JP2002135609A - Image processor, image processing method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, capable of pseudo-gradation processing of high precision by adopting thresholds and output gradation different by each color, even when combining at least two colors and using an error diffusion method. SOLUTION: The method is provided with adders 1-0 and 1-1 for adding respective error values E0 and E1, between each of the multi-valued pixel signal values of plural colors and the pseudo-gradation signal value of the same color and output-deciding parts 2-0 and 2-1 for outputting temporarily decided pseudo gradation signals to the respective output value of adding parts. The method is provided with first error calculation parts 3-0 and 3-1 for outputting an error between each of the temporarily-decided pseudo-gradation signals and an output corresponding to the adding parts, the second output deciding part 2-2 for outputting multicolor pseudo-gradation signals with respect to a color obtained by the plural colors, and output changing parts 4-0 and 4-1 for outputting each of the temporarily decided pseudo-gradation signals by changing or without changing it, based on the deciding result by an output change judging part 4 for deciding the need for changes, concerning each of the temporarily decided pseudo-gradation signals, based on the temporarily-decided pseudo-gradation signals and all outputs of the first error calculation part and the multicolor pseudo-gradation signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, an image processing method, and an image forming apparatus, and more particularly, to an image processing apparatus for performing pseudo gradation processing, an image processing method, and an image forming apparatus using the same.

[0002]

2. Description of the Related Art Conventionally, an error diffusion method is known as pseudo gradation processing for expressing a multi-valued image in binary ("An Adaptive Method").
Algorithm for Spatial Gray Scale "in society for I
nformation Display 1975 Symposium Digest of Techni
cal Papers, 1975, 36). In this method, the target pixel is P, its density is v, and the densities of peripheral pixels P0, P1, P2, and P3 of the target pixel P are v0, v1, v2, v3, and the threshold for binarization is T. , The binarization error E in the target pixel P is
This is a method in which weighting factors W0, W1, W2, and W3 empirically obtained are assigned to 1, P2, and P3, and the average density is macroscopically equal to the density of the original image.

For example, assuming that the output binary data is o, if v ≧ T, then o = 1, E = v−Vmax;. . . . (1) If v <T, then o = 0, E = v−Vmin; (where Vmax: maximum density, Vmin: minimum density) v0 = v0 + E × W0; . . . (2) v1 = v1 + E × W1; . . . (3) v2 = v2 + E × W2; . . . (4) v3 = v3 + E × W3; . . . (5) (Example of weighting factor: W0 = 7/16, W1 = 1/16, W2 = 5/16, W
3 = 3/16)

[0004] Conventionally, for example, when a multi-valued image is output using inks of four colors of cyan, magenta, yellow, and black, such as a color inkjet printer, pseudo gradation processing is performed independently using an error diffusion method or the like for each color. For this reason, when one color is viewed, even if the visual characteristics are excellent, good visual characteristics are not always obtained when two or more colors overlap.

In order to improve this problem, Japanese Patent Application Laid-Open No. Hei 8-2
Japanese Patent Application Laid-Open No. 79920 and Japanese Patent Application Laid-Open No. H11-10918 disclose an error diffusion method in which two or more colors are combined to obtain a pseudo halftone processing method that can obtain good visual characteristics even when two or more colors overlap. It has been disclosed.

Japanese Unexamined Patent Application Publication No. Hei 9-139841 discloses a method in which two or more colors are independently subjected to pseudo middle gradation processing, and then the output value is corrected by summing the input values, thereby making a similar improvement. It has been disclosed.

[0007]

However, Japanese Patent Application Laid-Open Nos. Hei 8-279920 and Hei 11-10918 disclose.
In the method disclosed in Japanese Patent Application Laid-Open Publication No. H10-260, the threshold value for binarization is common to each color, and the threshold value cannot be changed for each color.

Further, in the case of pseudo gradation processing in which the number of output gradations is larger than 2, that is, ternary, quaternary,. . . , N-value cannot be handled.

Further, when the number of output gradations of each color is different,
For example, cyan and magenta are quaternized, but yellow and black cannot be binarized.

On the other hand, the method disclosed in Japanese Patent Application Laid-Open No. Hei 9-139841 is a method in which the output value is corrected based on the sum of the input values. There is a problem that when data is accumulated, an erroneous determination is made and the processing accuracy deteriorates.

The present invention has been made in view of the above-mentioned problems of the prior art.
Even in the case where the error diffusion method is used by combining two or more colors, it is possible to adopt different threshold values for each color or to employ different output gradation numbers for each color, and to provide a pseudo-scale with high accuracy. It is an object of the present invention to provide an image processing apparatus and an image processing method capable of performing tone processing, and an image forming apparatus using the same.

[0012]

That is, the gist of the present invention is to generate a pseudo-tone signal having a predetermined number of tones for each of a plurality of colors from a multi-valued pixel signal of a plurality of colors and to output the image. A processing device, wherein for each of the multi-valued pixel signal values of a plurality of colors, an adding means for adding an error value between the multi-valued pixel signal value and a pseudo gradation signal value of the same color, and an output of the adding means. For each of the values, a first output determining means for comparing a predetermined threshold value and outputting a tentatively-determined pseudo-gradation signal, and an error between each of the tentatively-determined pseudo-gradation signal and a corresponding output of the adding means are calculated. First error calculating means for obtaining and outputting, and second output determining means for outputting, from all outputs of the adding means, a multi-color pseudo-tone signal which is a pseudo-tone output for a color obtained by combining a plurality of colors,
Output change determining means for determining whether or not to change each of the temporarily determined pseudo tone signals based on all of the temporarily determined pseudo tone signals and the output of the first error calculating means, and the multi-color pseudo tone signal; Output changing means for outputting each of the provisionally determined pseudo-gray-scale signals as a pseudo-gray-scale signal without changing or changing the pseudo-gray-scale signals based on the determination result of the output change-determining means; And output the second error
And an error calculating means.

Another aspect of the present invention resides in an image forming apparatus for forming an image of multivalued image data using the image processing apparatus of the present invention.

Another aspect of the present invention is an image processing method for generating and outputting a pseudo gradation signal having a predetermined number of gradations for each of a plurality of colors from a multi-valued pixel signal of a plurality of colors. An adding step of adding, to each of the multi-valued pixel signal values of a plurality of colors, an error value between the multi-valued pixel signal value and the pseudo-gradation signal value of the same color; and an output value of the adding step. On the other hand, a first output determining step of outputting a provisionally determined pseudo-gradation signal by comparing with a predetermined threshold value, and calculating and outputting an error between each of the provisionally-determined pseudo-gradation signals and the corresponding output of the adding step. A first error calculating step, a second output determining step of outputting a multicolor pseudo-tone signal that is a pseudo-tone output for a color obtained by combining a plurality of colors from all outputs of the adding step, and a tentatively-determined pseudo-tone Signal and the output of the first error calculation step. An output change determining step of determining whether or not to change each of the provisionally determined pseudo gradation signals based on the multicolor pseudo gradation signal; and a provisionally determined pseudo gradation signal based on the result of the output change decision step. And a second error calculation step of calculating and outputting an error between each of the pseudo gradation signals and the corresponding output of the adding step. An image processing method characterized by having

Another aspect of the present invention resides in an image forming apparatus for forming an image of multivalued image data using the image processing method of the present invention.

According to another aspect of the present invention, there is provided an image processing program for generating and outputting a pseudo gradation signal having a predetermined number of gradations for each of a plurality of colors from a multi-valued pixel signal of a plurality of colors. A computer-readable storage medium for adding a multi-value pixel signal value of a plurality of colors and an error value between the multi-value pixel signal value and a pseudo gradation signal value of the same color. A program for a first output determination step for comparing a value of each of the output values of the addition step with a predetermined threshold value and outputting a provisionally determined pseudo gradation signal;
A program for a first error calculation step for calculating and outputting an error between each of the provisionally determined pseudo-gradation signals and a corresponding output of the addition step, and a pseudo-tone for a color obtained by combining a plurality of colors from all outputs of the addition step. A program for a second output determining step of outputting a multi-color pseudo-tone signal as a tone output, all of the provisionally determined pseudo-tone signal and the output of the first error calculating step, and a multi-color pseudo-tone signal Based on the program of the output change determining step for determining whether or not to change each of the provisionally determined pseudo gradation signals, based on the result of the determination of the output change decision step, without changing or changing each of the provisionally determined pseudo gradation signals A program of an output changing step of outputting as a pseudo gradation signal; and a program of a second error calculating step of calculating and outputting an error between each of the pseudo gradation signals and a corresponding output of the adding step. Note Resides in the media.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The present invention will be described in detail below with reference to the drawings based on a preferred embodiment. FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus according to the first embodiment of the present invention. The image processing apparatus shown in FIG. 1 is an apparatus that converts 8-bit / pixel multi-value image data into binary data by performing pseudo gradation processing and outputs the binary data.

In this figure, I0 and I1 represent pixel data of color 0 (for example, cyan) and color 1 (for example, magenta) which form the image data to be converted, and each of them is 8 bits. This is multi-valued data having a gradation. These pixel data of color 0 and color 1 are input to adders 1-0 and 1-1, respectively.

In the adders 1-0 and 1-1, the multi-value data I
0, I1, and error data E0, E1 from the pixels which have already been subjected to the pseudo gradation processing, which are the outputs of the error calculators 5-0, 5-1 are added as inputs and output. Outputs I'0 and I'1 of the adders 1-0 and 1-1 are input to output determining units indicated by 2-0 and 2-1 respectively.

The processing in the output determining units 2-0 and 2-1 will be described with reference to FIG. FIGS. 2A and 2B show the input / output characteristics of the output determining units 2-0 and 2-1, respectively, where the horizontal axis represents the input value and the vertical axis represents the output value. Here, output decision unit 2-
Assuming that thresholds for determining output values at 0 and 2-1 (0 or 1 in this embodiment because a binary output is assumed) are th0 and th1, respectively, the output determination units 2-0 and 2 In the case of -1, the output values of the adders 1-0 and 1-1 are the respective inputs, so the possible range of the input values is (th0-255 to
255 + th0), (th1-255 to 255 + th1).

Output determining units 2-0 and 2-1 respond to these inputs.
The output value of is set to the thresholds th0 and th1 as boundaries, and 0
Becomes 255 (1 when considered with binary output) above the threshold. These are indicated by solid lines in FIG.

The outputs Ot0 and Ot1 of the output decision sections 2-0 and 2-1 are input to error calculation sections 3-0 and 3-1 respectively. Error calculator 3-
At 0 and 3-1, the outputs Ot0 and Ot1 of the output decision units 2-0 and 2-1 and the outputs I'0 and I'1 of the adders 1-0 and 1-1 are input and the error between them is calculated. And output.

That is, assuming that the outputs of the error calculators 3-0 and 3-1 are Et0 and Et1, respectively, Et0 and Et1 are respectively Et0 = I'0-Ot0: Ot0 = 0 or 255 Et1 = I'1-. Ot1: Ot1 = 0 or 255.

On the other hand, the outputs I'0, I'1 of the adders 1-0, 1-1 are
Is also input to the output determination unit 2-2. Output decision unit 2-2
In, the output is added to the output I'0,
It is determined based on I′1 and output as Ot2.

FIG. 3 schematically shows the processing in the output determining unit 2-2. The horizontal axis indicates the input I'0 of the output determining unit 2-2, and the vertical axis indicates the input I'1. Represents. The solid lines represented by l0 and l1 in the figure indicate the thresholds for determining the output value of the output determination unit 2-2, where I'0 and I'1 are on the left side of the straight line l0 (arrows in the figure). , The output becomes 0, and when I′0 and I′1 are between the straight lines l0 and l1 (the part indicated by two arrows in the figure, 1), The output is 1, and similarly, when it is on the right side of the straight line l1 (portion indicated by an arrow 2 in the figure), the output is 2.

Here, the fact that the output of the output determining unit 2-2 is 0 means that both the output of the color 0 and the output of the color 1 are 0, and the fact that the output is 1 means that 1 out of 2 colors
It means that the output of the color is 1, and similarly, the output of 2 means that the output of both colors is 1.

In this embodiment, the output determining unit 2-
As shown in FIG. 3, the threshold for determining the output of 2 is fixed to th0 and th1, and when two colors are combined, the threshold (A, B) at which both thresholds correspond to the other input value 0, 255 and (C,
It is assumed that they lie on straight lines I0 and I1 connecting D), but the present invention is not limited to this. That is,
As long as the output of the output determination unit 2-2 is determined based on the input values I'0 and I'1, any condition may be adopted.

For example, in order to suppress the so-called sweeping phenomenon in the error diffusion method, a method in which the threshold value is varied according to the input values is also conceivable. In such a case, ROM (read only memory) or RAM
This can be realized by constructing an LUT (lookup table) such as (random access memory) or the like that inputs I′0 and I′1 and inputs a pseudo grayscale output as an output value.

Output Ot of output decision unit 2-0, 2-1 and 2-2
0, Ot1, Ot2, outputs Et0, Et1 of error calculators 3-0, 3-1
Is input to the output change determination unit 4. The output change determining unit 4 determines whether to change the output values Ot0, Ot1 of the output determining units 2-0, 2-1 based on the inputs Ot0, Ot1, Ot2 and Et0, Et1, respectively.

The conditions under which the output values Ot0 and Ot1 are changed in the output change determination section 4 will be described with reference to FIG. In FIG. 3, regions (a), (b), (c), (d), (e), (f)
The portion indicated by is a portion where either the output value Ot0 or Ot1 is changed by the output change determination unit 4.

For example, in the area (c), the two colors are combined even though the outputs of the output decision units 2-0 and 2-1 which perform the pseudo gradation processing independently for each color are both 0. This means that either of the colors outputs 1 in the output determination unit 2-2 that performs the pseudo gradation processing.

Similarly, in the area (d), the outputs of the output decision sections 2-0 and 2-1 which perform pseudo gradation processing independently for each color are both used.
This means that either one of the colors outputs 1 in the output determination unit 2-2 that performs the pseudo gradation process by combining the two colors, although it is 1.

In the areas (a) and (b), one of the outputs from the output decision units 2-0 and 2-1 which perform pseudo gradation processing independently for each color is 1 and the others are 0. Nevertheless, this means that both output 0 in the output determination unit 2-2 that performs pseudo gradation processing by combining two colors.

Further, in the areas (e) and (f), one of the outputs of the output decision units 2-0 and 2-1 which perform pseudo gradation processing independently for each color is 1 and the others are 0. Nevertheless, this means that both output 1 in the output determination unit 2-2 that performs pseudo gradation processing by combining two colors.

Therefore, the output change judging section 4 outputs the output decision section 2-
By comparing the outputs Ot0 and Ot1 of 0 and 2-1 with the output (Ot2) of the output determining section 2-2, the output determining sections 2-0 and 2 are determined.
It is determined whether to change the output (Ot0, Ot1) of -1.

[0036]

[Table 1]

Table 1 shows the conditions.
In the cases (a) and (b), Ot1 and Ot0 are set to 0, respectively.
In cases (e) and (f), Ot0 and Ot1 may be changed to 1. In the case of (c), one of Ot0 and Ot1 may be changed to 1, and in the case of (d), either of Ot0 and Ot1 may be changed to 0. In these cases, which one to change is determined by comparing errors.

That is, the outputs Et0 and Et1 of the error calculators 3-0 and 3-1 are also input to the output change determiner 4. If the conditions (c) and (d) are satisfied, Et0 and Et0 are output. Et1 is normalized by the maximum value of the absolute value of the error for each color, and then the absolute value is compared to change the larger absolute value.

As described above, when it is determined that the outputs Ot0 and Ot1 of the output determining unit 2-0 or 2-1 are to be changed, the output change determining unit 4 sends the control signals C0 and C1 to the output to be changed. Output.

The control signals C0 and C1 and the outputs Ot0 and Ot1 of the output decision sections 2-0 and 2-1 are output change sections 4-0 and Ot1, respectively.
Input to 0 and 4-1. The output changing units 4-0 and 4-1 input the input signals Ot0 and Ot1 according to the control signals C0 and C1, respectively.
And output final output signals O0 and O1.

On the other hand, the final output signals O0 and O1 output by the output change units 4-0 and 4-1 are output together with the outputs I'0 and I'1 of the adders 1-0 and 1-1 and the error calculation unit. Input to 5-0 and 5-1 and the error is calculated again.

At this time, assuming that the outputs of the error calculators 5-0 and 5-1 are E0 and E1, respectively, E0 and E1 are E0 = I'0-O0: O0 = 0 or 255 E1 = I'1 -O1: O1 = 0 or 255.

The outputs E0 and E1 of the error calculators 5-0 and 5-1 are input to adders 1-0 and 1-1, respectively, and added to the next input pixel data I0 and I1. Since the processing for one input data is performed according to the above configuration, the pseudo gradation processing for the entire image can be performed by repeating the above processing while shifting the processing one pixel at a time in the processing direction.

In this embodiment, the error is always recalculated.
Recalculation may be performed only when 0 and C1 are output, that is, only when the output is changed. Specifically, as shown in FIG. 4, the control signals C0, C1
Selectors 6-0 and 6 for selecting and outputting one of the outputs Eto and Et1 of the error calculators 3-0 and 3-1 or the outputs E0 and E1 of the error calculators 5-0 and 5-1. The error calculators 5-0 and 5-1 perform calculations only when the control signals C0 and C1 are output, and the selectors 6-0 and 6-1 output the control signals C0 and C1. In this case, the outputs E0 and E1 of the error calculators 5-0 and 5-1 are used.
When the control signals C0 and C1 are not output, the outputs Eto and Et1 of the error calculators 3-0 and 3-1 are selected and output.

Also, the description has been made that the error distribution is added only to the next input pixel. However, as described in the description of the prior art, a configuration in which the error is distributed to a plurality of pixels is used. It is also possible to take

Further, in this embodiment, an example of a combination of two colors has been described, but a combination of three or more colors can be realized by adopting a similar configuration.

[Second Embodiment] FIG. 5 is a block diagram showing a configuration example of an image processing apparatus according to a second embodiment of the present invention. In the first embodiment, the case where both output values are binary is shown. However, in this embodiment, the output value O0 for the input I0 is ternary, and the output value O1 for the input I1 is binary. Has become.

Therefore, as is apparent from a comparison between FIG. 5 and FIG. 1, the configuration of the device relating to the input I1 is exactly the same as that of the first embodiment. Therefore, the description here will focus mainly on the differences from the first embodiment.

In FIG. 5, I0 and I1 represent input pixel data of color 0 (for example, cyan) and color 1 (for example, magenta), and are 8-bit multi-valued image data, respectively. These pixel data are input to adders denoted by 1'-0 and 1-1, respectively.

In the adders 1'-0 and 1-1, the multi-valued data I0 and I1 and the multi-valued data I0 and I1 and the error calculator
The error data E0 and E1 from the pixels already subjected to the pseudo gradation processing, which are the outputs 5'-0 and 5-1, are added as inputs and output. Outputs I'0 and I'1 of the adders 1'-0 and 1-1 are input to output determination units indicated by 2'-0 and 2-1 respectively.

FIG. 6 shows the processing in the output determining units 2'-0 and 2-1.
This will be described with reference to FIG. FIGS. 6A and 6B show the input / output characteristics of the output determining units 2′-0 and 2-1 respectively, wherein the horizontal axis represents the input value and the vertical axis represents the output value. Here the output decision unit
At 2′-0, since ternarization is performed, thresholds for determining output values (0, 1, or 2) are set to th0-0 and th0-1 (th0-0 <t
h0-1), in the output determination unit 2'-0, the output value of the adder 1'-0 is an input, and the possible range of the input value is (th0-1-255 to 255 + th0-0).

In response to this input, the output value of the output determining unit 2'-0 is set to a threshold value th0-0, th0-1 as a boundary, and to a value less than th0-0, 0
Is 128 (1 when considered with a ternary output) when it is greater than or equal to th0-0 and less than th0-1, and is 255 (when it is considered with a ternary output) when it is greater than th0-1. This is represented by the solid line in FIG.

On the other hand, in the output determining unit 2-1, since the binarization is performed in the same manner as in the first embodiment, if the threshold for determining the output value (0 or 1) is th1, the output determining unit 2-1 In 2-1, since the output value of the adder 1-1 is an input, the possible range of the input value is (th1-255 to 255 + th
1)

In response to this input, the output value of the output determination unit 2-1 is set at 0 below the threshold value th1 and 255 at the threshold value th1 or more (1 in the case of binary output). This is Figure 6
In (b), it is represented by a solid line.

The outputs Ot0 and Ot1 of the output decision sections 2'-0 and 2-1 are input to error calculation sections 3'-0 and 3-1 respectively. The error calculators 3′-0 and 3-1 output the outputs Ot0 and O2 of the output determiners 2′-0 and 2-1.
With t1 and the outputs I'0 and I'1 of the adders 1'-0 and 1-1 as inputs, the error between them is calculated and output.

That is, assuming that the outputs of the error calculators 3'-0 and 3-1 are Et0 and Et1, respectively, Et0 and Et1 are respectively Et0 = I'0-Ot0: Ot0 = 0 or 128 or 255 Et1 = I '1-Ot1: Ot1 = 0 or 255.

On the other hand, the outputs I'0 and I'1 of the adders 1'-0 and 1-1 are provided.
Is also input to the output determination unit 2'-2. Output decision unit 2 '
-2, the output is added to the output I 'of the adder 1'-0, 1-1.
0, determined based on I′1, and output as Ot2.

FIG. 7 schematically shows the processing in the output decision unit 2-2, in which the horizontal axis represents the input I'0 of the output decision unit 2'-2, and the vertical axis represents the input I'1. Each is represented. The solid lines represented by l0, I1 and l2 in the figure indicate the thresholds for determining the output value of the output determining unit 2'-2, and the I'0 and I'1 are on the left side of the straight line l0 ( The output is 0 at the portion indicated by the arrow 0 in the figure), and I'0 and I'1 are represented by straight lines l0 and l1.
(A portion indicated by two arrows in FIG. 1), the output becomes 1, and I′0 and I′1 are represented by a straight line l.
The output is 2 when it is between 1 and l2 (the part indicated by two arrows in the figure), and similarly when it is on the right side of the straight line l2 (the part indicated by 3 in the figure). ), The output is 3.

Here, the fact that the output of the output decision unit 2'-2 is 0 means that the outputs of both the color 0 and the color 1 are 0, and that the output is 1 Is one of two colors
A color output of 1 means that the output of 2 means that the sum of the outputs of the two colors is 2, and similarly, an output of 3 means that the output of the color is 3. This means that the sum of the outputs is 3.

In this embodiment, as shown in FIG. 7, the threshold of color 0 is fixed to th0-0 and th0-1, the threshold of color 1 is fixed to th1, and the threshold when two colors are combined is (A, B) at which the threshold of corresponds to the multicolor input values 0, 255,
Although it is assumed that the shape is a straight line connecting (C, D) and (E, F), the present invention is not limited to this.
That is, as long as the output of the output determining unit 2′-2 is determined based on the input values I′0 and I′1, any method may be used, as in the first embodiment. The same is true.

The output Ot of the output determining units 2'-0, 2-1 and 2'-2
0, Ot1, Ot2, outputs Et0, Et1 of error calculators 3'-0, 3-1
Is input to the output change determination unit 4 '. Output change judgment unit 4
In, based on the inputs Ot0, Ot1, Ot2 and Et0, Et1, the output value output values Ot0,
It is determined whether Ot1 is to be changed.

The conditions under which the output values Ot0 and Ot1 are changed in the output change judgment section 4 'will be described with reference to FIG. In FIG. 7, portions indicated by regions (a) to (j) indicate portions in which one of the output values Ot0 and Ot1 is changed by the output change determination unit 4 '.

[0063]

[Table 2]

Table 2 shows the conditions.
In the cases (a) and (b), Ot1 and Ot0 are set to 0, respectively.
In cases (e) and (f), Ot0 may be changed to 1, and in cases (i) and (j), Ot0 may be changed to 2 and Ot1 may be changed to 1.

In the case of (c), either Ot0 or Ot1 should be changed to 1, and in the case of (d), either Ot0 or Ot1 should be changed to 0. In the case of (g), Ot0 is 2
Or Ot1 should be set to 1. In the case of (h), Ot0 should be set to 1 or Ot1 should be selected to be 0. In these cases, which one to change is determined by comparing errors.

That is, the outputs Et0 and Et1 of the error calculators 3'-0 and 3-1 are also input to the output change determiner 4 '.
If the conditions are (c), (d), (g) and (h), E
It is sufficient to normalize t0 and Et1 with the maximum value of the absolute value of the error for each color and then compare the absolute values to change the larger value.

As described above, the output decision unit 2'-0 or 2-1
When it is determined that the outputs Ot0 and Ot1 are to be changed, the output change determining unit 4 'outputs control signals C0 and C1 for the output to be changed.

The control signals C0 and C1 and the outputs Ot0 and Ot1 of the output decision sections 2'-0 and 2-1 are respectively output to the output change section 4'-.
Input to 0 and 4-1. The output changing units 4-0 and 4-1 input the input signals Ot0 and Ot1 according to the control signals C0 and C1, respectively.
And output final output signals O0 and O1.

On the other hand, the final output signals O0 and O1 output from the output changing units 4'-0 and 4-1 are calculated together with the outputs I'0 and I'1 of the adders 1-0 and 1-1. Input to the units 5'-0, 5-1,
The error is calculated again.

At this time, assuming that the outputs of the error calculators 5-0 and 5-1 are E0 and E1, respectively, E0 and E1 are E0 = I'0-O0: O0 = 0 or 128 or 255 E1 = I '1-O1: O1 = 0 or 255.

The outputs E0 and E1 of the error calculators 5'-0 and 5-1 are input to adders 1-0 and 1-1, respectively, and added to the next input image signal. Since the processing for one input data is performed according to the above configuration, the pseudo gradation processing for the entire image can be performed by repeating the above processing while shifting the processing direction by one pixel.

In this embodiment, the recalculation of the error is always performed in the same manner as in the first embodiment. However, the configuration is the same as that of FIG. Recalculation may be performed only when the signals C0 and C1 are output, that is, only when the output is changed.

Although the description has been made such that the error distribution is added only to the next input pixel, a configuration in which the error is distributed to a plurality of pixels as described in the prior art section is described. It is also possible to take

In this embodiment, it is assumed that one color is ternary and one color is binarized. However, a combination of output gradations is freely adopted regardless of this combination. can do.

Further, in the present embodiment, an example of a combination of two colors has been described, but a combination of three or more colors can be realized by adopting a similar configuration.

As described above, according to the present invention, even if the number of output gradations of the pseudo gradation processing differs for each color, pseudo gradation processing combining a plurality of colors can be performed without any problem.

[0077]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
By executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instructions of the program code.
It goes without saying that a case where the functions of the above-described embodiments are implemented by performing some or all of the actual processing, and the processing performs the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0080]

As described above, according to the present invention,
Even in the case where the error diffusion method is used by combining two or more colors, different threshold values can be used for each color, and different numbers of output gradations can be used for each color. This has the effect of being possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating processing in output determination units 2-0 and 2-1 according to the first embodiment.

FIG. 3 is a diagram illustrating processing in an output change determination unit 4 according to the first embodiment.

FIG. 4 is a block diagram illustrating a configuration example of an image processing apparatus according to a modification of the first embodiment.

FIG. 5 is a block diagram illustrating a configuration example of an image processing apparatus according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating processing in an output determination unit 2′-0, 2-1 according to the second embodiment.

FIG. 7 is a schematic diagram showing a process in an output change determination unit 4 ′ of the second embodiment.

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Claims (13)

[Claims] 1. An image processing apparatus for generating and outputting a pseudo gradation signal having a predetermined number of gradations for each of the plurality of colors from a multi-valued pixel signal of a plurality of colors, the image processing apparatus comprising: Adding means for respectively adding the error value between the multi-valued pixel signal value and the pseudo gradation signal value of the same color to each of the value pixel signal values; and a predetermined value for each of the output values of the adding means. First output determining means for comparing the threshold value and outputting a tentatively-determined pseudo-gray-scale signal; and first calculating and outputting an error between each of the tentatively-determined pseudo-gray-level signal and a corresponding output of the adding means. Error output means, and second output determination means for outputting, from all outputs of the addition means, a multicolor pseudo-tone signal that is a pseudo-tone output for a color obtained by combining the plurality of colors, All of the output of the first error calculation means and Output change determining means for determining whether or not a change is required for each of the tentatively determined pseudo tone signals, based on the color pseudo tone signal; and Output changing means for outputting each of the pseudo gradation signals without changing or changing them; and second error calculating means for obtaining and outputting an error between each of the pseudo gradation signals and a corresponding output of the adding means. An image processing apparatus comprising: 2. The method according to claim 1, wherein the predetermined threshold value and / or the number thereof in the first output determination means are set independently for each output value of the addition means. Image processing device. 3. The output change determining unit according to claim 1, wherein the output change determining unit determines the necessity of the change by using a maximum value of each output of the first error calculating unit. Image processing device. 4. The apparatus according to claim 1, wherein the output change determining means determines the necessity of the change based on a value obtained by normalizing each output of the first error calculating means by a maximum error. Alternatively, the image processing apparatus according to claim 2. 5. A selecting means for selecting an output of said second error calculating means and an output of said first error calculating means in accordance with a decision result of said output changing means and inputting said output to said adder. The image processing apparatus according to claim 1, further comprising: 6. An image forming apparatus for forming an image of multi-valued image data using the image processing apparatus according to claim 1. 7. An image processing method for generating and outputting a pseudo gradation signal having a predetermined number of gradations for each of the plurality of colors from a multi-valued pixel signal of a plurality of colors, comprising: An adding step of adding, to each of the value pixel signal values, an error value between the multi-valued pixel signal value and the pseudo gradation signal value of the same color; and a predetermined value for each of the output values of the adding step. A first output determination step of comparing the provisional pseudo gray level signal with a threshold value and outputting an error between each of the provisional pseudo gray level signal and a corresponding output of the adding step; A second output determination step of outputting a multi-color pseudo-tone signal that is a pseudo-tone output for a color obtained by combining the plurality of colors from all outputs of the addition step; Key signal and said first error meter An output change determining step of determining whether or not a change is required for each of the provisionally determined pseudo-gradation signals based on all of the outputs of the steps and the multi-color pseudo-gradation signal, and based on a result of the output change determining step. An output changing step of outputting each of the tentatively determined pseudo-gradation signals as the pseudo-gradation signals without changing or changing the pseudo-gradation signals; and determining an error between each of the pseudo-gradation signals and a corresponding output of the adding step. A second error calculating step of outputting the image data. 8. The method according to claim 7, wherein the predetermined threshold value and / or the number thereof in the first output determination step are set independently for each output value of the adding step. Image processing method. 9. The method according to claim 1, wherein the output change determining step comprises:
9. The image processing method according to claim 7, wherein the change necessity is determined using the maximum value of each output of the error calculation step. 10. The output change determining step determines the necessity of the change based on a value obtained by normalizing each output of the first error calculating step by its maximum error. Or the image processing method according to claim 8. 11. A selecting step of selecting an output of the second error calculating step and an output of the first error calculating step according to a result of the determination of the output changing step and inputting the result to the adder. The image processing method according to any one of claims 7 to 10, further comprising: 12. The method according to claim 7, wherein
An image forming apparatus for forming an image of multi-valued image data by using the image processing method described in the section. 13. A computer-readable storage device storing an image processing program for generating and outputting a pseudo gradation signal having a predetermined number of gradations for each of the plurality of colors from multi-valued pixel signals of the plurality of colors. A storage medium, for each of the multi-color pixel signal values of the plurality of colors, a program of an addition step of adding an error value between the multi-value pixel signal value and the pseudo-gradation signal value of the same color, A program for a first output determining step of comparing each of the output values of the adding step with a predetermined threshold value and outputting a tentatively-determined pseudo-gradation signal; A program for a first error calculation step for calculating and outputting an error from a corresponding output of the step; and a multi-color pseudo-tone which is a pseudo-tone output for a color obtained by combining the plurality of colors from all outputs of the addition step. Output signal A program for a second output determining step; a tentatively determined pseudo-gradation signal based on all of the tentatively-determined pseudo-gradation signal and the output of the first error calculating step; A program for an output change determination step for determining whether or not each of them is required to be changed; and, based on the determination result of the output change determination step, outputting each of the provisionally determined pseudo gradation signals as the pseudo gradation signal without changing or changing each of them. A storage medium comprising: a program for an output changing step to be performed; and a program for a second error calculating step for calculating and outputting an error between each of the pseudo gradation signals and a corresponding output of the adding step.