JP3039675B2 - Color image processing equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus such as a color copier, a color scanner, and a color facsimile, and more particularly, to a color image processing apparatus having a function of performing color / monochrome discrimination. It is.

[Conventional technology]

In a conventional system for reading a color original, chromaticity / achromaticity is determined using the ratio of three components of three primary colors (RGB, XYZ, etc.) of an input image signal. For example, if the input levels of the three primary colors have similar values, it is determined that the color is an achromatic color, and if the levels vary, the color is determined to be a chromatic color. A technique is known in which the determination for each pixel is repeated for all the pixels of the document, and if a chromatic pixel is present, the document is colored, and if not, the document is black and white.

[Problems to be solved by the invention]

However, in the above prior art, when the reading accuracy of the color sensor for image input is not good, pixels around the black characters of the input image are often erroneously determined to be chromatic. Therefore, there is a problem that a monochrome document is erroneously determined as a color document. In some cases, an erroneous determination is made when the base of the document has a light color.

There are also the following problems. For example, consider a document in which black characters are printed on a background of a color having a saturation distribution in a shaded portion in FIG. 11, and it is desired that this is determined as a monochrome document. Further, if there is a low-saturation color document having a saturation distribution in the hatched portion in FIG. 11, this document should be discriminated as a color document. It is very difficult to determine the original of such a low-saturation original. Black and white manuscript
The following problem occurs when a color document is erroneously determined.

In the case of a color copying machine, when a black-and-white document is copied by superimposing color inks (CMY), characters, lines, and halftone dots are poorly tightened due to color misregistration and differences in spectral characteristics of the ink, making it difficult to see. In the case of a color facsimile, in addition to the above-described disadvantage of poor print quality, there is also a disadvantage that transmission of three primary colors, even though it is a black-and-white document, requires a long transmission time and increases communication costs.

The present invention has been made in view of the above problems, and provides a color image processing apparatus capable of satisfactorily distinguishing an image in which black characters are superimposed on a low-saturation background from a low-saturation color image. The purpose is to:

If the value corresponding to the number of pixels of the intermediate saturation included in the input color image signal is equal to or greater than a predetermined value, the determination criterion is controlled so that the target pixel can be easily determined to be black and white in the black / white / color determination. It is an object of the present invention to provide a color image processing apparatus that controls a determination criterion so as to make it easier to determine a color in the determination if a value according to the number of pixels of intermediate saturation included in a color image signal is equal to or less than a predetermined value. I do.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a determining means for determining chromaticity / achromaticity of an input color image signal, and a determination result by the determining means and determining whether a target image is monochrome or color. Determining means for determining the black and white / color of the target image represented by the input color image signal based on the determination criterion, and a value corresponding to the number of pixels of intermediate saturation included in the input color image signal being larger than a predetermined value In some cases,
The discrimination criterion is controlled so that the discrimination means can be easily discriminated as black and white, and when the value corresponding to the number of pixels of the intermediate saturation included in the input color image signal is less than a predetermined value, the discrimination means determines Control means for controlling the determination criterion so as to make it easier to determine

〔Example〕

(Principle of the present invention) A manuscript is read from a color scanner, and the data is read by NT.
Convert to SC RGB, and furthermore, brightness data Y and chromaticity data I
And Q. FIGS. 6 and 7 show IQ plotted on a graph.

FIG. 6 shows the distribution when a monochrome document is read, and FIG. 7 shows the distribution when a color document is read. It can be seen that when a black-and-white document is read, it is distributed near the origin, and for a color document, it is distributed away from the origin. Therefore, the origin (I =
(0, Q = 0), the color original is determined if there are many pixels farther away, and the monochrome original is determined if there are fewer pixels. The original can be determined based on such a concept.

(Scanner Reading Accuracy) When black and white characters are read from the scanner, if the accuracy of the scanner is not good, the input image will be an image having a color shift as shown in FIG. In this case, a pixel having a color misregistration is determined as a color pixel, and as a result, there is a possibility that a color original is erroneously determined in spite of a black and white original. Therefore, if a black pixel (black and white pixel and a dark pixel) exists around the input pixel, it is determined that the input pixel is a color-shifted pixel and is actually a black and white pixel. By doing so, it is possible to reduce the reading error of the scanner.

(For a document having pixels of intermediate saturation with low saturation) The pixels included in the hatched portions in FIG. 11 are determined as monochrome pixels because the saturation is lower than the threshold value α. Considering a black character original with a low-saturation color background (for example, recycled paper), if the saturation of the background portion is smaller than α, the original is a black-and-white original; Next, for a photo document with low saturation, the number of pixels distributed in the hatched portion becomes relatively large. In this case, since it is smaller than the threshold value α, it is determined that the document is a monochrome document. Therefore, in the case of a document with a low-saturation background, the number of pixels included in the shaded area is much larger than in the case of a photo document. Is larger than the predetermined value β, the control is performed so that it is easy to determine that the document is a monochrome document.

First Embodiment FIG. 9 shows a flowchart of the process. The processing is large, and the pixel discrimination processing (S1 to S4) and the pixel correction processing (S5 to S1)
1) and original discrimination processing (S12 to S15).
The pixel determination process is a process of determining whether the pixel of interest is color or monochrome, and the document determination process is a process of determining whether the entire document is a color document or a monochrome document. The details of the algorithm will be described below according to the flow.

<Pixel Determination Process> First, the color pixel determination process will be described. The color pixel determination is processed in S1 to S4. Whether the input pixel is a color pixel or a monochrome pixel is determined for each pixel.

In color space conversion processing S1, color space conversion processing is performed. That is, NTSC-RG
The data normalized to B is converted into a luminance signal Y and chromaticity signals I and Q according to equation (1).

Distance calculation In S2 and S6, in order to create saturation information from I and Q, the distance calculation unit Is calculated. This indicates how far the target color is from the origin on the IQ chromaticity diagram. If this value is large, it can be said that the saturation is high and the probability of being a color pixel is high.

The saturation comparison unit S3 compares the saturation of the target pixel with a threshold. As shown in FIG. 10 (A), if the target pixel C is a part of a character or a base (limited to white), the saturation is low, In order to satisfy the condition, the process proceeds to S4, and the number of black pixels BPIX is set to 1
Just increase. Then, the process returns to S2 to read the next pixel and perform the same processing.

When the target pixel is located at a position considered to be a color pixel as shown in FIG. The process proceeds to S5 without satisfying the condition of.

Pixel correction processing S5 to S11 are pixel correction processing units. This is because even if the Flow3 saturation comparison unit determines that a pixel is a color pixel, it may be erroneously determined to be a color pixel due to bleeding of a black character caused by a color shift of the sensor. Is provided to correct the error. Hereinafter, the pixel correction unit will be described.

In S5, the eight peripheral pixels S ₁ to S ₈ of the pixel of interest C of FIG. 5 1
Input for each pixel. In S6, RGB → YIQ conversion is performed by color space conversion (similar to S1).

S7 saturation information Is calculated (similar to S2). S8: Saturation of surrounding pixels And the luminance Y are compared with a threshold value. For example, if the surrounding pixel S ₁ is a character portion, the saturation brightness is low low In addition, the condition of Y <γ is satisfied. As a result, the pixel of interest C was determined to be a color pixel in the pixel determination process. However, it is actually due to a color shift of the sensor, and it is determined that the pixel of interest is originally a black pixel. increase.
For surrounding pixel S ₆ And proceeds to determining that S ₆ is not a black pixel in order not satisfy the condition of Y <γ Flow10. In step S10, a check is made to determine whether all the surrounding eight pixels have been input. In this way, it is checked whether the surrounding eight pixels include a black pixel by repeating the processing of S5 to S10 up to the eight pixels S1 to S9 around the target pixel. If at least one black pixel is included in the eight surrounding pixels, the target pixel C is determined as a black pixel and the process proceeds to S9. Around 8
If the pixel does not include any black pixels, the target pixel C
Goes to S11 not as a color pixel due to color misregistration but as a true color pixel, and the number CPIX of color pixels is increased by one.

<Color / Monochrome Document Discrimination> The above-described pixel discrimination (S1 to S11) is performed on all the pixels of the document, and the ratio between the color pixels CPIX and the monochrome pixels BPIX is obtained. If the condition of CPIX> δ is satisfied in S13, the target document is determined to be a color document, and if not, it is determined to be a monochrome document area.

The above is, for example, the flowchart in the case where the processing is performed by the software of the computer. The circuit configuration for performing the above processing will be described below with reference to FIG.

Place the manuscript on the scanner composed of 101 CCDs,
When the scan is performed, RGB data normalized to the NTSC standard is output. R output from 101 in the YIQ converter of 102
The GB data is converted into a lightness (luminance) signal Y and chromaticity signals I and Q. The pixel discriminating unit 103 discriminates whether the inputted one pixel is a monochrome pixel (saturation is low) or a color pixel. 104
Is a document discriminating unit, which totals the discrimination results for each pixel,
The ratio of the number of color pixels to the total number of pixels is obtained, and a 105 document discrimination signal indicating whether the document is color or black and white is output according to the ratio. 106 is an image processing unit, 107 is a display for displaying images, 108 is a facsimile transmission unit for transmitting images, 109 is a printer that reproduces images on a recording medium, 1
Reference numeral 10 denotes an intermediate saturation pixel counting unit, and 111 denotes a CPU. The image processing unit 106 performs different processes on a black-and-white document and a color document according to the document discrimination signal 105.

For example, for an image signal to be sent to the facsimile transmission unit 108, in the case of a color original, compression encoding is performed so that each of the R, G, and B signals can be stored.
The image is converted into a density (luminance) signal and subjected to normal compression coding such as MH, MR, and MMR.

For the image signal sent to the printer 109, in the case of a color original, logarithmic conversion is performed on the R, G, and B signals,
R, M, C, K
In the case of a black-and-white original, only a K (black) signal is generated to perform black monochrome printing.

The type of printer may be a laser beam printer, an ink jet printer, a thermal transfer printer, a dot printer, or any other printer capable of performing color printing.

FIG. 2 is a diagram showing a YIQ conversion unit, and calculates equation (1). 201, 202, and 203 are R, G, and B input signals, respectively. 204 to 212 are registers for setting the coefficient of equation (1), 213 to 221 are multipliers for multiplying the input data by the coefficient,
222, 223, 225 and 228 are adders, and 226 and 229 are subtractors. The result of the operation is Y at 224, I at 227, and Q at 230.
Is output.

For example, when calculating Y, register 204
0.3, 0.59 is set in the register 207, and 0.11 is set in the register 210. The R data 201 and the contents of the register 204 are multiplied by 213 by a multiplier. Similarly, a multiplier 216 uses the G data and the contents of the register 207, and a multiplier uses the G data and the contents of the register 210.
Multiply by 219. Then, the three multiplication results are added to the adder 222.
At 223, Y is finally obtained. Similarly, I and Q can be calculated.

FIG. 3 is a diagram showing a pixel determination unit. Y data is input to 301, I data is input to 302, and Q data is input to 303. I is squared by the multiplier 310. Q is squared by the multiplier 311. I ² and Q ² are added in adder 312. Next Is calculated by referring to a table.
For example, when the input of the ROM 313 is 2, the second address of the ROM is accessed, and data 1.414 is output. Further ROM
313 output Are input to the comparators 305 and 306. The threshold value β is set in the register 308, and the threshold value α is set in the register 309. Then, the threshold value β and the Are compared, In this case, 1 is output, and otherwise, 0 is output. In the comparator 306, the threshold α and Are compared, At the time of 1, 1 is output, and otherwise, 0 is output. This comparator 30
The output result of No. 6 is referred to as a primary determination result.

Next, for the lightness (luminance) signal, a threshold value γ is set in the register 307, and the comparator 304 compares Y with γ. Outputs 1 when Y <γ, 0 otherwise
Is output. The outputs of comparators 304 and 305 are AND gate 314
Is ANDed. That is, lightness (brightness) is low,
When the saturation is low, the AND gate 314 outputs 1, and otherwise outputs 0. The output result of the AND gate 314 is referred to as a secondary determination result. The output of the AND gate 314 is input to the line memories of flip-flops (FF) 318 and 315. The output of the line memory 315 becomes the input of the line memory 316 and the FF 312. Therefore, FF321
, A pixel delayed by one line is input to FF324. The FFs 318 to 326 hold the output result of the AND gate 314 in synchronization with the pixel clock. Therefore, assuming that the secondary determination result of the target pixel is held in FF322 at a certain point in time, FF318, 319, 3
20, 321, 323, 324, 325, and 326 hold the secondary determination results of the surrounding eight pixels. The secondary determination results of these eight pixels are ORed by OR gates 329, 330, 331, and 332. The output of the OR gate 332 becomes 1 if there is at least one pixel having the second discrimination result 1 among the eight surrounding pixels.
That is, if there is at least one black pixel out of eight pixels around the target pixel, the 332 outputs 1. This or gate 3
The output of 22 is called a pixel correction result. Also, the output of the comparator 306 (the primary determination result) enters the line memory 317 and is delayed by one line and flows to FF327 and FF328. That is,
FF328 and FF322 are the first determination result of the same pixel and the second determination result, respectively.
The next determination result is held.

Finally, the NOR of the pixel correction result and the primary determination result is determined by a NOR gate. When it is determined that the pixel is a color pixel, the color pixel determination signal 334 becomes 1, and when it is determined that the pixel is monochrome, it becomes 0.

 FIG. 4 is a diagram showing a document discriminating section.

Reference numeral 406 denotes an up-count, and as inputs, initial count data DAT 403, pixel clock 402, and a color pixel determination signal 401. The counter 406 counts up from the initial count data in synchronization with the pixel clock,
During the period in which the count-up is enabled, the color pixel determination signal is counted only when the color pixel determination signal is 1 as a result.

In addition, the 110 intermediate-saturation pixel counting unit in FIG. 1 counts the number of input pixels of intermediate saturation. That is, in FIG. 11, the saturation And saturation Is counted when the pixel of (1) is input. Document discriminator 10
4 and the threshold value δ is compared. CPU 111
If the number of color pixels> δ, it is determined that the document is a color document, and if the number of color pixels ≦ δ, it is determined that the document is a monochrome document. here,
Although the threshold value δ is set, the CPU 111 changes the threshold value in accordance with the count number of the intermediate chroma pixel count unit. That is, if the number of pixels with intermediate saturation is larger than the predetermined value β, the threshold value δ is increased, and the threshold tends to be determined as a black and white original. If the number of pixels with intermediate saturation is not large, the threshold value δ is decreased. Is set to tend to be judged as a color original, and set in DAT403.
As described above, a desired determination result can be obtained by changing the criterion for determining whether a document is black and white or color in accordance with the number of pixels having an intermediate saturation between the chromatic color and the achromatic color.

With the above processing, it is possible to determine whether the original is color or monochrome.

Second Embodiment FIG. 5 is a diagram for explaining a second embodiment. First
In the embodiment, the configuration of FIG. 2 is used to realize the calculation of Expression (1). However, in the second embodiment, the calculation of Expression (1) is approximated by the configuration of FIG. Equation 2 is approximated by adding the coefficient of equation (1) to a power of two. For example, the coefficient 0.3 in Equation 1 approximates 0.25 + 0.0625. By doing so, the calculation of 0.3 * R can be easily performed by adding the data obtained by shifting the input data by 2 bits and the data shifted by 4 bits.

Next, FIG. 4 will be described. R, G, B input data are set in 501, 502, and 503, respectively.
Numerals 519 and 520 denote circuits for shifting bits of input data by a bit shift unit. 514, 515, 516, 517, 518, 521, 52
3, 527 is an adder, and 524, 525, 526 are subtractors. In the finally calculated data, Y is output to 528, I is output to 529, and Q is output to 530.

Next, the data flow will be described. The calculation method is Y, I, Q
Since the same calculation is performed, Y is described here as an example, and I and Q are omitted. Equation 2 As the calculation of the term, a two-bit shift is performed at 504 and a four-bit shift is performed at 507, and the result is added by an adder 517. Also As the calculation of the term, the input G data is shifted by 1 bit at 509 and shifted by 4 bits at 510, and the result and the output of the adder 517 are added by the adder 522. The output of the adder 522 is the result of the addition of the R and G terms in the calculation of Y in Equation 2. Next, the input data 503 of B is shifted by 3 bits and input to the adder 523. Consequently adder 5
The output 528 of 23 becomes Y in Equation 2.

As described above, according to the embodiment of the present invention, means for separating each component signal of an input color signal into a brightness signal and a chromaticity signal, means for generating a saturation signal from the chromaticity signal, and Means for comparing the threshold value α with the threshold value β, means for comparing the lightness signal with the threshold value γ, and means for counting the number of input signals having intermediate saturation As a result of comparing the saturation signal of the target pixel with the threshold value, if the saturation signal is smaller than α, the means for increasing the number of black and white pixels by one is compared with the saturation signal of the target pixel and the threshold value.
Then, for the surrounding pixels, as a result of comparing the saturation signal with the threshold β, as a result of comparing the saturation signal <β and the brightness signal with the threshold γ, the brightness signal <γ is determined. If the pixel that satisfies this condition is included, the number of black and white pixels is increased by 1; otherwise, the number of color pixels is increased by 1.
Means for increasing, means for changing the threshold δ according to the total number of input signals having intermediate saturation, means for comparing the number of color pixels with the threshold δ, and comparison of the number of color pixels with the threshold δ As a result, if the number of color pixels> δ, by providing a means for judging a color original, if the accuracy of the scanner is not good, or if the base of the original has a light color,
In addition, it is possible to determine a document such as a photo document with low saturation without erroneous determination. As a result, it is possible to perform a process according to the type of the original, thereby improving print quality and reducing communication costs.

The image input means is not limited to the scanner, but may be an interface such as a host computer, a still video camera, or a video camera.

Further, the number of peripheral pixels to be referred to is not limited to eight. Also, a majority decision process may be performed instead of the OR process.

In addition, in addition to separating into (Y, I, Q), (L ^* , a ^* ,
b ^* ), (L ^* , u ^* , v ^* ), (Y, u, v) and the like may be separately determined.

〔The invention's effect〕

As described above, according to the present invention, when the value according to the number of pixels of the intermediate saturation included in the input color image signal is larger than a predetermined value, the target image is easily determined to be monochrome in the monochrome / color determination. In the case where the value according to the number of pixels of the intermediate saturation included in the input color image signal is less than a predetermined value, the discrimination criterion is controlled so that the discrimination is easily performed in the discrimination. Have. Therefore,
According to the present invention, for example, when the background of a black character image has a light color, the number of pixels of intermediate saturation indicating the background increases, and as a result, the image is easily determined to be black and white. Therefore, the possibility that the image is erroneously determined to be color can be reduced, and the image can be determined to be black and white. Also, for example, in the case of a low-saturation photographic image to be distinguished from color, the saturation value varies without concentrating the saturation value on the intermediate saturation like the background, so the number of pixels of the intermediate saturation decreases and the color It can be easily distinguished.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a color / monochrome original automatic discrimination device according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a YIQ conversion unit. FIG. 3 is a configuration diagram of a pixel determination unit, and FIG. 4 is a configuration diagram of a document determination unit. FIG. 5 is a configuration diagram of a YIQ conversion unit according to a second embodiment. FIG. 6 is a diagram showing the distribution of I and Q when a monochrome document is read. FIG. 7 is a diagram showing the distribution of I and Q when a color original is read. FIG. 8 is a diagram showing a state of color misregistration. FIG. 9 is a diagram showing an overall flow of color / monochrome document discrimination. FIG. 10 is a view for explaining pixel correction processing. FIG. 11 is a diagram showing the distribution of a medium-saturation original. 101: Scanner 102: YIQ conversion unit 103: Pixel discrimination unit 104: Document discrimination unit 105: Document discrimination signal

Claims (1)

(57) [Claims] A determination unit for determining whether the input color image signal is chromatic or achromatic; an input based on a determination result by the determination unit and a determination criterion for determining whether a target image is monochrome or color; Black and white of the target image represented by the color image signal /
Determining means for determining a color, and when a value corresponding to the number of pixels of intermediate saturation included in the input color image signal is larger than a predetermined value, the determination criterion is set so that the determining means makes it easy to determine black and white. Control means for controlling, when a value corresponding to the number of pixels of intermediate saturation included in the input color image signal is less than a predetermined value, controlling the discrimination criterion so that the discrimination means can easily discriminate the color. A color image processing apparatus comprising: