is generated, and if it is smaller, the image reproduction data 30 is drawn. The image reproduction data 30 of none is generated. That is, the multi-gradation data 10 for each dot is converted into the binary image reproduction data 30 for each dot.

The threshold matrix shown in FIG. 2 is a conversion table having correspondence between gradation data and image reproduction information indicating the presence or absence of drawing. That is, the threshold value of each dot in the conversion table can be referred to as image reproduction information indicating whether or not the gradation data should be drawn. The threshold value matrix 20 shown in FIG. 2 is a 4 × 4 matrix, which is a so-called dot concentration type in which the central portion is low and the peripheral portion is high.

FIG. 3 is a diagram for explaining the threshold matrix of the dither method. FIG. 3 shows an image reproduced for each gradation when the dot concentration type threshold matrix 20 of FIG. 2 is used. The images that can be reproduced when the gradation increases in order from the upper left to the right and from the lower left to the right are shown. That is, it is understood that the halftone dots grow from the center of the 4 × 4 halftone dot cell. It is known that the dot concentration type threshold matrix is superior to the dot dispersion type when the dot density becomes high to some extent.

FIG. 4 is a diagram showing changes in the shape of halftone dots formed by using the dither method. By using the conversion table composed of the dot concentration type threshold matrix shown in FIGS. 2 and 3, the dots in the halftone dot cells formed by m × m become gradually thicker according to the gradation degree (brightness). It is understood that it will grow. The gradation of the grayscale image is expressed by this two-dimensional density.

As shown in the example of the halftone dot in the middle of FIG. 4 (halftone dot in the middle portion), the growing direction of the halftone dot is set to the vertical direction and the horizontal direction in this example. The arrangement of the threshold matrix or the arrangement of thresholds in the matrix determines the growth direction of this halftone dot. Therefore, in the example of FIG. 4, the screen angle is 0 ° or 90 °.

FIG. 5 is a diagram showing a method of forming a screen angle. As shown in FIG. 5, halftone dots having a predetermined screen angle can be formed by appropriately arranging halftone dot cells 40 composed of m × m dots so as to be arranged.
In the example of FIG. 5, the m × m halftone dot cell is 4 on the right (N in the drawing).
When they are moved, they are placed one above the other, so they are placed at a: b = 4: 1. Therefore, the screen angle θ is θ = tan ⁻¹ (b / a) = tan ⁻¹ (1 /
4).

Here, the size N of the square threshold matrix 42 corresponding to one halftone dot period is N = LCM (a, b) × (b / a + a / b). However, LCM means the least common multiple.

The arrangement of the halftone dot cells 40 can be arbitrarily set by shifting the correspondence between the dots of the input data 10 and the threshold matrix 20. Alternatively, the screen angle can also be set by preparing in advance different threshold matrices for the square threshold matrix size and comparing the threshold matrix for the square threshold matrix 42 size with the input data.

As described with reference to FIG. 5, the screen angle of each color can be appropriately set by setting the arrangement of the threshold matrix 20 which is the conversion table. When the binary image reproduction data 30 is generated, the pulse modulation unit 68 generates drive data 69 with and without a laser drive pulse for each dot. The positional relationship of the preferable dot center of gravity of each screen corresponding to the density composition ratio or the density of each element color is evaluated by the image evaluation apparatus 100 described below with reference to FIG. In addition, the positional relationship of the halftone dot center of gravity of each suitable screen evaluated by the image evaluation apparatus 100 is as follows.
It is realized by. It is preferable that the evaluation by the image evaluation apparatus 100 is performed at the designing stage, and the positional relationship of the dot center of gravity is realized by the image setting apparatus 300 at the time of printing. The image evaluation apparatus 100 and the image setting apparatus 300 are configured by executing the image evaluation processing program by the host computer 50. This image evaluation processing program is normally in a form readable by the host computer 50, such as a floppy (registered trademark) disk or CD-ROM.
It is recorded on a recording medium such as and distributed. The program is read by a media reading device (CD-ROM drive, floppy disk drive, etc.) and installed in the hard disk. Then, the CPU is configured to read out a desired program from the hard disk as appropriate and execute a desired process.

FIG. 6 shows a block diagram of an image evaluation apparatus according to an embodiment of the present invention.

The image evaluation apparatus 100 includes an input unit 102 for inputting a screen basic condition; a spectrum generation for generating a predetermined spectrum based on the input screen condition and the set shift amount of the dot center of gravity. A unit 104; a spectrum calculation unit 106 that performs a predetermined calculation on the frequency components of the generated basic spectrum; a convolution execution unit 108 that performs a convolution calculation on the frequency spectrum of each screen; and a convolution calculation An evaluation value calculation unit 116 for outputting an evaluation value corresponding to a combination of dot center of gravity of each screen based on the operation result and the visual frequency characteristic (VTF) function; An optimum shift amount determination unit 118 that determines a combination; and an evaluation target screen that sets a screen to be evaluated. Configured with a; lean setting portion 122; a shift amount setting section 124 for setting a shift amount of the halftone dot centroid.

Next, the operation of the image evaluation apparatus 100 will be described.

First, in the input unit 102, basic screen conditions (screen halftone dot spacing, halftone dot size (diameter), pitch, angle) are input for the number of screens.
In this embodiment, the halftone dot shape is only circular.
Therefore, the dot size can be specified by the diameter. The pitch and angle of the screen will be described with reference to FIG. The halftone dot 102a is a halftone dot on the screen of one color (for example, cyan) of CMYK. Screen halftone dot 102a
Are arranged in a parallelogram shape, θ corresponds to an angle, and P1 and P2, which are intervals between opposing sides of the parallelogram, correspond to a pitch.

The evaluation target screen setting unit 122 sets the screen input to the input unit 102. here,
Set the screen as C, M and Y, and set the screen
The settings of C, M and K will be made.

The shift amount setting unit 124 sets the shift amount of the barycentric position of the screen halftone dot (for example, the start position of the screen located at the upper left of the screen). The shift amount is set in the spectrum generation unit 104.
The shift amount is determined for each screen, for example, in pixels from the original position of the halftone dot in the x direction and the y direction. There is a predetermined range for the shift amount (eg, x direction: 0 to 1, y direction: 1 to 3). Details of the shift amount will be described together with the description of the spectrum generation unit 104.

FIG. 8 shows the processing of the evaluation target screen setting unit 122 and the shift amount setting unit 124. First, the evaluation target screen setting unit 122 sets a screen to be evaluated in the input unit 102 (step 262).
Then, the shift amount setting unit 124 sets the shift amount for each screen in the spectrum generation unit 104 (step 264). Then, after all the combinations of shift amounts for each screen have been set (step 2
66, Yes), and it is determined whether the evaluation target screen setting unit 122 has completed the setting of all the evaluation target screens for the input unit 102 (step 268). If not completed (step 268, No), the process returns to the screen setting (step 262), and if completed (step 268, Yes), the process ends.

For example, suppose that there are two types of settings for the screen to be evaluated: setting the screen to C, M and Y and setting the screen to C, M and K. Further, it is assumed that there are three types of candidates for the shift amount of the halftone dot for C, M, Y and K on the screen. Then, the evaluation target screen setting unit 122 sets the screen to C, M and Y (step 262), and the shift amount setting unit 124 sets the shift amount of the halftone dot for each screen (C, M and Y). (Step 264). Since there are 3 × 3 × 3 = 27 combinations of shift amounts for each screen, if all shift amount combinations have been set (step 26
6, Yes), since the setting of the screens as C, M and K is not completed yet (step 268, No), the evaluation target screen setting unit 122 sets the screens as C, M and K.
Set to K (step 262). The shift amount setting (step 264) is the same as above, and when all the shift amount combinations have been set (step 266, Ye).
s), since the setting (two types) of the screen to be evaluated has been completed (Yes in step 268), the process is ended.

Next, the processing in the spectrum generator 104 will be described. When the screen condition is input to the conversion formula prepared for each halftone dot shape, the spectrum generation unit 104 generates spectra of appropriate orders in the vertical and horizontal directions for the number of screens.

FIG. 9 shows the processing in the spectrum generator 104. The spectrum generation unit 104 stores a spectrum generation formula calculated in advance. This spectrum generation formula corresponds to the case where the halftone dot shape of the screen is a circle. First, the screen halftone dot spacing and halftone dot size input from the input unit 102 are substituted into the spectrum generation equation (step 202). Then, the shift amount of the position of the center of gravity of the screen halftone dots (for example, the start position of the screen located in the upper left of the screen) is set (step 2
03). The shift amount is preferably in units of 1 pixel, but may be smaller or larger than that. For example, a shift amount of 0.5 pixel (pixel) unit in the main scanning direction (horizontal direction) and 1.0 pixel (pixel) unit in the sub scanning direction (vertical direction) may be set. And
It is preferable that the candidate of the position where the center of gravity is shifted is within a parallelogram formed by adjacent halftone dots. In the example of FIG. 7, the candidates are 1 to 7. That is, the position 1 of the original center of gravity, the positions 3, 5, and 7 moved by +1,2,3 pixel units in the Y-axis direction, and the pixels moved in the X-axis direction by +1 pixel, and then moved in the Y-axis direction by +1,2, Position 2 moved by 3 pixels
4 and 6 are candidates for shifting the center of gravity. However, if a shift amount of 0.5 pixel (pixel) unit in the main scanning direction (horizontal direction) and 1.0 pixel (pixel) unit in the sub scanning direction (vertical direction) is set, the candidates are positions 1 to 7. In addition to,
Positions 8-10 are also candidates. Positions 8, 9, 10
Move +0.5 pixels in the X-axis direction, then +1, in the Y-axis direction
It is the position moved by a few pixels. Further, a spectrum having an appropriate order (for example, up to the first order) in the vertical and horizontal directions is generated (step 204). Then, from step 202 above
After 204 has been executed for all screens (step 206, Yes), the processing in the spectrum generation unit 104 ends.

Next, the specific processing in the spectrum generation unit 104 will be described. FIG. 10 shows a halftone dot pattern with uniform gradation (FIG. 10a) and its spectrum (FIG. 10).
b) is shown. As an example, the frequency spectrum P (μ, ν) of a halftone dot manufactured using an orthogonal screen is shown in FIG.
The density distribution of halftone dots with uniform gradation density as shown in a is p
(X, y), where T is the periodic pitch of halftone dots, using the formula of Fourier integration,

[0060]

[Equation 1] It is expressed as. The frequency spectrum P (μ, ν) is
It is the spectrum generated in step 204.

The moire is perceived as having a spectrum in the region of high sensitivity due to the visual spatial frequency characteristic. In an actual image, Am, n corresponds to the content of the image, but in this example, only the moire spectrum is considered, and a halftone image with uniform gradation is targeted.

The spectrum generator 104 is adapted to the case where the halftone dot shape is a circle, and finds Am, n in this case. Figure 1
As shown in 1, when the halftone dot shape is a circle with a diameter of 2R,

[0063]

[Equation 2] Becomes

The spectrum when the center of gravity of the halftone dots is shifted in step 203 is

[0065]

[Equation 3] Becomes

For example, 2 pi in the x direction under the condition of resolution 600 dpi
When the center of gravity of the screen is shifted by 1 pixel in the xel and y directions, the amplitude is 5.0 and the spatial frequency in the x direction is 100 lpi, y
The spectrum with a spatial frequency of 150 lpi in the direction is

[0067]

[Equation 4] Becomes

That is, in this specific example, step 20
In step 2, the halftone dot spacing and halftone dot size of the screen input from the input unit 102 are substituted into the spectrum generation equation. Set the shift amount of (start position). In step 204, a spectral frequency spectrum P (μ, ν) of an appropriate order in the vertical and horizontal directions is generated. Then, after the above steps 202 to 204 are executed for all screens (step 206, Yes), the process in the spectrum generation unit 104 is ended. FIG. 18 shows an example of the output spectrum generated by the spectrum generation unit 104.

Next, the processing in the spectrum calculation unit 106 will be described. The spectrum calculation unit 106 operates the frequency components of the basic spectrum generated by the spectrum generation unit 104, and corresponds to slide / rotation / parallel movement (origin movement) of the screen in order to make the screen into a parallelogram shape. Repeat the calculation for the number of screens.

FIG. 12 shows the processing in the spectrum calculation unit 106. The spectrum calculation unit 106 performs screen slide processing (step 210). That is, an operation for arranging dots in a parallelogram grid is performed. FIG. 13 shows a diagram for explaining the screen slide process. As shown in FIG. 13, in the xy axis plane,
The vertical side of the screen in which halftone dots are arranged in a square lattice is transformed into a side inclined obliquely to the right (for example, y: x = 2:
The operation is 1) of the lateral displacement x on the frequency axis.
This corresponds to the operation of subtracting the displacement of / 2, that is, x / 2 from the frequency component in the y direction of the spectrum. When transforming into a parallelogram having an arbitrary slope, it is assumed that the displacement rate is a and the transformation of x ′ = x + ay is performed on the xy axis coordinate axes. Therefore, the transformation of y ′ = y−ax is performed on the frequency axis. Just go.

Next, the spectrum calculation unit 106 performs a screen rotation process (step 212). That is, the frequency of each spectrum is rotated around the origin using the following formula fx ′ = fxcos θ−fycos θ fy ′ = fxsin θ + fysin θ, and conversion corresponding to the rotation operation on the xy axes is performed. Where fx: frequency in the x direction before rotation (line per inch) fy: frequency in the y direction before rotation (line per inch) fx ': frequency in the x direction after rotation (line per inch) fy': rotation Later frequency in the y direction (line per inch) θ: rotation angle (screen angle).

Further, the spectrum calculation section 106 performs screen parallel movement processing (step 214). That is, in order to adjust the origin of the screen, each spectrum is given a phase component of an amount determined by the frequency component of each spectrum, halftone dot spacing, and origin position. The given phase component phase is represented by phase = (px × fx / lx) + (py × fy / ly). Where fx: frequency in the x direction of the spectrum fy: frequency in the y direction of the spectrum lx: number of lines in the x direction (line per inch) ly: number of lines in the y direction (line per inch) px: halftone dot spacing is 2π The amount of movement of the origin position in the x direction (rad) py (rad) py: The amount of movement of the origin position in the y direction (rad) where the halftone dot spacing is 2π (rad).

Then, after the processing in steps 210 to 216 has been executed for all screens (step 216, Yes), the processing in the spectrum calculation unit 106 is terminated. Among the calculation results of the spectrum calculation unit 106, the spectrum of the screen for C is
The spectrum of the screen for A _C and M is A _M , the spectrum of the screen for _Y is A _Y , and the spectrum of the screen for _K is A _K. In addition, when written as A _{Cm, n} , m and n indicate the dimension of the spectrum.

The processing in the spectrum generating section 104 and the spectrum calculating section 106 described above independently processes the information for each screen, but the convolution executing section 108 described below processes the information for each screen. Are combined into one piece of information.

Next, the processing in the convolution execution unit 108 will be described. The convolution execution unit 108 performs a convolution operation corresponding to the operation of multiplying each screen as an image of xy coordinates on the frequency spectrum of each screen.

FIG. 14 shows a diagram for explaining the convolution operation. Since only the calculation equivalent to the superposition of two sheets can be performed at the same time, when the superposition of four sheets is performed, three convolutional operations shown in the convolutional operation 1, the convolutional operation 2 and the convolutional operation 3 are required. Is. That is, in the convolution calculation 1, a calculation corresponding to the superposition of the screen 1 and the screen 2 is performed, and in the convolution calculation 2, a calculation corresponding to the superposition of the screen 3 and the screen 4 is performed. Then, in the convolution calculation 3, a calculation corresponding to the superposition of the screens 1 to 4 is performed. The convolution calculation result is supplied to the evaluation value calculation unit 116. The convolution operation has two screens (eg A _C and A _M ), 3 screens (eg A _C , A _M and A _K ) or 4 screens (eg A _C , A _M , A _Y)
And _AK ). The result of the convolution operation is written with the convoluted screen as a subscript. For example, A _CM . A _CM is A _C and A _M
Is the result of folding in. In addition, when written as A _{CMm, n} , m and n indicate dimensions.

FIG. 15 is a diagram for explaining the concept of the convolution operation. As shown in FIG. 15, the screen 1
Assuming the spectrum of screen 2 and the spectrum of screen 2, the spectrum after convolution is the origin of one spectrum (spectrum 1 in this example) superimposed on the other spectrum (spectrum 2 in this example). Then, the intensity of the spectrum corresponds to the product of each spectrum.

Next, the processing in the evaluation value calculator 116 will be described. The evaluation value calculation unit 116 multiplies the convolution calculation result by the visual frequency characteristic (VTF) function and sums the results (excluding the DC component) to calculate the evaluation value. In addition,
The combination of the candidates for the center of gravity position of the halftone dots on each screen when the evaluation value is the minimum is the center of gravity position of the halftone dots on each suitable screen with less moire.

FIG. 16 shows the processing in the evaluation value calculator 116. Here, how to obtain the evaluation value for A _{CMm, n} will be described. It should be noted that evaluation values relating to the convolution of other screens can be obtained in the same manner.

First, m and n within a predetermined range (for example,
A _{CMm, n} × (VTF function) is obtained for −1 ≦ m, n ≦ 1) (step 250). The VTF function is a function of the spatial frequency f, as will be described later. Where f = (fx x fx
+ Fy × fy) ^1/2 . That is, f is fx × fx + fy × f
is the square root of y. Here, fx is the spatial frequency of A _{CMm, n in} the x direction, and fy is the spatial frequency of A _{CMm, n in} the y direction. Then, the total sum of A _{CMm, n} × (VTF function) is obtained (step 252). Here, in A _{CMm, n} , the one having a spatial frequency of 0 is a direct current component and is not a moire. Since it is not appropriate to use such a DC component for evaluation value calculation when evaluating moire, use the DC component (the one whose spatial frequency becomes 0 at A _{CMm, n} ) when calculating the sum. Not in. This sum total is the evaluation value.

This evaluation value is used as the spectrum generation unit 10
4 corresponds to the shift amount of the center of gravity of the halftone dots on the screen set in step 4 (step 203: see FIG. 9).

FIG. 17 shows an example of the VTF function. FIG. 17
FIG. 17 (B) shows a general VTF function in FIG.
Shows the VTF function that is not attenuated at low frequencies. FIG. 17
The general VTF function shown in (A) is an upwardly convex curve that attenuates at low frequencies, but it has the same sensitivity as the peak below the frequency at which it peaks, as shown in FIG. 17 (B). It can also be a VTF function. For the evaluation of the presence or absence of moire, the VTF function that does not attenuate at low frequencies as shown in FIG. 17B is more suitable. Here, FIG. 17 (B)
The VTF function as shown in can be defined as, for example, the following expression. In this case, the value of the VTF function is 1 up to f = 26 lpi, and the value of the VTF function decreases as f exceeds 26 lpi.

[0083]

[Equation 5] The VTF function assumes that the distance between the printed matter and the human eye is constant. However, in reality, when a human observes the printed matter, the observation distance between the eyes and the printed matter is not constant but may vary. That is, it is conceivable that moire that was not noticeable at the standard observation distance becomes noticeable as the moire approaches the printed matter or moves away from the printed matter. Since the printed matter always contains frequency components of the constituent elements of the printed matter such as the number of lines and the dot shape of the screen, it is difficult to search for screen conditions with few high-frequency components that become noticeable when approaching the printed matter. Is. On the other hand, the presence or absence of a low frequency component that becomes more noticeable as the distance from the printed matter depends on the screen setting condition, and therefore it is possible to search for a condition with a low low frequency component.

That is, by using a VTF that outputs a large evaluation value (a bad evaluation value) for low-frequency components, it is possible to distinguish from better screen conditions with few low-frequency components. It will be possible.

However, when a VTF that attenuates in a low frequency region is used in an evaluation unit (not shown), when a screen condition where a certain low frequency moire occurs is observed at a distance from the printed matter. Although there is a noticeable moiré, the evaluation unit cannot detect this point and may determine that the screen condition is suitable. Therefore, it is considered that the VTF that attenuates in the low frequency region is not suitable for use in the evaluation section.

Since the evaluation value is a scalar quantity, it can be used for relative comparison of screens and absolute evaluation of screens. That is, in the case of comparing moire when the halftone dot center position of the screen is changed, by comparing these evaluation values, it is possible to rank the presence or absence of moire. Also, as the reference evaluation value, the evaluation value at the halftone dot position of a certain screen,
It is also possible to judge the degree of the moire conspicuousness based on the comparison between the reference evaluation value and the evaluation value at the halftone dot position of another screen.

The optimum shift amount determining unit 118 determines the combination of the dot center of gravity of each screen according to the density composition ratio. As described above, the evaluation value can be used to rank the presence or absence of moire. Therefore, the shift amount of the dot center of gravity of each screen when the evaluation value is the minimum is set as the optimum shift amount. This optimum shift amount is determined by the image setting device 300.
Sent to.

For example, suppose that the screens to be evaluated are C, M and Y, and the evaluation value is the minimum when C (0,0), M (0,1) and Y (0,2). . Therefore, the screen to be evaluated
The optimal shift amount for C, M and Y is C (0,0), M (0,
1) and Y (0,2). This is because the screen center of gravity position for M is shifted from the screen center of gravity position for C by 0 pixel in the X axis direction and 1 pixel in the Y axis direction, and the center of gravity position of the screen for Y is in the X axis direction from the center of gravity position of the screen for C. It means 0 pixel shift and 2 pixel shift in Y-axis direction. It is also assumed that the evaluation target screens are C, M, and K, and the evaluation value is the minimum when C (0,0), M (0,0), and K (1.5,2.0). Therefore, when the screens to be evaluated are C, M, and K, the optimal shift amount is C (0,0), M
(0,0) and K (1.5,2.0). In this way, the optimum shift amount is determined for each type of screen to be evaluated. This is because the optimum shift amount in the area where the CMY density
This means that the optimum shift amount of the portion having a high concentration composition ratio of is determined.

The image setting device 300 divides an image into areas at the time of printing, determines a density composition ratio for each area, and shifts the halftone dot center of gravity of each screen by an optimum shift amount according to the density composition ratio.

The image setting apparatus 300 divides an image into areas at the time of printing, and a density composition ratio determination unit 302 that determines a density composition ratio for each area; a screen of each screen by an optimum shift amount according to the density composition ratio. And a printing shift amount setting unit 304 for shifting the point centroid.

The operation of the image setting device 300 will be described. The configuration of the image setting device 300 is shown in FIG.

An image is sent from the halftone processing unit 66 to the density composition ratio determination unit 302 during printing. The image is divided into regions, and it is determined for each region whether the density composition ratio of CMY is high such as gray or the density composition ratio of CMK is dark such as dark blue. At this time, it is preferable to determine whether or not the area is a solid area, an area surrounded by a white area of paper, or an area of a graph or a character. These regions do not affect the periodicity of the surrounding regions even if the halftone dot center of gravity is shifted. That is, the boundary between the region of interest and the periphery can be made clear, and even if the shift amount is changed, the periodicity of halftone dots does not collapse at the boundary of the region. Therefore, it is preferable that the printing shift amount setting unit 304 shifts the halftone dot center of gravity only in these areas.

The printing shift amount setting unit 304 sets the shift amount (during printing) of the dot center of gravity of each area of the image according to the determination result of the density component ratio determining unit 302. For example, in an area having a high density composition ratio of CMY such as gray, the optimum shift amount when the screen to be evaluated is C, M, and Y is set as the shift amount of the dot center of gravity of the region (at the time of printing). This shift amount is sent to the halftone processing unit 66, and the image is printed with the halftone dot center of gravity shifted according to this shift amount. However, if the density composition ratio of CMY is neither high nor the density composition ratio of CMK is high, the shift amount is not changed.

In the above embodiment, the shift amount of the dot center of gravity (during printing) is changed based on the density composition ratio of each area of the image. However, the shift amount of the halftone dot center of gravity (during printing) may be changed based on the density of each element color in each area of the image. In this case, the evaluation target screen setting unit 122 sets the density of each element color of the screen input to the input unit 102 (for example, the density of C of 256 gradations is set.
0, 100, or 200). Then, the optimal shift amount determination unit 118 determines the type of density of each set element color (eg,
The optimum shift amount is determined according to the C concentration of 0, 100 or 200). The density component ratio determination unit 302 divides the image into areas and determines which type the density of each element color in the area corresponds to (for example, if the density of C is less than 100, the density of C is 0). (Corresponding to the type), the optimum shift amount corresponding to the type is the shift amount of the dot center of gravity.

Example First, the halftone dot arrangement of the screen corresponding to CMYK is as shown in FIG. That is, on the screen corresponding to C (see FIG. 20A), the vector (2,4),
An adjacent halftone dot is placed at the position indicated by (-2.5,1). These vectors that define the relative position of the center of the halftone dot are called displacement vectors. Screen corresponding to M (Fig. 20 (b))
The displacement vector is (2.5,1), (− 2,4), and the displacement vector is (2,3), (− 2,3) on the screen corresponding to Y (see FIG. 20 (c)). , K on the screen (see FIG. 20 (d)), the displacement vector is (3,4),
It is (−3,4). The size of the halftone dot has an area coverage of 3
It is set to be 0%. Here, in each screen, the center of gravity of the halftone dot is set at the origin at the upper left of the image. Therefore, the halftone dot center of gravity does not shift on any screen.

FIG. 21 shows the screen shown in FIG. 20 in which CMY is superposed (see FIG. 21 (a)) and in which CMK is superposed (see FIG. 21 (b)). In both cases, a conspicuous pattern (moire) is generated.

Therefore, the evaluation target screen setting unit 122
Sets the screen to C, M and Y and the screen to C, M and K (step 26).
2: See FIG. 8). For each setting, set all combinations of shift amounts for each screen (Step 2
66, Yes: refer to FIG. 8), and the evaluation value calculation unit 116 obtains an evaluation value (step 252: refer to FIG. 16). As a result, the screens to be evaluated are C, M and Y,
It is assumed that the evaluation value is the minimum when the halftone dot center of gravity is C (0,0), M (0,1), and Y (0,2). In this case, the optimum shift amount determination unit 1
18 is the optimum shift amount of the portion where the CMY density composition ratio is high.
Let (0,0), M (0,1), and Y (0,2). The screens to be evaluated are C, M and K, and the halftone dot center of gravity is C (0,0), M.
Assume that the evaluation value is the minimum in the case of (0,0) and K (1.5,2.0). In this case, the optimum shift amount determination unit 118 determines the optimum shift amount of the portion having a high CMK density component ratio as C (0,0), M (0,
0) and K (1.5, 2.0). Here, note that M
That is, the shift amount of the dot center of gravity of the screen is different between the portion having a high CMY density composition ratio and the portion having a high CMK density composition ratio.

Here, an image obtained by shifting the dot center of gravity of each screen by such an optimum shift amount and superimposing the images is shown in FIG. 22A for superimposing C, M and Y.
Fig. 22 (b) shows the superposition of C, M and K.
Shown in. It can be seen that the moire in FIG. 22 is less noticeable than the moire in FIG.

FIG. 23 shows an image in the case where the shift amount of the dot center of gravity of the M screen is M (0,1) and C, M and K are superposed. Originally, the optimum shift amount of the dot center of gravity of the screen of M when C, M and K are overlapped is M
It is (0,0). However, since the shift amount of the dot center of gravity is M (0,1), the moire in FIG. 23 becomes more conspicuous than the moire in FIG. Thus, it is effective to reduce the moire by changing the shift amount of the center of gravity of the halftone dot between the portion having a high CMY density composition ratio and the portion having a high CMK density composition ratio.

The above steps are performed at the time of designing, and at the time of printing, the density composition ratio determination unit 302 divides the image into areas, and for each area, the density composition ratio of CMY is high such as gray or CMK such as dark blue. Determine if the concentration composition ratio is high. Then, according to the determination result, the printing shift amount setting unit 304
Set the shift amount of the dot center of gravity (during printing). The areas with high CMY density composition ratios are C (0,0), M (0,1), Y (0,2), and CMK
High concentration composition ratio of C (0,0), M (0,0), K (1.5,2.0)
And

FIG. 24 is a block diagram of an image output system according to another embodiment of the present invention. This system configuration example is a modification of the system configuration example shown in FIG. Figure 2
In the system of No. 4, the driver 80 installed in the host computer 50 uses the rasterizing function 5
4. It has a color conversion function 64, a halftone processing function 66, an image evaluation function 100 and an image setting function 300. Each of these functions 54, 64, 66, 100 is the same as the function of the same reference number shown in FIG. Then, the image reproduction data (pulse width data) 30 for each color generated by the halftone processing function is converted into the pulse width modulation unit 6 of the controller 62 in the image output device 60 such as a page printer.
8 is supplied to the engine 70, converted into desired drive data 69, and provided to the engine 70.

In the system example of FIG. 24, the driver 80 installed on the host computer side performs the color conversion process, the halftone process, and the image evaluation process. In the example of FIG. 1, the color conversion process and the halftone process are performed by the controller in the image output device.
In the example of FIG. 24, it is performed on the host computer 50 side.
When the price reduction of the image output device 60 is required, it is required to lower the price by lowering the capacity of the controller 62. In this case, it is effective to partially implement some of the functions performed by the controller of FIG. 1 by the driver program installed in the host computer. When halftone processing is realized by the driver 80, a recording medium in which a program for causing the computer to execute the above halftone processing procedure is stored is built in the host computer 50.

FIG. 25 is a block diagram of an image output system according to still another embodiment of the present invention. This system configuration example is a modification of the system configuration example shown in FIG.
The difference from the system configuration example shown in FIG. 1 is that the image evaluation apparatus 100 is separate from the host computer 50 and that the image setting apparatus 300 is built in the image output apparatus 60.

In this case, before the host computer 50 gives the image data 56 to the image output device 60, the image evaluation device 100 preliminarily sets the combination of the barycentric positions of the screen corresponding to the density component ratio (or density) of the smallest moire. (That is, the screen layout) is determined and provided to the image setting device 300. The image setting device 300 divides an image into areas at the time of printing, determines the density composition ratio (or density) for each area, and determines the dot center of gravity of each screen by the optimum shift amount according to the density composition ratio (or density). shift. That is, the screen layout is selected according to the density composition ratio (or density). The halftone processing unit 66 processes the gradation data 10 using the combination of the barycentric positions of the screen set by the image setting device 300.

For example, the host computer 50 is a personal computer and the image output device 60 is a laser printer. Further, the image setting device 300 is a ROM (Read Only
Memory). Image output device (laser printer)
Before the shipment of 60, the image evaluation apparatus 100 records in the ROM of the image setting apparatus 300 a combination of the barycentric positions of the screen corresponding to the density component ratio (or density). The image setting device 300 reads the combination of the barycentric positions of the screens according to the density component ratio (or density) from this ROM and shifts the dot center of gravity of each screen.

The halftone processing unit 66 may be configured by executing the halftone processing program by the image output device 60. This halftone processing program is normally used by the image output device 6
0-readable form of floppy disk, CD-RO
It is recorded on a recording medium such as M and distributed. The program is read by a media reading device (CD-ROM drive, floppy disk drive, etc.) and installed in the hard disk. Then, the CPU is configured to read out a desired program from the hard disk as appropriate and execute a desired process. Alternatively, the image output device 60 may have a recording medium such as a ROM, and the halftone processing program may be recorded in this ROM.

Further, the image setting device 300 may be configured by executing the image setting processing program by the image output device 60. This image setting processing program is normally recorded in a recording medium such as a floppy disk or a CD-ROM in a form readable by the image output device 60 and distributed. The program is read by a media reading device (CD-ROM drive, floppy disk drive, etc.) and installed in the hard disk. Then, the CPU is configured to read out a desired program from the hard disk as appropriate and execute a desired process. Alternatively, the image setting device 300 may have a recording medium such as a ROM, and the image setting processing program may be recorded in this ROM.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image output system.

FIG. 2 is a diagram illustrating a binarization method for tone reproduction of a grayscale image by a dither method.

FIG. 3 is a diagram illustrating a threshold matrix of a dither method.

FIG. 4 is a diagram showing a shape change of a halftone dot formed by using a dither method.

FIG. 5 is a diagram showing a method of forming a screen angle.

FIG. 6 shows a block diagram of an image evaluation device according to an embodiment of the present invention.

FIG. 7 is a diagram showing screen pitches, angles, and halftone dot candidates.

FIG. 8 is a flowchart for explaining processing of an evaluation target screen setting unit 122 and a shift amount setting unit 124.

FIG. 9 is a flowchart for explaining the processing in the spectrum generation unit 104.

FIG. 10 is a diagram showing a halftone dot pattern with uniform gradation (FIG. 10a) and its spectrum (FIG. 10b).

FIG. 11 is a diagram for explaining the size of a halftone dot shape when the halftone dot shape is circular.

FIG. 12 is a flowchart for explaining a process in spectrum calculation section 106.

FIG. 13 is a diagram for explaining screen slide processing.

FIG. 14 is a diagram for explaining a convolution operation.

FIG. 15 is a diagram for explaining the concept of a convolution operation.

FIG. 16 is a flowchart for explaining processing in the evaluation value calculation unit 116.

17A is a diagram showing a general VTF function, and FIG. 17B is a diagram showing a VTF function that is not attenuated at a low frequency.

FIG. 18 is a diagram showing an example of an output spectrum generated by the spectrum generation unit 104.

FIG. 19 is a block diagram showing a configuration of an image setting device 300.

FIG. 20 is a diagram showing a halftone dot arrangement of a screen corresponding to CMYK in the embodiment, which is a halftone dot arrangement of a screen corresponding to C (FIG. 20A) and a halftone dot arrangement of a screen corresponding to M (FIG. 20). 20 (b)), the halftone dot arrangement of the screen corresponding to Y (FIG. 20 (c)), and the halftone dot arrangement of the screen corresponding to K (FIG. 20 (d)).

FIG. 21: CMY superposition without shifting the halftone dot center of gravity (FIG. 21A), CMK superposition (FIG. 21)
It is a figure which shows (b)).

FIG. 22 is a diagram showing CMY superposition (FIG. 22 (a)) and CMK superposition (FIG. 22 (b)) in the case of superimposing by shifting the halftone dot center of gravity of each screen by the optimum shift amount. is there.

FIG. 23 shows the shift amount of the halftone dot center of the screen of M as M (0,
It is a figure which shows the image of CMK's superposition at the time of 1).

FIG. 24 is a configuration diagram of an image output system according to another embodiment of the present invention.

FIG. 25 is a configuration diagram of an image output system according to still another embodiment of the present invention.

[Explanation of symbols]

10 Input data, gradation data 20 Conversion table, threshold matrix 30 image reproduction data 50 host computer 60 controller 66 Halftone processing unit 70 engine

Continued front page    F term (reference) 5B057 BA26 CA01 CA08 CA12 CA16                       CB01 CB08 CB12 CB16 CC01                       CE08 CE13 CE17 CE18 CH08                       CH11 CH18 DA04 DA08 DA16                       DB02 DB06 DB09 DC03 DC06                 5C077 LL03 LL12 LL17 MM27 MP02                       MP08 NN04 NN08 PP33 PP39                       PP49 PQ08 PQ12 PQ22 RR10                       RR11 SS02 TT03 TT06                 5C079 HA19 HB03 JA28 KA17 LA24                       LC05 LC14 MA01 MA10 MA11                       NA02 NA27 PA02 PA03

Claims (28)

[Claims] 1. An image evaluation method for evaluating an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots, each element color Each time, a spectral data generation process that generates a plurality of spectral data based on the positional relationship between the data resulting from the density of the input data, the screen angle, and the center of gravity of the halftone dots on each screen, and for each element color An image evaluation method comprising: a spectrum data combining step of combining a plurality of spectrum data; and an image evaluation step of evaluating an image corresponding to a density composition ratio of each element color based on the combined spectrum data. 2. An image evaluation method for evaluating an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed by a plurality of dots, each element color Each time, a spectral data generation process that generates a plurality of spectral data based on the positional relationship between the data resulting from the density of the input data, the screen angle, and the center of gravity of the halftone dots on each screen, and for each element color An image evaluation method, comprising: a spectrum data combining step of combining a plurality of spectrum data; and an image evaluation step of evaluating an image corresponding to the density of each element color based on the combined spectrum data. 3. The image evaluation method according to claim 1, wherein the optimum screen halftone is changed by changing the barycentric position of the halftone dot of the screen in the spectrum data generated in the spectrum data generating step. An image evaluation method for obtaining the position of the center of gravity of a point. 4. The image evaluation method according to claim 1, further comprising the step of deforming a screen shape based on the spectrum data generated in the spectrum data generation step according to a predetermined rule. Further equipped image evaluation method. 5. An image evaluation apparatus that evaluates an image output by an image output apparatus that reproduces an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots, Each time, the spectrum data generation means for generating a plurality of spectrum data based on the positional relationship between the data resulting from the density of the input data, the screen angle, and the center of gravity of the halftone dots of each screen, and each element color are generated. An image evaluation device comprising: a spectrum data composition means for composing a plurality of spectrum data; and an image evaluation means for evaluating an image corresponding to a density composition ratio of each element color based on the composed spectrum data. 6. An image evaluation device for evaluating an image output by an image output device which reproduces an image by expressing gradation of each element color by a halftone dot formed of a plurality of dots, each element color Each time, the spectrum data generation means for generating a plurality of spectrum data based on the positional relationship between the data resulting from the density of the input data, the screen angle, and the center of gravity of the halftone dots of each screen, and each element color are generated. An image evaluation apparatus comprising: a spectrum data composition means for combining a plurality of spectrum data; and an image evaluation means for evaluating an image corresponding to the density of each element color based on the combined spectrum data. 7. A computer is caused to execute an image evaluation process for evaluating an image output by an image output device which reproduces an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots. Is a program, for each element color, based on the positional relationship between the data resulting from the density of the input data, the screen angle and the center of gravity of the halftone dots of each screen, a spectrum data generation process for generating a plurality of spectrum data, A computer is provided with a spectrum data combination process for combining a plurality of spectrum data generated for each element color, and an image evaluation process for evaluating an image corresponding to the density composition ratio of each element color based on the combined spectrum data. Program to run on. 8. A computer is caused to execute an image evaluation process for evaluating an image output by an image output device for reproducing an image by expressing a gradation for each element color by a halftone dot formed of a plurality of dots. Is a program, for each element color, based on the positional relationship between the data resulting from the density of the input data, the screen angle and the center of gravity of the halftone dots of each screen, a spectrum data generation process for generating a plurality of spectrum data, The computer executes the spectral data composition process that combines the multiple spectrum data generated for each element color, and the image evaluation process that evaluates the image corresponding to the density of each element color based on the combined spectrum data. A program to let you. 9. A computer-readable recording medium in which the program according to claim 7 or 8 is recorded. 10. A halftone dot according to an evaluation value corresponding to a density composition ratio of each element color obtained based on a combination of spectral data of two or more screens arbitrarily selected from a plurality of screens. A screen layout in which the positional relationship of the center of gravity of is determined according to the density composition ratio of each element color. 11. The center of gravity of halftone dots according to an evaluation value corresponding to the density of each element color obtained based on a combination of spectral data of two or more screens arbitrarily selected from a plurality of screens. A screen layout in which the positional relationship of is determined according to the density of each element color. 12. The screen arrangement according to claim 10, wherein the positional relationship of the center of gravity of the halftone dots is an integer of 0.5 pixels in the main scanning direction from the position of the center of gravity of the halftone dots on a predetermined screen. A screen layout in which the center of gravity of the halftone dot of another screen is located at a position doubled and moved by an integral multiple of 1.0 pixel in the sub-scanning direction. 13. The screen arrangement according to claim 10, wherein in the spectrum data, the shape of the halftone dots is a circle, the brightness value of the paper is 1.0, and the brightness value of the halftone dot area is 0.0. Screen layouts up to the first order calculated hypothetically. 14. The screen arrangement according to claim 10, wherein the evaluation value is a combination of spectral data of two screens arbitrarily selected from a plurality of screens, and a low frequency. A screen layout that is obtained based on a product of a visual frequency characteristic function that is not attenuated by a part. 15. The screen arrangement according to claim 10, wherein the positional relationship of the centers of gravity of the halftone dots is determined so that the evaluation value is minimized. 16. An image processing comprising: a step of recording the screen layout according to claim 10; and a step of selecting the screen layout corresponding to a density composition ratio of each element color of a target pixel of an input image. Method. 17. A step of recording the screen arrangement according to claim 10, and a step of selecting the screen arrangement corresponding to a density composition ratio of each element color in a peripheral region of a target pixel of an input image. Image processing method. 18. An image processing method comprising: a step of recording the screen arrangement according to claim 11; and a step of selecting the screen arrangement corresponding to the density of each element color of a pixel of interest of an input image. 19. An image processing comprising: a step of recording the screen arrangement according to claim 11; and a step of selecting the screen arrangement corresponding to a density of each element color in a target pixel peripheral region of an input image. Method. 20. Image processing, comprising: means for recording the screen layout according to claim 10; and means for selecting the screen layout corresponding to the density composition ratio of each element color of the pixel of interest of the input image. apparatus. 21. A means for recording the screen arrangement according to claim 10, and a means for selecting the screen arrangement corresponding to a density composition ratio of each element color in a peripheral region of a target pixel of an input image. Image processing device. 22. An image processing apparatus comprising: a unit for recording the screen arrangement according to claim 11; and a unit for selecting the screen arrangement corresponding to the density of each element color of a target pixel of an input image. 23. Image processing comprising: means for recording the screen layout according to claim 11; and means for selecting the screen layout corresponding to the density of each element color in the peripheral region of the target pixel of the input image. apparatus. 24. A computer is caused to execute a process of recording the screen layout according to claim 10 and a process of selecting the screen layout corresponding to a density composition ratio of each element color of a target pixel of an input image. Program for. 25. A computer is provided with a process of recording the screen layout according to claim 10, and a process of selecting the screen layout corresponding to a density composition ratio of each element color in a peripheral region of a target pixel of an input image. A program to run. 26. A process for causing a computer to execute the process of recording the screen layout according to claim 11, and the process of selecting the screen layout corresponding to the density of each element color of the pixel of interest of the input image. program. 27. A computer is made to execute the processing for recording the screen layout according to claim 11 and the processing for selecting the screen layout corresponding to the density of each element color in the peripheral region of the target pixel of the input image. Program for. 28. A computer-readable recording medium in which the program according to any one of claims 24 to 27 is recorded.