JPH04158680A - Picture processing system - Google Patents

Abstract

PURPOSE:To output a picture excellent in resolution, gradation and contrast by arranging a picture subjected to density conversion attended with an increase in the gradation of an input picture signal in a way that picture elements in a matrix are covered and the picture element is subjected to density conversion in the unit of one picture element and in the order of density and gradation. CONSTITUTION:A matrix is divided into adjacent sub matrices 1-4 comprising four picture elements with picture elements P11, P13, P31, P33 used as apexes. Every time an input picture data D' is incremented by one, a sub matrix is changed sequentially by one picture element in the sub matrix and a density of a minute picture element DPIJK of a white density is changed sequentially into a black level so that a picture element increasing the density and gradation succeedingly is not spatially close and all picture elements Pij are covered, and the picture is arranged so that density change sequence in one picture element Pij changed as the D' increases is changed from a smaller K (located to the left) of the minute picture element DPIJK. Thus, the visually smooth picture with excellent gradation, resolution and contrast is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used in image forming apparatuses such as copying machines, and performs image processing that processes digital image signals and outputs them as image data representing a halftone image. Regarding the method.

[Conventional technology]

Conventionally, as is well known in the image processing method of image forming apparatuses such as digital copying machines, input image density signals are quantized to 2" level and converted to digital multi-value image data that expresses the density using n bits. Image processing is commonly performed.

Among them, the dither method and density pattern method use the integral effect of the human eye to effectively convert digital multi-value image data into binary image data representing halftones to express light and shade. It is frequently used in the above devices because it has good restoration accuracy and is easy to handle.

[Problem to be solved by the invention]

However, whether using the dither method or the density pattern method, when expressing a halftone image by changing the number of recording dots, there is a drawback that gradation expression ability and resolution are not compatible. That is,
If you increase the size of the matrix pattern to increase the number of gradations of image density, the resolution will decrease, and if you decrease the size of the matrix pattern to improve the resolution, you will not be able to increase the number of gradations of image density. .

Also, if we pay attention to the type of matrix pattern, the number of black pixels (100χ density - the same below) increases as the density increases, but in the case of a dot concentration type that grows around a certain core pixel, the number of black pixels increases. Although the density gradation of the corresponding output image changes nearly linearly, the resolution is slightly lowered. On the other hand, in the case of the dot dispersion type, which uniformly increases the number of black pixels without creating core pixels, the resolution does not decrease much, but the number of black pixels in the matrix and the density gradation of the output image change. linearity deteriorates (there was an appeal).

As one method to solve these problems, a multi-level dither method has been proposed that allows multiple darkness values to be set for one pixel to enable multi-level density output. No solution has been reached.

That is, when using a dot-concentrated matrix pattern based on the above method, the resolution problem cannot be solved;
Further, when a dot-distributed matrix-nox pattern is used, there is a problem in that the recorded image of fine pixels tends to become unstable.

The present invention has been made in view of the following circumstances.In an image processing method that expresses a halftone image using a matrix pattern of multi-tone pixels, the resolution does not deteriorate and the gradation and contrast of the output image are improved. The purpose of the present invention is to provide an image processing method that can output visually smooth images with excellent image quality.

[Means to solve the problem]

In order to solve the above problems, the present invention provides an image processing method that uses a pixel matrix consisting of multi-tone pixels to perform image processing on an input image signal and convert it into image data representing a half-tone image. In the pixel matrix, the pixel matrix is arranged so that the pixels whose density is converted as the gradation level of the input image signal increases covers all the pixels in the matrix, one pixel at a time, and in the order of the density gradation. It is.

Further, in the second means, in the first means, the pixels of the pixel matrix whose density is converted as the gradation level of the input image signal increases are divided into a certain pixel and a pixel located spatially away from the pixel. The pixels are arranged in a distributed array with pixels distributed sequentially.

Further, in the third means, in the second means, the pixel distributed array configures the pixel matrix with a plurality of sub-matrices, and the pixels whose density is converted as the gradation level of the input image signal increases are arranged in each sub-matrix. They are arranged so that they are distributed sequentially.

Further, in the fourth means, in the second or third means, the multi-gradation pixels are formed by an output image signal whose gradation is controlled by pulse width modulation, and the Ill! The pixels of the pixel matrix whose density is converted as the intensity increases are such that the order of density gradation conversion within the pixel is made different between adjacent pixels.

Further, the fifth means is a pixel concentration type in which, in the second means, the pixels of the pixel matrix whose density is converted as the gradation level of the input image signal increases are sequentially distributed to a predetermined pixel and pixels adjacent to the pixel. It is arranged by array.

[Operation] The input image signal is subjected to image processing using the above-mentioned image processing method, and is converted into image data representing a halftone image using a pixel matrix consisting of multi-tone pixels. The pixel matrix used at this time is arranged so that as the gradation level of the input image signal increases, the pixels whose density is converted cover the pixels in the matrix one by one, and the density is converted one by one density gradation. Arranged.

When the gradation level of the input image signal increases, for example, in a pixel distributed array, black pixels are output discretely within the matrix, and in a pixel concentrated array, black pixels are concentrated in the vicinity of a predetermined pixel within the matrix. is output to.

Further, in a pixel distributed array in which a pixel matrix is composed of a plurality of sub-matrices, pixels whose density is sequentially converted for each sub-matrix are output as the i-scale of the input image signal increases.

In addition, multi-gradation pixels are formed using the output image signal whose gradation is controlled by pulse width modulation, and the density of pixels whose density is converted as the gradation of the input image signal increases is determined by the density gradation within the pixel between adjacent pixels. In pixel distributed arrays with different orders of transformation,
Fine pixels of black density of pixels whose density is converted as the gradation of the input image signal increases can be output close to each other.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a schematic block diagram of an image processing circuit of a digital copying machine according to an embodiment of the present invention. In the figure, 1 is a line image sensor (LIS) that reads a document image line by line and converts it into an analog image signal A, and 2 is an A/D converter that converts the converted analog image signal into a digital image signal. , 3 is a shading correction circuit that corrects image distortion and image density variation caused by uneven illuminance on the document surface and sensitivity variation of the line image sensor 1.

4 is a multi-value processing unit that performs multi-value processing to bit-convert the digital image signal D' into a multi-value number using a multi-value dither, a multi-value density pattern method, etc., and outputs image data D' corresponding to the image density. . 5 is an output control circuit which outputs a reproduced image signal C according to the input image data D''. 6 is a multilevel printer which outputs the image signal C input from the output control circuit 5.
The reproduced image is recorded on paper or the like based on the information. A control unit 7 outputs control signals such as synchronization signals to each of the circuit units 1 to 6, and controls image processing operations.

FIG. 4 is a diagram showing the timing control control signals in the control unit 7 in correspondence with the reading operation of the original image, where M is the original, FGATE is a signal representing the effective original width in the sub-scanning direction, and LGATE is the main signal. A signal representing the effective document width in the scanning direction, LSYNC, is a synchronization signal for reading in the main scanning direction.

The original M image is read line by line in the main scanning direction in synchronization with LSYNC, and becomes an effective image signal only when FGATE, I, and GATE are both HIGH. The read image signal is output from the line image sensor 1 pixel by pixel in synchronization with the reference signal CLK of the control unit 7.

FIG. 1 is a block diagram showing an internal circuit of a multi-value processing unit 4 using a multi-value dither method. In this embodiment, the output image data D'' has four values of O to 3.

A main scanning counter 41 counts pixels in the main scanning direction according to CLK and outputs an address signal CNTl. A sub-scanning counter 42 similarly counts lines in the sub-scanning direction according to LSYNC and outputs an address signal CNT2. 40 is a dither ROM (DROM) with a dither threshold TH, (n
= 1 to 3) and the value of the input image data D', the value of the output image data D'' is determined and output.The main scanning counter 41 and the sub-scanning counter 42 have a ring counter configuration, and the CNT1 and CNT2 is DRO
It corresponds to each image address in M4O. Therefore, D.R.
The OM40 compares the magnitude relationship between the darkness value data TH and the input image data D' at each address and outputs multivalued image data D'' corresponding to the recording density.CNTl and CN
T2 is also output to the output control circuit 5 to control the timing of pulse width modulation.

Dark value data TH, stored in the DROM 40.

It is possible to form various dither matrices by changing .

FIG. 2 is a block diagram showing the internal circuits of the output control circuit 5 and the multilevel printer 6. In the figure, 51 is a delay circuit (DEL), 52 is a logic circuit composed of AND-OR logic, and 53 is a data selector. , 62 is a laser diode (LD), and 61 is an LD drive circuit. In this embodiment, the output control circuit 5 controls one pixel with a different pulse width (0
This is a pulse width modulation circuit that outputs four-valued pulses (including
The multivalue printer 6 is composed of a laser printer.

In the output control circuit 5, a signal obtained by delaying the reference signal CLK by a DEL 51 is used and combined in a logic circuit 52 to generate pulse signals having different pulse widths. These pulse signals are image data D'' representing the density of the pixel output from the multivalue processing unit 4, and address signals CNT1.CN.
T2 selects the data selector 53 and outputs the reproduced image signal C.

In the multilevel printer 6, the reproduced image signal C is inputted as a pulse width modulation signal, and an LD drive current I controlled by the pulse width modulation signal is passed from the LD drive circuit 61 to the LD 62 to generate a light emission time corresponding to the pixel density. LD62 at the timing.
emits light.

FIG. 5 is a relationship diagram showing the values of multi-value image data D'' output from the multi-value processing unit 4 of the digital copying machine according to the first embodiment according to the values of input image data D'. FIG. 6 ia) shows the pulse waveform of the reproduced image signal C output from the data selector 53 according to the value of the multi-value image data D″, and FIG. It shows the output density pattern of one pixel according to the value of D''.

As shown in the figure, as the value of D' increases, the black density of the fine pixels within the pixel changes sequentially from the left in the figure.

Figure 8 shows 4X4=16 pixels P8 in DROM40,
ci, j = 1 to 4), one pixel is further divided into three fine pixels D
This figure shows a dither matrix composed of Pi7m (k=1 to 3). In this embodiment, one pixel p ij is divided into three fine pixels DPijk (k
= 1 to 3), and one pixel has 4 values (D' = O~
3) enables gradation output.

FIG. 9 shows the dither matrix I when outputting the halftone output image data D'' of the DROM 40.
In the figure, the large frame represents the pixel p iJ, and the narrow frame represents the fine pixel DP, k, and the numerical value within the frame represents the threshold data TH corresponding to each fine pixel.

This shows the value of . Input image data D' takes 49 values, that is, values from θ to 48, where O and 48 correspond to white and black densities, respectively.

Therefore, in dither matrix I, for example, P.

Focusing on the pixels, when the input image data D' is 1 to 16, the fine pixel DP+++ is, and when the input image data D' is 17 to 32, the fine pixel DP is
When l and DPzz are 33 or more, all fine pixels DP++
+ to DP+++ are output as black density output image data D#.

The feature of the dither matrix I of this embodiment is that the matrix has a pixel pH+P+! + P31 and P. When divided into mutually adjacent submatrices I (11 to I(4)) each consisting of four pixels, each having a vertex of D', the submatrix I
The submatrix I+w is sequentially changed for each pixel in s' (al = (1) to (4)) so that the pixels whose density gradation is to be increased next are not spatially close to each other, and all pixels P, A so-called dot-distributed dither matrix array is used in which the density of fine pixels DPiJk of white density is sequentially changed to black so as to cover DPiJk, and the density changes as the value of input image data D' increases. The difference is that the order of density change within one pixel p is arranged in such a way that the density changes in the fine pixels DP, .

FIGS. 13(a) to 13(d) show the output density patterns of the matrix corresponding to the values of input image data D' of uniform density by changing the values of the input image data D'.
al, (bl, (C) and (d) show output density patterns when the values of input image data D' are 4.8.16 and 2o, respectively.

First, when the values of input image data D' are uniformly 4, (a
As shown in l, each submatrix I+n(m-(1
) to (4)), upper left pixel pH, Pl:ll P:
ll and P. The fine pixel D P +z on the left side of
DP3:11, DP+1+, and DP331 are output as black density in the order of keyaki. When D'=8, as shown in (b), @density conversion for each pixel in the next submatrix goes through one cycle, and the fine pixel DPZZ1 in the pixels located diagonally below each of the above pixels in the submatrix Ts+ , DP441 , DPz4+ ,
DP4ZI is output as a black density, and a mesh density pattern is output.

When D'=16, all pixels p, (i.tC).

j = 1 to 4) left-side fine pixel D PiJk (k =
1) becomes @density, and a thin line striped density pattern is output. When D'=20, the first pixel pH as fdl
Returning to
By repeating the density conversion for each submatrix II, a density pattern in which the black density of one fine pixel is sequentially added to the thin line striped pattern is output.

FIG. 10 shows the DRO of the digital copying machine according to the second embodiment.
This figure shows the dither matrix ■ when outputting the M40 halftone output image data D″, and the other configurations are the first
This is the same as the embodiment.

The feature of the dither matrix (■) of this embodiment is that until the value of input image data D' reaches 8, the pixels whose density gradation is to be increased next are not spatially close to each other until the value of the input image data D' reaches 8. Change the submatrix ■■ one pixel at a time in the submatrix ■- ((1) to (41), and cover all the pixels at diagonal positions where the vertices of the pixels P and J touch. , change the density of the fine pixel DP, .
16, in the same way, submatrix IIm is changed one by one pixel in submatrix ■■ to convert the density of the remaining pixel Pt, but at that time, the density conversion of fine pixel DPiJk The point is that the order is from the one with the largest value of k (towards the right). Furthermore, when the value of the input image data D' increases, the position of the pixel to be subjected to density conversion is the same as in the first embodiment, but when performing density conversion of the upper right and lower left pixels in the submatrix I[im, it is shifted to the right. Concentration conversion is performed from micropixels.

That is, in this embodiment, the appearance of the density pattern differs depending on whether the value of the index i+j of the pixel P ij is an even number or an odd number. When i + j - even number, the density pattern of pixel P, j appears from the smaller k value of fine pixel DPijk, whereas when i + j - odd number, the density pattern of pixel P, j appears from the smaller k value of fine pixel DP = Jk. appear. FIG. 6(b) shows image data D# and address signal CNT l.

It shows the pulse waveform of the reproduced image signal C output from the data selector 53 according to the value of CNT2.

There are two sets each of even number and odd number combinations of CNT1 and CNT2 that give the same pulse waveform for the value 1.2 of the same image data D''.

FIG. 7 (bl shows the density patterns of pixels P and J of the recorded image formed according to the multivalued image data D'' in the order of the value of D''. As shown in the figure, As it increases, when i+j=even, pixel p, fine pixel DPi within i=,
The black density changes in descending order of the k value (from the left), whereas when i+j=odd, the black density changes in the order of the large k value (from the right) of the fine pixels DPi. .

FIGS. 14(a) to 14d) show the output density pattern of the matrix corresponding to the input image data D' of uniform density by changing the value of the input image data D', and (δ)
, ff1), fc) and (dl) indicate output density patterns when the values of input image data D' are 4.8.16 and 20, respectively.

First, the value of input image data D' is relatively small D'=4
When (as shown in al., submatrix IIs
The density of the white density fine pixels located on the left is changed one by one to black. That is, starting from the upper left pixel P, the leftmost fine pixels DPI++, DPti+, DP1□ in the order of pixels P331 Paff, P3+.
, 0Psr1 are output as the black density. When it comes to D'-8, the submatrix IIs of the above pixel as shown in (b)
Fine pixel DPz within each pixel located diagonally below
i+ , DPaa+ , DPta+ , DPat
+ is output as black density, and the next submatrix ■
A cycle of black density conversion for each pixel p i within - is outputted, and a string pattern density pattern is output. When D'=16, like tei, the submatrix ns+ is sequentially changed pixel by pixel in the submatrix row as in cases (a) and (1)), and the remaining pixel P8. The density of the fine pixels DP and J is converted.

The density conversion order is changed to black density in order from the one with the largest k value (towards the right). As a result, adjacent pixels p and p
iJ. Fine pixels with a black density of 1 are adjacent to each other, forming a mesh pattern of thick black dots. When D'=20, as in (d), 1 in the submatrix row is the same as in (a).
As a result of sequentially changing the density of the fine pixels D Pijz of white density located on the left pixel by pixel to black, the black pixel of the above rope pattern becomes thicker, and four pixels of the size of one pixel are created in the matrix. It is formed.

FIG. 11 shows the DRO of the digital copying machine according to the third embodiment.
This figure shows a dither matrix m when outputting M40 halftone output image data D'. Other configurations are first
This is the same as the embodiment.

The feature of the dither matrix ■ of this embodiment is that as the value of the input image data D' increases, starting from pixel P2□, the density of adjacent pixels is sequentially increased pixel by pixel, and the white color on the left side within the pixel is The point is that a dither matrix arrangement similar to a so-called concentrated dot type is used in which the density is converted by changing the black pixels one by one.

15(a) to (dl) are output density patterns of the matrix corresponding to the input image data D' of uniform density by the dither matrix ■, with the values of the input image data D'changed; ( ane (b), (member and (dl)
show the output density patterns when the values of the input image data D' are 4, 8°16, and 20, respectively.

(al indicates the output density pattern when the input image data D' has a uniform value of 4, and the four adjacent pixels P
11 P 13. P22. Fine pixel DP in PZ.

, DP I+ll , DP z□, DPzs+
This figure shows the state in which the black density is output. D
'=8, the above pixel P0. 4 western elements Ptr, Ptal adjacent to the side and bottom of Pzz
Psz, the density of the fine pixels within Psz changes to black. When D'=16, all pixels P=J(
i, j = 1 to 4), the left-side fine pixel DPij, (k
= 1) is the black density, and a crepe striped density pattern is output. When D'=20, the first pixel P as shown in (d)
Return to 2Z, set the value of k of the fine pixel DPig to be density-converted to 2, and apply the same procedure as +3> to the four adjacent pixels P1.
□-P+3+P! The density of 2+P tx is increased by one tone.

Figure 12 shows the DROM 40 of a digital copying machine according to a reference example.
The dot-concentrated dither matrix ■ used when outputting halftone output image data D'' is also shown in FIGS. 16(a) to (
d) shows the output density pattern of the matrix corresponding to the input image data D' of uniform density by the dither matrix ■ by changing the value of the input image data D'; (a), (b), (C) and fd), the values of the input image data D' are uniformly 4.8.16. and 20.

In this dither matrix ■, each time the value of D' increases by one, the black density is changed one by one for the minute pixels DPzzm (k-1 to 3) within the pixel, with the pixel P2□ on the upper left of the center as the core. The density gradation of the pixel is continuously increased, and when the pixel P2□ becomes completely black, the adjacent pixel P. Moving on to pixel P2. This is a typical dot concentration type arrangement in which the density gradation of the pixel P1 is successively increased, and then the same density conversion is performed one after another on the adjacent pixel P1.

With such a dither matrix ■, the density gradation output method is similar to the binary dither method, so the W of FJ 11 degrees! ,
The number of pixels and the number of gradations become linear, improving the contrast of the output image, but since the halftone image is expressed as a collection of dots, the grain of the output image becomes rough, the resolution deteriorates, and the contrast of the line image increases. The merits of the multilevel dither method are not fully utilized, such as when problems occur and problems occur.

On the other hand, in the density gradation output using the dither matrix ■ according to the first embodiment, each time the value of the input image data D' increases by one, the next pixel whose density gradation is to be increased is not spatially close to each other. This is a so-called dot-distributed dither matrix arrangement in which the submatrix I+ is sequentially changed to increase the density gradation of each pixel in the submatrix knee, so that the background part of the original is recorded in a regular dot arrangement. It is possible to prevent the image from being output as an image, and output a visually smooth recorded image with excellent resolution, especially in the case of a photographic image or the like, which has relatively little change in density.

On the other hand, in the density gradation output using the dither matrix (2) of the second embodiment, basically, the density gradation output method is a dot-distributed type, and the output density patterns of adjacent pixels are output in close proximity. It can also have dot-intensive properties.

Therefore, it is possible to compensate for the instability of a minute recording pixel of one output minute pixel and the nonlinearity of the number of pixels converted to black density and recording density, and reproduce tone without significantly deteriorating resolution. This makes it possible to output visually smooth recorded images with good quality and contrast.

In addition, in the density gradation output using the dither matrix (3) of the third embodiment, by arranging the pixels to be density-converted in a dot-concentrated type and converting the pixel density one tone at a time, it is possible to achieve a dot-concentrated type. It prevents the distortion of line images, which is a drawback of matrix arrays, and outputs recorded images with excellent resolution and gradation reproducibility and contrast.

FIG. 17(a), (bl, fcl) shows input image data D' representing a substantially uniform low-density matrix pattern, a matrix pattern representing low-density diagonal lines, and a matrix pattern representing high-density diagonal lines, respectively. Yes, Fig. 18 (I), <IN), (III) and (
IV) are dither matrices of almost uniform low-density matrix patterns shown in FIG. 17 (at!, n
, m, and ■, and FIGS. 19(1), (n), (III), and (IV) are dithered matrix patterns representing low-density diagonal lines shown in FIG. 17(b), respectively. Matrix I, II, I[[
FIG. 20 (I) shows the output density pattern according to and ■.

(n), (I[r) and (IV) show the output density patterns by dither matrices I, II, I and ■, respectively, of the matrix pattern representing the high density diagonal lines shown in Figure 17 (C1). be.

As is clear from these figures, the output density pattern (IV) based on the dither matrix ■ for the uniform low-density input image data D' shown in FIG.
pattern), resulting in an image with rough grain. On the other hand, in the output density pattern (1) by dither matrix I, the output fine pixels are uniformly distributed, so although there is some instability in the recorded pixels, the recorded image is a smooth image with fine grain. Become. Furthermore, since the output density pattern (n) based on the dither matrix H has dots uniformly distributed and is output with slightly thicker pixels, the output image is smooth without any image distortion and the grain is not so rough. Output density pattern by dither matrix ■ (II
In case I), the dots are uniformly dispersed and the dots are concentrated, resulting in a similar output density pattern, so although the stability of the recorded pixels is somewhat lacking, image blur does not occur and a smooth image with fine grains is obtained.

The output density pattern (IV) of the matrix pattern representing the diagonal lines of low density shown in FIG. 17(b) is a dot-like (array) pattern of a black image, so it is Similarly, the image will have rough grain. On the other hand, dither matrices I, II and ■
The matrix output density pattern (I), (II
) and (Dlr), the output image portions are almost uniformly distributed, resulting in a smooth output image.

The output density pattern (rV) in FIG. 20 based on the dither matrix (2) of the input image data D' representing a high-density diagonal line shown in FIG. 17 fc1 causes image jiggling in the image (line) direction and lacks smoothness. On the other hand, dither matrix 1
．． Output density pattern according to ■ and ■ Figure 20 (i),
In (ii) and (iii), not only no image (stripe) toggle occurs, but also a smooth line image is output. In particular, the output density pattern (n) by the dither matrix H is a pseudo-dot concentrated type, so it looks a little rough visually, but it has excellent density gradation and contrast.

In the explanation of the above embodiment, the pixel pins of the dither matrix whose density is converted are arranged using one of the dot concentrated type and dot dispersed type, but the method is not limited to this. However, other arrangement methods may be used, or a matrix arrangement of the same type but with different patterns may be used. The dither matrix size is not limited to 4×4 pixels, but can be implemented in the same manner even if it is of another size.

Furthermore, although the image processing method for converting the image density signal into digital image data representing a halftone image has been explained using the dither method as an example, it is also possible to use other image processing methods such as the density pattern method. I do not care.

In addition, we have explained how to make the pixel density multivalued by pulse width modulation, which divides the lighting time for one pixel to form fine pixels. For example, when a laser printer is used as a recording device, the amount of laser light is Multi-value means such as controlled intensity modulation may also be used.

〔Effect of the invention〕

As explained above, according to the present invention, the pixel matrix is arranged so as to cover the pixels in the matrix one by one, and the density gradation of the pixel is converted one by one as the gradation level of the human image signal increases. Since the image processing is performed on the human image signal and converted into multi-tone image data that represents a half-tone image using , the resolution of the output image does not deteriorate.
It is possible to output visually smooth recorded images with excellent gradation and contrast. Furthermore, by using a pixel matrix arranged in a pixel-distributed or pixel-concentrated type, a recorded image that is adapted to the characteristics of the input image signal can be obtained.

In addition, multi-gradation pixels are formed using the output image signal whose gradation is controlled by pulse width modulation, and the order of density conversion within the pixel is changed as the gradation level of the input image signal increases. If so, the instability of low-density recorded images can be compensated for.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an internal circuit of a multi-value processing unit of a digital copying machine according to an embodiment of the present invention, FIG. 2 is a block diagram showing an output control circuit and an internal circuit of a multi-value printer, and FIG. 4 is a schematic block diagram of an image processing circuit of a digital copying machine, FIG. 4 is an explanatory diagram showing control signals for timing control in correspondence with document image reading operations, and FIG. 5 is an illustration of output image data of a multivalue processing unit. Relationship diagrams showing values according to input image data values, Figure 6 (al, (b))
7(at) is a pulse waveform diagram of the reproduced image signal output from the data selector, (bl is an explanatory diagram showing the density pattern of pixels formed according to the multilevel output image data, and FIG. 9, 10, 11, and 12 are block diagrams showing a dither matrix composed of 4×4 pixels according to the example, respectively. A configuration diagram showing such a dither matrix,
Figures 13 fa) to (d), Figure 14 (al to (d)),
Figures 15(a) to (d) and Figures 16 to (d)
FIG. 17 (a ) to (C) are explanatory diagrams showing pixel matrices of input image data representing diagonal lines, FIGS. 18 and 19.
20 and 20 are explanatory diagrams showing output density patterns of input image data representing uniform low density, low density, and high density diagonal lines shown in FIGS. 17(a) to 17(c). 4... Multivalue processing unit, 40... Dither ROM,
41... Main scanning counter, 42... Sub-scanning counter. Figure 1 Figure 4 Figure 5 Figure 6 (a) Figure 6 (b) Figure 7 (a) Figure 7 (b) D'' 0 1 2 3 Figure 8 Series 9 Figure 10 Figure ti Figure $ 12 Figure 13 (c)
(d) Figure 14 (a) (
b) Figure 15(a)
(b) Fig. 16 Fig. 17 (a) Fig. 17 (b) Fig. 17 (c) Fig. 20 After'Q

Claims (5)

[Claims] (1) Using a pixel matrix consisting of multi-tone pixels,
In an image processing method that performs image processing on an input image signal and converts it into image data representing a halftone image, the pixel matrix is such that the pixels whose density is converted as the gradation of the input image signal increases are the pixels in the matrix. An image processing method characterized in that the image processing method is arranged so that the density is converted one by one pixel by pixel and in the order of density gradation to cover the area. (2) In the statement of claim 1, the pixels of the pixel matrix whose density is converted as the gradation of the input image signal increases are a certain pixel and a pixel located spatially apart from the pixel. An image processing method characterized in that pixels are arranged in a distributed array in which pixels are distributed sequentially. (3) In the description of claim 2, in the pixel distributed array, a pixel matrix is composed of a plurality of submatrices, and pixels whose density is converted as the gradation level of an input image signal increases are arranged in each submatrix. An image processing method characterized in that an image is arranged so as to be sequentially distributed. (4) In the statement of claim 2 or 3, the multi-gradation pixel is formed by an output image signal whose gradation is controlled by pulse width modulation, and the gradation of the input image signal increases. The pixels of the pixel matrix whose density is converted according to
An image processing method characterized in that the order of density gradation conversion within a pixel is made different between adjacent pixels. (5) In the statement of claim 1, the pixels of the pixel matrix whose density is converted as the gradation level of the input image signal increases are concentrated in a predetermined pixel and pixels adjacent to the pixel, which are sequentially distributed. An image processing method characterized by arrangement using a type array.