JPH099054A - Color picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely judge whether an input picture is a binary picture or a half-tone picture and to execute a processing corresponding to the judged result by judging intermediate density by means of first, second and third comparison means and a judgement means and inhibiting a half-tone processing. SOLUTION: A comparator 270 being the first comparison means compares the respective picture signals of Y, M and C with a threshold TH1 being a first reference level. The respective Y, M and C signals are impressed on the maximum value selection circuit 280 of the third comparison means 280 and 290 through gate circuits 274-276 which cause low levels to pass through. The picture signal whose gradation level is the largest is selected and outputted among the picture signals. The output signal is impressed on the comparator 290 and it is compared with a threshold TH3. Then, a binary signal corresponding to the result is outputted. A density inclination judgement circuit 310 being the second comparison means is provided with multiple gate circuits G1-G15 and it generates a control signal SG5 for deciding the processing of the picture signal to be a simple binary processing or the half-tone processing. A signal SG4 is that for selecting a judgement mode and it can arbitrarily be switched by an indication from an operation board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus, and more particularly to a color image processing apparatus which automatically determines whether the type of an input image is halftone or binary and switches the processing content according to the result.

[0002]

2. Description of the Related Art When an image is recorded by the dot matrix method, a normal recording apparatus can adjust the density level of each dot to only about four levels at maximum. However, for example, in a digital color copying machine, in order to faithfully reproduce colors, generally 64 (64) for each basic color of recording such as yellow (Y), magenta (M), cyan (C), and black (BK). Gradation representation of stages is required.

When performing such multi-gradation expression, conventionally, a comparatively large dot area composed of a plurality of dots (for example, 8 × 8) is used as a unit of a gradation processing area, and a recording dot is set for each dot area. And the number of non-recorded dots are adjusted to express the density level of each gradation processing area. This kind of halftone expression method is called an area gradation method.

However, for example, when an 8 × 8 dot area is used as a gradation processing unit, the recording resolution is reduced to ⅛ of that when one dot is used as a gradation processing unit. For example, in an image such as a photograph, even if the resolution is low, if the halftone, that is, the density of each pixel is accurately expressed, the recording quality is highly evaluated. However, in the case of a line drawing or a character, a reduction in resolution immediately leads to a reduction in recording quality.

Generally, in an image including a line drawing and characters, black /
In many cases, gradation expression is unnecessary like white. Therefore, it has been proposed to switch the image information processing to either binary processing or gradation processing according to the content of the image to be handled.

When the processing mode (binary processing / gradation processing) is switched by the manual operation of the operator, the operator discriminates the type of the original image, so that the proper processing mode can be selected. However, when the processing mode is automatically switched, the judgment is difficult.

The prior art for making this type of determination is disclosed in, for example, Japanese Patent Laid-Open Nos. 59-205876 and 59-2.
No. 05872 and Japanese Patent Laid-Open No. 60-66575. In the prior art, if the difference between the maximum density and the minimum density in the multiple dot area is greater than or equal to a predetermined value,
The area is determined as a binary image area. In the case of color image information, the determination is made by using only one black signal BK or the logical sum of the determination results of the Y, M, C color signals.

When the binary image is drawn only in a relatively dark black color, the presence or absence of the binary image can be accurately determined even in the conventional technique.

[0009]

However, for example, in the case of a multicolor map image, chromatic colors of various hues are often used for displaying characters and lines, and this kind of In the image, it is inevitable that the result of the judgment becomes inaccurate.

That is, in the prior art, when the difference between the maximum density and the minimum density in the plural dot area is very large, the image is judged to be a binary image, so that the chromatic characters and the background overlap. In the area where the background density, that is, the minimum density is relatively large, even if the character density, that is, the maximum density level is very large, the level difference between the maximum density and the minimum density is small, and the halftone is erroneously determined. It may be done. Further, since the difference between the maximum density and the minimum density is individually determined for each basic color, an error is likely to occur in the determination in the case of a color expressed by combining a plurality of basic colors.

According to the present invention, characters and lines are R (red), G (green), and B (bull) in a color input image.
Alternatively, even if the input image is drawn in each color of Y, M, and C, it is possible to accurately determine whether the input image is a binary image such as a character or a line drawing or a halftone image, and perform a process according to the determination result. To aim.

[0012]

The color image processing apparatus of the present invention is an image information input means (7r, g, b, 101 to 105) for outputting color image information which is color-separated into a plurality of basic colors; First comparing means (270) for comparing the level of each basic color signal of the image information output by the image information input means with a first reference level (TH1); the image information input means (7r, g, b, 101
~ 105) monitor the signal of each basic color of the image information output,
For each predetermined area composed of a plurality of pixels of each signal, a change amount of the signal level in the area is compared with a second reference level (TH2).
Comparing means (310y, m, c = 210,230,240,251,252); the first reference level (T
H1) Third comparing means (280,290) for comparing the signal level of the signal with the third reference level (TH3); the level of the signal of at least one basic color of the image information being the first reference level (TH1) and at least one of the signals larger than the first reference level (TH1), the signal level change amount in the predetermined region is the second reference level (TH
2) It is above, and when the level of all the basic color signals below the first reference level (TH1) is lower than the third reference level (TH3), a determination means for determining that halftone processing is prohibited
(G1 to G15); and an image output from the image information inputting means (7r, g, b, 101 to 105) using the judgment results of the judging means (G1 to G15) Signal processing means (320y, m, c) for processing the signal of each basic color of information is provided. In addition, in order to facilitate understanding, the reference numerals of the corresponding elements or corresponding matters of the embodiments shown in the drawings and described later are added in parentheses for reference.

Generally, in characters, line drawings and the like (binary image) drawn in color, the colors Y, M and C which are the primary colors of ink or the red (R) and G (green) which are the primary colors of light are used. -B) is often used. When these colors are expressed by the levels of Y, M, and C color signals, the density of one or two of Y, M, and C is large, and the density of the remaining two or one is very small. That is, there is no intermediate concentration. In the present invention, this is the first comparison means (270) and the second comparison means (310y, m, c = 21).
0,230,240,251,252), the third comparing means (280,290) and the judging means (G1 to G15) make the judgment, and the judging means (G1 to G15) prohibit the halftone processing. As a result, the halftone processing of the signal processing means (320y, m, c) is prohibited in the case of a colored binary image, and the deterioration of the resolution due to the gradation processing of the colored binary image is prevented.

[0014]

In a preferred embodiment of the present invention, the second comparing means (310y, m, c) extracts the maximum value and the minimum value of the signal level within a predetermined area, and the extracted both The level difference of is compared with the second reference level (TH2). Further, the signal processing means (320y, m, c) is input with first processing means, that is, binarization processing means, which outputs a result of comparing the input signal with one fixed threshold value. The signal is determined according to the scanning position of the image input means among a plurality of types of threshold values 1
And a second processing means for outputting the result of comparison with one, that is, a halftone processing means.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0016]

FIG. 1 shows the components of a mechanical section of a digital color copying machine of one type embodying the present invention, and FIG. 2 shows a schematic configuration of an electrical section. Referring first to FIG. 1, the document 1 is placed on the platen (contact glass) 2, is illuminated by the document illumination fluorescent lamp 3 _1, 3 _2, the reflected light first mirror 4 ₁ moveable comprises first 2 mirror 4 ₂ and 3rd mirror 4
_The light is reflected at ₃ , passes through the imaging lens 5, enters the dichroic prism 6, and is split into light of three wavelengths, red (R), green (G), and blue (B). The split light is a CCD 7r, 7 which is a solid-state image sensor.
g and 7b. That is, red light enters the CCD 7r, green light enters the CCD 7g, and blue light enters the CCD 7b.

The fluorescent lamps 3 ₁ and 3 ₂ and the first mirror 4 ₁ are mounted on the first carriage 8, and the second mirror 4 ₂ and the third mirror 4 ₃ are mounted.
Is mounted on the second carriage 9, and the second carriage 9 moves at half the speed of the first carriage 8, so that the optical path length from the original 1 to the CCD is kept constant. And the second carriage is scanned from right to left. The first carriage 8 is coupled to the carriage driving wire 12 wound around the carriage driving pulley 11 fixed to the shaft of the carriage driving motor 10.
A wire 12 is wound around a moving pulley (not shown) on the second carriage 9. As a result, the first carriage 8 and the second carriage move forward (original image reading scan) and return (return) by the forward and reverse rotations of the motor 10, and the second carriage 9 moves to half of the first carriage 8. Move at speed.

When the first carriage 8 is at the home position shown in FIG. 1, the first carriage 8 is detected by the home position sensor 39 which is a reflection type photo sensor. When the first carriage 8 is driven to the right by the exposure scanning and deviates from the home position, the sensor 39 does not receive light (carriage non-detection), and when the first carriage 8 returns to the home position, the sensor 39 receives light ( (Carriage detection), and the carriage 8 is stopped when non-light-receiving changes to light-receiving.

Referring now to FIG. 2, CCD 7r, 7
The outputs of g and 7b are subjected to analog / digital conversion and subjected to necessary processing in the image processing unit 100, and recording color information of black (BK), yellow (Y), magenta (M) and cyan (C). It is converted into a binary signal for activating each recording. Each of the binarized signals is generated by the laser driver 112bk, 112y, 112m and 112.
The laser driver is input to the semiconductor laser 113.
By energizing bk, 113y, 113m, and 113c, laser light modulated by a recording color signal (binarized signal) is emitted.

Referring again to FIG. The emitted laser beams are reflected by rotating polygon mirrors 13bk, 13y, 13m, and 13c, respectively, and are output from f-θ lenses 14bk, 14bk.
After passing through y, 14m and 14c, the fourth mirror 15bk,
15y, 15m and 15c and the fifth mirror 16bk, 1
After being reflected by 6y, 16m and 16c, through the polygon mirror tilt correction cylindrical lenses 17bk, 17y, 17m and 17c, the photosensitive drums 18bk, 18y and 18
Image and illuminate m and 18c.

The rotating polygon mirrors 13bk, 13y, 13m and 13c are polygon mirror driving motors 41bk, 41y and 41, respectively.
The motors are fixed to the rotating shafts m and 41c, each motor rotates at a constant speed, and drives the polygon mirror to rotate at a constant speed. By the rotation of the polygon mirror, the above-mentioned laser light is scanned in a direction perpendicular to the rotation direction (clockwise direction) of the photosensitive drum, that is, the direction along the drum axis.

The surface of the photosensitive drum is a charge scorotron 19 connected to a negative voltage high voltage generator (not shown).
It is uniformly charged by bk, 19y, 19m and 19c. When the laser light modulated by the recording signal (binarized signal) is applied to the uniformly charged surface of the photosensitive member, the charge on the surface of the photosensitive member flows to the equipment ground of the drum body by photoconductive development and disappears. . Here, the laser is not turned on in the portion where the original density is high, and the laser is turned on in the portion where the original density is low. Thereby, the photosensitive drum 18b
On the surfaces of k, 18y, 18m, and 18c, a portion corresponding to a portion having a high density of the original becomes a potential of −800V, and a portion corresponding to a portion having a low original density becomes about −100V,
An electrostatic latent image is formed corresponding to the light and shade of the original. The electrostatic latent images are respectively transferred to the black developing unit 20bk, the yellow developing unit 20y and the magenta developing unit 20.
m and a cyan developing unit 20c to develop, to form black, yellow, magenta and cyan toner images on the surfaces of the photoconductor drums 18bk, 18y, 18m and 18c, respectively. The toner in the developing unit is positively charged by agitation, the developing unit is biased to about -200 by a developing bias generator (not shown), and the surface potential of the photoconductor adheres to a place higher than the developing bias, and the A corresponding toner image is formed.

On the other hand, the recording paper 267 stored in the transfer paper cassette 22 is fed out by the feeding operation of the feed-out roller 23, and is fed to the transfer belt 25 by the registration roller 24 at a predetermined timing. The recording paper placed on the transfer belt 25 sequentially passes below the photosensitive drums 18bk, 18y, 18m, and 18c as the transfer belt 25 moves, and passes through the photosensitive drums 18bk, 18y, 18m, and 18c. During this time, the toner images of black, yellow, magenta and cyan are sequentially transferred onto the recording paper by the action of the transfer corotron below the transfer belt. The transferred recording paper is then sent to the thermal fixing unit 36, where the toner is fixed to the recording paper, and the recording paper is transferred to the tray 3
It is discharged to 7.

On the other hand, the residual toner on the surface of the photoconductor after transfer is
Cleaner units 21bk, 21y, 21m and 21
removed in c. The cleaner unit 21bk for collecting black toner and the black developing unit 20bk are connected by a toner recovery pipe 42, and the cleaner unit 21bk is connected.
The black toner collected in step 3 is collected in the developing unit 20bk. The black toner is reversely transferred from the recording paper to the photosensitive drum 18y at the time of transfer, so that the yellow, magenta, and cyan toners collected by the cleaner units 21y, 21m, and 21c are different from the different color developing device in the preceding stage of those units. Since the toner is mixed, it will not be collected for reuse.

The recording paper is transferred from the photosensitive drums 18bk to 18c.
The transfer belt 25 fed in the direction of
It is stretched around the drive roller 27, the idle roller 28, and the idle roller 30, and is driven to rotate counterclockwise by the drive roller 27. The drive roller 27 is pivotally attached to a left end of a lever 31 pivotally attached to a shaft 32. Lever 31
A plunger 35 of a black mode setting solenoid (not shown) is pivotally attached to the right end of the solenoid. A compression coil spring 34 is disposed between the plunger 35 and the shaft 32, and the spring 34 applies a clockwise rotational force to the lever 31.

When the black mode setting solenoid is not energized (color mode), as shown in FIG. 1, the transfer belt 25 on which the recording paper is placed is the photosensitive drums 44bk, 44y, 44.
m and 44c. In this state, when the recording paper is placed on the transfer belt 25 and toner images are formed on all the drums, the toner image of each image is transferred onto the recording paper as the recording paper moves (color mode). When the black mode setting solenoid is energized (black mode), the lever 31 rotates counterclockwise against the repulsive force of the compression coil spring 34, the driving roller descends by 5 mm, and the transfer belt 25 moves to the photosensitive drum 4
4y, 44m and 44c away from the photosensitive drum 44
It remains in contact with bk. In this state, since the recording paper on the transfer belt 25 only contacts the photosensitive drum 44bk, only the black toner image is transferred to the recording paper (black mode). The recording paper is the photosensitive drums 44y, 4
Since the recording paper does not come into contact with 4m and 44c, no toner (residual toner) adhered to the photosensitive drums 44y, 44m and 44c is attached to the recording paper, and stains such as yellow, magenta and cyan do not appear at all.

Referring to FIG. Image processing unit 100
Converts the three color image signals read by the CCDs 7r, 7g and 7b into respective recording signals of black (BK), yellow (Y), magenta (M) and cyan (C) necessary for recording. The BK recording signal is given to the laser driver 112bk as it is, but the Y, M and C recording signals are respectively supplied to the buffer memories 108y, 108m and 10.
After being held at 8c, it is given to the laser drivers 112y, 112m and 112c after a time delay of reading out after a predetermined delay time and converting into a recording signal. In addition,
The image processing unit 100 is supplied with the three color signals from the CCDs 7r, 7g and 7b in the copying machine mode as described above. In the graphics mode, the three color signals are supplied from the outside of the copying machine through the external interface 117.

The shading correction circuit 101 of the image processing unit 100 converts the output signals of the CCDs 7r, 7g and 7b into 8-bit color gradation data, and outputs optical unevenness of illuminance and internal CCDs 7r, 7g and 7b. The read color gradation data is created by correcting the sensitivity variations of the unit elements.

The multiplexer 102 is a correction circuit 101.
One of the output grayscale data and the output grayscale data of the interface circuit 117 is selectively output.

The input γ correction circuit 103 that receives the output (color gradation data) of the multiplexer 102 corrects the signal output by the input γ correction circuit 103 according to the characteristics of the image input device, and obtains any input characteristics according to preference. It is for.

R, G, output from the input γ correction circuit 103
The B color signal is output by the masking processing circuit 104 to Y,
Converted to M and C.

Y output from the masking processing circuit 104,
The signal of each bit of M and C is applied to the output γ correction circuit 105. The output γ correction circuit 105 performs processing for correcting the nonlinear characteristic between the number of recording dots and the actual recording area ratio (effective area ratio), which is caused by the recording system. That is, it is ideal that the correlation between the number of recording dots controlled by the electric circuit and the recording area ratio of the surface actually printed by it is 1: 1, but in reality it changes due to various causes. I will correct it.

Output Y correction circuit 105 outputs Y, M,
Each 6-bit signal of C is converted into a binary signal by the gradation processing circuit 106. That is, the input multivalued data is compared with a predetermined threshold level, and a binary signal corresponding to the magnitude is output. In this example, as will be described later, it is automatically determined whether the image density is binary or halftone, and if it is binary, simple binarization processing is performed, and if it is halftone, dither processing is performed. In the dither processing, the number of “1” s indicating the recording dots and the number “0” s indicating the non-recording dots are adjusted for each 8 × 8 area of the recording dots, and gradation expression is performed by the area ratio of the recording dots. .

The binary signal output from the gradation processing circuit 106 is applied to the black separation / undercolor removal circuit 107. This circuit 107 has Y, M, and C when the four-color mode is selected.
3 color signals are converted into Y, M, C and BK 4 color signals.
That is, when Y, M, and C are all "1" (recording level),
Since the composite color is black, the black signal BK is set to "1" and Y, M, and C are set to "0" (non-recording level).

The signal BK output from the black separation / undercolor removal circuit 107 is directly applied to the laser driver 112bk, and the other signals C, M and Y are respectively supplied to the buffer memory 108.
The timing is adjusted through c, 108m, and 108y and applied to each laser driver.

A concrete structure of the gradation processing circuit 106 is shown in FIGS. 3, 4, 5 and 7. First, a description will be given with reference to FIG.

The comparison circuit 270, which is the first comparison means,
It is composed of three digital comparators 271, 272 and 273, and the Y, M, and C image signals (Yin, Min, Cin) output from the output γ correction circuit 105 are the first reference level threshold. Compare with the value TH1. Signal SG output from each digital comparator 271, 272 and 273
1y, SG1m, and SG1c are the signals Yi, respectively.
When n, Min and Cin are larger than the threshold value TH1, the level becomes high level H (that is, "1"), and otherwise becomes low level L (that is, "0"). In this example, the threshold value TH1 is a predetermined fixed value and is set to 31 which is an intermediate value of the gradation level values (0 to 63).

The Y, M and C signals are applied to the maximum value selection circuit 280 which is a part of the third comparison means (280, 290) via the gate circuits 274, 275 and 276, respectively. The gate circuits 274, 275, and 276 have signals SG1y, SG1m, and SG1c at low level L, respectively.
Pass the signal at. At the high level H, the output level is 0, that is, all bits are "0".

The maximum value selection circuit 280 is for each gate circuit 2
Among the Y, M, and C image signals output by 74, 275, and 276, the one with the highest gradation level is selected and the selected signal is output. That is, of the Y, M, and C image signals having the gradation equal to or lower than the threshold value TH1, the image signal having the maximum gradation is selected and output.

The digital comparator 281 compares the gradations of the Y and M signals, the digital comparator 282 compares the gradations of the M and C signals, and the digital comparator 283 compares the gradations of the C and Y signals. Compare the tones. The decoder 285 generates a control signal in accordance with the combination of the comparison results of the digital comparators 281, 282 and 283 and outputs it to the multiplexer 28.
4 is applied. As a result, multiplexer 284
Of the signals, the M signal and the C signal, the one with the highest gradation level is output. In addition, all the gradations of Y, M, and C are TH1.
, The outputs of the comparators 281, 282 and 283 all become low level L. At this time, the multiplexer 284 sets the gradation level of the signal it outputs to 0.

The signal output from the maximum value selection circuit 280 is
It is applied to the digital comparator 290 which is the rest of the third comparing means (280,290). The comparator 290 compares the image signal output by the maximum value selection circuit 280 with a threshold TH3 that is the third reference level, and outputs a binary signal SG3 according to the result. This binary signal becomes high level H when the image signal is smaller than the threshold value TH3, and becomes low level L otherwise. The threshold value TH3 is a fixed value in this example, and is set to a comparatively small gradation level 8.

Therefore, the signal SG3 is the output γ correction circuit 1
When at least one of the Y, M, and C image signals output by 05 is between two threshold levels TH1 and TH3, the level is low L, and otherwise it is high H. .

Next, referring to FIG. The determination circuit 260 shown in FIG. 4 determines whether the input image signal is an achromatic color or a chromatic color. The decision circuit 260 includes subtracters 261 and 26.
2, 263, maximum value selection circuit 264 and comparatively 265.

The subtractor 261 outputs the difference between the Y signal and the M signal, the subtractor 262 outputs the difference between the M signal and the C signal, and the subtractor 263 outputs the difference between the C signal and the Y signal. . The maximum value selection circuit 264 uses the subtractors 261 and 26
Among the signals output from the output terminals 2 and 263, the one having the maximum absolute value is selectively output. Therefore, the configuration of the maximum value selection circuit 264, except that a circuit for calculating the absolute value of the input value is added,
This is the same as the maximum value selection circuit 280 in FIG.

The comparator 265 compares the level of the image signal output by the maximum value selection circuit 264 with the threshold value TH4. In the signal SG2 output from the comparator 265, the level of the image signal output from the maximum value selection circuit 264 is the threshold value TH.
High level H when less than 4 and low level L otherwise. The threshold value TH4 is a fixed value in this example and is set to 6. That is, if the gradation difference between Y, M, and C of the input image signal is 5 or less, the color of the image signal is determined to be achromatic, and the signal SG2 is set to H.
In the case of a chromatic color, the signal SG2 becomes L.

Next, referring to FIG. The circuit shown in FIG.
It is a circuit that generates a control signal SG5 that determines whether the image signal processing is simple binary processing or halftone processing (dither processing). This circuit includes three density gradient determination circuits 310y, 310m and 310c and a large number of gate circuits G.
1 to G15 are provided. The three density gradient determination circuits in FIG. 5 have the same configuration.

FIG. 6 shows one configuration of the density gradient determination circuits 310y, 310m and 310c, which is the second comparison means. Referring to FIG. 6, this circuit includes a two-dimensional buffer memory 210, a maximum value selection circuit 230, a minimum value selection circuit 240, a subtractor 251, and a comparator 252. The two-dimensional buffer memory 210 includes nine latch circuits 211 to 219, two sets of line buffer memories 220,
221, which is 3 × 3 composed of three pixels adjacent to each other in the main scanning direction and three pixels adjacent to each other in the sub scanning direction.
The pixel signals of 9 pixels in the pixel area are output at the same timing. Since the input image signal is time series, only one pixel data can be referred to at a time as it is. Therefore, by holding the data of the previously appearing pixel in the memory, it is possible to simultaneously refer to the 9 pixel data of the 3 × 3 pixel 1 pixel area.

That is, the 1-line buffers 221 and 220
Respectively store the pixel data group for one line in the main scanning direction, the latches 211, 212 and 213 are the nth
The latches 214, 215 and 216 output the data of the (n-1) th line when the data of the line 2 is output.
17, 218 and 219 output the data of the (n-2) th line. Further, since each latch stores the data of each pixel at the timing of each pixel, when the latches 211, 214 and 217 output the mth pixel of each line, the latches 212, 215 and 218 make the m−1th pixel. , And the latches 213, 216, and 219 output the (m−2) th pixel.

Therefore, assuming that the output pixel data of the latch 215 is the data D (x, y) of the pixel of interest on the x-th column and the y-th line, each latch 211, 212, 213, 214, 2 is used.
16, 217, 218 and 219 are D (x +
1, y + 1), D (x, y + 1), D (x-1, y +
1), D (x + 1, y), D (x-1, y), D (x +
1, y-1), D (x, -1) and D (x-1, y-
The data of each pixel in 1) is output at the same timing as D (x, y).

The gradation data of each pixel output from each of the latches 211 to 219 is applied to the input terminals of the maximum value selection circuit 230 and the minimum value selection circuit 240, respectively. The operation of the maximum value selection circuit 230 is the same as that of the maximum value selection circuit 280 of FIG. 3 except that the number of data to be selected is nine. The operation of the minimum value selection circuit 240 is the same as that of the maximum value selection circuit 230 except that the minimum value is selected instead of the maximum value.

The subtractor 251 generates data indicating the difference between the gradation data output by the maximum value selection circuit 230 and the gradation data output by the minimum value selection circuit 240, and applies it to the comparator 252. To do. That is, the value of the signal output by the subtractor 251 is the difference between the maximum gradation and the minimum gradation in the 9 pixels in the 3 × 3 pixel area.

The comparator 252 compares the value output by the subtractor 251 with the threshold value TH2 which is the second reference level, and outputs the result as a binary signal. This binary signal becomes H when the output of the subtractor 251 is larger than TH2, and otherwise becomes L. In this example, the threshold value TH2 is a fixed value and is set to 30.

When the input image is, for example, a line drawing drawn with a thin line, at least one of the 3 × 3 pixel regions corresponds to the background pixel. In that case, since the density difference between the line drawing portion and the background portion is relatively large, the value output by the subtractor 251 becomes larger than the threshold value TH2, and the signal output from the comparator 252 becomes high level H. Become.

Returning to FIG. 5, the description will be continued. Signal SG4
Is a signal for selecting the determination mode, and this signal can be arbitrarily switched by an instruction from the operation board 300 shown in FIG. When the signal SG4 is at high level H, this circuit is in the achromatic judgment mode, and SG4 is at low level L.
At the time of, it becomes the chromatic color determination mode.

In the achromatic color determination mode, the color of the binary image is determined to be an achromatic color for determination. In the chromatic color determination mode, it is determined that the color of the binary image is not limited to the achromatic color. When the achromatic color determination mode is selected, the signal SG5 becomes high level H (“1”) when all the following conditions (a), (b) and (c) are simultaneously satisfied. . (A) The logical sum (output of G6) of the outputs of the Y, M, and C density gradient determination circuits is at a high level H. (B) The signal SG2 is at the high level H. (C) The logical product of signals SG1y, SG1m, and SG1c (G
4 output) is at high level H.

That is, in the achromatic color determination mode, Y, M,
In at least one of C, the difference between the maximum density and the minimum density in the 3 × 3 pixel region is larger than TH2, the gradation level difference among Y, M, and C is smaller than TH4, and Y, M, and
Only when all the gradation levels of C are higher than TH1, the image data is judged to be binary data, and the signal SG5 is set to the high level H.

When the chromatic color determination mode is selected, the signal S
G5 becomes the high level H in the following (d), (e),
It is when the conditions of (f) and (g) are simultaneously satisfied. (D) At least one of the signals SG1y, SG1m, and SG1c is H. (E) At least one of the signals SG1y, SG1m, and SG1c is L. (F) The signal SG3 is H. (G) Logical product of the density gradient determination circuit 310y and the signal SG1y (output of G1), logical product of the density gradient determination circuit 310m and the signal SG1m (output of G2), logic of the density gradient determination circuit 310c and the signal SG1c. The logical sum (output of G7) of the product (output of G3) is H.

That is, in the chromatic color mode, at least one gradation of Y, M, and C is TH1 or higher, and the gradation is TH.
In at least one of the signals (Y, M, C) larger than 1, the difference between the maximum density and the minimum density in the 3 × 3 pixel area is larger than TH2, and the gradations of the signals smaller than TH1 are all TH3. The image data is determined to be binary data (binary image such as characters and line drawings) only when
G5 is set to high level H. This signal SG5 = H instructs the simple binarization processing / gradation processing circuit shown in FIG. 7 to prohibit the gradation processing and to select the simple binarization processing.

In this embodiment, the signal SG4 switches between the achromatic color determination mode and the chromatic color determination mode, but the logical sum of these two determination modes may be output as SG5. In that case, the gates G12 and G14 of FIG. 5 are omitted, and the output terminals of the gates G9 and G10 are
It may be directly connected to each input terminal of the gate G15.

The signal SG5 output from the circuit of FIG.
Applied to the circuit of FIG. Referring to FIG. 7, this circuit includes three read-only memories (ROMs) 320y, 3Oy.
It is 20m and 320c. The signal SG5 is
It is applied to the address terminal of each memory. Data of a threshold table as shown in FIGS. 8A and 8B is stored in advance in these memories. 8A shows a threshold table for halftone processing (dither processing), and FIG. 8B shows a threshold table for simple binarization processing.

When the signal SG5 is at the low level L, that is, when the image is determined to be halftone, the threshold table of FIG. 8A is selected, and SG5 is at the high level H, that is, the image is determined to be a binary image. 8B, the threshold table shown in FIG. 8B is selected. Memories 320y, 320m and 320
c compares the Y signal, the M signal, and the C signal with one value in the threshold table, and outputs the result as a binary signal. The threshold value to be used is selected from the threshold value table by the main scanning signal and the sub scanning signal representing the scanning position of the image signal.

The binary signals Yout, Mout and Cout output from the memories 320y, 320m and 320c are applied to the black separation / under color removal circuit 107 as Y, M and C binary signals, respectively.

The values of the thresholds TH1, TH2, TH3 and TH4 shown in each circuit of the above embodiment are examples, and these values change appropriately according to the characteristics of the device, the type of image and the like. Therefore, it may be changed according to the situation at that time.

Further, in the above embodiment, the density gradient determination circuit targets the 3 × 3 pixel area, but
The size of this area may be arbitrarily changed according to the read separability of the image input device and the thickness of the line on the image.

[0065]

As described above, according to the present invention, it is accurately determined whether a chromatic image is a binary image such as a character or a line drawing, or a halftone image. Since the processing is prohibited, deterioration of the resolution of the binary image due to gradation processing can be prevented.

[Brief description of drawings]

FIG. 1 is a front view showing the internal configuration of a digital color copying machine of one type embodying the present invention.

FIG. 2 is a block diagram showing an outline of an electric circuit of the copying machine of FIG.

3 is a block diagram showing a configuration of a first comparison circuit and a fourth comparison circuit of the gradation processing circuit 106 of FIG.

FIG. 4 is a block diagram showing a part of the configuration of the gradation processing circuit 106 in FIG.

5 is a block diagram showing another part of the configuration of the gradation processing circuit 106 in FIG.

FIG. 6 is a density gradient determination circuit 310y, m, shown in FIG.
It is a block diagram which shows one structure of c.

7 is a block diagram showing the rest of the configuration of the gradation processing circuit 106 of FIG.

8 (a) and (b) are the memory 3 shown in FIG.
FIG. 3 is a plan view showing two-dimensionally expanded contents of data of threshold tables for gradation processing and simple binarization processing inside 20y, 320m, and 320c.

[Explanation of symbols]

7r, 7g, 7b: CCD 106: gradation processing circuit 21
0: Two-dimensional buffer memory 230, 264, 280: Maximum value selection circuit 240: Minimum value selection circuit 252, 265, 271-273, 281-283, 2
90: Digital comparator 270: Comparison circuit 274, 275, 276: Gate circuit 310y, 310m, 310c: Concentration gradient determination circuit 320y, 320m, 320c: Read specialized memory G15: OR gate TH1: Threshold TH
2: Threshold TH3: Threshold TH
4: Threshold

Claims (3)

[Claims] 1. Image information inputting means for outputting color image information color-separated into a plurality of basic colors; a level of a signal for each basic color of image information output by the image information inputting means is set to a first level. First comparing means for comparing with a reference level; a signal of each basic color of the image information output by the image information inputting means is monitored, and a signal level within the area is determined for each predetermined area consisting of a plurality of pixels of each signal. Second comparing means for comparing the amount of change in the signal level with a second reference level; the signal level of a plurality of basic color signals of the image information that is equal to or lower than the first reference level is referred to as a third reference level. A third comparing means for comparing;
The level of the signal of at least one basic color of the image information is higher than the first reference level, and the signal level change amount in the predetermined area is the second level in at least one of the signals higher than the first reference level. When the levels of all the basic color signals that are equal to or higher than the reference level and are lower than the first reference level are lower than the third reference level, determination means that determines that halftone processing is prohibited; A color image processing apparatus comprising: a signal processing unit that includes a signal of each basic color of the image information output by the image information input unit using the determination result of the determination unit. 2. The second comparing means extracts the maximum value and the minimum value of the signal level in the predetermined area, and compares the extracted level difference between them with a second reference level. 1
The described color image processing device. 3. The first signal processing means outputs a result of comparing an input signal with one fixed threshold value.
And a second process for outputting the result of comparing the input signal with one of a plurality of types of threshold values determined according to the scanning position of the image input means. Item 2. The color image processing device according to item 2.