JPH07182510A - Cell tone image data converting method - Google Patents

Abstract

PURPOSE:To make a boundary line clear and to reproduce an image close to the original cell tone image by forcedly replacing a less-frequency color with a highest-frequency color without sampling a part where a numerical value is not stabilized. CONSTITUTION:The color of light is delicately changed corresponding to the degree of brightness to mix three colors of red (R), green (G) and blue (B). The gradation data of primary colors are converted so that the color number in cell tone image data can be subtracted to the number of colors to be expressed by a target computer device. Since the gradation-changed data are data corresponding to the number of colors to be reproduced, in order to prepare final data, the color number is further decreased to the color number to be simultaneously generated by sampling the data. In this case, the part where the numerical value is not stabilized is not sampled for the unit of a character but the less-frequency color is forcedly replaced with the highest-frequency color, and the colors are subtracted by performing sampling to investigate the frequency of colors to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of reducing cell image tone image data captured by an image scanner or the like as computer image data.

[0002]

2. Description of the Related Art The three primary colors of colored light are red (R), green (G) and blue (B). As shown in FIG. 1, these three colors mix to create various colors. In the case of light, the color changes subtly depending on the degree of mixed brightness. Gradation indicates this brightness in stages. For example, if red and blue are mixed, it becomes purple,
Increasing the degree of red (gradation) makes it reddish, and increasing the degree of blue makes it bluish.

Image data of an image scanner or video is captured as a set of dots. This dot is expressed in a state where the three primary colors are mixed. In order to quantify this, each primary color is represented by a gradation of several bits. For example, when each gradation of R, G, and B has 256 levels, 256 × 256 × 256 = 16M 2, and 16M colors can be reproduced. At this time, in order to represent each primary color with 256 gradations, 8 bits are required as shown in FIG.

[0004]

If a natural image or the like is captured in a computer in 16M colors with an image scanner or a video camera, an image with very good reproducibility can be obtained. However, as mentioned earlier, it takes 2 to represent 1 dot.
Since 4 bits (= 8 bits × 3) are required, if this configuration is used for all dots on the entire screen, a huge amount of data is required.

Therefore, in general, the number of colors reduced to 8, 16, 512, etc. is used in consideration of the memory. In this case, the number of reproducible colors: m may be the same as the number of colors capable of simultaneous color development: n, but in some cases, m> n may be set. Generally, for example, when 16 colors out of 512 colors can be simultaneously developed, the reproducibility of colors is far superior to a device capable of simply developing 16 colors. Therefore, most computer devices of recent years have m> n. Equipped with a type of coloring mechanism.

In order to handle large image data such as 16M colors read by a scanner with a computer device of the above m> n type, first, primary colors RG up to reproducible m colors are processed.
It is necessary to reduce the gradation of B to reduce the number of colors. And
The number of colors that can be simultaneously developed is reduced to n for each screen.

On the other hand, a cell image-like image is basically line-to-line,
Alternatively, there is a single color between the boundary colors. However, if it is captured by an image scanner and the color is simply reduced as it is, the reproducibility deteriorates. In particular, there are many cases where the boundary between colors is blurred.

The present invention provides a method for reducing the color of an image captured by a scanner so as to maintain the image quality closer to the original image.
The purpose of the present invention is especially to reduce the color and shape of the original image, for example, on the reproducibility of the contour line or the shadow portion of the face.

[0009]

In order to solve the above-mentioned problems, the present invention does not simply reduce the color, but the cell image tone image data is basically line-to-line or boundary-to-boundary-color single-color. The color is reduced by utilizing the regularity that it is often filled with one color. That is, the present invention employs the following color reduction method.

First, in order to reduce the number of colors that can be expressed by the target computer apparatus to the original image data of the cell image tone: m (generally, the number of colors that can be simultaneously developed: n is less than this), the gradation of the primary colors is reduced. Convert data. Usually, this is done by dropping the lower bits of the primary color gradation data.

Since the data whose gradation is changed by such an operation corresponds to the number of reproducible colors: m, the data is sampled up to the number of colors capable of simultaneous color development: n in order to create the final data. You have to reduce the color.

As a sampling method, the frequency of the color used for each character unit, which is a small unit constituting the screen, is checked. Normally, 8 × 8 dots are often used as a character unit.

At this time, when it is judged that the part where the numerical value is not stable is the contour line or the gradation (border where brightness changes), sampling is not performed. In addition, the infrequent color is forcibly replaced with the most frequent color. According to such a conversion method, the boundary line becomes clear, and the image can be reproduced as an image close to the original cell image-like image.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, a case will be described in which original color data of 16M colors is subjected to color reduction in accordance with a computer device capable of simultaneously handling up to 16 colors out of 512 colors.

In this computer, the image data is divided and managed in units of characters, which are a set of 8 × 8 dot pixels, in consideration of high speed processing. A table for managing it is called BAT (background attribute table). The character code of BAT points to the actual image data (CG: character generator), and the content is displayed on the screen. This table is created in VRAM and has the structure shown in FIG.

Colors are managed by the color palette shown in FIG. RGB has 3 bits each and can represent up to 512 colors. However, since 16 colors can be actually displayed at the same time, 16 colors out of 512 colors are selected and displayed. A block is a collection of 16 colors of the simultaneous display unit.

The 512 colors are 3 bits each when they are made into bits because each primary color can be 8 gradations (when 0 is included) when it is separated into RGB. Converting 16M color original image data into 256 color image data means
At the primary color level, the gradation of each primary color of 16M is 0 to 25.
5, the gradation of each of the 256 primary colors is dropped to 0-7.

That is, if 0 to 255 are divided into 8 equal parts and the numerical values are assigned to 0, 1 and 2 to 7, the color can be automatically reduced. For example, if the R (red) gradation of the original image data is 11111111 (decimal number 255), the subtracted R gradation is 111 (decimal number 7).

The character reduced in color by the above method is shown in FIG.
Let's say the gradation becomes like. For convenience, the upper left character is called A, the right side is B, the lower left character is C, and the right side is D.

First, the gradations of A are tabulated: gradation 0:63, gradation 1: 2, gradation 2: 1. Since the gradations 1 and 2 are much less frequent than the gradation 0, the gradations of this character are all 0. A gradation of 0 means that if the primary color is R, the brightness of red is 0,
That is, red represents that it does not mix with the color combination (0 represents that it does not shine completely).

Next, when the character B is aggregated, the gradation is 0:10, the gradation is 1: 2, the gradation is 2: 6, the gradation is 3: 9, the gradation is 4: 8, and the gradation is 5:29. is there. As for the frequency of appearance, it can be considered that gradations 0, 3, and 4 are almost the same. However, for gradation 0, numerical values appear collectively, but for others, the appearance is unstable.

Therefore, the gradations 3 and 4 in which the appearance is unstable are excluded from the sampling target in accordance with the regularity of the cell image-tone image data. Further, since gradations 1 and 2 are less frequent, they are also excluded from sampling. As a result, the character B will be color-coded with gradation levels 0 and 5.
The middle gradation divides the gradation between 0 and 5. That is, gradations 1 and 2 are gradation 0, and gradations 3 and 4 are gradation 5.

When the character C is tabulated, the gradation is 0:43, the gradation is 1: 3, the gradation is 2: 5, the gradation is 3: 7, the gradation is 4: 3, and the gradation is 5: 3. The frequency of appearance of other gradations is lower than that of gradation 0. However, the total number is too large to be integrated into the gradation 0 (43 gradations 0, the other total is 21). Then, the adjacent character (here, character D) is determined and decided. That is, although the frequency of appearance of the gradation 5 is low, the value of the adjacent gradation is determined as another corresponding gradation. As a result, the other gradation is set to 5. That is, the character C is divided into two gradations, gradation 0 and gradation 5.

Such an operation is also performed on other characters. As a result, character A has a gradation of 0, character B has 0 and 5, character C has 0 and 5, and character D has 5
And is converted into data as shown in FIG.

[0025]

EFFECTS OF THE INVENTION Since the cell image tone image data is often the same color except on the boundary line and the portion where the color changes, the present invention has the effect of faithfully reproducing the original cell image.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of three primary colors of colored light and colors created.

FIG. 2 is an explanatory diagram of a bit configuration when representing 16M colors.

FIG. 3 is an explanatory diagram of a configuration of BAT and CG of the computer device used in the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a color palette of the computer device used in the embodiment of the present invention.

FIG. 5 is a diagram showing gradations of original image data according to the embodiment of the present invention.

FIG. 6 is a diagram showing data of an example in which color reduction was performed by the method of the present invention.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H04N 1/46 Z

Claims (1)

[Claims] 1. A method of reducing the color of cell image-tone image data according to the function of a computer to be used, wherein the cell image-tone image data is converted according to the color gradation that can be handled by the computer. For the tone-converted image data, the part where the numerical value is not stable is not sampled for each character, and the infrequent colors are forcibly replaced by the most frequent colors. A cell image-like image data conversion system characterized by performing sampling for checking the frequency to reduce the color.