JPH0946511A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with a sharp border by providing a border discrimination means outputting a border flag and an image forming means printing out output image data from a color smoothing means in multi-gradation so as to attain a high transfer rate. SOLUTION: A color conversion means 2 applies color conversion processing to raster data outputted from an image data entry section 1 and having sets of R, G, B of picture elements into sets of three primary colors subject to subtractive color mixture having integral values from '0' to '255'. Then the operator sets threshold levels (k) from '0' to '255' to threshold level decision section 5 by means of a key board 4. Then a border discrimination means 6 compares a threshold level from the threshold level decision section 5 with border information from a color smoothing means 3 to generate a border flag f1, which is outputted to a color smoothing means 3. Then a print engine 7 forms an image onto an image recording medium based on CMY output image data outputted from the color smoothing means 3 by the sublimation thermal transfer system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus which receives low-resolution image data as an input and forms an image of higher resolution.

[0002]

2. Description of the Related Art In recent years, technology relating to image forming apparatuses, particularly printers, has advanced, and at the same time that the density of minimum pixels has increased, multi-gradation expression in color has become possible. Along with this, the amount of image data required for image formation increases dramatically, and in addition to reading image data from the recording medium on which the image is recorded, serial data transfer is performed during the data transfer process from the recording medium to the image forming engine. If such a slow transfer protocol exists, it takes a very long time to transfer the image data, which lowers the overall throughput.

For this reason, many image forming apparatuses have been proposed so far in which the amount of data is reduced by image compression. However, image compression and decompression generally require complicated processing, and the compression and decompression itself. However, there are problems such as taking time and preparing a dedicated integrated circuit (IC).

On the other hand, it is conceivable to input the original image data in a low resolution representation with a small data amount and form an image based on this image data. In this case, the color of one pixel of the original image data is simply converted. If the values are directly assigned to the pixels of a plurality of output pixels and an image is formed at a resolution lower than the resolution of the original image data, the output image has a resolution lower than the input image, the outlines of characters and the like are jagged, and color changes The problem of not being smooth arises.

To solve this problem, a conventional image forming apparatus for smoothing the outline of a binary expression such as a character can be applied (Japanese Patent Laid-Open No. 2-155760). That is, in this conventional image forming apparatus, the input image data is stored by the storage means, and the image data stored by the storage means around the pixel of interest to be interpolated belongs to a binary representation image or a multi-value representation image. It is configured to determine whether the image belongs to the image by the determination unit, and generate the interpolation data of the pixel of interest by the data interpolation unit by the calculation method according to the determination result.
Even when low-resolution image data is input, it is possible to form an image as high-resolution image data having a smooth contour in the binary image portion.

[0006]

However, the above-described conventional image forming apparatus smoothes the contour of the binary representation portion of the image data, and there is no improvement to the problem that the color change is not smooth. In a general image processing device, it is known that each pixel of an output image obtains color data by interpolation from color data of a pixel near a corresponding position of an original image, and the resolution is converted. When the color data is created by using one pixel, the color of one pixel and the color of the adjacent pixel are correlated with each other, so that the sharpness of a boundary portion such as a character edge portion or an object contour is reduced, which causes a problem that image quality is deteriorated.

The present invention has been made in view of the above points, and is necessary for image formation by inputting low-resolution small image data and performing high-quality image output by utilizing the high resolution of the printer. It is an object of the present invention to provide an image forming apparatus that can reduce the amount of image data and speed up handling such as reading and transfer of image data.

[0008]

In order to achieve the above object, the present invention provides image data for inputting first image data of a first resolution having a set of values of three primary colors of additive color mixture for each pixel. An input unit, an image data input unit for inputting first image data of a first resolution having a set of values of three primary colors of additive color mixture for each pixel, and first image data from the image data input unit. For each pixel of the output image, the color conversion means for converting into the second image data of the set of the values of the three primary colors of the subtractive color mixture, the threshold setting part for setting an arbitrary threshold value, and the second input from the color conversion means. Of the pixels in the vicinity of the corresponding position in the image data, the values of the pixels that are not separated by the boundary determined by the boundary flag are substituted, and further interpolation processing is performed to obtain the second resolution twice the first resolution. Smoothing means for generating image data of The difference information between each pixel of the second image data input from the color smoothing unit and the adjacent pixel is compared with the threshold value from the threshold value setting unit, and when there is a color difference larger than the threshold value, it is determined that there is a boundary. The boundary determining means for outputting the boundary flag and the image forming means for printing the output image data of the color smoothing means on the medium in multiple gradations are provided.

Further, the color smoothing means of the present invention has a value which is at least twice the maximum value as the value of one of the three primary colors of the pixel representing the outside of one pixel of the input second image data. , The difference information from the adjacent pixel is calculated and output to the boundary determining means, and among the pixels in the vicinity of the corresponding position of the second image data input from the color converting means, the boundary from the boundary determining means is calculated. It is characterized in that the pixel values not separated by the boundary discriminated by the flag are substituted, and interpolation processing is further performed to generate output image data of a second resolution twice the first resolution.

Further, the boundary determining means of the present invention makes all the values and thresholds of the three primary colors of subtractive color mixture of the difference information between each pixel of the second image data input from the color smoothing means and the adjacent pixel large and small. The comparison is characterized by outputting a boundary flag which determines that there is a boundary when the value of at least one of the three primary colors is larger than the threshold value.

In the present invention, the color smoothing means separates each pixel of the output image by the boundary determined by the boundary flag among the pixels in the vicinity of the corresponding position of the second image data input from the color converting means. Since the value of the pixel which is not assigned is substituted and the interpolation processing is further performed to generate the output image data of the second resolution which is twice the first resolution, the input image data of the low resolution is converted to the high resolution. Can be output as image data.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of an image forming apparatus according to the present invention. In this embodiment, a sublimation type thermal transfer system, which is a well-known technique, is adopted as the image forming means, and the resolution of the output image is 150 dpi.
A full color is expressed for one pixel by mixing three primary colors of subtractive colors of 256 gradations of cyan (C), magenta (M) and yellow (Y). Also, in this embodiment,
With respect to the output resolution of 150 dpi, 75 dpi data which is half the resolution is input to form an image.

As shown in FIG. 1, the image forming apparatus of this embodiment has an image data input unit 1, a color conversion unit 2, a color smoothing unit 3, a keyboard 4, a threshold value setting unit 5, a boundary determination unit 6 and It is composed of the print engine 7. In addition, the color conversion unit 2, the color smoothing unit 3, and the boundary determination unit 6
The portion surrounded by the broken line consisting of is assumed here to be realized by software, but it is obvious that the same processing can be realized by hardware.

The image data input unit 1 has a resolution of 75 dpi consisting of three color planes of red (R), green (G) and blue (B) which are three primary colors of additive color mixture from a recording medium (not shown).
Image data of "0" to "2" for each pixel
It is read as a raster data string having a set of R, G, and B values having an integer value of 55 ″, and is output to the color conversion means 2.

The color conversion means 2 performs color conversion processing, which is a well-known technique, on the raster data string output from the image data input section 1 and having a set of R, G, and B values of each pixel.
Converted to a set of values of cyan (C), magenta (M), and yellow (Y), which are the three primary colors of subtractive color mixture, having an integer value from 0 "to" 255 "(hereinafter referred to as" color vector ") To do.

The color smoothing means 3 determines the boundary information between adjacent pixels for each pixel of the color vector data having a set of C, M and Y values output from the color converting means 2 by the boundary determining means 6.
And the boundary flag f output from the boundary determining means 6 is used to perform the color smoothing processing described later,
The CMY output image data of the print engine 7
Output to

The operator sets a threshold value k from "0" to "255" in the threshold value determining section 5 through the keyboard 4. The boundary determining means 6 is provided with a threshold value determining unit 5 as described later.
And the boundary information from the color smoothing means 3 are compared to generate a boundary flag fl, and the boundary flag fl is output to the color smoothing means 3. The print engine 7 forms an image on the image recording medium by the sublimation thermal transfer method from the CMY output image data output by the color smoothing unit 3.

Next, the operation of the color smoothing means 3 will be described with reference to the flowchart of FIG.

The CMY image data extracted from the color conversion means 2 is first subjected to a vector variable A (x, y) having a 2-byte integer type C value, M value and Y value in the color smoothing means 3.
(Step 21). Where X ₁ or more X
_max and integer x of the range, the integer y of _{Y 1} or _{Y max} the range represents the pixel represented by the vector variable A, the transverse direction, the vertical position, (x, y) = ( X 1 ，
Y ₁ ) is the upper left corner of the image, (x, y) = (X _max , Y
_max ) indicates the upper right corner of the image.

Next, the color smoothing means 3, vector variable _{A (X} 1 -1 representing the one pixel outside of the input image data,
y), A (X _max +1, y), A (x, Y ₁ −1) and A (x, Y _max +1) (where x is X ₁ or more and X
integer less than or equal to _max , y is an integer greater than or equal to Y _{1 and} less than or equal to Y _max )
"255" which is the maximum value of the normal C value for the C value of
Substituting "512" which is more than twice (step 22).

This is because a color smoothing algorithm is used in which the color of the pixel inside the image is not affected by the pixel if the color difference between the color of the adjacent pixel is larger than a certain range. By substituting a very large value for the C value of the pixel outside one pixel of the image data, the pixel in the image always causes a large density difference with the pixel outside the image, which is originally indefinite, and the influence is exerted. This is to avoid receiving it.

Subsequently, the color smoothing means 3 is a vector variable F (x, y) representing each pixel of the output image (where x is 2).
The vector variable A (x, y) of the input image at the corresponding position is substituted into an integer of X ₁ -1 or more and 2X _max or less, and y is an integer of 2Y ₁ -1 or more and 2Y _max or less (step 2
3). That is, as shown in FIG. 5, since one output pixel having a resolution of 150 dpi corresponds to four pixels for one input pixel having a resolution of 75 dpi, the same value of one input pixel is assigned to all four pixels.

Then, the color smoothing means 3 completes the image conversion by calling a color smoothing routine, which will be described below, for all the pixels of the input image data to perform color smoothing processing (step 24).

Next, the color smoothing routine used in step 24 will be described with reference to the flowchart of FIG.
First, the difference vector between the color vector A (m, n) of the pixel of interest and the color vector A (m, n−1) of the pixel adjacent to it is substituted into the vector variable D (step 3).
1).

As a result, the vector variable D representing the boundary information is obtained, the boundary determination routine is called with this vector variable D as an argument (step 32), and the value of the boundary flag which is ON or OFF is obtained as the return value. .

Here, the above-described boundary determination routine is performed by the routine shown in FIG.
In the routine executed by the boundary determining means 6 shown in
As shown in the flowchart in FIG. 4, first, the threshold value k is read from the threshold value setting unit (5 in FIG. 1) (step 41),
Then, the C value of the vector variable D, which is an argument, is compared with the threshold value k (step 42). When the C value of the vector variable D is less than or equal to the threshold value k, the M value of the vector variable D and the threshold value k are compared. When the M value of the vector variable D is less than or equal to the threshold value k (step 43), Y of the vector variable D is compared.
The value is compared with the threshold value k (step 44).

When all the C, M and Y values of the vector variable D are below the threshold value k, that is, when there is no abrupt color change between the pixel of interest and the adjacent pixel, the value of the boundary flag is turned off. (Step 45). On the other hand, C of vector D
If any one of the value, the M value, and the Y value is larger than the threshold value k, that is, when there is a rapid color change between the pixel of interest and the adjacent pixel, the value of the boundary flag is turned on (step 46). ). This boundary flag is, as described above,
It is input to the color smoothing means 3.

Returning to FIG. 3 again, the boundary flag obtained by the boundary determining routine is received, and the color smoothing routine of the color smoothing means 3 determines whether or not the value of this boundary flag is ON. (Step 33). If the boundary flag is off, color smoothing processing with the upper adjacent pixel is performed in the next step 34, and if the boundary flag is on, step 34 is skipped and the process proceeds to step 35 described later.

In other words, many pixels are made up of a combination of smooth surfaces that undergo a smooth color change, and based on the assumption that the color changes are discontinuous at the boundaries between the surfaces, the distance between adjacent pixels is increased. When there is no abrupt color change, that is, when the boundary flag is off, it is determined that the target pixel and the adjacent pixel belong to the same plane, and the color smoothing process in step 34 is performed. When there is an abrupt color change, that is, when the boundary flag is on, it is determined that the area is between the surfaces, and the color smoothing processing beyond the boundary is not performed.

In the color smoothing process of step 34,
The color of the output pixel is determined by linear interpolation from the positional relationship between the output pixel and the input pixel. That is, the vector variable F (2x-1,2y-1) representing each pixel of the output image is added with a value obtained by multiplying the vector variable D, which is the difference vector between the pixel of interest and the upper adjacent pixel, by 1/4, and The addition result is F
Substitute for (2x-1, 2y-1). Further, the addition result obtained by adding the value of ¼ times the vector variable D to the vector variable F (2x, 2y−1) is substituted into F (2x, 2y−1).

By this primary interpolation, for example, in FIG. 5, assuming that A, C, B, and f are color vectors of respective pixels, it is clear that f = C + {(A−C) / 4} + {(B− C) / 4} (1) can be approximated. When there is a boundary with the upper adjacent pixel, the second term on the right side of equation (1) disappears, and when there is a boundary with the left adjacent pixel, the third term on the right side of equation (1) is deleted. ing.

After the color smoothing process in step 34 of FIG. 3 is completed, the color vector A (m, n) of the pixel of interest is adjacent to the color vector A (m, n) below the pixel in the same manner as in steps 31 to 34 described above. After substituting the difference vector with the pixel color vector A (m, n + 1) into the vector variable D, the boundary determination routine is called to determine the value of the boundary flag obtained by comparing the vector variable D and the threshold value k. Color smoothing process is performed or not and the process proceeds to the next step (step 3
5).

Steps 36 and 37 are also steps 31 to 34.
In the same manner as above, color smoothing processing is performed on the left adjacent pixel and the right adjacent pixel of the pixel of interest (may not be performed depending on the boundary flag).

FIG. 6 shows an example of the input image and the output image of the gray scale image according to the above embodiment. Here, the threshold value k is “64”. The input image in FIG. 6A is an image having a resolution of 75 dpi, which has a rectangular portion having a value “255” in the upper left portion and a gradation portion in which the value monotonously changes in the right portion. in this case,
The output image with a resolution of 150 dpi obtained in the present embodiment has a value "in the upper left part of the input image, as shown in FIG. 6 (B).
Well preserved the edge of the rectangle with 255 ",
Further, it can be seen that the gradation part on the right side of the input image is a finer gradation part in the output image.

[0035]

As described above, according to the present invention,
Since the low-resolution input image data is output as the high-resolution image data, the image data can be small, the transfer speed can be increased, and the handling can be simplified. Further, according to the present invention, it is possible to form a high-quality image of image data originally having a small resolution with a high resolution, a smooth color change, and a sharp boundary portion such as a character edge portion or an object contour.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the color smoothing means.

FIG. 3 is a flowchart showing the color smoothing routine of FIG.

FIG. 4 is a flowchart showing the boundary routine of FIG.

FIG. 5 is a schematic diagram showing correspondence between input images and output images.

FIG. 6 is a diagram showing an example of an input image and an output image.

[Explanation of symbols]

 1 image data input unit 2 color conversion unit 3 color smoothing unit 4 keyboard 5 threshold value setting unit 6 boundary determination unit 7 print engine

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04N 1/46 H04N 1/46 Z

Claims (3)

[Claims] 1. An image data input unit for inputting first image data of a first resolution having a set of values of three primary colors of additive color mixture for each pixel, and the first image data input unit from the image data input unit. A color conversion unit that converts the image data into second image data of a set of three primary color values of the subtractive color mixture, a threshold value setting unit that sets an arbitrary threshold value, and each pixel of the output image is input from the color conversion unit. Of the pixels in the vicinity of the corresponding position of the second image data, the values of the pixels which are not separated by the boundary determined by the boundary flag are substituted, and further interpolation processing is performed,
A color smoothing unit that generates output image data having a second resolution twice the first resolution, and a difference between each pixel of the second image data input from the color smoothing unit and an adjacent pixel. Boundary determination means for comparing the information with the threshold value from the threshold value setting part and outputting the boundary flag for determining that there is a boundary when there is a color difference larger than the threshold value; and output of the color smoothing means. An image forming apparatus comprising: an image forming unit that prints image data on a medium in multiple gradations. 2. The color smoothing means sets a value that is at least twice the maximum value as the value of one of the three primary colors of the pixels that represent the outside of one pixel of the input second image data. After substituting, the difference information with respect to the adjacent pixel is calculated and output to the boundary determining means, and the boundary determining is performed among the pixels in the vicinity of the corresponding position of the second image data input from the color converting means. The value of the pixel which is not separated by the boundary determined by the boundary flag from the means is substituted, and the interpolation processing is further performed to generate the output image data of the second resolution twice the first resolution. The image forming apparatus according to claim 1, wherein: 3. The boundary determining means sets all values of the subtractive primary colors of the difference information between each pixel of the second image data input from the color smoothing means and an adjacent pixel and the threshold value. 2. The boundary flag that determines that there is the boundary is output when at least one of the three primary colors has a value larger than the threshold value.
Or the image forming apparatus according to 2.