JP3654449B2 - Cell image data conversion method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for reducing color of cell image-like image data captured by an image scanner or the like as image data for a computer.
[0002]
[Prior art]
The three primary colors of colored light are red (R), green (G), and blue (B). As shown in FIG. 1, these three colors are mixed to create various colors. In the case of light, the color changes slightly depending on the brightness of the light. This level of brightness is called gradation. For example, if red and blue are mixed, it becomes purple, but if the degree of red (gradation) is increased, it becomes red, and if the degree of blue is increased, it becomes bluish.
[0003]
Image scanner and video image data are captured as a collection of dots (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, B is 256 levels,
256 × 256 × 256 = 16M
Thus, 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]
[Problems to be solved by the invention]
If a natural image or the like can be captured in a computer with 16M colors by an image scanner or a video camera, an image with very good reproducibility can be obtained. However, as described above, 24 bits (= 8 bits × 3) are required to represent one dot, so if this configuration is used for all dots on the entire screen, a huge amount of data is required. It becomes.
[0005]
Therefore, in general, a color reduced to 8 colors, 16 colors, 512 colors, or the like is used in consideration of the memory. In this case, the number of reproducible colors: m and the number of colors that can be developed simultaneously: n may be the same, but m> n may be set. In general, for example, it is much better to reproduce 16 colors out of 512 colors than a device capable of developing 16 colors. Therefore, most modern computer devices have m> n. A type of coloring mechanism is provided.
[0006]
In order to handle large image data such as 16M colors read by a scanner in the above-mentioned computer apparatus of the m> n type, it is necessary to reduce the number of colors by reducing the gradation of the primary colors RGB to m colors that can be reproduced. is there. Further, the color is further reduced to n colors that can be developed simultaneously for each screen.
[0007]
On the other hand, the cell image is basically a single color between lines or between boundary colors. However, if you capture it with an image scanner and simply reduce the color as it is, the reproducibility deteriorates. In particular, the border between colors is often blurred.
[0008]
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 that of the original image, and in particular, considers the reproducibility of the color and shape of the original image, for example, on the contour line or on the shadow of the face. The purpose is a color reduction method.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problem, the present invention does not simply reduce the color, but the cell image data is basically filled with a single color from line to line or from boundary color to boundary color. The color is reduced using the regularity. That is, in the present invention, the following color reduction method is adopted.
[0010]
First, in order to reduce the original image data of cell image to the number of colors that can be expressed by the target computer device: m (generally, the number of colors that can be developed simultaneously: n is less than this), the conversion of the primary color gradation data I do. Usually, this is done by dropping the lower bits of the primary color gradation data.
[0011]
Since the data whose gradation has been changed by such an operation is data corresponding to the number of reproducible colors: m, in order to create the final data, the data is further sampled and subtracted from the number of colors that can be developed simultaneously: n. Must.
[0012]
As a sampling method, the frequency of colors used for each character unit which is a small unit constituting the screen is examined. Normally, 8 × 8 dots are often used as the character unit.
[0013]
At this time, if it is determined that the portion where the numerical value of the gradation data is not stable is a contour line or a gradation (border where brightness changes), sampling is not performed. The “part where the numerical value is not stable” as used herein means a part that does not constitute a grouped area with the same numerical value. Also, the infrequent color is forcibly replaced with the most frequent color. According to such a conversion method, the boundary line becomes clear and can be reproduced as an image close to the original cell-tone image.
[0014]
【Example】
As an embodiment of the present invention, a case will be described in which 16M color original image data is reduced in accordance with a computer apparatus that can handle up to 16 of 512 colors simultaneously.
[0015]
In this computer, 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 actual image data (CG: character generator), and the content is displayed on the screen. This table is created in the VRAM and has the structure shown in FIG.
[0016]
Colors are managed with the color palette shown in FIG. RGB has 3 bits each and can express up to 512 colors. However, since 16 colors can be actually displayed at the same time, 16 colors are selected from 512 colors and displayed. A group of 16 simultaneous display units is called a block.
[0017]
The color 512 color means that each primary color may have 8 gradations (including 0) when separated into RGB, and therefore 3 bits each. The conversion of the 16M color original image data to 256 color image data means that, when viewed at the primary color level, the gradation of 0 to 255 for each of the 16M colors is 0 to 7 for the 256 primary colors. Will be dropped.
[0018]
That is, the color can be automatically reduced by dividing 0 to 255 into 8 and applying 0, 1, 2 to 7 from the smallest numerical value. For example, if the R (red) gradation of the original image data is 11111111 (255 decimal), the reduced R gradation is 111 (7 decimal).
[0019]
Assume that the character that has been reduced in color by the above method has the gradation shown in FIG. For convenience, the upper left character is called A, the right side is called B, the lower left character is called C, and the right side is called D.
[0020]
First, when summing up the gradation for A,
Gradation 0:63 gradations 1: 2 gradations 2: 1 gradations. Since gradations 1 and 2 are much less frequent than gradation 0, the gradation of this character is all 0. For example, if the primary color is R, the gradation 0 indicates that the lightness of red is 0, that is, red is not mixed in the color composition (0 indicates that it does not shine completely).
[0021]
Next, when summing up for character B, gradation 0:10 gradation 1: 2 gradation 2: 6 gradation 3: 9 gradation 4: 8 gradation 5:29 gradation. As the frequency of appearance, the gradations 0, 3, and 4 may be considered to be substantially the same. However, numerical values appear together for gradation 0, but the appearance of others is unstable.
[0022]
Therefore, in accordance with the regularity of the cell tone image data, the unstable gradations 3 and 4 that appear are excluded from the sampling target. The gradations 1 and 2 are also excluded from sampling because they are infrequent. As a result, the character B is color-coded with gradations 0 and 5, but the intermediate gradation is divided between 0 and 5. That is, gradations 1 and 2 are gradation 0, and gradations 3 and 4 are gradation 5.
[0023]
When summed up for character C, the gradation is 0:43, gradation 1: 3, gradation 2: 5, gradation 3: 7, gradation 4: 3, gradation 5: 3. Compared to gradation 0, the frequency of appearance of other gradations is low. However, the total number is too large to be integrated into gradation 0 (43 gradations 0, and the total number of other elements is 21). Therefore, it is determined by looking at the adjacent character (here, character D). That is, although the appearance frequency of the gradation 5 is low, an adjacent gradation value 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 of gradation 0 and gradation 5.
[0024]
Such an operation is performed for other characters. As a result, character A has gradation 0, character B has 0 and 5, character C has 0 and 5, character D has 5, and is converted into data as shown in FIG.
[0025]
【The invention's effect】
Since the cell image-tone image data often has the same color except on the boundary line and the portion where the color changes, there is an effect that the original cell image can be faithfully reproduced by using the present invention.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of three primary colors of color light and colors to be 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 a BAT and a CG of a computer device used in an embodiment of the present invention.
FIG. 4 is an explanatory diagram of a color palette of a computer device used in an embodiment of the present invention.
FIG. 5 is a diagram illustrating gradation of original image data according to the embodiment of the present invention.
FIG. 6 is a diagram showing data of an embodiment reduced in color by the method of the present invention.

Claims (1)

In a computer device that divides and manages image data into characters that are a set unit of pixels, in a method for reducing the color of cell image data in accordance with the function of the computer device to be used,
For the gradation-converted image data converted according to the color gradation that can be handled by the target computer, the cell tone image data,
For each character unit,
(1) The color appearance frequency is sampled except for the pixel area part where the numerical value of the gradation data does not constitute an area where the numerical values of the gradation data are the same numerical value, and where the numerical value of the gradation data is not stable,
(2) Replace a color with a low appearance frequency with a color with a high appearance frequency,
A cell image-like image data conversion method characterized in that color reduction is performed.

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