JP3015050B2 - Image processing method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image processing method and apparatus, and more particularly, to an image processing method and apparatus for converting n-value image data into m-value image data (n <m). .

[Related Art] As a method of restoring multi-valued image data from binary image data whose density is stored, a method of setting a window (opening) around a target pixel and using an average value in the opening is general. is there. However, there is a problem how to make the size of the opening. On the other hand, two methods have been conventionally proposed. One is to prepare a plurality of apertures having different sizes around the pixel of interest, estimate multi-valued image data from the average value of the binary image data in the selected aperture,
The estimated image data is binarized again by the systematic dither method, and an aperture whose pattern matches the pattern of the original binary image is adopted.

The other is to provide an aperture in the same manner and estimate multi-valued image data, and then select a size of the aperture that satisfies the estimated value in a given conditional expression, thereby adopting the multi-valued image data. It is.

Generally, when an aperture (window) process is performed on a gradation image, the larger the aperture, the better the gradation, but the resolution is inferior. Conversely, the smaller the aperture, the better the resolution but the lower the gradation.

For this reason, in the conventional example, the size of the opening in the image can be freely changed, and the opening is small when the density change of the image is sharp (edge portion), and the opening is large when the image is smooth. It is.

[Problems to be Solved by the Invention] However, in the conventional method, no consideration is given to a color image, and it is not always sufficient to convert n-value color image data into m-value color image data (m> n). There was a problem that it could not be said.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing method and apparatus which can solve the above problem and convert satisfactorily when converting n-valued color image data into m-valued color image data (m> n).

Means for Solving the Problems In order to achieve the above object, the present invention provides an n-valued color image data of a pixel of interest according to a distribution state of the n-valued color image data within an opening set around the pixel of interest. To m-valued color image data (n <m), wherein a black component is detected from the n-valued color image data, and a black component is detected as compared with a case where no black component is detected. In this case, the conversion is performed using a small-sized aperture.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

The image data in the present embodiment is intended for color image data. For example, RGB, which is the three primary colors of colors, or CMY pixels having a complementary color relationship therebetween is used, but the present invention is not limited to this embodiment.

In the following embodiment, a black component is formed by such a combination of RGB or YMC.

That is, the mixed color of CYAN, MAGENTA, and YELLOW produces a gray color, and a portion having a high density forms a black component.

FIG. 1 is a block diagram for extracting a Black component from RGB or CMY 8-bit data. 2 shown as color correction in the figure
One block is a color correction section (masking section), and the arrangement may be either. The following equation is shown.

 Complementary color conversion Yellow = 255-Blue Magenta = 255-Green Cyan = 255-Red However, 8-bit image data is 0 to 255.

Color correction (masking) _{(primary) Yellow = a 11 · Yellow +} a 12 · Magenta + a 12 · Cyan Magenta = a 21 · Yellow + a 22 · Magenta + a 22 · Cyan Cyan = a 31 · Yellow + a 32 · Magenta + a Black claim on claim ₃₃ · Cyan Is the block side indicated as YMCK.

 The same applies to RGB.

In the block shown as Black Generation in the figure, a black component is created from YMC data according to the following equation.

Black = min (Y, M, C) k UCR (Under Color Removal) subtracts the black component from each color component.

Yellow ′ = Yellow−Black Magenta ′ = Magenta−Black Cyan ′ = Cyan−Black With the above correction, the Black component is extracted and the binarization unit performs density preservation type binarization such as error diffusion. Obtain the valued data YMCK.

As described above with reference to FIG. 1, RGB or Y
Assume that there is YMCK binarized data including Black from the MC color data.

FIG. 2 shows a model of the present embodiment, FIG. 3 is a block diagram, FIG. 4 is a flowchart, and FIG. 5 shows an edge portion in an image.

In this embodiment, for example, in FIG. 2, only the K data among the YMCK binarized data is focused on, and when the K data is 1, a small aperture is selected, and CMYK in the same pixel is selected.
For example, 1 in a pixel is counted at a 3 × 3 opening including the periphery, and a “1” “0” ratio is obtained. The ratio is corrected so that it is in the same range data as the other apertures.

For example, if there are 1 pixels for 6 pixels in a 3 × 3 aperture, 6/9 × 255 =
Obtain 170 data. In this embodiment, in FIG. 2, when the K data is 0 among the YMCK binarized data, the data having a large aperture is selected, and the CMYK in the same pixel is, for example, a 7 × 7 aperture including the periphery. Is counted, and the ratio of “1” to “0” is obtained. The ratio is corrected as before. For example, if one of the 7 × 7 apertures has 30 pixels Obtain the data

 Thereby, multi-valued image data is estimated.

Next, a block diagram of an embodiment of the present invention will be described with reference to FIG.

The YMCK binarized data passes through the input means 30 via the transmission path and is temporarily stored in the image memory 31. The target pixel data latch circuit 32 latches the K data of the target pixel. If 1 is set, a smaller one is selected than the aperture generating circuit 34, and the address generating circuit 35 accesses a pixel included in the image memory in a size corresponding to the aperture, and
The addition and correction as described above are applied by 37 to obtain YMCK multi-value data.

When the K data latched by the data latch circuit 32 is "0", the address generating means 35 selects a large aperture,
The same processing as that for the small opening is performed.

 The operation described above is shown in the flowchart of FIG.

Here, it is assumed that the smaller opening is 3 × 3 and the larger opening is 7 × 7, but the size is not particularly limited, and may be m1 × m2 or n1 × n2. The shape may be other than a rectangle.

Although the description has been made before and after, generally, a black component always exists in an image, and when printing on a color printer, black plays a role of tightening the image.

For example, an edge portion in an image such as a portion in an image as shown in FIG. 5 has a high black component and a high resolution is required, and a flat portion such as a portion requires a gradation property rather than the resolution. You.

Therefore, according to the present embodiment, in a method of restoring multi-valued image data using a predetermined opening in a binary image, particularly in restoring color image data, if there is a black pixel, the size of the opening is reduced, and By increasing the size of the aperture when there are no pixels, the resolution of black, which is often included in the contour components of the image, is improved. Further, the occurrence of color unevenness in flat areas is improved, and the gradation is improved. Can be done.

Another Embodiment Next, another embodiment of the present invention will be described.

In the above-described embodiment, the case where CMYK is used as binarized color image data has been described, but the present invention is not limited to this, and CMY data or RGB data may be used.

When CMY data is given, binary data is "1"
When "1" or "1", it is regarded as a black component, and a small aperture may be selected. Hereinafter, such an embodiment will be described.

Fig. 6 shows a block diagram for CMY data input.
FIG. 7 shows a flowchart in the case according to FIG.

In FIG. 6, the CMY binarized data is input to the image memory from the input means 40, and the pixel data latch circuit 42
Latch the CMY data of the target pixel. Black component determination circuit 49
When the YMC data are all "1", a command signal is sent to the aperture generating means 44 and the arithmetic means 47 to select a small aperture.

If at least one of the CMY data is "0", the aperture generating means 4
A command signal is sent to 4 and the arithmetic means 47 to select a large aperture.

The calculating means 47 estimates multi-valued image data based on the ratio of “1” and “0” in the opening.

 The following operation is shown in FIG.

The other configuration operation is the same as that of the embodiment shown in FIG.

As described above, according to the present embodiment, a method for estimating multi-valued image data from binary image data provided with a means for selecting the size of an aperture using a black component of an image is performed by a human. The resolution of the edge in the visually conspicuous portion is increased, and the gradation is emphasized in the other portions.

As a result, in the restored multi-valued image data, dot-like color unevenness is reduced, and an image with clear divisions can be obtained.

In the above embodiment, the input data is binary data. However, the input data is not limited to this, and it may be a ternary or quaternary input. The present invention can be applied to any case as long as the output data is multi-valued data than the input data. When the input data is quaternary, for example, if the YMC data input as quaternary data is all "1.1", the size of the aperture may be increased.

Further, in the present embodiment, the black component is extracted using the input n-valued color data.
Alternatively, a black component may be extracted from the converted data.

In this embodiment, the black component is used as the specific color component. However, the present invention is not limited to this, and another component such as YMC or RGB may be used.

[Effects of the Invention] As described above, according to the present invention, it is possible to satisfactorily convert n-valued color image data into m-valued (m> n).

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a circuit for converting multi-valued color data into binary data, FIG. 2 is a diagram showing a state of selecting an aperture size according to black data, and FIG. Fig. 4 is a block diagram of one embodiment of the present invention, Fig. 4 is a flowchart showing the operation of one embodiment of the present invention, Fig. 5 is a diagram showing edges in an image, Fig. 6 is a diagram of the present invention. FIG. 7 is a block diagram showing another embodiment of the present invention. 31 Image memory 32 Data latch circuit 34 Opening circuit 35 Address generating circuit

Claims (2)

(57) [Claims] 1. Image processing for converting n-value color image data of a target pixel into m-value color image data (n <m) according to the distribution state of the n-value color image data within an opening set around the target pixel. A method for detecting a black component from n-valued color image data, and performing the conversion using an aperture of a smaller size when a black component is detected as compared with a case where no black component is detected. Image processing method. 2. A conversion means for converting n-value color image data of a target pixel into m-value color image data (n <m) according to the distribution state of the n-value color image data within an aperture set around the target pixel. And a detecting means for detecting a black component from the n-valued color image data, wherein the converting means uses an opening having a smaller size when a black component is detected as compared with a case where no black component is detected. An image processing apparatus for performing the conversion.