JP3190527B2 - Color image processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus,
In particular, the present invention relates to a color image processing apparatus which requires a small circuit scale and can obtain smooth gradation.

[0002]

2. Description of the Related Art In recent years, colorization of images has been promoted in the field of printers, and with this, color images have been processed and transmitted and received in facsimile machines and the like. In a conventional color image processing method, after converting RGB multi-value data of a color image input by an image input unit into CMY multi-value data, a Bk signal component is generated, and error diffusion processing is performed in four CMYK sequences. I was Such conventional color image processing methods include those shown in FIGS. FIG. 14 is a block diagram showing the overall configuration of a conventional color image processing apparatus. In this figure, reference numeral 1 denotes a color correction unit for inputting red (R), green (G), and blue (B) (hereinafter, referred to as RGB) signals of an image read by a color image reading device and performing color correction; Reference numeral 2 denotes RGB (color-corrected) RGB signals for cyan (C), magenta (M), and yellow (Y).
(Hereinafter referred to as CMY) RGB / CM
The Y color conversion means 3 is a Bk signal generating section for generating a black (Bk) signal, and 4 is an error diffusion section for binarizing and outputting the multi-value data of each of the RGB colors.

In such a configuration, the RGB multi-valued data input by the color image reading device as the image input means is subjected to color correction processing by the color correction unit 1 and then to R
The data is converted into CMY multi-value data by the GB / CMY color conversion means 2. Then, the CMY multi-value data is input to the Bk signal generation unit 3 to generate a Bk signal component,
A color image is output by performing a binarization process by performing an error diffusion process on the four series of YK. In this case, as a method of generating the Bk signal component, a method called an under color removal method or a skeleton black method has been used.

First, a method of generating a Bk signal component by the under color removal method will be described. In this method, an RGB signal input from a color image reading device is converted to RGB / CMY.
The color conversion means 2 converts the data into CMY multivalued data. At this time, there is a relationship of C = 1−RM = 1−GY = 1−B. CMY after RGB / CMY color conversion
FIG. 15A is a graph showing each color signal component. In this figure, the horizontal axis indicates the type of each CMY color signal, and the vertical axis indicates the intensity of each CMY color signal component. In the under color removal method, the common component of each of the CMY color signals (the lower part cut off by a horizontal dotted line in FIG. 15A) is used as a Bk signal component, and the Bk signal component replaced with the CMY color signals. Is used as a formal CMY color signal component. That is, in this case, the following equation is established. Bk = Min {C, M, Y} × β C ′ = C−Bk M ′ = M−Bk Y ′ = Y−Bk where CMY: signal strength C ′ input from the color image reading device, M ′, Y ′: signal intensity after the undercolor removal method is performed β: coefficient of Bk component Each signal component of C'M'Y'Bk thus obtained is shown in FIG. Next, a method of generating a Bk signal component by the skeleton black method will be described. This method is a modification of the undercolor removal method. In this method, similarly to the undercolor removal method, first, the RGB signals input from the color image reading device are converted into the CM signals by the RGB / CMY color conversion means 2.
Convert to Y multi-value data. FIG. 16A is a graph showing the CMY color signal components after the RGB / CMY color conversion.
In the skeleton black method, when the weakest signal component exceeds a certain threshold in the graph of each CMY color signal, the component exceeding the threshold (the horizontal dotted line in FIG. (Corresponding to the exceeded Y signal portion) as a Bk signal component, and a component obtained by subtracting the Bk signal component from each CMY color signal is used as a formal CMY color signal component. That is, in this case, the following equation is established. if Min {C, M, Y}> α, Bk = Min
{C, M, Y} −α C ′ = C−Bk M ′ = M−Bk Y ′ = Y−Bk where CMY: signal strengths C ′, M ′, input from the color image reading device Y ′: signal strength after skeleton black method implementation α: Bk generation determination threshold FIG. 16B shows the signal components of C′M′Y′Bk obtained in this manner.

[0005]

However, in the above-described conventional color image processing apparatus, when the Bk signal is generated, the color conversion is performed from the RGB system to the CMY system using the multi-value data.
A Bk signal is generated from the CMY system by the above-described under color removal method or the skeleton black method, and the CMYK 4 signal is generated.
The error diffusion processing of the series signals is performed independently, and the binarization is performed, so that the circuit configuration and the circuit scale are increased.

For a binary printer such as an ink-jet printer, which does not have a very high resolution, smooth gradation reproduction is achieved by a combination of the conventional method (under color removal method, skeleton black method, etc.) and error diffusion processing. Was not obtained. The cause is that the BMY component and the CMY (RGB) component are separated from the CMY (RGB) multi-valued data by some method (under color removal method, skeleton black method, etc.)
When printing is to be performed after error diffusion processing is performed independently of each other, printing of Bk and printing of each color of CMY (RGB) usually overlap. However, since only one of the printings can be performed on the pixel, the result is that a reflectance corresponding to the data level expected before the error diffusion processing cannot be obtained. Therefore, the combination of the under color removal method, the skeleton black method, and the like with the error diffusion processing is a fatal defect in a system in which the resolution of the reading system and the resolution of the recording system are required to substantially match. . For example, the following describes the problems when the Bk component is generated by the above-described conventional Bk component generation method, error diffusion processing is performed independently for each color, and the error is output to the ink jet printer, and the causes thereof. In the undercolor removal method, the saturation of a color image is extremely reduced. In particular, the middle lightness portion becomes white and blurred. This is because the components in which the common part of each CMY color signal is replaced with a Bk signal component are subtracted from each CMY color signal, so that the components of each CMY color signal are reduced as a whole. In the skeleton black method, a portion where smooth color reproduction cannot be performed occurs. This is because a remarkable level difference in saturation occurs near the threshold for determining whether to generate a Bk signal.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a color image processing apparatus which requires a small circuit scale and can obtain smooth gradation.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a color image processing apparatus for determining whether a given pixel is an achromatic color or a chromatic color based on multi-value data of each of RGB colors of a predetermined pixel. An achromatic color judging means for judging, and a binarization processing means for binarizing and outputting the multi-value data of each of the RGB colors;
For pixels determined to be achromatic by the achromatic color determination means, achromatic data is generated and output based on the binarized data, while for pixels determined to be chromatic, the pixels are binarized. The gist of the invention is to provide a color conversion means for directly outputting data.

[0009]

According to the present invention, the RGB multi-valued data input from the image input means is input to the binarization processing means and converted into binary data on the one hand, and is input to the achromatic color judgment means on the other hand. Then, it is determined whether the pixel is achromatic or chromatic. The data after the binarization processing is input to the color conversion means, where the color conversion is performed based on the determination result from the achromatic color determination means. In this color conversion processing, achromatic data is generated and output based on the binarized data for a pixel determined to be achromatic, while the binarized data is generated for a pixel determined to be chromatic. Is output as is.

[0010]

FIG. 1 is a block diagram showing a color image processing apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 11 denotes R of an image read by a color image reading apparatus.
An error diffusion processing unit as binarization processing means for inputting multi-valued data of each color of GB, that is, multi-valued digital input signal 14 and converting it into binary data, 12 converts the multi-valued digital input signal 14 of a predetermined pixel to An achromatic color determination unit that determines whether the pixel is an achromatic color or a chromatic color based on the input, based on the binarized data, for a pixel determined to be achromatic by the achromatic color determination unit. An achromatic color reproduction color conversion unit as color conversion means for generating and outputting achromatic color data and outputting the binary data as it is for pixels determined to be chromatic. In this embodiment, the multi-level digital input signal 14 has GCID (7: 0),
8-bit digital data of RCID (7: 0) and BCID (7: 0) is used.

The error diffusion process executed by the error diffusion processing unit 11 is a process in which an error generated when binarization is performed at a certain slice level is diffused to peripheral pixels.
In the color image processing apparatus according to the present embodiment, the error diffusion processing unit 11 performs multi-valued digital input signals 14 (GCID (R), G, and B) input from a color image reading apparatus. 7: 0), RCID (7: 0),
BCID (7: 0)) is subjected to error diffusion processing for each of the RGB colors independently, and the resulting RGB binary data 15 is output to the achromatic color reproduction color conversion unit 13.

In this embodiment, the achromatic determination unit 12
For example, a maximum value / minimum value detection type as shown in FIG. 2 is used. The achromatic color determination unit 12 outputs multi-valued digital input signals (GCID (7: 0), RCID (7: 0), and BCID) of three colors of R, G, and B from the color image reading device.
(7: 0)) 14 to input a MAX detection circuit 21 for detecting the strongest signal among the RGB color signals, a MIN detection circuit 22 for detecting the weakest signal, and a MAX detection circuit 2
1 and a difference value 25 for calculating the difference between the maximum value 23 output from the MIN detection circuit 22 and the minimum value 24 output from the MIN detection circuit 22. ) / A divider 28 for obtaining a maximum value 27 and a selector 29 for selecting a threshold value 30 for achromatic color determination between a threshold value 1 and a threshold value 2 based on a threshold value selection signal MRM0.
, A comparator 31 that compares the calculation result (maximum value−minimum value) / maximum value 27 of the divider 28 with a threshold value 30 for achromatic color determination, and a flip-flop circuit that holds the comparison result 32 by the comparator 31 33 and 34, an AND circuit 35 for calculating all logical products of the comparison results per pixel, and a timing adjustment circuit 36 for adjusting the delay of the processing time in the error diffusion processing unit 11 and outputting the achromatic color determination signal MOIA. ,
A clock circuit 37 is used to determine the operation timing of each functional unit in performing the achromatic color determination process.

The achromatic color reproduction color conversion section 13 includes a binary signal 15 output from the error diffusion processing section 11 and the achromatic color determination section 1.
The image data is converted based on the achromatic color determination result 16 output from the second unit 2 and output as an image processing result 17. The determination of printing / non-printing of the Bk signal is performed by substituting the binarized result of G (green) or the like (without newly performing error diffusion processing of multi-value data for Bk) to reproduce black or white. It has been converted to The color conversion theoretical formula of the achromatic color reproduction color conversion unit 13 is shown below. A list of conversion codes for executing the color conversion theoretical formula is shown in FIGS. 10 to 13 described later.

[0014]

The operation of the color image processing apparatus according to the present embodiment having the above configuration will be described below. This color image processing apparatus operates by inputting multi-valued digital input signals 14 of RGB three series in parallel by a color image reading apparatus. In the achromatic color determination unit 12, two types of threshold values 1 and 2 are prepared in advance by using the input data of the selector 29, and the threshold value 30 for the achromatic color determination is determined by the selector 29 using the selection signal MRM0. Selected. On the other hand, R, G, B multi-valued digital input signals 14 (GCID (7: 0), RCID) input from the color image reading device
(7: 0), BCID (7: 0)), the MAX detection circuit 21 and the MIN detection circuit 22 detect the maximum value 23 and the minimum value 24, respectively, and then calculate the maximum-minimum value difference 26. Finally, (maximum value−
The minimum value / maximum value 27 is calculated by the divider 28.
The calculation result (maximum value−minimum value) / maximum value 27 is compared with the threshold value 30 for the achromatic color determination by the comparator 31.
The comparison result of the signal 27 output in time series is held in flip-flops 33 and 34, and the logical product of all (three types) of the comparison results per pixel is obtained by an AND circuit 35 to determine whether the corresponding pixel is achromatic. Determine whether The determination result is adjusted by the timing adjustment circuit 36 to adjust the delay of the time required for the image processing in the error diffusion processing unit 11, and the achromatic color reproduction color conversion unit 13 is controlled so that the determined pixel and the determination result have the same timing. Is output.

The achromatic color reproduction color conversion unit 13 generates achromatic data by replacing the binarized data with respect to the pixel determined to be achromatic by the achromatic color determination means 12 and forcibly converts the achromatic color. And outputs the binary data as it is for pixels determined to be chromatic. In replacing the data,
In this embodiment, it is assumed to be performed using the result of the G (green) signal.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The color image processing apparatus according to this embodiment includes:
Before the error diffusion processing unit 11 and the achromatic color determination unit 12,
R, G, B multi-value digital input signals (GCID (7: 0), RCID (7:
0), BCID (7: 0)) 14 and input GR, R-
A color difference calculation unit 41 that generates color difference signals 44 for B and BG
And GR and R- generated by the color difference calculation unit 41.
A matrix color correction unit 42 for performing color correction based on each of the B, B-G color difference signals 44 and the multi-level digital input signal 14
A control unit 43 for controlling the operation of the entire color image processing apparatus according to this embodiment; and an R1, G1, and B1 color image signal 45 corrected by the matrix color correction unit 42. An error diffusion processing unit 11 for binarizing with the above, an achromatic color determining unit 40 which receives the multi-level digital input signal 14 of a predetermined pixel and determines whether the pixel is an achromatic color or a chromatic color based on the input, For pixels determined to be achromatic by the achromatic color determination means, achromatic data is generated and output based on the binarized data, while for pixels determined to be chromatic, the binarized data is generated. And an achromatic color reproduction color conversion unit 13 as a color conversion means for outputting the image data as it is. The achromatic color reproduction color converter 13 converts the binarized R
2, G2, B2 color image signal 15 and achromatic color determination unit 4
The achromatic color is forcibly reproduced from the determination result 16 of 0.

The color difference calculation section 41 and the matrix color correction section 42 have, for example, a configuration as shown in FIG. The color difference calculation unit 41 is a two-group (8-bit configuration) three-input one-output first group provided in parallel to receive the multi-valued digital input signals 14 of R, G, and B colors input in parallel. And a second selector 52, and a differentiator 53 that outputs a color difference signal 44 by taking the difference between the output values of the selectors 51 and 52.

The matrix color correction section 42 includes a color difference calculation section 4
A color difference signal 44 input in time series from
Look-up table (comprising a memory such as a ROM) 54 as a correction coefficient storage unit that outputs a matrix correction coefficient 47 in response to a selection signal 46 input thereto.
, A latch circuit 55 for holding a matrix color correction coefficient 47 output in time series, and a 6-input 1-output selector for selecting intermediate data in the middle of addition with the multi-valued digital input signals 14 of R, G, and B colors 56, an adder 57 that adds the output of the selector 56 and the output value of the latch circuit 55 for holding the coefficient, and first to third latches that hold the intermediate data and the final result during the addition at their respective timings. Circuits 58, 59, and 60 round the final addition result (9 bits or more to 8 bits), and output the color image signal 45 obtained as a result of the R, B, and G3 series operation to the error diffusion processing unit 11. And third to third clamp circuits 61, 62 and 63.

As shown in FIG. 5, the achromatic color judging section 40 is of an absolute color difference type different from the achromatic color judging section 12 in the first embodiment. The achromatic color determination unit 40 receives the G-
R, RB, and BG color difference signals (CMXA (8:
0)) The absolute value conversion unit 64 that takes an absolute value 46 of 44 and the threshold value 30 for achromatic color determination are set between two types of threshold values 1 and 2 that are set in advance as an achromatic color determination range. A selector 29 for selecting based on the threshold value selection signal MRM0,
A comparator 31 for comparing the absolute value 46 of each of the color difference signals 44 with the threshold value 30; and flip-flop circuits 33 and 34 for holding a comparison result 32 output from the comparator 31 in time series.
And an AND circuit 35 for calculating all logical products of the comparison results per pixel; a timing adjustment circuit 36 for adjusting the delay of the processing time in the error diffusion processing unit 11 to output the achromatic color determination signal MOIA; A clock circuit 3 that takes the operation timing of each functional unit in performing the determination process
7 is comprised. The achromatic color reproduction color conversion unit 1
The configuration, conversion contents, and logical formulas of 3 are the same as in the first embodiment.

Here, the color conversion method (linear primary conversion) employed in the color image processing apparatus according to the present embodiment will be described. The color conversion method using a 3 × 3 matrix is generally used as a method that can be easily realized. However, if the 3 × 3 coefficient is arbitrarily determined, the achromatic color may change to a chromatic color. Therefore, the coefficient is usually determined such that the eigenvalue of the matrix becomes 1. The matrix determined in this way can be represented as the following determinant (1).

[0022]

Therefore, the input signal of a certain pixel is converted to (Rin, G
in, Bin) and output signals after color conversion are (Rout, Gout,
Bout), and color conversion is performed in a 3 × 3 matrix as shown in the following equation (2).

[0024]

That is, (output after color conversion) = (color conversion matrix) × (input image signal). Here, when the above equation (2) is expanded and arranged, it can be arranged as the following equation (3). Rout = Rin + (Gin−Rin) × M12 + (Rin−Bin) × (−M13) Gout = (Gin−Rin) × (−M21) + Gin + (Bin−Gin) × M23 Bout = (Rin−Bin) × M31 + ( Bin−Gin) × (−M32) + Bin (3) Here, (Gin−Rin) × M12 = D12 (Rin−Bin) × (−M13) = D13 (Gin−Rin) × (− M21) = D21 (Bin−Gin) × M23 = D23 (Rin−Bin) × M31 = D31 (Bin−Gin) × (−M32) = D32 If Expression (3) is given, Rout = Rin + D12 + D13 Gout = Gin + D21 + D23 (4) Bout = Bin + D31 + D32. Therefore, in this embodiment, color correction is performed based on the content of equation (4).

Next, the operation of this embodiment will be described. The color image processing apparatus according to the second embodiment also uses a color image reading apparatus to perform RGB3 processing similarly to the first embodiment.
The multi-valued digital input signals 14 of the series are input in parallel to operate. This multi-level digital input signal 14 (GCID
(7: 0), RCID (7: 0), BCID (7:
When 0)) is input, the color-difference calculator 41 includes a first selector 51 and a second selector 52, which are two-system selectors.
And the color difference signals 44 of GR, RB, and BG are output in chronological order using the subtractor 53. The output method is to divide the cycle of one pixel into four, and in one of the times, G and R are selected by the first and second selectors 51 and 52, and the output is input to the differentiator 53 and The respective color difference signals 44 of −R are calculated. Similarly, time 2 is RB, time 3 is B
-G is calculated and the color difference signal 44 is output (time 4 is the same as time 3 but BG is calculated, but it is a don't care). The color difference signal 44 is a 9-bit signal with the MSB as a sign bit.

The matrix color corrector 42 is provided with a color difference calculator 4.
The 9-bit color difference signal 44 input from 1 is used as a lower address, and the 3-bit control signal input from the controller 43 is used as an upper address, from a look-up table 54 implemented by a ROM in which data has been written in advance. Matrix color correction coefficient according to each color difference (D in equation (4)
12, D21, D31, D13, D23, and D32) are output in chronological order. And first of all,
D12 of matrix color correction coefficient 47 input in time series
Is held in the coefficient holding latch circuit 55, and the A input (corresponding to Rin in the equation (4)) selected by the selector 56 is added thereto by the adder 57. The addition result by this operation is (Rin + D12). The result of this addition is the first
At the same time as the latch circuit 58 for holding the coefficient, the latch circuit 55 for holding the coefficient
, And together with B selected by the selector 56
The input (corresponding to Gin in equation (4)) is added by the adder 57. The addition result by this operation is (Gin + D21). The result of this addition is held in the second latch circuit 59, and at the same time, the coefficient holding latch circuit 55 holds D31 of the next matrix color correction coefficient 47, and at the same time, the C input ((4 ) Equivalent to Bin)
Are added by the adder 57. The addition result by this operation is (Bin + D31). The addition result is held in the third latch circuit 60, and at the same time, the coefficient holding latch circuit 55 holds D13 of the next matrix color correction coefficient 47, and the D input (first signal) selected by the selector 56 together therewith. Output of the latch circuit 58, that is, Rin + D1
2) in the adder 57. The addition result by this operation is (Rin + D12 + D13). The result of the addition is held in the first latch circuit 58 again, and at the same time, the latch circuit 55 for holding the coefficient holds D23 of the next matrix color correction coefficient 47, and the selector 5
The E input selected at 6 (the output of the second latch circuit 59, that is, equivalent to Gin + D21) is added by the adder 57. The addition result by this operation is (Gin + D21 +
D23). The result of the addition is held in the second latch circuit 59 again, and at the same time, the latch circuit 55 for holding the coefficient is held.
Holds the D32 of the next matrix color correction coefficient 47, and also the F input selected by the selector 56 (corresponding to the output of the third latch circuit 60, ie, Bin + D31)
Are added by the adder 57. The addition result by this operation is (Bin + D31 + D32).

Next, each addition result is rounded down to 8 bits by the first to third clamp circuits 61, 62 and 63 (M
SB is a sign bit), R, B, G3 sequence operation result (R
in + D12 + D13, Gin + D21 + D23, Bin + D
31 + D32) to obtain the color image signal 45
Are output to the error diffusion processing unit 11 in synchronization.

The achromatic color judging section 40 prepares two kinds of thresholds for achromatic color judgment in advance, a threshold value 1 and a threshold value 2, and uses the selection signal MRM0 to select a reference value for the achromatic color judgment (after selection). Is selected. On the other hand, in the absolute value conversion section 64, the color difference signal 44 (CM
XA (8: 0)), the absolute value 46 of the input is obtained, and the absolute value 46 is compared with the threshold value 30 of the achromatic color determination by the comparator 31.
The comparison result 32 output in time series is held in flip-flops 33 and 34, and the logical product of all (three types) of the comparison results per pixel is calculated by an AND circuit 35 to determine whether the corresponding pixel is achromatic. Is determined. The determination result is adjusted by the timing adjustment circuit 36 to adjust the delay of the time required for the image processing in the error diffusion processing unit 11, and the achromatic color reproduction color conversion unit 13 is controlled so that the determined pixel and the determination result have the same timing. Is output.

Next, the operation of the achromatic color reproduction color conversion section 13 is the same as that described in the first embodiment. As described in the description of the first embodiment, the error diffusion processing 11 diffuses an error generated when binarization is performed at a certain slice level to peripheral pixels. In the color image processing apparatus of the second embodiment, the color image signal (multi-value) 45 of each color of RGB output from the matrix color correction unit 42 is performed.
Is subjected to an error diffusion process independently for each of the RGB colors,
The color image signal 15 including the value data is output to the achromatic color reproduction color conversion unit 13.

As described above, in the first and second embodiments,
Although the example of the “maximum value / minimum value detection type” or the “color difference absolute value type” has been described as the achromatic color determination units 12 and 40,
A different type of achromatic judgment unit may be used. The achromatic color determination unit 70 shown in FIG. 6 is an example of a color difference calculation / maximum value detection type achromatic color determination unit belonging to such another type. The achromatic determination unit 70 is a multi-level digital input signal (GCID (7: 0), RCID (7: 0), BID) of three colors of R, G, and B from the color image reading device.
CID (7: 0)) 14 and an RGB / CMY conversion unit 71 for converting this signal into a CMY-sequence multi-valued digital signal, and M signals between the RGB / CMY converted image signals.
A color difference calculation unit 72 for generating color difference signals 73 of G, GY, and YM; a maximum value detection circuit 74 for detecting the strongest signal among the CMY color signals, that is, a maximum value 75; MG, GY, which are input in time series from 72,
An absolute value conversion unit 76 for obtaining an absolute value 77 of each of the Y-M color difference signals 73 and a threshold 30 for achromatic color determination are set to two types of threshold 1 and threshold 2 which are set in advance as achromatic color determination ranges.
And a multiplier 78 for calculating the product of the maximum value 75 detected by the maximum value detection circuit 74 and the threshold value 30 output from the selector 29; Absolute value 77 of color difference signal 73
And comparator 31 comparing operation result 79 of multiplier 78
And flip-flop circuits 33 and 34 for holding the comparison results 32 output in time series from the comparator 31 and an AND circuit 35 for calculating the logical product of all the comparison results per pixel
A timing adjustment circuit 36 that adjusts the delay of the processing time in the error diffusion processing unit 11 to output the achromatic color determination signal MOIA; and a clock circuit 37 that takes the operation timing of each functional unit in performing the achromatic color determination process. It is configured.

With this configuration, the achromatic determination unit 70
Two types of thresholds for achromatic color determination, threshold 1 and threshold 2, are prepared in advance, and the selector 29 selects a reference value for achromatic color determination (the selected threshold 30) using the selection signal MRM0. On the other hand, the RGB / CMY conversion unit 71 converts the R, G, B multi-valued digital input signal 14 from the color image reading device into a CMY sequence multi-valued digital signal, and the color difference calculation unit 72 performs the RGB / CMY conversion. , G-Y, and Y-M color difference signals 73 are generated between the image signals of the respective colors.
Then, the absolute value conversion unit 76 takes the absolute value 77 of each of the MG, GY, and YM color difference signals 73 input in time series from the color difference calculation unit 72. Further, the maximum value detection circuit 74
The maximum value 75 of each color signal is detected.
Is multiplied by the multiplier 78 with the threshold value 30 of the achromatic color judgment, and the multiplication result 79 is compared with the previously obtained absolute value 77 by the comparator 31. The comparison result 3 output in time series
2 are held in the flip-flops 33 and 34, and the logical product of all (3 types) of the comparison results per pixel is output to the AND circuit 3
In step 5, it is determined whether the corresponding pixel is achromatic. The determination result is adjusted by the timing adjustment circuit 36 to adjust the delay of the time required for the image processing in the error diffusion processing unit 11, and the achromatic color reproduction color conversion unit 13 is controlled so that the determined pixel and the determination result have the same timing. Is output. The “color difference calculation / maximum value detection type” achromatic color determination unit 70 can be replaced with the achromatic color determination unit 12 used in the first embodiment.

Here, an achromatic color judging method by the achromatic color judging sections 12, 40 and 70 will be described. FIG. 7 is a model diagram illustrating the principle of the achromatic color determination method by the achromatic color determination unit 40 described in the description of the second embodiment. This means that the color space and the arrangement of each color element when each color appears in an RGB sequence and a CMY sequence are represented by cubic coordinates, and the method of achromatic color determination in this color space is a “method based on simple color difference”.
FIG. In this figure, reference numeral O1 indicates the origin of coordinates for representing a color in the RGB sequence, and the position of the origin O1 corresponds to the color "black". On the other hand, in the drawing, reference numeral O2 indicates the origin of coordinates for representing a color in the CMY sequence, and the position of the origin O2 corresponds to the color "white". Further, between the color elements of the RGB series and the color elements of the CMY series, R and C, B and Y, and G and M are complementary to each other. They are set so that they are both ends of a diagonal line.

In the method using the simple color difference, in the RGB color space, the range satisfying | RG− ≦ S | GB | ≦ S (5) | BR− ≦ S is achromatic. Is determined to be a copy. Here, S: achromatic color determination range.

The achromatic color determination range defined by the above equation (5) is represented by Bk (R = G = B
= 0) and W (R = G = B = 255: at the time of 8-bit precision) correspond to the inside of a hexagonal prism having a constant diameter with a center axis as a central axis, and this range is an achromatic portion.

Further, two types of thresholds, threshold 1 and threshold 2, are prepared using the distance from the center of the hexagonal prism shown in FIG. 7 to the intersection of each side as a parameter of the achromatic color determination range, and color image processing is performed. By changing the threshold value according to the image to be performed, a good color image processing result can be obtained.

FIG. 8 is a model diagram for explaining the principle of the achromatic color judging method by the achromatic color judging section 12 mentioned in the description of the first embodiment. Also in this case, the point in which the color space and the arrangement of each color element are represented by cubic coordinates is determined by the achromatic determination unit 4.
0, but the achromatic determination unit 40
Unlike the case of FIG. 1, a conceptual diagram in a case where the method of achromatic color determination in this color space is a “method considering high brightness” is shown.

In this method considering the high brightness, RGB
In the color space, a range satisfying {Max (R, G, B) −Min (R, G, B)} / Max (R, G, B) ≦ S (6) is defined as an achromatic portion. Here, S: achromatic color determination range.

The achromatic judgment range defined by the above equation (6) is represented by Bk (R = G = B
= 0) and W (R = G = B = 255: at the time of 8-bit precision), the central axis is the center axis, and the origin O1 (that is, Bk
Side) corresponds to the inside of a hexagonal pyramid having the vertex at the origin and the bottom of the origin O2 (that is, the W side) having a constant diameter, and this range is an achromatic portion.

Further, two types of thresholds, threshold 1 and threshold 2, are prepared using the distance from the center of the hexagonal pyramid shown in FIG. 8 to the intersection of each side as a parameter of the achromatic color determination range, and perform color image processing. By changing the threshold value according to the image to be performed, a good color image processing result can be obtained.

In this system, color image processing can be performed by multi-valued data of RGB system by setting a wide range of achromatic portions on the side of high lightness. Therefore, the hardware configuration for this processing is small. Yes. Also, there is no need to pay much attention to the vicinity of black reproduction in the achromatic portion.
Useful for system-based printers (without Bk ink).

The expression (6) is replaced by the following expression (7). {Max (| R−G |, | GB |, | BR |)} / Max (R, G, B) ≦ S (7) where M = Max (R, G, B) In other words, the equation (7) is expressed as follows: | R−G | ≦ S | M | GB | ≦ S · M (8) | B−R | ≦ S · M Here, S: achromatic color determination range.

This equation (8) is obtained by multiplying the right side of the above equation (5) by a variable M. The achromatic color judging section 7 shown in FIG.
From 0, it can be realized even in a configuration in which the RGB / CMY conversion unit 51 is omitted.

FIG. 9 is a model diagram for explaining the principle of the achromatic color judgment method by the achromatic color judgment section 70 shown in FIG.
Also in this case, the point in which the color space and the arrangement of each color element are represented by cubic coordinates is the same as in the achromatic color determination unit 40 or 12, but unlike the case of the achromatic color determination units 40 and 12, this color FIG. 6 is a conceptual diagram illustrating a case where a method of determining achromatic color in a space is a “method considering low brightness”.

In this method considering low brightness, RGB
In the color space, the range that satisfies | CM | ≦ SM | MY | ≦ SM (9) | YC | ≦ SM is defined as an achromatic portion. here,

[0046]

Is as follows. The achromatic color determination range defined by the equation (9) is Bk (R
= G = B = 0) and W (R = G = B = 255: at 8-bit precision) as the central axis, the origin O2 (ie, W side) as the vertex, and the origin O1 (ie, Bk side). Corresponds to the inside of a hexagonal pyramid whose bottom surface has a constant diameter, and this range is an achromatic portion.

Also, two types of thresholds, threshold 1 and threshold 2, are prepared using the distance from the center of the hexagonal pyramid shown in FIG. 9 to the intersection of each side as a parameter of the achromatic color determination range, and color image processing is performed. By changing the threshold value according to the image to be performed, a good color image processing result can be obtained.

In this method, the boundary between achromatic and chromatic colors can be smoothly reproduced by setting a wide range of achromatic colors on the low brightness side. The reason is that there is a characteristic that human eyes do not feel much saturation at low brightness. In addition, the achromatic color determination method according to this method is based on a printer (for example, an ink jet printer) in which there is a difference between black due to a mixture of CMY inks and black using only Bk ink in the vicinity of a black reproduction portion among achromatic color portions. Printer) etc., smooth reproducibility in the vicinity of the achromatic black portion is possible.

The circuit configuration of the achromatic color judging section 70 is as shown in FIG. 6, and as described above, the multi-value digital input signal 14 is converted from the RGB system to the CM
The color difference is once converted into a Y system, and thereafter, a color difference is calculated by a color difference calculation unit 72, a maximum value 75 is calculated by a maximum value detection circuit 74, and an absolute value 77 of the color difference is calculated by an absolute value conversion unit 76. On the other hand, the selector 29 selects two types of thresholds 1 and 2 set in advance as the achromatic color determination range with the switching signal MRM0, outputs the achromatic color determination threshold 30, and outputs the maximum value 7
The multiplier 78 multiplies 5 by the threshold value 30 for the achromatic color determination. The result of the multiplication 79 is compared with the absolute value 77 previously obtained by the comparator 31, and the result of the comparison 32 is held in the flip-flops 33 and 34. The product is calculated by an AND circuit 35 to determine whether the corresponding pixel is achromatic. The determination result is adjusted by the timing adjustment circuit 36 to adjust the delay of the time required for the image processing in the error diffusion processing unit 11, and the achromatic color reproduction color conversion unit 13 is controlled so that the determined pixel and the determination result have the same timing. Output. And the same operation is shown in FIG.
In the achromatic determination section 12 shown in FIG. 5, the RGB / CMY conversion section 51 is connected to the MAX detection circuit 21 and the MIN detection circuit 2.
It can also be realized by additional connection at the stage preceding the second stage.

FIGS. 10 to 13 are diagrams showing a list of conversion codes for executing the color conversion theoretical formula of the achromatic color reproduction color conversion unit 13 used in the color image processing apparatus of the present invention. FIG. 10A shows achromatic color determination units 12, 40,
FIG. 7 is a diagram showing a conversion code list when achromatic color reproduction color conversion from an RGB system to an RGBK system is performed by an achromatic color reproduction color conversion unit 13 when it is determined that the color is an achromatic color in 70. At the time of achromatic color determination, data “1” is output as the signal MOIA (achromatic color determination signal 16). The achromatic color reproduction color conversion unit 13 generates achromatic data by replacing the binarized data with respect to the pixel determined to be achromatic by the achromatic color determination unit, and forcibly reproduces the achromatic color. Has already been described in the description of the first embodiment. In addition, according to the present invention, it has been described that the data replacement is performed using the result of the G signal.

When data is replaced by this method,
In FIG. 10A, the input data determined to be achromatic at the uppermost stage is R = 1, G = 1, B = 1, so that the converted output data is also R = 1, G = 1, B = 1. Since this represents achromatic "white", Bk is output as 0 (no printing). Next, the input data determined to be achromatic in the second stage is R = 1, G = 0, B = 0. In this case, since the input signal of G is 0, the input signal of R is converted from 1 to 0. Since the input signal of B was originally 0, it is left as it is. After such a conversion process, the output data after the conversion becomes R = 0, G = 0, B = 0. Since this represents achromatic "black", Bk is output as 1 (to be printed). . Further, the input data determined to be achromatic in the third row is R = 0, G = 1, B = 0. In this case, since the input signal of G is 1, the input signal of R is converted from 0 to 1, and the input signal of B is also 0.
Is converted to 1. After such conversion processing, the output data after conversion is R = 1, G = 1, B = 1. Since this represents achromatic "white", Bk is output as 0 (no printing). You. Similarly, G of the input data
The data is converted to match the signal, and the achromatic color is forcibly reproduced.

FIG. 10B shows the achromatic color judging sections 12 and 4.
FIG. 10 is a diagram showing a list of conversion codes when achromatic color reproduction color conversion from an RGB system to an RGBK system is performed by an achromatic color reproduction color conversion unit 13 when it is determined that the color is a chromatic color in 0 and 70. At the time of chromatic color determination, data “0” is output as the signal MOIA (achromatic color determination signal 16).
In this case, the achromatic color reproduction color conversion unit 13 outputs the binarized data as it is. Since a chromatic color is output as the Bk signal, Bk is output as 0 (no printing).

FIG. 11A shows the achromatic color judging sections 12 and 4.
FIG. 7 is a diagram showing a conversion code list when achromatic color reproduction color conversion from an RGB system to a CMYK system is performed by an achromatic color reproduction color conversion unit 13 when it is determined that the color is an achromatic color in 0 and 70. Also in this case, FIG.
As in the above case, data replacement is performed using the result of the G signal. However, since the achromatic color reproduction color conversion is performed from the RGB system to the CMYK system, the R, G, and B data of the output data in FIG.

FIG. 11B shows the achromatic color judging sections 12 and 4.
FIG. 10 is a diagram showing a list of conversion codes in a case where achromatic color reproduction color conversion from an RGB system to a CMYK system is performed in an achromatic color reproduction color conversion unit 13 when it is determined that a color is a chromatic color in 0 and 70. Also in this case, FIG.
As in the case of, the achromatic color reproduction color conversion unit 13 outputs the binarized data as it is. Since a chromatic color is output as the Bk signal, Bk is output as 0 (no printing). However, CMYK from RGB system
Performs achromatic color conversion conversion to the system, so that R,
G and B data are inverted.

FIG. 12A shows the achromatic color judging sections 12 and 4.
FIG. 9 is a diagram illustrating a conversion code list when the achromatic color reproduction color conversion unit 13 performs achromatic color reproduction color conversion from RGB to RGB in the case where it is determined that the color is an achromatic color in 0 and 70 (Bk signal). Is not output). In this case as well, as in the case of FIG. 10A, the data is replaced using the result of the G signal, and the output data is R, G, B of the output data in FIG. 10A.
It is exactly the same as the data.

FIG. 12B shows the achromatic color judging sections 12 and 4.
FIG. 9 is a diagram showing a conversion code list when performing achromatic color reproduction color conversion from RGB to RGB in the achromatic color reproduction color conversion unit 13 when it is determined that the color is a chromatic color in 0 and 70 (Bk signal). Is not output). In this case as well, as in the case of FIG. 10B, the achromatic color reproduction color conversion unit 13 outputs the binarized data as it is, and the output data is the R of the output data in FIG. 10B. , G, B data.

FIG. 13A shows the achromatic color judging sections 12 and 4.
FIG. 9 is a diagram showing a conversion code list when performing achromatic color reproduction color conversion from RGB to CMY in the achromatic color reproduction color conversion unit 13 when it is determined that the color is an achromatic color in 0 and 70 (Bk signal). Is not output). In this case, as in the case of FIG. 10A, data replacement is performed using the result of the G signal. However, RG
Since achromatic color reproduction color conversion is performed from B system to CMYK system,
The R, G, and B data of the output data in FIG. 10A are inverted, and are exactly the same as the C, M, and Y data of the output data in FIG.

FIG. 13B shows the achromatic color judging sections 12 and 4.
FIG. 9 is a diagram showing a conversion code list when performing achromatic color reproduction color conversion from RGB to CMY in the achromatic color reproduction color conversion unit 13 when it is determined that the color is a chromatic color in 0 and 70 (Bk signal). Is not output). Also in this case, as in the case of FIG. 10B, the achromatic color reproduction color conversion unit 13 outputs the binarized data as it is. However, since the achromatic color reproduction color conversion is performed from the RGB system to the CMY system, the output data R and R in FIG.
G and B data are inverted, and FIG.
This is exactly the same as the C, M, and Y data of the output data in (b).

In the above description, data replacement at the time of achromatic color determination is performed using the result of the G signal. However, the present invention is not limited to this method, and the result of the R signal or the B signal is used. May be performed.

[0061]

As described above, according to the present invention,
Determining means for determining whether the pixel is an achromatic color or a chromatic color based on the multi-valued data of each of the RGB colors; a binarizing processing means for binarizing and outputting the multi-valued data of each of the RGB colors; For pixels determined to be achromatic by the determination means, achromatic data is forcibly generated and output based on the data subjected to the binarization processing, and for pixels determined to be chromatic, Since the processing means for outputting the valued data as it is is provided, it is possible to realize a color image processing apparatus which requires a small circuit scale and can obtain smooth gradation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a color image processing apparatus according to the present invention.

FIG. 2 is a block diagram showing a configuration example of an achromatic color determination unit used in the embodiment.

FIG. 3 is a block diagram showing a second embodiment of the color image processing apparatus according to the present invention.

FIG. 4 is a block diagram showing a configuration example of a color difference calculation unit and a matrix color correction unit used in the second embodiment.

FIG. 5 is a block diagram showing a configuration example of an achromatic color determination unit used in the second embodiment.

FIG. 6 is a block diagram showing an example of a configuration of an achromatic color judging unit which is used in the first embodiment instead.

FIG. 7 is a model diagram for explaining the principle of the achromatic color determination method of the achromatic color determination unit shown in FIG. 5;

FIG. 8 is a model diagram for explaining the principle of the achromatic color determination method of the achromatic color determination unit shown in FIG. 2;

FIG. 9 is a model diagram for explaining the principle of the achromatic color determination method of the achromatic color determination unit shown in FIG. 6;

FIG. 10A is a diagram illustrating a case where an achromatic color determination unit determines that an image is an achromatic color;
Showing the conversion code list when performing achromatic color reproduction color conversion from the system to the RGBK system. (B) When the achromatic color determination unit determines that the image is a chromatic color, the achromatic color reproduction color conversion unit converts the RGB system. RG
Diagram showing a conversion code list when performing achromatic color reproduction color conversion to BK system

FIG. 11A is a diagram illustrating a case where an achromatic color determination unit determines that an image is an achromatic color;
Showing a list of conversion codes when performing achromatic color reproduction color conversion from a system to a CMYK system. (B) When an achromatic color determination unit determines that a color is a chromatic color, the achromatic color reproduction color conversion unit converts the RGB system. CM
Diagram showing a conversion code list when performing achromatic color reproduction color conversion to YK system

FIG. 12A is a diagram illustrating a case where an achromatic color determination unit determines that an image is an achromatic color;
Showing a list of conversion codes when performing achromatic color reproduction color conversion from a system to an RGB system. (B) When an achromatic color determination unit determines that a color is chromatic, the achromatic color reproduction color conversion unit converts the RGB system RG
Diagram showing a conversion code list when performing achromatic color reproduction color conversion to B system

FIG. 13A is a diagram illustrating a case where an achromatic color determination unit determines that an image is an achromatic color;
Showing a list of conversion codes when performing achromatic color reproduction color conversion from a system to a CMY system. (B) When an achromatic color determination unit determines that a color is a chromatic color, an achromatic color reproduction color conversion unit converts the RGB system CM
Diagram showing a list of conversion codes when performing achromatic color reproduction color conversion to Y system

FIG. 14 is a block diagram illustrating an example of a conventional color image processing apparatus.

FIG. 15A is a diagram illustrating a conventional color image processing, in which RGB / C is used when a Bk signal component is generated by an under color removal method;
A graph showing the CMY signal after the MY color conversion. (B) A graph showing the C′M′Y′Bk signal after the above-mentioned under color removal method is performed.

16A is a graph showing CMY signals after RGB / CMY color conversion when generating a Bk signal component by the skeleton black method in the conventional color image processing. FIG. 16B is a graph showing C′M after the skeleton black method is performed. 'Y'
Graph showing Bk signal

[Explanation of symbols]

 Reference Signs List 11 error diffusion processing unit 12, 40, 70 achromatic color determination unit 13 achromatic color reproduction color conversion unit 14 multi-value digital input signal 15, 45 color image signal 16 achromatic color determination signal 21 MAX detection circuit 22 MIN detection circuit 25 differentiator 28 Divider 29 Selector 31 Comparator 33, 34 Flip-flop 35 AND circuit 36 Timing adjustment circuit 41 Color difference calculation unit 42 Matrix color correction unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46-1/64

Claims (9)

(57) [Claims] 1. A achromatic color determining means for determining whether the pixel is achromatic or chromatic color on the basis of multi-value data of RGB colors of a predetermined pixel, a predetermined type the multivalue data of the RGB colors
Binarization at the slice levels of
Over data and binarization means for outputting, said the pixels determined as achromatic by the achromatic color determining means said each color 2
While the coded data is forcibly replaced with achromatic data and output, for pixels determined to be chromatic,
Color conversion means for outputting binary data as it is
If the achromatic color determination means determines that the color is achromatic,
Data of any one of the binary data of each color
The achromatic data is used, and the other two colors are also used as the achromatic data.
Feature to reproduce achromatic color by replacing
Color image processing apparatus according to. 2. A color difference calculation means for generating a color difference signal from multi-value data of each of RGB colors of a predetermined pixel, and said color difference signal is input from the color difference calculation means, and color correction of each color is performed by a linear masking method based on the color difference signal. A color difference signal from the color difference calculation means, and an achromatic color determination means for determining whether the pixel is an achromatic color or a chromatic color based on the color difference signal, and an output from the matrix color correction means. Input the multi-value data of each of the RGB colors and
Is binarized by Isureberu, and binarization means for <br/> outputting binary data of RGB colors, the achromatic color determining means by achromatic been judged for pixels each color 2 Nekade
Data is forcibly replaced with achromatic data and output, while the pixels determined to be chromatic are binary
A color image processing apparatus comprising: a color conversion unit that outputs converted data as it is. 3. An absolute value calculating means for outputting an absolute value of a color difference between each color from multi-value data of each color of RGB of a predetermined pixel, and an absolute value calculating means for each of the output absolute values and a predetermined threshold value. Comparing means for comparing; achromatic determining means for determining whether a pixel corresponding to the multivalued data of each color of RGB is achromatic or chromatic according to the result of the comparing means; and inputting the multivalued data of each color of RGB. Binarization at specified slice level
Binarization processing means for outputting binary data of each of the RGB colors; and for pixels determined as achromatic by the achromatic color determination means, the binary data of each color is forcibly converted to an achromatic color.
A color image processing apparatus comprising: a color conversion unit that outputs binary data of each color as it is for a pixel determined to be chromatic while replacing the data with data . 4. A color image processing apparatus according to claim 3, wherein the threshold value used in said comparing means can be variably set. 5. An achromatic color judging means for judging whether a predetermined pixel is an achromatic color or a chromatic color based on the multi-valued data of each of RGB, and a predetermined slide which receives the multi-valued data of each of the RGB and receives a predetermined slide.
Is binarized by Sureberu, and binarization means for <br/> output the binary data of the RGB colors, binarization of each color for pixels determined as achromatic by the achromatic color determining means Day
Data is forcibly replaced with achromatic data and output,
For pixels determined to be chromatic, the binarized data
And a color converting unit that outputs the over data, the achromatic color determining means, or criteria is chromatic or achromatic to have a predetermined width, and reference is in accordance with the brightness of each color A color image processing apparatus, wherein 6. An achromatic color judging unit for judging whether a predetermined pixel is an achromatic color or a chromatic color based on the multi-valued data of each of the RGB colors, and a predetermined slide which receives the multi-valued data of each of the RGB colors and inputs the data.
Is binarized by Sureberu, and binarization means for <br/> output the binary data of the RGB colors, binarization of each color for pixels determined as achromatic by the achromatic color determining means Day
Data is forcibly replaced with achromatic data and output,
For pixels determined to be chromatic, the binarized data
And a color converting unit that outputs the over data, the achromatic color determining means color image processing, characterized in that with different criteria or a chromatic color or an achromatic color in accordance with the brightness of each color apparatus. 7. The method according to claim 6, wherein the determination of the achromatic color is linearly increased as the lightness increases.
Placing the color image processing apparatus. 8. The method according to claim 6, wherein the determination of the achromatic color is linearly reduced as the lightness increases.
Placing the color image processing apparatus. 9. An achromatic color judging means for judging whether a predetermined pixel is an achromatic color or a chromatic color based on the multi-valued data of each of RGB, and a predetermined slide which receives the multi-valued data of each of said RGB and receives a predetermined slide.
Is binarized by Sureberu, and binarization means for <br/> output the binary data of the RGB colors, binarization of each color for pixels determined as achromatic by the achromatic color determining means Day
Data is forcibly replaced with achromatic data and output,
For pixels determined to be chromatic, the binarized data
Storing a color conversion unit that outputs over data as the color conversion information corresponding to the previously plurality of color systems, thereby convert the data output from said color conversion means based on the color conversion information to the desired color system A color image processing apparatus comprising a coloring system conversion unit .