JPH0583542A - Image processor - Google Patents

Abstract

PURPOSE:To reproduce color images with high resolution and fidelity of black color by outputting black signals to an output device when it is judged by the combination of chrominance signals after conversion that the image signals are black. CONSTITUTION:Concerning respective output signals M, Y and C from a color conversion table, a simple binarizing circuit 114 executes a binarizing processing and a dither processing is executed while successively comparing those signals with dither patterns from a reference memory 116 for dither pattern by a comparator 115. Further, the respective signals are inputted to a multiplexer 117 for simple binarizing/dithering and switched by the output signal of a switching code conversion ROM 13. When all the outputs of the respective color multiplexers 117 are '0' or '1', the result of synthesizing the chrominance signals is turned to white or black and therefore, it is detected by a circuit 118. At such a time, a gate circuit 119 for black-and-white signals is opened to output signals to a printer (a), gate circuits 120-122 for respective color signals are closed at the same time, and the outputs of chrominance signals are stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device for displaying an image including halftone.

[0002]

2. Description of the Related Art In the case of displaying an image including a halftone density by a conventional color image processing apparatus, conventionally, density display by a dither method is known. However, the dither method generally has drawbacks such that when a large number of gradations are expressed, the display resolution is reduced and irregular noise is noticeable.

Particularly, in an image processing apparatus in which a color input image is separated into white, yellow, and cyan colors, color conversion is performed, and then color synthesis is performed again and output to a color printer or the like, the original input image signal is If it is black,
A method has been employed in which after color separation and color conversion, magenta, yellow, and cyan colors are combined to output black.

[0004]

However, in an image processing apparatus of a system in which an input signal of a color image is color-separated and the color signals are combined to reproduce black, as a result of combining black, dither is generated. Blurring by the method sometimes failed to faithfully reproduce black. In particular, when black is not faithfully reproduced and is reproduced in a blurry manner, there is a problem that an output image from a printer or the like becomes very unsightly.

The present invention eliminates the above drawbacks and provides an image display device capable of reproducing a color image with high resolution and faithfully in black.

[0006]

SUMMARY OF THE INVENTION In the present invention, a color image signal input means, a means for separating the input image signal into color signals, and the separated color signals are matched to the characteristics of an output device. In the image processing device, which comprises a converting means, a means for dithering the converted color signal, and a means for outputting the processed signal to the output device, the color signal separated by the separating means. Or a means for judging the black color of the image signal based on the color signal converted by the converting means, and a means for outputting the black signal to the output means according to the judgment result.

[0007]

In the present invention, when an image signal is input,
When the color signal is converted into the color signal as usual and the color signal is converted in accordance with the characteristics of the output device, a means for determining whether the image signal is black is provided by the combination of the converted color signals, and the image signal is black. If it is determined that the black signal is output to the output device.

In the case of expressing a black image signal in this manner, instead of synthesizing color signals to express black, a black signal different from magenta, yellow, and cyan is output, so that black is highly resolved. It is possible to express the image with high hue fidelity, and it is possible to output an image that is natural to the human eye.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the image processing apparatus of the present invention. Reference numeral 90 denotes a color image input device, and an image input by this color image input device is separated into white (W), yellow (Y), and cyan (C) color signals (analog electric signals). These color signals w,
The y'and c'are input to the A / D converter 91 and converted into digital quantities by the A / D converter 91.

Next, the logarithmic conversion circuit 110 reduces the number of representation bits. Specifically, a conversion ROM having the characteristics shown in FIG. 2 is prepared, and logarithmic conversion is performed by addressing the ROM data. However, for example, in the case of converting from 6 bits to 4 bits, it is possible to obtain better characteristics by using the dead region as shown by the following equation than by simply performing logarithmic conversion.

When x> a, y = 15.lnx / (ln64-lna) -15.lna / (ln64-lna) (2) When x <a or x = a, y = 0 However, x is an input signal. And y is the output signal. Further, a is the upper limit value of the dead area, and it is suitable that it is about 2 to 3.

The reason for reducing the number of representation bits here is as follows. First, it is necessary to match the gradation of the color printer 92 capable of output display. Further, the calculation with the color conversion matrix 94 found in the previous embodiment may not provide good color reproduction depending on the characteristics of the ink.

In such a case, in particular, all the color combinations are calculated in advance to create a table, and the color is calculated by drawing this table. By doing so, even extremely complicated calculations can be processed in real time. Further, since it is sufficient that the table created here corresponds to the combination of colors that can be expressed by the color printer, the number of expression bits can be reduced for these reasons.

Next, a matrix circuit 111 for color conversion is passed through a signal obtained by reading the original so as to match the spectral characteristics of the ink of the printer.

This circuit 111 comprises a product-sum operation circuit as shown in FIG. 3, for example, and performs the following operations.

M = a11w + a12y '+ a13c' Y = a21w + a22y '+ a23c' C = a31w + a22y '+ a33c' where w, y ', and c'correspond to the signal from the input device 90, respectively to white, yellow, and cyan. Correspond. Further, M, Y and C are color conversion matrix circuits 11
The signal is converted into a signal according to the color development characteristics of the color printer 92 by 1, and corresponds to magenta, yellow and cyan, respectively. a11 to a33 are matrix coefficients for conversion.

The operation of this circuit will be described with reference to FIG.
The gate circuit 101 produces the w signal at terminal 102.
Next, the product-sum calculation circuit 103 extracts the coefficient of a11 from the parameter memory 104 for this signal, calculates the product, and stores the product in the internal accumulator. Next, the y'signal is generated at the terminal 102 by the gate circuit 101, and the same operation as described above is performed to multiply by the coefficient a12 and add by the internal accumulator. Further gate circuit 10
1 is used to select c ', the coefficient a13 is multiplied in the same manner as the above-mentioned operation, and addition is performed by the internal accumulator. If this result is output, M can be obtained. Y and C are calculated in the same manner. In this way, it is possible to convert the signal into a signal that matches the color development characteristics of the color printer 92.

In FIG. 1, the differential circuit 10 obtains a local variation rate for a part of the separated color signals. Specifically, two-dimensional differentiation is performed by a convolution operation circuit as described later. In this circuit, a line memory unit 11 for preparing a part of two-dimensional data based on a signal input as one-dimensional information, and a product-sum operation unit 12 for two-dimensionally differentiating the two-dimensional data. (See Figure 4).

6 is a structural example of the monochrome image processing apparatus of FIG.

FIG. 1 shows an image of a manuscript 1 with a linear light source 2 such as a fluorescent lamp.
Illumination by CC, and self-occlusion lens array 3 for CC
An image is formed on the one-dimensional sensor 4 such as a D sensor. The image signal output from the one-dimensional sensor is converted into a digital signal by the A / D converter 5.

Next, the density characteristics are adjusted through density conversion ROMs 6, 7 and 8 for matching the density characteristics of the display printer 22. At this time, depending on the density characteristic of the original document 1, that is, a dark original document, a thin original document, or an original document with no contrast, the output of the density conversion ROMs 6, 7, 8 is selected by the switch 9 to select an appropriate one.

However, since the high-frequency component of the signal generated by the optical system such as the self-locking lens array 3 is deteriorated, the high-frequency component is deteriorated. A clearer image can be obtained by correcting by adding.

Therefore, using the output signal of the central line of the line memory 11 and the output signal from the product-sum calculation unit 12,
Processing is performed by simple binarization or the dither method.

In this case, if all of the high frequency components are added, overcorrection results and the image quality deteriorates. Therefore, the correction coefficient K (0 <
K <1) is multiplied by the signal by the multiplier 15, and the adder 1
Enter in 6.

If the multiplier 15 is simplified so that the correction coefficient K is limited to one power of 2, even if the multiplier 15 is omitted and only the upper bits are input to the adder 17. The purpose can be achieved.

Now, the output signal of the product-sum calculation unit 12 is
It is delayed from the output signal of the line memory unit 11 due to the processing time of the product-sum calculation unit. Therefore, the signal of the line memory unit 11 is delayed via the delay circuit 17, and is synchronized with the output of the product-sum calculation unit 12 to be combined with the correction signal.
It is input to the adder 16. Since the output of the product-sum calculator 12 is added to the output signal of the line memory unit 11 in the adder 16, a signal with better high frequency characteristics than that in FIG. 8B is output. However, it is better not to correct too much.

This signal is then sent to the two comparators 1.
8 and 19 are input. The signal input to the comparator 18 is compared with a predetermined value 20 and simple binarization is performed. The purpose can be achieved even if the comparator 18 is omitted and the upper 1 bit of the output signal of the adder 16 is used as the binarized output signal. However, subtle adjustment cannot be expected.

On the other hand, the signal input from the adder 16 to the comparator 19 is sequentially compared with the data of the reference matrix memory 21 called a dither pattern and is output from the comparator 19 as a dithered signal.

The signal processed through these two processing paths is input to a signal switcher, for example, multiplexer 14, and either signal is selected. The input signal is switched by the output signal from the switching code converter 13 described above, and either of these two types of signals is selectively output.

The matrix of FIG. 5 shows a group of parameters for high-frequency emphasis, and it is possible to control the degree of high-frequency emphasis in directions orthogonal to each other. The parameter a1 to c5 in this figure is sequentially producted on the two-dimensional image data, and the result of addition is called a convolution operation. High-frequency emphasis can be performed by selecting that parameter.

In order to execute this product, for example, considering the matrix shown in FIG. 5, data for 5 lines are required at the same time. The line memory unit 11 prepares this data. This configuration is shown in FIG. 6, and the line memory 70 is prepared for 6 lines, and while one line is writing, the other 5 lines are reading.

That is, one write line is selected by the switching multiplexer 71, and data is written in the line memory. Next, for the line memory 70 which is not written by the decoding multiplexer 72,
The output out1 to the output out5 are output by switching so that the order of the data is not disturbed in the paper feeding direction. Next, each time one data is input to the input I0, 5 outputs are read out to the respective outputs out1 to out5 to prepare 5 × 5 data. This data is input to the product-sum calculation unit 12.

FIG. 7 shows the configuration of the product-sum calculation unit 12. The operation matrix is the first row and the fifth row as shown in FIG.
The line, the second line, and the fourth line have the same parameters.
Therefore, the outputs out1 to out of the line memory 70
Input 5 into SI1 to SI5 in FIG. 7, and first enter SI1 and S5.
The adder 80 calculates the sum of I5 and the adder 81 calculates the sum of SI2 and SI4. Next, the output results of the adders 80 and 81 and SI3 are respectively calculated by multiplying and adding operation circuits 82, 83 and 8
Input to 4. This product-sum operation circuit takes in the respective parameters 85, 86, 87 and executes the product and the sum. That is, it is executed five times each time one data is input to I0 shown in FIG.

Using the result, all the sums are calculated by using the adder 88 and the adder 89, respectively, and the convolution operation is executed. Then, the signal emphasized in the high frequency band is output to the output SO. In this way, high-frequency emphasis is executed at high speed.

The function of the differentiating circuit 10 will be described below. Here, in order to facilitate the explanation, consider a one-dimensional signal. Figure 8
It is assumed that a signal as shown in (a) is input as an input image. Then, an electric signal obtained by the optical transfer characteristic becomes a signal as shown in FIG.

When this signal is input to the differentiating circuit 10, it becomes a differentiated signal as shown in FIG. This signal is input to the simple binarization or dither method switching code conversion unit 13 (made up of ROM). In the switching code conversion unit 13, of the signals shown in FIG. 8C, the level higher than the broken line 31 or the broken line 32 is shown.
For an input signal having a smaller level, a first code signal for selecting the processed signal is generated by the simple binarization described later and the signal is sent to the multiplexer 14.
When there is an input signal having a level between the broken line 31 and the broken line 32, a second code signal for selecting the signal processed by the dither method described later is generated and the signal is sent to the multiplexer 14.

Next, color conversion is performed by looking up the color conversion table 111. RA table 111 here
It can be freely converted by inputting the contents of this table from the ROM 112. For example, if the contrast of the original is low, or the background of the original is too dark, etc., by replacing the contents of this table,
It can also be an intelligent printer or copy.

Now, when the convolution operation is performed in the portion surrounded by the broken line in FIG. 1, the following procedure is required.

That is, in the embodiment, the line memory unit 10 is provided with a line memory of 5 lines or more.
In order to process the image signal included in one line at the center of the lines, it is necessary to capture image signals for at least two lines each before and after. This means that in order to perform image processing for one line, the image signal delayed by two lines is waited for and processed.

To perform a 5 × 5 calculation, first send the data for two rows to the convolution calculation section,
Then try to actually calculate. Then, the deviation between the selection signal processed in the part surrounded by the broken line in FIG. 1 and the color conversion output signal of the color conversion table 111 is two lines. Therefore, the delay circuit 113 delays the output of magenta, yellow, and cyan by two lines, respectively, and synchronizes with the selection signal for image processing.

Next, simple binarization processing and dithering processing are performed for each color. That is, for each of the output signals M, Y, and C from the color conversion table, the simple binarization circuit 1
The binarization process is performed at 14, and the dither process is performed by the comparator 115 while sequentially comparing with the dither pattern from the dither pattern reference memory 116.

These signals are input to the multiplexer 117 for selecting simple binarization / dithering, and switched by the output signal of the switching code conversion ROM 13. When the outputs of the color multiplexers 117 are all 0 or 1, white or black is output as a result of synthesizing the color signals. Therefore, this is detected by the circuit 118, and at this time, the gate circuit 119 for the black and white signals is output. At the same time as opening and outputting a signal to the printer, the gate circuits 120, 121 and 122 for the respective color signals are closed to stop the output of the color signals.

The signal thus obtained can be input to a color printer to obtain an output image including color halftones.

In this method, there is a possibility that the degree of freedom such as high-frequency emphasis independent for each color may be limited, but for white and black, a high-frequency emphasized sharp image can be obtained. Also for a color image, high resolution display by binarizing the line component and halftone expression by dither are possible. Further, it is sufficient to provide at least one convolution circuit having a somewhat complicated configuration, so that the circuit scale can be reduced and the system can be downsized.
Further, when performing color conversion, it is only necessary to subtract the corresponding data from the table, and therefore the circuit can be further simplified.

Here, when outputting a black image signal,
Although the output of each color signal of M, Y, and C is stopped, they can be overlaid. In this case, various colors can be expressed by appropriately changing the configuration of the ROM 112 that stores the contents of the color conversion table 111.
Furthermore, by changing the parameters for performing dithering, it is possible to change the density gradient for each color, and set the parameters according to the characteristics of the ink used in the printer to reproduce more natural colors. It can be realized.

As described above, in the color expression of a four-color printer or the like in which the three colors are expressed in color and black is added to the lack of the density level, if the added black is blurred by the dither method, it becomes very unsightly. Therefore, if only the line component of the black signal is detected and displayed, such unpleasantness is eliminated.
Furthermore, when this black is displayed with high resolution, there is no unnaturalness even if the resolution with other colors is reduced, and rather it is possible to improve the fidelity of hue, so that it is natural to the human eye. There is an effect that it can be felt as an image.

FIG. 9 is a circuit obtained by further simplifying the circuit of the embodiment shown in FIG. This circuit is characterized in that the convolution circuit 10 and the decision ROM 13 are provided with a portion for generating a selection signal for selecting a simple binarization process or a dithering process. Then, the color conversion table 111
Is a circuit for converting white, yellow, and cyan into magenta (M), yellow (Y), cyan (C), and black (B). This magenta, yellow, cyan,
For each color component of black, a processed signal by simple binarization or dithering is selected as in the previous embodiment. By doing so, it becomes possible to further simplify the circuit.

In the above embodiment, even if the local fluctuation rate is large to some extent, as long as it does not exceed the threshold for simple binarization,
No white-to-black or black-to-white inversion occurs. However, for human eyes, it may be possible to improve the image quality by providing the portion where the above-mentioned color inversion occurs with sharpness. In order to perform such processing, the circuit as shown in FIG. 10 may be used by changing the output signal selection determination circuit of the simple binarization processing and dithering processing of the previous embodiment.

In this circuit, the convolution circuit 1
0 and the decision ROM 13 outputs the decision signal of the output signal of the simple binarization process and the dither process, but here, the following decision is made.

First, when the absolute value of the local fluctuation rate is sufficiently large (when it is larger than a certain first threshold value), that is, when the local fluctuation rate is sufficiently large or sufficiently small,
If the value is large, it is determined to be black, and if it is small, it is determined to be white. Next, when the absolute value of the local fluctuation rate is large to some extent (smaller than the first threshold value and larger than the second threshold value), that is, when the local fluctuation rate is large to some extent or small to some extent. Determines to select the output signal by the simple binarization process. Further, when the absolute value of the local fluctuation rate is smaller than a certain value (smaller than the above second threshold value), it is determined to select the output signal by the dithering process.

By doing so, if there is a large local variation, inversion of the density always occurs and a sharp image can be obtained. However, if the input image has noise, it may be unsightly.

[0053]

INDUSTRIAL APPLICABILITY The present invention is an image processing apparatus that reproduces a color input image, and it is possible to faithfully reproduce black with high resolution.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining bit reduction conversion.

FIG. 3 is a diagram showing a configuration example of a product-sum calculation unit.

FIG. 4 is a diagram showing a configuration of an image processing apparatus.

FIG. 5 is a diagram showing a matrix of convolution operation.

FIG. 6 is a diagram showing a line memory unit.

FIG. 7 is a diagram showing a product-sum calculation unit.

FIG. 8 is a diagram illustrating signal processing of the present invention.

FIG. 9 is a diagram showing another embodiment of the present invention.

FIG. 10 is a diagram showing a modification of the switching circuit.

[Explanation of symbols]

 10 ... Convolution circuit 13 ... Judgment ROM 14 ... Multiplexer 22 Printer

Continuation of front page (72) Inventor Shuzo Miura 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Toshiba Research Institute

Claims (2)

[Claims] 1. A color image signal input means, a means for separating the input image signal into color signals, a means for converting the separated color signals according to the characteristics of an output device, and the converted means. In an image processing apparatus comprising means for dithering a color signal and means for outputting the processed signal to the output device, a color signal separated by the separating means or converted by the converting means. An image processing apparatus comprising: a unit that determines whether an image input signal is black based on the color signal; and a unit that outputs a black signal to the output unit based on the determination result. 2. An image processing apparatus comprising: means for controlling a means for outputting the processed signal to an output device based on the determination result of the black color determining means.