JPH03241972A - Method and device for binarizing image - Google Patents

Abstract

PURPOSE:To suppress overlapping of colors by specifying a threshold level to be compared at binarization in response to the result of binarization of other component. CONSTITUTION:A multilevel image data is inputted from an IIN and an adder 1 and a binarizing error is inputted from a line buffer 6 to the adder 1, in which the error is added to the data. The result of sum is compared with a threshold level the being an output of an adder 7 at a comparator 2, binarized and inputted once to a latch 3 and outputted from an IOUT synchronously with an external clock. On the other hand, a binarization data outputted from the comparator circuit 2 and the multilevel data outputted from the IOUT are inputted to a subtractor 4, in which the binarization error is subtracted and the result is inputted to a distribution arithmetic section 5. In this case, binarization data '0', '1' being outputs of the comparator circuit 2 are converted at the subtractor 4 in response to the dynamic range of the multilevel data. Thus, the overlapping of colors is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image binarization method and apparatus, and more particularly to an image binarization method and apparatus for binarizing a color image.

[Prior Art] Conventionally, many methods have been proposed for binarizing color images. For example, in image binarization using the dither method, the threshold value of the dither matrix is changed for each color. By controlling the overlapping of Y, M, C, and B inks and toners, changing the shape of the dither matrix itself for each color, and setting screen angles for each color, toner and toner
A method has been proposed for controlling ink printing and overlapping in the same way as printing.

[Problem to be solved by the invention] However, despite the error diffusion method's smooth gradation reproduction ability and edge preservation, it is difficult to binarize black and white images and handle exceptions to improve image quality. (For example, large edge portions do not propagate errors.) However, at present, no special processing has been considered for color images. Usually, the exact same processing is performed on three or four color images, and unlike the dither method, it is not possible to control the overlapping of the developer of each color at all.
It has drawbacks such as color moiré, affecting masking processing, and narrowing the color reproduction range.

Furthermore, when the developer is toner used in electrophotography, the charges of the toner repel each other in the overlapping areas of the colors, causing toner scattering, and when developing with ink, the ink is removed in the overlapping areas of the ink. There was a drawback that bleeding occurred.

In addition, in terms of the overlapping of the above-mentioned developers, Y, M, C, and BK are usually used as toners, but when Y, M, and C developers overlap, each has different spectral absorption characteristics for absorbing light. There are relatively few problems even when toners overlap, because two or more colors overlap and absorb only a small number of wavelengths, or even for wavelengths that overlap, the absorption rate varies greatly depending on the toner. However, when BK toner and toner of another color overlap, since BK toner absorbs light in almost all wavelength ranges, the spectral absorption of the other color toner completely overlaps, and in the end, the overlapping color becomes black. , other color toners would be equivalent to not having them at all.

In order to prevent this phenomenon, Y
There is a technique called OCA in which a value UCA amount based on the black signal is added to each of the , M, and C amounts, but it is very difficult to determine the optimal UCA amount.

Separately from the above, it has also been noted that when outputting a low-density image, the fewer dots overlap, the greater the number of dots, giving the impression of a smoother image with coarse-resolution printers.

The present invention was made to solve the above problems, and
It is an object of the present invention to provide an image binarization method and device that can suppress the overlap of each color by specifying a threshold value to be compared during binarization according to the binarization results of other color components. do.

[Means and effects for solving the problem] In order to achieve the above object, the image binarization method of the present invention binarizes color image data of two or more colors by comparing it with a predetermined threshold value. An image binarization method in which a threshold value to be compared during binarization is specified according to other image data, binarization is performed using the specified threshold value, and the overlapping state of each color image data is controlled. It is characterized by

Preferably, one aspect of the specification is to calculate a predetermined bias component and a threshold value according to other image data.

More preferably, one aspect is that each color image data is controlled to be difficult to overlap or easy to overlap with each other.

Further, an image binarization method of another invention is an image binarization method in which color image data of two or more colors is binarized by comparing it with a predetermined threshold value, and the image data to be binarized is is operated in accordance with other image data, binarization is performed using a predetermined threshold value, and the overlapping state of each color image data is controlled.

Further, the image binarization device of the present invention is an image binarization device that binarizes color image data of two or more colors by comparing it with a predetermined threshold value, and the image binarization device performs binarization by comparing color image data of two or more colors with a predetermined threshold value. a specifying means for specifying a threshold value according to other image data; a binarizing means for performing binarization according to the threshold value specified by the specifying means; and each color image binarized by the binarizing means. The present invention is characterized by comprising a control means for controlling an overlapping state of data.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows the configuration of a monochromatic binarization section 10 in an embodiment of the present invention. FIG. 2 is a schematic block diagram.

The monochrome binarization unit 10 is a processing unit that processes only one color of a color image using the error diffusion method, and the monochrome binarization unit 10 is configured by combining each color separately. FIG. 3 is a schematic block diagram shown in FIG. 2;

Description of Monochrome Binarization Unit (FIGS. 1 and 6) First, the operation of the monochrome binarization unit io in the embodiment will be described below.

As shown in the figure, multivalued image data is input from IIN and input to adder 1. In this adder l, 2
Value errors are input from the line buffer 6 and added. The added result is compared with a threshold value th, which is the output of the adder 7, in the comparator 2, and is binarized. Then, the signal is inputted to latch 3 and outputted from l0UT in synchronization with an external clock (not shown).

On the other hand, the binarized data output from the comparator 2 and the adder l
The multivalued data before binarization, which is the output of , is input to a subtracter 4 , from which the binarization error is subtracted, and then input to the distribution calculation section 5 . At this time, the subtracter 4 outputs 2 which is the output of the comparator 2.
The value data “O°゛“1” is converted according to the dynamic range of the multi-value data.In other words, the input image data is
In the case of bits, "O" and "l" become "O" and "255".

Next, the distribution calculation unit 5 is a calculation unit that distributes the error to surrounding pixel positions for the error of interest as shown in FIG. After being multiplied by the conversion error, it is written to the corresponding position in the line buffer 6. This line buffer 6 has three lines of F.
It can be configured with an IFO and an adder.

Further, the threshold value th given to the comparator 2 is the result of adding a predetermined threshold value thl and a bias component ■S, which will be described later, in the adder 7. This bias component vS is
This is the result of selecting either the predetermined bias VSI or bias VS2, and the selection control signal is BI
Input from N. For example, if BIN is “l”,
If VS2 is selected as VS and conversely “O゛”, then V
VSI is selected as S.

That is, if BIN is "1", the threshold th=thl
+VS2 (VS2>O), and if BIN is “O”, the threshold value th=thl+Vs1 (vsi≦O).

Here, if VS 1 = O and VS2 is a positive value, when BIN = 1, the threshold th becomes large and the binarization result in the comparator 2 is “1゛° (that is, data>t
h) becomes less likely, and it becomes difficult to obtain an output of "1".

In this example, "1°" of the binarized data.

corresponds to hitting a dot, and when "1" is input to BIN, it becomes difficult to hit a dot.

In other words, it becomes possible to control the dots so that they are less likely to overlap. Normally, if vsi=o or a negative value, no problem will occur in operation, but if VS2>VS1, positive and negative conditions can be ignored.

Furthermore, if the dynamic range of multivalued image data is 8 bits and 256 gradations, the difference between VS2 and VSI is 8 to 3
Although a sufficient effect can be obtained if the value is 2 or more, this value is not particularly limited.

<First embodiment (Fig. 2)> Next, a control circuit that suppresses the overlap between black dots and dots of other color components using the monochromatic binarization unit 10 described above is installed in a second embodiment.
This will be explained below with reference to the figures.

First, from the three color signals Y, M, and C, a black signal B is generated by the four color generation section 15. At the same time, Y and MC signals are UCR
After processing, an amount equal to or commensurate with the black component is subtracted. The generated four-color image signals Y, M, C, and BK are sent to latches 11, 12, and 12, respectively. It is input to the latch 13 and IIN of the monochrome binarization section 10-4.

The BIN of this monochrome binarization section 10-4 has a signal ZERO.
(="0") is input, and as mentioned above, the threshold th=t
It is in the normal state of hl+Vs1. Then, the binarized output from l0UT is output from the monochrome binarization unit 10-1.
10-2 and 10-3 respectively. Also, Y, M.

Each color signal of C is matched in phase with the monochrome binarization unit 10-4 by latches 11, 12.
1.10-2.10-3 are input to IIN, respectively.

Therefore, when the black signal BX="1", Y at the same position
, M, and C are less likely to become “i” and l
Output from 0UT. The output of the monochrome binarization unit 10-4 is once latched by the latch 14, and synchronized to the same phase as the outputs of the other monochrome binarization units 10-1, 10-2, 10-3.

In the above manner, a normal error diffusion image can be obtained, so BX
It is possible to reduce the overlap between toner and toner of other colors.

<Second Embodiment (FIG. 3)> Next, a second embodiment using the monochromatic binarization section according to the present invention will be described below with reference to FIG. 3.

Components that operate in the same way as in the first embodiment are given the same numbers and will not be described here.

In the figure, the l0UT output of the monochrome binarization unit 10-4 is
The C signal is input to the BIN of the monochrome binarization unit 10-3, and its overlap with the black signal is controlled.

Further, the l0UT output of the C signal monochrome binarization unit 10-3 is input to the BIN of the M signal monochrome binarization unit 10-2,
Control is performed to suppress dot overlap between the C signal and the M signal. Similarly, the output from l0UT of the monochrome binarization unit 10-2 is input to the BIN of the monochrome binarization unit 10-1,
Control is performed to suppress dot overlap between the M signal and the Y signal, and a binary signal of the Y signal is output from the monochromatic binarization section 10-1.

Further, each of the latches 21 to 32 is supplied with a synchronization clock (not shown), and performs a latch operation.

This is to ensure that the processing in each of the monochromatic binarization units 10-1 to 10-4 is performed on the pixel of interest at the same position, and phase adjustment is performed by these latches 21 to 32.

In this second embodiment, the BK dots of the black signal hardly overlap with the C dots, and the C dots are B.

It is difficult to overlap with the dots of and M. Further, M dots are difficult to overlap with C and Y dots, and Y dots are difficult to overlap only with M dots.

In this way, dot overlapping control can be freely set depending on how l0UT and BIN of the monochrome binarization section are connected.

Next, to briefly touch on the modification of the second embodiment shown in FIG. The logical sum of l0UT of the monochromatic binarizing unit 10-2, the output of the latch 28, and the output of the latch 31 is input to the BIN of the monochromatic binarizing unit 10-1. Then, BK dots and C dots are difficult to overlap, M dots are difficult to overlap with BK and C dots, and Y dots are B, C, and M dots.
As a result, each of the four color components becomes less likely to overlap with each other than with respect to all remaining colors.

Third Embodiment (FIG. 4) The schematic block diagram shown in FIG. 4 is a third embodiment of the present invention, and the operation is basically the same as that of the first embodiment. However, the black signal Bx is input to the edge detection section 45, and the result of detecting black edges such as black characters is input to the decoder 46.

The decoder 46 also receives the binary result of black B8, and when the edge detection result is an edge and the BK binary signal is "1", the decoder 46 outputs "O゛'
Output. In other cases, the binary signal of B is output as is.

By the above operation, in the case of a black text portion, the control for suppressing the overlap between KK and other color components is canceled. This is to prevent dots of other color components from being placed around the black text area.

In this third embodiment, the dot overlapping suppression control is canceled by the edge of the black component, but it can be canceled by using the edge of another color component or the logical sum of these edges.
good.

It is also theoretical that this cancellation mechanism can be applied to the second embodiment.

According to the embodiments described above, the occurrence of color moiré can be prevented;
LICR1ICR prevents the influence on masking processing, widens the color reproduction range, minimizes ink smearing due to scattering due to repulsion between toners, and does not require complicated UCA theory.
1 regeneration.

In addition, even if you switch between outputting in 3 colors and outputting in 4 colors, there is little overlap of black, so there is almost no need to change the masking coefficient, giving a large degree of freedom to the masking circuit. This also solves the problem of increased circuit scale.

[Other Embodiments] FIG. 5 shows another embodiment according to the present invention, and is another example for realizing the monochromatic binarization section shown in FIG. 1.

In the embodiment shown in FIG. 1 described above, the threshold value th applied to the comparator 2 was controlled, but in this embodiment, in order to add a bias component to the data itself, the comparator 2 performs binarization using the threshold value th. An adder 51 is provided immediately before. Further, the selector 52 moves exactly the same as the selector 8 described above.

However, V S D l is equivalent to V S 2 , and VS
D2 corresponds to VSI, and VSDI>VSD2 must be satisfied. If this condition is met, for example, VSD1
20. VSD2<O may also be satisfied.

Such data is added to the adder 51, and the ease with which "0" and "1" are generated in binarization is controlled in the same manner as in the embodiment shown in FIG.

By the way, the binary output image of the error diffusion method is very random, and for example, when MH or MMR encoding is performed,
Compression efficiency is very poor. Furthermore, in the case of color images, apart from text, the color correlation in the halftone areas is also very low.
It has been difficult to improve the compression efficiency of color images using correlation.

However, according to the embodiment described above, it is possible to increase the correlation between colors even in an image obtained by the error diffusion method.

In addition, in the first to third embodiments, the relationship between VSI and VS2 given to the selector 8 in the monochrome binarization section 10 is
>VS2, the control to suppress the overlap between colors in each embodiment can be controlled to promote the overlap between colors. In other embodiments, the VSDI and VSD provided to the selector 52 in the monochrome binarization section
Similar control can be achieved by setting the relationship VSD2>VSDI.

In addition, in the embodiments described above, Y, M, and C.

I have described the processing for BK, but the three colors Y, M, C and R
,G,B may be used. In this case, “l”, “0”
Even if the meaning of " is reversed, it is exactly the same in terms of whether it makes it easier or harder to produce binarized results of the same polarity, and the same circuit configuration can be used.

[Effects of the Invention] As explained above, according to the present invention, overlapping of each color can be suppressed by specifying the threshold value to be compared during binarization according to the binarization results of other color components. It has the effect of being able to.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing the configuration of a monochromatic binarization section in the embodiment, FIG. 2 is a schematic block diagram showing the configuration of the control circuit in the first embodiment, and FIG. 3 is a schematic block diagram showing the configuration of the control circuit in the second embodiment. FIG. 4 is a schematic block diagram showing the configuration of the control circuit in the third embodiment; FIG. 5 is a schematic block diagram showing the configuration of the monochromatic binarization section in another embodiment. FIG. 6 is a diagram showing a diffusion matrix in the error diffusion method. In the figure, 1...Adder, 2...Comparator, 3...Latch, 4...Subtractor, 5...Distribution calculation section, 6...Line buffer, 7...Addition Device, 8...Selector, 1
0...Single color binarization section, 11-14...Latch, 15
...Four color generation section, 21-32...Latch, 41-4
4... Latch, 45... Edge detection section, 46...
Decoder 52...Selector.

Claims (5)

[Claims] (1) An image binarization method in which color image data of two or more colors is binarized by comparing it with a predetermined threshold, and the threshold to be compared during binarization is set according to other image data. 1. An image binarization method characterized in that the image binarization method is characterized in that the color image data is specified, binarization is performed using the specified threshold value, and the overlapping state of each color image data is controlled. (2) The image binarization method according to claim 1, wherein the threshold value is specified by calculating a predetermined bias component and the threshold value according to other image data. (3) The image binarization method according to claim 1, wherein the overlapping state is controlled so that each color image data is difficult to overlap or easy to overlap with each other. (4) An image binarization method in which color image data of two or more colors is binarized by comparing it with a predetermined threshold, and the image data to be binarized is manipulated according to other image data. An image binarization method characterized by performing binarization using a predetermined threshold value and controlling the overlapping state of each color image data. (5) An image binarization device that binarizes color image data of two or more colors by comparing it with a predetermined threshold, the threshold being compared during binarization depending on other image data. a specifying means for specifying by the specifying means, a binarizing means for performing binarization according to the threshold value specified by the specifying means, and an overlapping state of each color image data binarized by the binarizing means. An image binarization device comprising: a control means.