JPH0793675B2 - Pixel density conversion processor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for performing pixel density conversion on a binary image to obtain an image having a different pixel density.

[Conventional technology]

FIG. 8 is, for example, Journal of Image Electronics Engineers, Vol. 7, No. 1, pp 11-18.
It is a block diagram which shows the conventional pixel density conversion processing apparatus which performs the conversion processing shown by (1978). In the figure, 1 is an original image file storing a binary image to be subjected to pixel density conversion processing, 2 is an image file input from the original image file 1, and image input for allocating pixels to a buffer in line units The first and second line buffers 3 and 4 store pixels for one line, respectively, and the pixel density conversion of the original image is performed by the pixel buffer 5, so that the pixels of the original image to be converted are converted from the line buffers 3 and 4. An original image pixel extraction unit for extraction, 7 is a conversion pixel determination unit that determines pixels of an image (converted image) to be pixel-converted using the pixels extracted by the original image pixel extraction unit 5, and 9 is a temporary storage of conversion pixels. The line buffer 12 keeps track of whether all the pixels in the buffer of the image input unit 2 have been processed or all the pixels of the original image have been processed. End of processing to send a signal A monitoring unit, 13 is an image output unit that outputs the pixels in the line buffer 9 to a file, and 14 is an image file that stores the image whose pixel density has been converted.

The pixel density change referred to here is, for example, assuming that the pixel density of a binary original image is 8 dots vertically by 8 dots per mm, and if the conversion magnification is 1/2, the pixel density of the converted image is 4 × 4. To get an image. In other words, if the occupied area per dot is 8 × 8, it will be (1/8) × (1/8) mm ² but will become (1/4) × (1/4) mm ² , so 4 × 4 is a coarser image than the original image. FIG. 9 shows an example in which the original image has a pixel density of (horizontal direction) 8 × (vertical direction) 8 and is converted at a conversion ratio of 1/2.

Next, a conventional image density conversion method will be described. As shown in FIG. 9, when the conversion corresponding pixels of the original image are projected on the conversion pixels of the converted image, the 2 × 2 pixel portion of the original pixel corresponds to the converted 1 × 1 pixel. Become. Therefore, the method shown in Fig. 10 is used to obtain the converted pixels. The method is to first calculate the average density W of four pixels (a, b, c, d) to be converted in the original image, compare W with a certain threshold value α,
When W is larger than α, the converted pixel X is black (= 1), and when it is small, white (= 0).

Here, a specific processing operation will be described assuming that the pixel density of the original image is m × n and conversion is performed at a conversion magnification of 1/2 to obtain a converted image having a pixel density of (m / 2) × (n / 2). To do.

In FIG. 8, first, 2 m pixels for 2 lines from the original image file 1 are input to the image input unit 2, and the first one line is stored in the line buffer 3 and the next one line is stored in the line buffer 4. . Then, the original image pixel extraction unit 5
2 pixels (a, b in FIG. 9) from the line buffer 3 and 2 pixels (c, d in FIG. 9) from the line buffer 4 are extracted. Then, based on the values of these 4 pixels, the conversion pixel determining unit 7
Determines the value of the converted pixel by the formula of FIG. 10 (X in FIG. 9) and outputs it to the converted pixel line buffer 9. Next, the pixel pointers in the line buffers 3 and 4 are advanced, and the original image pixel extraction unit uses the same two pixels (8th pixel) from the line buffer 3 as described above.
2e from the line buffer 4 (e, f in the figure) (g,
h) is extracted, the conversion pixel is determined, and output to the conversion pixel line buffer 9. This operation is repeated until all 2m pixels in total in the line buffers 3 and 4 storing the original image pixels are converted. The processing end monitoring unit 12 constantly monitors this end.

When the processing of all the pixels in the line buffers 3 and 4 is completed and m / 2 converted pixels are output to the converted pixel line buffer 9, the processing end monitoring unit 12 outputs a 1-line end signal to the image output unit 13. Then, m / 2 pixels in the converted pixel line buffer 9 are output to the pixel density converted image file 14. The end signal is also sent to the image input unit 2 and the original image pixel extraction unit 5, and the pixels of the 3rd and 4th lines of the original image are input by the image input unit 2 and the conversion target pixels in the 3rd and 4th lines of the original image are input. The extraction is performed by the original image pixel extraction unit 5 to perform pixel conversion. These processes are repeated until the processing of n lines in the vertical direction of the original image is completed, that is, until n / 2 lines are output as a converted image. As a result, the original image of m × n is converted into 1 / magnification.
It is converted by 2 and a converted image of (m / 2) × (n / 2) is obtained.

[Problems to be Solved by the Invention]

The conventional pixel density conversion processing device is configured as described above, and since the image density conversion is performed only in the portion where the original image is projected, the pixel converted image becomes coarse and the converted image faithful to the characteristics of the original image. There was a problem that it was difficult to obtain.

For example, suppose that there is an original image pattern as shown in FIG. Even though the original image looks like a striped pattern, there is a problem in that when the threshold value α in the conventional pixel density conversion method is 0.5, all are black, and when α = 0.75, it is pure white.

The present invention has been made in order to solve the above-mentioned problems of the conventional ones, and it is possible to perform the conversion by reflecting the change of the original image pixel, and particularly to perform the conversion that matches the characteristics of the original image. An object is to obtain a pixel density conversion processing device capable of

[Means for Solving the Problems]

The pixel density conversion processing device according to the present invention is a pixel density conversion processing device that obtains an image having a resolution different from that of an original image by performing pixel density conversion from a binary or halftone original image. , A conversion reference pixel forming a conversion target area which is the latest unconverted area of the original image or an area including the same, and the upward and leftward directions of the conversion target area output from the buffer. A conversion pattern table that stores the pixel values of the conversion pixels obtained by performing pixel density conversion on the conversion target pixels that form the conversion target area by referring to the already-converted pixels located in The conversion pattern table is searched on the basis of the pixel to perform pixel conversion, and a pixel conversion unit is provided.

[Action]

According to the present invention, with the above-described configuration, the conversion target area that is the latest unconverted area of the original image or the conversion reference pixel that constitutes the area including the conversion target area, and the conversion target output from the buffer Since the converted pixels located above and to the left of the area are referred to, the change information of the original image is stored, and the pixel density converted image faithfully reflects the characteristics of the original image.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a pixel density conversion processing device according to an embodiment of the present invention. In the figure, the same or corresponding parts as those of the conventional device of FIG. 8 are designated by the same reference numerals. In FIG. 1, 1 is an original image file, 2 is an image input unit, 3 and 4 are line buffers that store conversion target pixels in the original image, 5 is an original image pixel extraction unit, and 6 is a pixel that has already undergone pixel conversion. A pixel conversion image pixel extraction unit for extracting the corresponding pixel for reference, 7
Is a conversion pixel determination unit that determines conversion pixels based on the pixels extracted from both pixel extraction units 5 and 6, 8 is a conversion pattern table used when conversion pixel determination unit 7 performs conversion, and 9 is conversion pixel determination unit 7 The current conversion line buffer for temporarily storing the converted pixels output by the above, 10 is a previous conversion line buffer for storing the pixels of the line immediately preceding the current line in the already pixel-converted image, and 11 is the current conversion line buffer 9 Is a copy buffer unit that copies all the pixels in the previous line buffer 10, 12 is a processing end monitoring unit that constantly monitors the end of processing, 13 is an image output unit, and 14 is a pixel conversion unit that stores the pixel density converted image. It is an image file.

Next, a specific processing operation will be described.

FIG. 2 shows the flow of the processing, and FIG. 3 shows the image of the pixel density conversion target and the meanings of the variables used in FIG.

As with the conventional pixel density conversion device, the image input unit 2 takes out 2H pixels of 2 lines from the original image file 1 in the same manner as in the conventional pixel density conversion device, and the odd number (1, 3, 5,
…) Line pixels are stored in the line buffer 3 in even-numbered (2,
, 4, ...) are allocated to the line buffer 4 (steps ST1, ST2). After that, the original image pixel extraction unit 5 extracts the reference pixel (a, b, c, d) by the pixel pointer K in the line buffer (steps ST3, ST4). Further, the corresponding pixel is extracted to refer to the converted pixel. In the case of this embodiment, the reference pixel in the already-converted pixel is 2 in the vicinity of the converted pixel (X) which is currently undergoing pixel conversion.
We will take pixels. Specifically, it is directly above and to the left,
Let these be e and f, respectively. Since the pixel f immediately above is taken, a buffer for storing the previous conversion line is required.

Extraction of already-converted pixels is performed by the pixel-converted image pixel extraction unit 6, and is extracted by the pointer L from the current line buffer 9 and the previous line buffer 10 (step ST6).

Next, the original image extraction pixel (a, b, c, d) and the already-converted pixel extraction pixel (e, f) are input to the conversion pixel determination unit 7 to determine the conversion pixel. The conversion pixel is determined by the conversion pattern table 8
To search for. The pixel conversion table 8 has the configuration shown in FIG. 4, and the address in the row direction of the table is 0 (white) and 1 (black) of the four pixels (a, b, c, d) of the original image extraction pixel.
To each bit, and for the address in the column direction, 2 pixels (e, f) of the already-converted pixel extraction pixels are assigned to each bit, and the address corresponding to the appearance pattern is obtained to determine the converted pixel (step ST5, ST7,
ST8). The pixel conversion table 8 is a ROM in which the patterns shown in FIG. 5 in which all the possible patterns are listed are classified and inputted by the row address by the original image extracted image and the column address by the changed pixel.

The conversion rule shown in FIG. 5 is based on the fact that the change is first introduced and the signal is changed early in order to store the change information. FIG. 6 shows a part of it taken out. In the pattern shown in FIG. 6, in the conventional pixel density conversion processing device, when α = 0.5, all were black, but when changing from black to white by paying attention to the vertical or horizontal direction, The converted pixel (X) is white, and when it is changed from white to black, the converted pixel (X) is black. As a result, even if the original image pattern as shown in FIG. 7 appears, the striped pattern as shown in FIG. 11 does not disappear, and an image density converted image according to the characteristics of the original image can be obtained.

As described above, the conversion pixel determining unit 7 obtains the conversion pixel (X) and outputs it to the current conversion line buffer 9 (step ST9).
Until this processing is completed for all the pixels in the line buffers 3 and 4 input from the original image file 1, that is, the pixels (H / 2) for one line of the pixel conversion image are output to the current conversion line buffer 9. Is repeated until it is done. The process end monitoring unit 12 constantly monitors this end. 1 above
When the processing for the lines is completed, the pixels for one line are output to the pixel conversion image file 14 by the image output unit 13 (step ST13). When one line of the image-converted pixel is output, the reference line of the current image is lowered by two lines (step ST16), and the process for obtaining the converted pixel of the next line of the pixel-converted image is started. Therefore, in the pixel-converted image, what has been treated as the current line needs to be treated as the previous line. Therefore, the buffer copy unit 11 moves all the pixels in the original conversion line buffer 9 to the previous conversion line buffer 10 (step ST14). After that, pixels obtained by lowering the reference line of the original image by two lines are input to the buffer by the image input unit 2, and the conversion process of the two lines in the original image is completed until the process for the vertical direction V of the original image is completed, that is, pixels Repeat until V / 2 lines are output as a converted image. As a result, the H × V original image is converted at a conversion magnification of 1/2, and an image with a pixel density change of (H / 2) × (V / 2) can be obtained.

In the above-described embodiment, the reference pixel of the already-converted pixel is set to be immediately above and immediately to the left of the current converted pixel (X). It may be possible to refer to already-converted pixels, and by doing so, it is possible to increase the types of original images whose characteristics are not lost even when the pixel density is converted. In this case, the conversion pattern table may be created by increasing the column address by 1 bit, changing the table from four in the column direction to eight, and inserting conversion pixels corresponding to the conversion pattern.

Further, the reference pixels of the original image are not limited to the pixels in the conversion area (a, b, c, d in FIG. 5), and pixels in the vicinity thereof may be added. The number of reference lines at that time can be increased by increasing the corresponding reference line memory if it is necessary to increase both or one of the original image reference line and the converted line.

Further, in the above-described embodiment, the case of converting a black-and-white binary image has been described, but it is naturally applicable to a black-and-white halftone image, and the same effect as that in the above-described embodiment is obtained.

〔The invention's effect〕

As described above, according to the pixel density conversion processing apparatus of the present invention, in the pixel density conversion processing apparatus that performs pixel density conversion from a binary or halftone original image to obtain an image with a resolution different from the original image, A buffer for storing already-converted already-converted pixels, a conversion reference pixel forming a conversion target area which is the latest unconverted area of the original image or an area including the same, and the conversion target output from the buffer A conversion pattern table containing the pixel values of the conversion pixels obtained by performing pixel density conversion on the conversion target pixels forming the conversion target area by referring to the already-converted pixels located in the upper and left directions of the area, and the original image Since the conversion reference table and the pixel conversion means for performing pixel conversion by searching the conversion pattern table based on the already converted pixel are provided,
There is an effect that the image whose pixel density has been converted can be an image that reflects the characteristics of the original image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a pixel density conversion processing apparatus according to an embodiment of the present invention, FIG. 2 is a flow chart showing an outline of the processing of the above embodiment, and FIG. 3 shows variables used in FIG. 4 and 5 are diagrams showing the structure of a conversion pattern table, FIG. 5 is a view showing all possible conversion patterns, and FIG. 6 is a diagram showing a characteristic partial pattern selected from the patterns shown in FIG. FIG. 7 is a diagram showing an example of pixel density conversion in the above embodiment, FIG. 8 is a block diagram showing a conventional pixel density conversion processing device, and FIG. 9 is a diagram showing a concept of image density conversion. FIG. 10 is a diagram showing a conventional pixel density conversion system, and FIG. 11 is a diagram showing an embodiment of a conventional pixel density conversion processing device. In the figure, 6 is a pixel conversion image pixel extraction unit, 7 is a conversion pixel determination unit, 8 is a conversion pattern table, 10 is a previous conversion line buffer, and 11 is a buffer copy unit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A pixel density conversion processing device for obtaining an image having a resolution different from that of an original image by performing pixel density conversion from a binary or halftone original image, and a buffer for storing already converted already converted pixels. , A conversion reference pixel forming a conversion target area which is the latest unconverted area of the original image or an area including the conversion target area, and already-converted pixels output from the buffer above and to the left of the conversion target area The conversion pattern table containing the pixel values of the conversion pixels obtained by performing the pixel density conversion of the conversion target pixels forming the conversion target area, and the conversion based on the conversion reference pixels of the original image and the already converted pixels. A pixel density conversion processing device, comprising: a pixel conversion unit that searches a pattern table and performs pixel conversion.