JP3064896B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for judging whether a color image or a black-and-white image is output in the case of a color original and performing full-color output processing and in the case of a black-and-white original development output processing of black toner. About.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration of a digital color image processing apparatus, FIG. 5 is a diagram showing a configuration example of a conventional edge processing circuit, and FIG. 6 is a diagram showing a configuration of a hue detection circuit.

Generally, in a color copying machine, Y (yellow), M (magenta), C (cyan), K (black)
A full-color original is reproduced by executing the developing process of four colors. At this time, an extremely large memory capacity is required to store the full-color image data obtained by one original reading scan for performing the developing process four times. Therefore, the signal processing is performed and the developing process is executed while repeatedly performing the original reading scan for each developing color.

In reading an original, read image data is fetched optically using color separation signals of B (blue), G (green), and R (red) using a line sensor, and an END conversion 31, as shown in FIG. The color toner signals Y, M, and C are converted through color masking (color correction) 32. Thereafter, black plate (K) generation and under color removal are performed by the UCR 33, and a hue separation type nonlinear filter section, T
The toner signal X of the developed color is turned on / off through an RC (tone adjustment) 40 and an SG (screen generator) 41.
Convert to quantified data. The charged photoreceptor is exposed by controlling the laser beam with the binarized data, and the images of the respective colors are superimposed on the basis of the halftone dots to reproduce a full-color original.

Usually, in a digital color image processing apparatus,
Prior to the main scan for copying a document, a pre-scan is performed first, and the size of the document is detected and the color document or the black-and-white document is identified by the pre-scan. Then, based on the information at the time of the main scan, full-color output processing is performed for a color original, and K
Control of copy operation, switching of parameters, and the like, such as performing output processing only for (black). In addition, non-linear filter processing is introduced for originals having different types of images such as a mixture of binary images such as characters and line drawings and halftone images such as photographs and halftone prints. Various methods have been proposed for performing edge enhancement processing to obtain a binary image such as a character or a line image with high sharpness. FIG. 4 shows an example of a configuration including a hue separation type nonlinear filter section as one example.

The hue separation type non-linear filter section includes a UCR
At 33, the image data X of the development color selected in accordance with the development process from the Y, M, C, and K signals generated by performing the black plate generation and undercolor removal processing is input, and branched into two systems. One of them is subjected to smoothing processing by a smoothing filter 34, and the other is subjected to edge enhancement processing by a γ conversion 36, an edge detection filter 37, and an edge enhancement LUT 38. These outputs are finally added to the adder 39.
And output as a nonlinear filter signal. FIG. 5 shows a configuration example of the edge processing circuit.

In the edge processing, the hue of the input image is detected by the hue detection circuit 35, and it is determined whether or not the developed color at that time is a necessary color. Here, if the input image is a black area, control is performed such that only K is enhanced in accordance with the edge amount without performing edge enhancement of the chromatic signals of Y, M, and C.

As shown in FIG. 6A, a hue detection circuit 35 includes a maximum / minimum circuit 42 for obtaining the maximum and minimum values of Y, M, and C, a multiplexer 43 for selecting a developed color, and a maximum and minimum value. , A subtractor 45 for calculating the difference between the minimum value and the developed color, and a comparator 46
~ 48. Comparators 46 to 48 compare with the threshold value, and when they are larger than the threshold value, r, m, c ′, m ′,
The output of y 'is set to logic "1". Then, from this output, a judgment hue is derived based on the judgment condition shown in FIG. 7B, and further, the necessary color “1” is determined for the developed color by the necessary color / unnecessary color judgment condition shown in FIG. It is determined whether the color is “0”. As the determination hue, W (white), Y, M, C,
Targets eight colors B, G, R, and K.

As is clear from the necessary / unnecessary color judging conditions, when the hue is, for example, B, m and c are required colors in the developed colors, and the other colors are unnecessary colors. Therefore, in this case, the edge is enhanced by the edge enhancement LUT 38 in the cycle of the necessary color, and the signal is not edge-enhanced by the edge enhancement LUT 38 in the cycle of the unnecessary color.

[0010]

FIG. 7 is a diagram for explaining a character fattening phenomenon, and FIG. 8 is a diagram for explaining edge emphasis processing.

As described above, in the edge enhancement processing, the threshold value t
The hue is identified by comparing with h, and the edge detection signal is converted by the edge enhancement LUT based on the result to generate an edge enhancement signal. However, as shown in FIG. 7A, the MTF characteristics of the IIT deteriorate as the frequency increases. Moreover, the degree of deterioration of the MTF differs depending on the color and the main and sub scanning directions. Due to such deterioration of the MTF, even if the density distribution of the document is, for example, as shown in FIG.
As shown in (1), the data is collapsed. In the hue detection, the signal b is compared with the threshold th to determine the hue. Therefore, the hue is originally determined in a state where the width of w is considerably thick like w ', and this is regarded as the processing range of the edge enhancement. You. Based on this determination, an edge emphasizing signal d as shown in FIG. 9C is added to emphasize the edge, and thus the character is reproduced as a bold character as shown in FIG. 9B. Further, the thickening of the character appears due to not only the IIT but also the IOT developer, the developing method, the developing characteristics, and the like.

In the above system, black character reproduction can be improved as compared with other conventional systems in which all the Y, M, C, and K signals are emphasized, but the smoothed signal is included in the Y, M, and C signals. Remains. That is, as shown in the edge enhancement LUT 38 in FIG. 5, necessary colors are only further emphasized and unnecessary colors are simply removed, so that, for example, a black character filter input signal as shown in FIG. , Y, M, and C are not emphasized, but only the K signal is emphasized. In the smoothing filter, as shown in FIG. , A smoothed processing signal is generated. Therefore, when these are finally combined, smoothed signals of Y, M, C, and K remain as shown in FIG.

Normally, even in the case of a black character, not only K but also Y, M, and C signals are carried, so that the smoothed colors of Y, M, and C appear at the edge portion. Black characters cannot be reproduced in K1 color. In such a configuration, as compared with the case of K1 color reproduction, there is a problem that color change or turbidity of the edge occurs due to thickening of the line, misregistration, and the like, so that sharpness is lost and image quality is deteriorated.

Further, in a case where it is easy to specify each original or region in a binary image such as a character or a line drawing and a halftone image such as a photograph or a halftone print, it is possible to specify each original or region separately. By specifying the image type for each area, the optimal parameters can be selected for each area, and the reproducibility can be improved. However, in the case of these mixed images, both the binary image and the halftone image are used. The parameters that can be reproduced as such are selected. Therefore, optimal processing is not performed on both binary images and halftone images, and it is difficult to obtain images that are satisfactory for both. For example, in a binary image, there is a problem that edge enhancement is weakly blurred and characters are not clear, and black characters are turbid at an edge portion or a small letter portion. On the other hand, in the case of the halftone image, the vicinity of the edge detection frequency is emphasized, so that the halftone image loses smoothness, resulting in a rough image in which strange moire and edges are strangely emphasized.

[0015] In addition, as a device for identifying an image tone, a device using an average value and a standard deviation in a predetermined pixel block (for example, JP-A-63-205783) or a plurality of dither transforms having different phases are used. There is one that uses binary output (for example, JP-A-63-193770).
There is a problem that even a character cannot be distinguished from a color character, a black character, and a halftone image.

[0016]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and makes it possible to easily identify a color image or a black and white image, thereby facilitating image area identification in block units. Things.

For this purpose, the present invention provides a blocking means for blocking input image data into a block composed of a plurality of pixels, and a block color determining means for determining a block color representative of color information contained in the block. Counting a block color determined by the block color determining means, and determining means for determining whether the image data is a color image or a black and white image based on the count value of the block color, Determining means for determining whether the image data is a color image or a black-and-white image based on a comparison between the frequency of a chromatic color and the frequency of a non-chromatic color from the determination result by the block color determining means, or Comparing means for comparing the frequency of a chromatic color with a threshold from the judgment result by the color judging means; Is characterized in that Hazuki said image data to determine whether the monochrome image or a color image.

A blocking means for blocking the input image data into blocks each comprising a plurality of pixels;
A block color determining unit that determines a block color representative of the color information included in the block; counting the block colors determined by the block color determining unit; and the image data is a color image based on the count value of the block colors. A black-and-white image or a black-and-white image, and an output unit that selects black-only output or full-color output based on the result of the determination and outputs an image based on the image data. An image processing apparatus for determining whether a color original or a black-and-white original based on image data obtained by a main scan, and a block forming unit configured to block the scanned image data into blocks each including a plurality of pixels; Block color determining means for determining a block color representing color information included in the block; The block color determined by the determination unit is counted, and the determination unit determines whether the image data is a color image or a black and white image based on the count value of the block color. An output means for switching and outputting between only output and full-color output is provided.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in which it is possible to automatically and accurately select an operation corresponding to a color original or a black and white original by performing block color judgment by dividing pixels. Form will be described. FIG. 1 is a diagram showing an embodiment of an image processing apparatus using block color judgment of the present invention.

In FIG. 1A, a black block counter 12 counts the number of black blocks determined by the block color determination section 11, and a color block counter 13
Is for counting the number of color blocks other than the background W and black K. Ratio calculation unit 14 performs the rate calculation and the count value f _c of the count value f _b and the color block counter 13 of a black block counter _{12 (f c / f b)} , the determination unit 15, is the ratio A color original or a black-and-white original is identified by determining whether or not a certain threshold value is exceeded. Since the color document and the black and white document can be distinguished by the above configuration, a pre-scan is executed to make this determination,
By using the signal of the determination unit 15 at the time of the main scan, a full-color output process is performed for a color original,
In the case of a black-and-white document, K development output processing can be performed. Also, as shown in FIG. 2B, the black block counter is omitted, the color blocks are counted using only the color block counter 22, and the output is compared with the threshold value t by the comparator 23.
Alternatively, a configuration may be adopted in which a color original or a black-and-white original is distinguished from h.

Next, an image processing apparatus which determines whether the original is a character area or a half-tone area for a mixed original of characters and halftones, and switches the parameters for each determined original area to adjust and generate image data. Will be described more specifically with reference to FIG.

FIG. 2 is a diagram showing an embodiment of an image processing apparatus of an image area identification system configured to determine whether the original is a character area or a halftone area for a document in which characters and halftones are mixed.
FIG. 3 is a diagram for explaining the operation of the circuit shown in FIG.

In FIG. 2, a hue detecting section 1 detects one of eight colors (Y, M, C, K, W, B, G, R) for each pixel, and a comparator 2 Is YM
It is to detect whether or not the largest one of C is equal to or _larger than a threshold thmax. The hue detection unit 1 also detects low-density noise and the like, and in this case, the run-length described below becomes short, and a problem arises in that the hue is incorrectly recognized as a character area. Therefore, in order to make a pixel having at least a certain density or higher as a character candidate, a comparison with a threshold th _max is performed to remove noise.
It is.

The blocking unit 3 includes several pixels, for example, as shown in FIG.
As shown in (a), each pixel is divided into blocks of 4 × 4 to 8 × 8. In this case, as the block size is increased, the identification accuracy is increased, but there is a problem that the hardware scale is increased because the number of lines is increased. Therefore, it varies depending on the scan speed on the premise of pre-scanning.

The block determination section 4 performs a seven-color determination. The seven-color determination is based on seven colors except for W (Y, M, C, K,
For B, G, and R), the color with the highest frequency in the block is determined, and that color is determined as the block color. An explanation will be given by showing an actual example. As shown in FIG. 3A, when the frequency of each color is counted with 4 × 4 pixels as one block, K = 6, M = 2, R = 1, C = 1, W = 6. The color that is the maximum of the color / black pixels excluding W is adopted as the block color. In this case, since K is the maximum, the block color is K. When the block color is obtained in this manner, as shown in FIG. 3D, in the run length in pixel units, the run becomes short, and the run length of the halftone dot region which is difficult to separate from the character becomes long. On the other hand, in the case of the character area, the block run length is short because the distance between the characters is longer than the pitch of the halftone dots. As described above, it is possible to separate the blocks based on the block run length.

The main scan direction color run count unit 6 receives one bit indicating W (0) or another color black (1) from the block color judgment unit 4, and determines the color / black block in the main scan direction. The run length is counted, and the comparator 7 determines whether or not the count value (run length) of each block as shown in FIG. 3C is shorter than the threshold value th _run . Here, if the run length of the color / black block is shorter than the threshold value th _run , it becomes a character candidate.

The sub-scanning direction edge detecting section 5 is shown in FIG.
As shown in (1), it is detected whether or not there is an edge in a range of several blocks in the sub-scanning direction. If there is an edge, it is determined as a character candidate. This is because the horizontal line used in the character area also has a long run length, and is not a character candidate with the above-described run length in the main scanning direction. Therefore, even in such a case, the character is detected as a character candidate. .
Therefore, for example, as shown in FIG. 3B, for example, five blocks are taken in the sub-scanning direction, and if there is a white block as seen from both sides of the target block, it is determined as a character candidate.

When the OR gate 8 and the AND gate 9 indicate that a character candidate exists in either the main scanning direction or the sub-scanning direction and the max flag of the block is 1, the block is mapped to the character area. And outputs the block color signal determined by the block color determination unit 4. The max flag is a signal indicating that there is one or more pixels in the block for which the largest YMC among the comparators 2 is determined to be _{equal to} or greater than the threshold thmax.

The above embodiment focuses on the short run length around the character portion. That is,
The character portion is composed of a block of character blocks and a block of the background, and is located in the background of the background, so that the density changes sharply, whereas the image portion is located in the background of the image and has a moderate density. Therefore, when the run length is observed, the run length is short in the character area and long in the halftone area. Moreover, it is difficult to discriminate a halftone area from a character area on a pixel-by-pixel basis. However, in the case of a halftone dot, the run length is increased by blocking, so that the halftone area should be recognized instead of the character area. Can be. That is, the halftone dot patch portion having a high frequency is likely to be generated as a color block having a long run length due to blocking, and can be captured as a halftone region. Also,
Simply detecting a character candidate using the main scan direction color run count unit 6 and the comparator 7 may mistakenly detect a line having a long run length in the main scan direction. The recognition accuracy is also increased by using the character candidates.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the hue detection is performed using the YMC signal, but a chromaticity signal such as a ^* , b ^* , or IQ may be used. Also, the hue was determined for each pixel to obtain the block color.
A block color may be obtained after averaging for each pixel. In the past, since color judgment was performed on a pixel-by-pixel basis, a color reading error was likely to occur particularly at the edge of a character due to the reading device or sensor, even though the document was actually a black character document. In many cases, the total was mistaken for a color original. This point can be greatly improved by the determination based on the block color of the present invention. Needless to say, the addition of the line buffer enables identification at the same time as the main scan without the need for the prescan.

[0031]

As is apparent from the above description, according to the present invention, each pixel is divided into blocks to determine a block color, and a color original or a black-and-white original is discriminated based on the counted value. Since the processing corresponding to the original can be performed, it is also possible to eliminate the useless operation for the monochrome original. In addition, identification hardware can be identified with high accuracy by a simple configuration.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of an image processing apparatus using block color determination according to the present invention.

FIG. 2 is a diagram illustrating an embodiment of an image processing apparatus of an image area identification method configured to determine whether a document is a character area or a halftone area for a mixed document including characters and halftones.

FIG. 3 is a diagram for explaining the operation of the circuit shown in FIG. 2;

FIG. 4 is a diagram illustrating a configuration of a digital color image processing apparatus.

FIG. 5 is a diagram illustrating a configuration example of a conventional edge processing circuit.

FIG. 6 is a diagram illustrating a configuration of a hue detection circuit.

FIG. 7 is a diagram for explaining the character fattening phenomenon.

FIG. 8 is a diagram illustrating edge enhancement processing.

[Explanation of symbols]

11, 21: block determination unit, 12: black block counter, 13, 22: color block counter, 14: ratio calculation unit, 15: determination unit, 23: comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46-1/64 G06T 7/00

Claims (5)

(57) [Claims] 1. Blocking means for blocking input image data into a block composed of a plurality of pixels; Block color determining means for determining a block color representing color information included in the block; An image processing device comprising: a counting unit that counts the block colors determined by the determining unit and determines whether the image data is a color image or a monochrome image based on the count value of the block colors. 2. The image processing apparatus according to claim 1, wherein the determination unit determines that the image data is a color image based on a comparison between a frequency of a chromatic color and a frequency of a non-chromatic color based on a determination result by the block color determination unit. Or an image processing apparatus that determines whether the image is a monochrome image. 3. The image processing apparatus according to claim 1, wherein the determining unit includes a comparing unit that compares a frequency of a chromatic color with a threshold from a result of the determination by the block color determining unit. An image processing apparatus for determining whether the image data is a color image or a monochrome image based on a result. 4. Blocking means for blocking input image data into blocks each including a plurality of pixels; block color determining means for determining a block color representing color information included in the blocks; The block color determined by the determination unit is counted, and the determination unit determines whether the image data is a color image or a monochrome image based on the count value of the block color. And an output unit for selecting an output of the image data and a full-color output and outputting an image based on the image data. 5. An image processing apparatus for determining whether a document is a color document or a monochrome document based on image data obtained by a main scan, comprising: a block forming unit configured to block the scanned image data into blocks each including a plurality of pixels; A block color determining unit that determines a block color representative of color information included in the block; counting the block colors determined by the block color determining unit; and the image data is a color image based on the count value of the block colors. An image processing apparatus comprising: a determination unit configured to determine whether the image is a monochrome image or a monochrome image; and an output unit configured to switch between black-only output and full-color output based on a determination result by the determination unit.