JPH0783432B2 - Image processing device - Google Patents

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 lowered and irregular noise is noticeable.

In particular, in an image processing apparatus in which a color input image is decomposed 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 used in which after color separation and color conversion, each color of magenta, yellow, and cyan is 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]

Image processing apparatus according to the present invention
This is the means for inputting the color image signal and this input.
Means for separating the image signals into color signals, and
Means for converting the color signal according to the characteristics of the output device, and
The color signal separated by the separating means or the conversion
The local fluctuation rate of the color signal converted by the means
The means and the conversion according to the obtained local variation rate
Processing and halftone processing for binarized color signals
The result of applying any of the processing that makes the signal expressing the density
Means for outputting the output signal from the output device
And a means for outputting the
Means to determine if the signal being
If it is determined to be black by the step, the output device
The signal output to the storage device is replaced with the output signal.
In addition, it is characterized by comprising means for producing a black signal .

[0007]

According to the present invention, an image signal is input and a color signal is input.
And color signals are converted according to the characteristics of the output device.
After conversion, the color signal after conversion is converted according to the local fluctuation rate of the color signal.
Output the result of simple binarization of the
Whether to output the result of dithering which is a density expression
To control. That is, the part of the line component with a large local variation
The minute does not blur the image by performing simple binarization.
The area with a small local fluctuation rate is represented by dithering.
It is possible to express the halftone density of the image.

Further, according to the present invention, the image
Based on the result of processing according to the characteristics of
The signal that is displayed is black, and it is determined that it is black.
If it is set, a black signal is output to the output device. When expressing a black image in this way, instead of synthesizing color signals to express black, a black signal different from magenta, yellow, and cyan is output , and as described above.
Depending on the characteristics of the image, the criterion for determining whether or not it is black is
Since it is the result of processing, mixed characters and photographic images
Although it is possible to express halftone density in the image
, Black without losing the resolution of the outline of the characters
Can be expressed with high resolution. Therefore , it is possible to output an image with high hue fidelity and natural to human eyes.

[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 the 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 zone, and about 2 to 3 is appropriate.

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 the signal obtained by reading the original so as to match the spectral characteristics of the ink of the printer.

This circuit 111 is composed of 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 developing characteristic 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 operation 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 that described above is performed to multiply by the coefficient a12 and add by the internal accumulator. Furthermore, the gate circuit 10
1 is used to select c ', the coefficient a13 is multiplied in the same manner as in the above-mentioned operation, and the result is added 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 calculation 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 calculation unit 12 for performing two-dimensional differentiation from 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.
Illuminated by the CC and the self-occlusion lens array 3
An image is formed on the one-dimensional sensor 4 such as a D sensor. The image signal output by 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 characteristics of the original document 1, that is, a dark original document, a thin original document, or an original document without 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 center 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 the high frequency components are added, the image quality is deteriorated due to overcorrection. 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 1 to a 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.

The output signal of the product-sum calculation unit 12 is
Due to the processing time of the product-sum calculation unit, the output signal of the line memory unit 11 is delayed. 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. In the adder 16, the output of the product-sum calculator 12 is added to the output signal of the line memory 11, so that a signal with better high frequency characteristics than in FIG. 8B is output. However, it is better not to overcorrect.

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 conversion unit 13 described above, and either of these two types of signals is selectively output.

The matrix of FIG. 5 shows a parameter group 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 shown in this figure is sequentially producted to two-dimensional image data, and the result is added, which is called a convolution operation. High-frequency emphasis can be performed by selecting the 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 outputs out1 to out5 are output by switching so that the order of 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 structure 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 S
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 as product-sum 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 obtained by using the adder 88 and the adder 89, respectively, and the convolution operation is executed. Then, the high-frequency emphasized signal 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 from 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 (which is composed of a ROM). In the switching code converting unit 13, of the signals shown in FIG. 8C, the level higher than the broken line 31 or the broken line 32 is used.
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 a signal processed by the dither method described later is generated and the signal is sent to the multiplexer 14.

Next, the 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 is also possible to use an intelligent printer or copy.

Now, in the case of performing the convolution operation 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 an image signal included in one line at the center of the lines, it is necessary to capture at least two lines of image signals for each of the front and rear. This means that in order to perform image processing for one line, the image signal delayed by two lines is waited for and processed.

In order to perform a 5 × 5 calculation, the data for two rows is first sent to the convolution calculation section,
Next, 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.

Each of these signals is input to the multiplexer 117 for selecting simple binarization / dithering, and is 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 the 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 is limited, but for white and black, a sharp image with high-frequency emphasis is 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, it is also possible to overtype these. In this case, by appropriately changing the configuration of the ROM 112 that stores the contents of the color conversion table 111, it is possible to express various colors.
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 insufficient 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 decreases, and it is also possible to improve the fidelity of hues, so that it is natural to the human eye. It has the effect of being 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 simple binarization processing or dithering processing. 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 the human eye, 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 shown in FIG. 10 may be used by changing the output signal selection determination circuit of the simple binarization processing and dither processing of the above-described 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, the 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 (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H04N 1/46 G06F 15/68 310 A H04N 1/46 Z (72) Inventor Shuzo Miura Kawasaki City, Kanagawa Prefecture Komukai-shi, Toshiba Town 1 Toshiba Research Institute Ltd. (56) References JP-A-57-99644 (JP, A) JP-A-57-119561 (JP, A) JP-B-56-48869 (JP, B2) )

Claims (1)

[Claims] 1. A color image signalToinputDoMeans andThis Means for separating the input image signal into a color signal,This Converts the separated color signals of the output according to the characteristics of the output device
Means to doThe above Color signal separated by separating meansWellOr the above strange
Color signal converted by the converting meansLocal variation of
Means, According to the obtained local variation rate, the converted color
Shows the binarized signal processing and halftone density for the signal
Outputs the result of performing any of the processing that makes the signal appear
Means, Means for outputting the output signal to the output device; The signal obtained by combining the output signals is black.
Ru Means for determining whether or not,If it is determined to be black by this means,
Replace the signal output to the output device with the output signal
In addition to or in addition, a means for producing a black signal is provided. This
An image processing device characterized by: