KR20050062834A - Half toning processing method including color information - Google Patents

Abstract

The half-toning processing method including color information according to the present invention calculates information on luminance values, saturation, and density of RGB values of pixels to be printed, and sets a plurality of halftone patterns arranged in advance for each color. Among them, the density is represented by selecting a corresponding halftone pattern array according to the calculated color information.

According to the present invention, it is possible to express the difference in the color included in the color document as the difference in the dot arrangement pattern, and the expression function in black and white printing can be improved by including the color information.

Description

Half toning processing method including color information}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital halftoning processing method used in an inkjet printer or a laser printer. More particularly, the present invention relates to a halftone pattern array corresponding to a color of a pixel input to a printer when a monochrome document is output to a color document. The present invention relates to a half-toning processing method including color information capable of converting to express density.

When printing document data using an inkjet printer or a laser printer, in image processing, it is required to convert a color given in multiple values to binary pixel values, and this processing is called digital halftoning processing.

In general digital halftoning processing, a method of converting a continuous gray pixel value using a predetermined threshold array into a binary pixel is known. In a printer, a mode for printing using only toner or ink is generally provided, and color input is performed. With regard to data, it is necessary to convert these into black and white binary values, that is, black and white one-bit values indicating only the presence or absence of dots.

1 is a view for explaining a conventional half-toning processing method.

First, the value of each pixel of a specific resolution is stored in the RGB value buffer 1a according to the coordinates according to the content of document data subject to print processing in the printer, and then sequentially read out as input data for half-toning processing. In general, 24 bits are used for one pixel in the RGB value buffer 1a.

In addition, a black and white 1-bit buffer 1i is provided to store the output data of the half-toning process. Since the output pixel value indicates the presence or absence of dot output in each XY coordinate, one bit is used for each pixel. .

Next, the halftone pattern array 1e is previously defined as internal data necessary for halftone processing, and is prepared as fixed data. The halftone pattern array 1e is implemented as an integer two-dimensional array, and integer values as array elements are used as thresholds when binarizing multi-valued input data.

In general, an RGB value 1b corresponding to a pixel located at a specific XY coordinate is read from an RGB value buffer 1a containing color data composed of 24 bits of RGB, and a density value 1c is calculated from the RGB value. . At this time, there are various conversion equations cited, but for example, Equation 1 may be used.

Density value = 255-0.311 x (Red value) + 0.626 x (Green value) + 0.063 x (Blue value)

Including the equation (1), this conversion corresponds to the color of each pixel eventually to achromatic gray color, where the information about the color is completely lost.

The XY coordinate value 1d is referenced to the predefined halftone pattern array 1e as an index, and the threshold value 1f is derived. More specifically, the description will be made according to the format of the C language.

The defined half-toning pattern array is referred to as HT, and its size is referred to as an integer two-dimensional array. Currently, for the XY coordinates (x, y) defined as positive integers, the threshold value T _h is obtained by the following expression (2).

Th = HT [y% M] [x% Y]

Here,% is an operator to calculate the remainder.

This is equivalent to assigning the same halftone array repeatedly tiled to all faces on the XY coordinate system. The halftone pattern needs to be defined to connect smoothly at the stagnant position of the tiling. In addition, the comparison processing section 1g executes a comparison process by inputting the obtained concentration value 1c and the threshold value 1f.

This comparison process compares the density value 1c and the threshold value 1f, and outputs a dot value 1h as 1 when the density value is less than or equal to the threshold value, and in other cases is larger than the threshold value. Outputs a dot value 1h as zero. Here, the dot is taken when the dot value is 1, and the dot is not taken when the dot value is 0.

This dot value 1h is recorded at the pixel position corresponding to the corresponding X, Y coordinate value 1d in the monochrome 1-bit buffer 1i. The X and Y coordinate values 1d are changed to sequentially scan all the pixels in the RGB value buffer 1a, and the above operation is repeated to complete the processing for all the pixels in the buffer.

In such a conventional half-toning process, even when the colors are different from each other on the document data, when the same density values are converted to black and white, the same dot pattern is formed, and thus, differences in the original colors cannot be expressed in the printed output.

The technical problem to be solved by the present invention is to express information on density or more on an output by utilizing original color information even in black and white printing.

In addition, a half-toning processing method comprising changing the halftone pattern that can be used when expressing the density in a dot pattern based on color information and including color information that can be expressed by a different halftone pattern corresponding to each color. To provide.

Halftoning processing method including color information for achieving the above technical problem of the present invention,

Information about luminance, saturation and density of RGB values of the pixel to be printed is calculated, and a corresponding halftone pattern arrangement is generated according to the calculated color information among a plurality of halftone pattern arrangements set in advance for each color. It is characterized by expressing the concentration by selecting.

Further, the selection of the halftone pattern array is based on the luminance value calculated from the RGB value of the pixel and information on the saturation and color. Among the patterns, an optimal halftone is selected by a threshold range domain division method.

In addition, the basic three colors are characterized in that the red, green, blue.

The selection of the halftone pattern array is characterized in that the corresponding halftone pattern of the nearest gray or color is selected according to whether the RGB value of the pixel is in the vicinity of gray or a plurality of primary colors.

In addition, the plurality of basic colors may be red, green, blue, cyan, magenta, and yellow.

 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram for explaining a half-toning process according to the first embodiment of the present invention.

RGB value buffer 2a suitable for input data of digital halftoning process, black and white 1-bit buffer 2o suitable for output data, and a blend used to mix different half-toning patterns in the same area in superimposed proportions. The pattern arrangement 2f is provided. This blend pattern array 2f records the threshold value like a normal halftone pattern.

Similarly, pattern arrays 1 to 7 (2j), which are halftone pattern arrays, are provided. These halftone pattern arrays 2j are defined according to the characteristics of the printer or other specifications. For example, in laser printers, it is standard to use dot-intensive halftones that focus the extension direction of dots around a specific nucleus. Enemy In particular, when the nuclei are arranged in a square lattice shape, the halftone sizes are the same in the X and Y directions.

In the present invention, each halftone pattern arrangement is defined for each of seven colors of a predetermined predetermined primary color such as red, yellow, green, cyan, blue, magenta, and gray, and is easily patterned when comparing patterns of the same density. The number of lines forming the pattern, the angle of the line, and the halftone shape are changed to identify the difference between them. At this time, the size of each halftone pattern array may differ from each other.

In addition, binarizing the RGB values of the pixels based on the information about the color calculated from the RGB values 2b of the pixels to be printed, that is, the hue and saturation 2d, and the threshold value 2g that is an element of the brand pattern array. In order to select an optimal pattern array, halftone array selection 2h is provided, and one array is selected from the pattern arrays based on the selection result. The selected halftone pattern array 2k represents the pattern array selected by this selection process 2j.

In addition, this configuration compares the density value 2c calculated from the RGB value 2b with the threshold value 21, which is an element of the selected halftone pattern array 2k, and compares the comparison processing unit 2m for outputting the dot value. Equipped.

The configuration of the first embodiment of the present invention differs from the conventional method shown in Fig. 1 by selecting a pattern from a plurality of halftone pattern arrangements, calculating the color and saturation 2d for the selection, and blend pattern arrangement. (2f), halftone pattern arrangement selector 2h, and the like are added. Operation other than the selection of the halftones is the same as the conventional method shown in FIG. 1, and a detailed description thereof will be omitted.

Hereinafter, a method of selecting a halftone pattern array from the RGB values 2b will be described in detail.

3 is a view for explaining that the input RGB values in FIG. 2 are processed by synthesizing three adjacent halftone patterns, and projecting the RGB color space onto a plane perpendicular to the gray axis.

In FIG. 3, halftone patterns corresponding to the seven primary colors of red, yellow, green, cyan, blue, magenta, and gray are respectively set, gray is assigned to the center, and one grid point is assigned to each grid point. The default color of is assigned. Adjacent grid points form six triangular regions in contact with each other.

The point 40 indicated by the double ring represents the RGB value of the input pixel. The RGB values of all the pixels correspond to somewhere in Fig. 3 by applying an appropriate conversion process, which is included in at least one of the six triangular areas.

In this embodiment, halftoning processing is performed for inputting RGB values in the region by synthesizing the halftone patterns of three vertices of the triangular region. The color is represented by two colors other than gray in the corresponding triangular area, namely the specification of the main color and the sub color and the weighting coefficient Wmain of the mixture thereof.

An example of the calculation process of the actual color will be described with reference to FIG. 4 and Table 1. FIG. Red, green, blue, luminance, saturation, and Wmain are defined in the range 0.0 to 1.0.

4 is a flowchart illustrating a method of selecting three primary colors close to the RGB values of the pixel of FIG. 2.

Compare the RGB values and set the color of the largest value to the main color, and set the color to the middle color with the second largest value, and in the position where the main color and the middle color cross at right angles to each other in Table 1 below. The color is determined as a subcolor (steps 50 and 51).

In addition, by comparing the RGB values, the color of the smallest value is set to the low color (step 52), and the main color value is compared with the low color value (step 53). In step 53, if the color values are different from each other, set Wmain = (main color value-middle color value) / (middle color value-low color value) (step 54), and if the color values are the same, set Wmain to 0 ( Step 56).

Next, calculation of brightness, density value, and saturation from RGB values will be described. The luminance is calculated by the following equation.

Luminance = Cred × Red Value + Cgreen × Green Value + Cblue × Blue Value

However, Cred + Cgreen + Cblue = 1.0 and Cred> 0, Cgreen> 0, and Cblue> 0.

The concentration value 2c of FIG. 2 is calculated by the following equation (4) from the luminance value.

Density value = Density Max × (1.0-luminance)

Here, DensityMax is the maximum value of the concentration value.

Saturation is calculated by the following equation.

Saturation = 0.0 (when luminance is 0.0 or 1.0)

    = max (1.0-Red / luminance, (Red-luminance) / (1.0-luminance)

, (1.0-Green / Brightness, (Green-Brightness) / (1.0-Brightness)

 , (1.0-Blue / luminance, (Blue-luminance) / (1.0-luminance)) (when luminance is anything other than 0.0 and 1.0)

Here, Max (a, b, c, d, e, f) means the largest value among a, b, c, d, e, f. In the above, the calculation of the specification, saturation and Wmain of the main color and the sub color is completed.

A process of synthesizing three different halftone patterns using the calculated value will be described with reference to FIG.

FIG. 5 is a diagram for explaining a method of synthesizing three kinds of halftone patterns in the first embodiment of the present invention.

First, the threshold value T is calculated by referring to the blend pattern array 2f from the XY coordinate values 2e using Equation (2).

The calculated threshold value T is compared with the magnitudes of the two boundary values obtained from the values of saturation and Wmain, and the three-divided main color area 61 and subcolor area 60, gray area 62 and threshold value are compared. It is determined which area of the area is included, and the corresponding halftone pattern array is selected from the result of the decision.

The above-described processing will be referred to as threshold range region division method below.

Using the halftone pattern array selected in the above method, the half-toning process is performed according to the above-described conventional technique. According to the method of this embodiment using the threshold range region dividing method, other halftone patterns can be seamlessly changed, and a natural binary image can be obtained for color documents having continuous color changes.

6 is a diagram for explaining a half-toning process according to the second embodiment of the present invention.

The second embodiment is composed mostly of the same processing steps as the first embodiment shown in FIG. 2, and the same parts will be omitted and only different processing steps will be described.

Selecting an appropriate pattern array from the halftone pattern arrays corresponding to the respective primary colors defined in advance is the same, but the halftoning process of the second embodiment does not include the blend pattern array 2f, and the plurality of halftone patterns Rather than synthesizing into a simulation, it is simply changed and half-toned. Further, the processing shown in halftone pattern arrangement selection 3d is performed using only the RGB value 3b.

A part different from the operation of the configuration of the first embodiment is a halftone pattern array selection processing method, wherein the halftone pattern array processing flows RGB values 3a and uses the halftone pattern arrays according to the determination conditions shown in Table 2 below. Determine. When the RGB value is close to the six primary colors after removing gray, the halftone pattern of the corresponding color is used, and the other halftone pattern array for gray is used.

In the case of using the above method, a sudden change in the dot pattern near the primary color occurs for successive gradations of RGB values ranging from achromatic to primary colors. However, the basic color does not appear in a normal color photograph image, and the practical value is not reduced.

As described above, the half-toning processing method including the color information according to the present invention can express the color difference included in the color document as the difference of the dot array pattern, and includes the color information to express the expression function in black and white printing. Can be improved.

1 is a diagram for explaining a half-toning processing method in a conventional printer.

2 is a view for explaining each processing step of half toning according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining that RGB values of the input pixel of FIG. 2 are processed by synthesizing adjacent three kinds of halftone patterns.

4 is a flowchart illustrating a method of selecting three primary colors close to the RGB values of the pixel of FIG. 2.

FIG. 5 is a diagram for explaining a method of synthesizing three kinds of halftone patterns in the first embodiment of the present invention.

6 is a diagram for explaining a half-toning process according to the second embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

2a, 3a ... RGB value buffer, 2f ... blend pattern array

2h, 3d ... halftone pattern array selection, 2k, 3g ... selected halftone baton array

2m, 3j ... computing section, 2o, 3l ... monochrome 1-bit buffer

60 ... sub-collar area, 61 ... main-color area

62 ... in grayscale area.

Claims (5)

Information about luminance, saturation and density of RGB values of the pixel to be printed is calculated, and a corresponding halftone pattern arrangement is generated according to the calculated color information among a plurality of halftone pattern arrangements set in advance for each color. Halftoning processing method comprising the color information, characterized in that to express the concentration by selecting. The method according to claim 1, wherein the selection of the halftone pattern array is performed after specifying three basic colors in the vicinity of the RGB value based on the luminance value calculated from the RGB value of the pixel and information on the saturation and color. A half-toning processing method comprising color information characterized in that an optimal halftone is selected by a threshold range region division method among kinds of halftone patterns. The halftoning processing method of claim 1, wherein the basic three colors are red, green, and blue. 2. The method of claim 1, wherein the selection of the halftone pattern array selects the corresponding halftone pattern of the closest gray or color depending on whether the RGB value of the pixel is near gray or a plurality of primary colors. Halftoning processing method including color information. 5. The half-toning processing method of claim 4, wherein the plurality of basic colors are red, green, blue, cyan, magenta, and yellow.