JPH07123260A - Multilevel picture dot processing unit - Google Patents

Abstract

PURPOSE:To select optionally reproducibility of gradation with less arithmetic processing. CONSTITUTION:When a multilevel picture is converted into a dot picture, a picture element exhaust section 1 overlaps a mask pattern 1a onto a multilevel picture to extract a picture element group at a specific area. A gradation level calculation section 2 calculates an address corresponding to a gradation level of a picture element group at a specific area to obtain an address from the total sum of gradation levels of each element for example. A dot pattern corresponding to the gradation level is stored in each address of a dot pattern storage section 3. A dot pattern output section 4 extracts the dot pattern from the dot pattern storage section 3 from an address obtained by the gradation level calculation section 2. A dot pattern overwriting section 5 overwrites the dot pattern on an unprocessed part of the dot picture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation image halftone dot processing device for converting a gradation image into a halftone dot image.

[0002]

2. Description of the Related Art In order to print a gradation image of a photograph or the like, there is a gradation image halftone dot processing device which represents this gradation by a set of halftone dots in which one dot is binary. This gradation image halftone dot processing device inputs a certain gradation image and outputs a halftone dot pattern corresponding to this image. Conventionally, there has been the following method for generating binary halftone dot data in such a gradation image halftone dot processing device.

FIGS. 10 and 11 are explanatory views of a conventional method of generating binary halftone dot data, and FIG. 10 is a quadrant.
rant) system, and FIG. 10 shows a dither system. (A) Quadrant method This method generates one halftone dot image data from four pixels of gradation data. As shown in (a) of FIG. 10, one halftone dot having a point A at the center is used. When a dot region (a part surrounded by a square with a solid line) is converted into a halftone dot, this region is first divided into four triangular blocks (to be referred to as quadrants). Then, 8-bit, 256-level gradation image data is input to each of these four blocks, and black dots are made in the order of the numbers shown in FIG. The halftone dot area, which has as a center, is converted into halftone dots.

That is, as shown in (b), a threshold value is determined in advance for a plurality of halftone dot elements constituting one halftone dot, and this threshold value and the gradation level of the gradation image should be compared. Is used to determine which halftone dot element is converted to a black dot. For example, in the example shown in (b), the threshold values are set to 1, 5, 9, ... From the pixel closer to the center A in the area. In such a state, the gradation of the original image, that is, the gradation of the pixel is compared with these values, and it is determined whether or not to make a black dot according to the magnitude relationship. For example, if the pixel gradation of the original image is 12, this is the threshold value 1 of the halftone image,
Since these values are larger than 5 and 9, these halftone dot elements 1,
The positions of 5 and 9 are black, black, and black. As described above, in the quadrant method, the size of one halftone dot is determined according to the grayscale levels of the four pixels of the grayscale data, and the grayscale data is converted into halftone dot data.

(B) Dither method There are various methods in this method as well, but in these methods, one pixel of a gradation image corresponds to one pixel of halftone image data. Typical of these methods are the minimum mean error method and the systematic dither method. The average error minimum method is a method for minimizing the error between the read density and the display density of the original image as an average, and the threshold value of the pixel of interest is obtained from the error of the neighboring pixels that have been binarized first. The binary halftone image data is obtained by setting a black pixel when the gradation level of is larger than the threshold value and a white pixel in other cases.

In the systematic dither method, as shown in FIG. 11 (a), a comparison reference is made in which 100 pixels including pixels forming one halftone dot and pixels of four adjacent halftone dots are one pattern. Table 11 is prepared, and this comparison reference table 11
And the gradation image data are compared pixel by pixel to determine whether the pixel is a black pixel or a white pixel. For example, in FIG.
As shown in (b), a certain gradation image data 12 and the comparison reference table 11 are made to correspond pixel by pixel, and when the level of the gradation image data 12 is smaller than the value of the comparison reference table 11, black pixels, etc. In the case of, by using white pixels,
The binary halftone image data 13 is obtained.

In addition to this, for example, JP-A-63-10
As disclosed in Japanese Patent No. 9659, one pixel of gradation data is made to correspond to partial halftone dot data of an arbitrary size,
Some also obtain binary halftone image data.

[0008]

However, in the quadrant method of the above (a), since the size of the gradation image and the image size after halftoning are fixed, they lack flexibility. This is because in the method, one halftone dot is created from four pixels of the original gradation, and there is a problem that the gradation reproducibility of the original image is poor.

Further, in the above-mentioned (b) dither method, since one pixel of the gradation image data is converted into one halftone dot, the reproducibility of the fine line is excellent, but the gradation image and the halftone image are Since there is a one-to-one relationship, a large-scale gradation image is required compared to the quadrant method, which is disadvantageous in terms of image data input time, transfer time, and data storage capacity when processed by a computer. There was a problem like that.

Further, in the method disclosed in the above publication,
There has been a problem that a comparison calculation and a table search have to be performed for each pixel of the gradation image data, resulting in a large number of calculations.

The present invention has been made in order to solve the above-mentioned conventional problems, and provides a gradation image halftone dot processing device which requires a small number of calculations and can select various gradation reproducibility. The purpose is to

[0012]

A gradation image halftone dot processing apparatus according to the first invention is a gradation image halftone dot processing apparatus for converting a gradation image into a halftone dot image corresponding to the gradation level. A pixel extraction unit that extracts a pixel group in a specific region from a gradation image, a gradation level calculation unit that calculates an address corresponding to the gradation level of the pixel group, and a network corresponding to the gradation level of the pixel group. A halftone dot pattern storage unit that stores the pattern of the dot group, and a pattern of the corresponding halftone dot group is extracted from the halftone dot pattern storage unit at the address calculated by the gradation level calculation unit and used as the halftone dot pattern of the pixel group. A halftone dot pattern output unit for outputting is provided.

The gradation image halftone dot processing apparatus of the second invention is the first invention.
In the invention, the pixel extraction unit superimposes the mask pattern having a size corresponding to a specific region and the mask pattern on the gradation image, validates the pixels in the region of the mask pattern, and identifies the remaining pixels as invalid. And an extraction unit for extracting a pixel group in the area (1).

The gradation image halftone dot processing apparatus of the third invention is the first invention.
Alternatively, in the second invention, a halftone dot pattern pasting unit that overwrites the halftone dot pattern output from the halftone dot pattern output unit on an unprocessed portion of the halftone dot image to create a halftone dot image corresponding to the gradation image is provided. It is characterized by having.

[0015]

In the gradation image halftone dot processing apparatus of the first invention,
First, the pixel extraction unit extracts a pixel group in a predetermined specific area from the gradation image. The gradation level calculation unit calculates the address corresponding to the gradation level of the pixel group in the specific area, for example, by obtaining the address from the sum of the gradation levels of each pixel. On the other hand, the halftone dot pattern storage unit stores in advance a halftone dot pattern corresponding to the grayscale level of a pixel in a specific region, and the halftone dot pattern output unit uses the address output from the grayscale level calculation unit. Based on this, the halftone dot pattern storage unit is accessed. The halftone-dot pattern output unit extracts a halftone-dot pattern from the designated address in the halftone-dot pattern storage unit and outputs the halftone-dot pattern as a halftone-dot pattern corresponding to a pixel group in a specific area.

In the gradation image halftone dot processing apparatus of the second invention, the pixel extracting unit superimposes the input gradation image data and the mask pattern data, extracts the gradation data for the area of the mask pattern, and extracts the gradation data. Is output as data of a pixel group in a specific area.

In the gradation image halftone dot processing apparatus of the third aspect of the invention, the halftone dot pattern pasting unit positions the halftone dot pattern output from the halftone dot pattern output unit at a position corresponding to the halftone dot pattern in the halftone dot image. To overwrite. Then, this processing is repeated for each halftone dot pattern to convert a gradation image having a predetermined size into a corresponding halftone dot image.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the principle of a gradation image halftone dot processing apparatus according to the present invention. The apparatus shown in the figure comprises a pixel extraction unit 1, a gradation level calculation unit 2, a halftone dot pattern storage unit 3, a halftone dot pattern output unit 4, and a halftone dot pattern pasting unit 5.

The pixel extracting unit 1 inputs the gradation image data and extracts a pixel group in a specific area from the gradation image, and is composed of a mask pattern 1a and an extracting unit 1b. The mask pattern 1a is mask data stored in a memory to be described later, which is used for validating a designated pixel from each pixel of the gradation image and invalidating the remaining pixels. Further, the extraction unit 1b has a function of extracting a pixel group in a specific area by using the mask pattern 1a. The gradation level calculation unit 2 calculates the address of the halftone dot pattern stored in the halftone dot pattern storage unit 3 corresponding to the gradation level of the pixel group extracted by the pixel extraction unit 1.

The halftone dot pattern storage unit 3 stores the pattern data of the halftone dot group corresponding to the gradation level of the pixel group, and specifically comprises a memory described later.
The halftone dot pattern output unit 4 has a function of extracting the corresponding halftone dot pattern from the halftone dot pattern storage unit 3 based on the address calculated by the gradation level calculation unit 2. The halftone dot pattern pasting unit 5 inputs preset halftone dot image data, and overwrites the halftone dot image data with the halftone dot pattern data output from the halftone dot pattern output unit 4.

FIG. 2 is a block diagram showing a concrete configuration of the above embodiment. The device shown in FIG.
Memory address processing unit 102, memory access control unit 1
03, image buffers 104 to 107, an image data adding unit 108, an image mask / halftone dot pattern attaching unit 109, and buses 110 and 111.

The memory 101 stores the gradation image data which is the original image, the above-mentioned mask pattern 1a, the halftone dot pattern and the created halftone dot image. The memory address processing unit 102 is for instructing the memory access control unit 103 about the addresses of the gradation image, the mask pattern, the halftone dot pattern, and the halftone dot image stored in the memory 101. The memory access control unit 103, based on the address output from the memory address processing unit 102,
If necessary, the memory 101 and each image buffer 104
It has a function to transfer the image data between 107 and 107.

The image buffers 104 to 107 temporarily store individual data, and the memory 101
Data read from the image data adding unit 108
And the data processed by the image mask / dot pattern attaching unit 109 are stored. Image data addition unit 108
Is for calculating the sum of the gradation levels in the gradation image of the specific region extracted by the image mask / dot pattern attaching unit 109.

The image mask / dot pattern attaching unit 109 performs a mask operation for the original image and the mask pattern 1a, and also performs an operation process for overwriting the dot image data with the dot pattern. Also, buses 110, 1
Reference numeral 11 denotes a bus for transferring data between the image buffers 104 to 107, the image data adding unit 108 and the image mask / dot pattern attaching unit 109.

The blocks shown in FIG. 1 and the configuration shown in FIG. 2 mainly correspond to each other as follows. That is, the pixel extracting unit 1 is in the memory 101 and the image mask / dot pattern attaching unit 109, the gradation level calculating unit 2 is in the image data adding unit 108, the dot pattern storing unit 3 is in the memory 101, and the dot pattern output is The section 4 corresponds to the memory access control section 103, and the halftone pattern attaching section 5 corresponds to the image mask / halftone pattern attaching section 109, respectively.

Next, the halftone dot image generation processing in the gradation image halftone dot processing device thus configured will be described. Figure 3
Is a diagram showing the processing procedure thereof, and will be described below along the numbers in the figure. (1) The memory address processing unit 102 calculates the memory address of the original image, and the memory address control unit 103 reads the original image data into the image buffer 104. (2) Similarly, the memory address processing unit 102 calculates the memory address of the mask pattern data, and the memory access control unit 103 reads the mask pattern data into the image buffer 105. If the mask pattern does not change, this data transfer need not be performed again.

(3) The image mask / dot pattern attaching unit 109 performs a mask operation on the original image data in the image buffer 104 with the mask data in the image buffer 105, and writes it in the image buffer 106. (4) The image data addition unit 108 obtains the sum of the gradation levels of the masked original image data in the image buffer 106, and writes the result in the image buffer 104. (5) The memory address processing unit 102 obtains the memory address of the halftone dot pattern from the sum of gradation levels stored in the image buffer 104.

(6) The memory access control unit 103 reads the halftone dot pattern into the image buffer 104. (7) The memory address processing unit 102 calculates the memory address of the halftone image, and the memory access control unit 103 writes the corresponding area of the halftone image in the image buffer 106. (8) Image mask / halftone dot pattern pasting unit 109
Then, the previously read halftone image and halftone pattern are combined and written in the image buffer 107. (9) The memory access control unit 103 writes the combined halftone dot image in the image buffer 107 to the memory 101. Through the above processing, a halftone image corresponding to the gradation image is obtained.

Next, the above processing will be described in detail. Figure 4
It is a figure which shows original image data and mask pattern data.
In the original image data, one pixel is data of 8 bits (256 gradations), and one word (64 bits) contains 8 pixels. The mask pattern is 1-bit data each, and is left-aligned regardless of the data position of the original image.

In FIG. 4, (a1) shows the original image data when the halftone dot angle is 0 °, and (a2) shows the mask pattern when the halftone dot angle is 0 °. In addition, (b
1) is the original image data when the halftone dot angle is 45 °, (b
2) shows a mask pattern when the halftone dot angle is 45 °. Note that these are merely examples, and the sizes and the arrangement of data are not limited to those shown here.
Of the original images shown in (a1) and (b1), only the data surrounded by the thick frame is the pixel required for the halftone dot pattern calculation in this case. Therefore, in the mask patterns (a2) and (b2), the element at the position corresponding to these necessary pixels is "1", and the element at the positions corresponding to other unnecessary pixels is "0".

The positions of the data (a1) and (a2) are displaced, but this is corrected by the shift operation during the image mask calculation. Further, when the width of the masked pixel exceeds 8 pixels, it is corrected when the image mask is calculated.

Next, the mask calculation will be specifically described. FIG. 5 shows an image mask / dot pattern attaching section 109.
It is a figure which shows the mask calculation in. Incidentally, here, description will be made using the original image data and the mask pattern data at 45 ° shown in FIG. Further, the illustrated state shows the calculation processing of the second row of the original image (a) and the mask pattern data (b).

First, one word each of the original image data and the mask data is extracted, and the value of the mask data is used as a control signal of the selector to select the value of each pixel of the original image data or "0". That is, the mask data value is "0"
In the case of, the selector selects "0", and in the case of "1," the value of the original image data is selected. Incidentally, in addition to the method using such a selector, a method of multiplying the pixel data of the original image data and the data of the mask data may be used.

The first pixel is "1", but the output is "0" because the mask data is "0". Since the mask data of the next pixel is also "0", the output is "0". Since the mask data of the third pixel is "1", the value "3" of the original image is output as it is. In the same manner, "6,0,0,0,0" is obtained, and the second row of the masked original image data (c) is obtained. By performing the above processing on each row, masked original image data (c) which is a pixel group of a specific area is obtained.

Next, the gradation level calculation processing in the pixel group of the specific area obtained by the mask calculation will be described. FIG. 6 is a diagram showing, as an example of a gradation level calculation process, a total calculation of gradation levels of a pixel group in a predetermined area in the image data adding unit 108. The original image data stored in the image buffer 104 is 8 words per word.
There are pixels. Therefore, when 1 word is read, 8 at the same time
Eight adders are prepared so that addition can be performed for each pixel.

Each adder first adds the value "0" and the pixel data, and thereafter adds the previous addition result and the newly input pixel data. Therefore, when the masked original image data is read out 6 times, the adder performs addition 6 times to obtain the sum total of each column. For example, in the illustrated case, it is “4, 10, 19, 23, 9, 5, 0, 0”.
Then, these partial addition results are added by the adder to obtain the total sum "70".

Next, calculation of an address for extracting a halftone dot pattern in the memory address processing unit 102 will be described. FIG. 7 is a diagram showing the calculation method. The memory address of the halftone dot pattern is obtained from the sum of the gradation levels of the pixel groups of the specific area obtained previously and the base address.
First, in the original image, each pixel is 8 bits, and 60 pixels are extracted from 16 original image pixels (for example, the pixels shown in FIGS. 4 to 6).
Consider the case of generating a dot pattern of dots.

FIGS. 8 and 9 are diagrams showing a process of synthesizing a halftone dot pattern and a halftone dot image, and these halftone dot data show the case where the halftone dot angle is 45 °. As the halftone dot pattern, a plurality of halftone dot dot patterns as shown in FIG. 8B are held in the memory 101 according to the gradation level. In this case, one dot is 1 bit for one dot. There
One pattern is held in 16 bytes. In addition, this 16
The byte value is the number of bytes that can represent 60 dots and is determined from the viewpoint of data processing.

Returning to FIG. 7, the memory address (byte address) is represented by 32 bits. First, the lower 4 bits are set to "0000". Also, the sum of the original image pixels is the sum of 16 8-bit pixels, so 1
It is represented by 2 bits. Since this is divided into 60 ways, the lower 6 bits of the sum are ignored, and the upper 6 bits are set to bits 4 to 9 of the memory address. Also,
The remaining base address in the memory address indicates the start address of the halftone dot pattern data. Further, when the halftone dot pattern extends over a plurality of words in the memory 101, the address is incremented by one word. By the above operation, the halftone dot pattern corresponding to the gradation level of 16 pixels of the original image can be selected.

Next, a halftone dot pattern attaching process for synthesizing the obtained halftone dot pattern with the halftone dot image will be described. As described above, FIGS. 8 and 9 show a state in which a new halftone dot pattern is pasted on a halftone dot image that has already been processed. In FIG. 8, (a) shows a halftone image that has already been processed, and a section indicated by a thick line is a region corresponding to one halftone dot pattern. Here, the upper left and lower left sections are processed, and the central section is processed this time. (Because the halftone dot image data in the upper left and lower left sections is halftone, 1 is included. However, the upper right and lower right sections are all 0).

Further, as described above, FIG. 8B shows a halftone dot pattern to be newly attached which is indicated by the halftone dot pattern address. That is, the pattern of dots in the thick line section of (b) is pasted to the central thick line section of (a) to obtain the halftone dot image shown in FIG. 9 (c). Therefore, in this pasting processing, the logical sum operation of the data of (a) and the data of (b) is performed.

In the examples of FIGS. 8 and 9, the processing of the third row is shown, and the processing operation of 8 bits from the left of the word will be described below. The left 8 bits of the word extracted from the halftone dot image are "1, 1, 0, 0, 0, 0, 0, 0", and the left 8 bits of the halftone dot pattern are "0, 0, 0, 0, 1, 1,
0,0 ". Here, since the start position of the word of the halftone dot image data and the position of the partition to which the halftone dot pattern is attached this time are shifted by 2 bits, the data taken in from the halftone dot pattern is shifted right by 2 bits by the shifter. 0 is put in the bit which became empty at this time. Then, the obtained two data are logically ORed for each bit to obtain the data shown in FIG.
New halftone dot image data shown in the third line of (c) is obtained.

In the above embodiment, the sum of the gradation levels of the pixel group is used as a method for obtaining the address corresponding to the gradation level of the original image. The sum is not limited, and may be, for example, the sum of nth power of a pixel group, an integral value, or a differential value. Further, various calculations may be performed by multiplying each pixel of the pixel group by a weighting coefficient.

[0044]

As described above, according to the gradation image halftone dot processing apparatus of the first invention, a pixel group of a specific area is taken out from the gradation image and the gradation level of this pixel group is dealt with. In addition to calculating the address, the halftone dot pattern corresponding to the gradation level of the pixel group is stored in advance at a predetermined address, and when converting an arbitrary pixel group into a halftone dot image, Since the halftone dot pattern is extracted from the corresponding address and output, the number of calculations is small,
Moreover, the reproducibility of gradation can be freely selected.

According to the gradation image halftone dot processing apparatus of the second invention, in the first invention, a mask pattern for extracting a pixel group in a specific area is prepared in advance, and the mask pattern is specified based on this mask pattern. Since the area is obtained, no matter what the size or halftone dot angle is, it is only necessary to prepare a mask pattern of that shape, and there is an effect that complicated arithmetic processing is not required.

Further, according to the gradation image halftone dot processing apparatus of the third invention, in the first or second invention, halftone dot image data consisting of a set of each halftone dot is provided in advance, and this halftone dot image data is provided. Since a halftone dot pattern corresponding to a pixel group is obtained by overwriting the halftone dot pattern obtained for the halftone dot image, it is possible to obtain a halftone dot image without performing complicated calculation processing. It is possible to quickly perform the entire processing on the point image.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram in a gradation image halftone dot processing apparatus of the present invention.

FIG. 2 is a block diagram of the overall configuration of a gradation image halftone dot processing apparatus of the present invention.

FIG. 3 is an explanatory diagram of halftone image generation processing in the gradation image halftone processing device of the present invention.

FIG. 4 is a diagram showing original image data and mask pattern data in the gradation image halftone dot processing apparatus of the present invention.

FIG. 5 is an explanatory diagram of mask calculation processing in the gradation image halftone dot processing apparatus of the present invention.

FIG. 6 is an explanatory diagram of gradation level calculation processing in the gradation image halftone dot processing apparatus of the present invention.

FIG. 7 is an explanatory diagram of an address calculation method in the gradation image halftone dot processing apparatus of the present invention.

FIG. 8 is an explanatory view (No. 1) of the combining processing of the halftone dot pattern and the halftone dot image in the gradation image halftone dot processing apparatus of the present invention.

FIG. 9 is an explanatory diagram (No. 2) of the combining process of the halftone dot pattern and the halftone dot image in the gradation image halftone dot processing device of the present invention.

FIG. 10 is an explanatory diagram (part 1) of a conventional method of generating binary halftone dot data.

FIG. 11 is an explanatory view (No. 2) of a conventional method of generating binary halftone dot data.

[Explanation of symbols]

 1 Pixel extraction unit 2 Gradation level calculation unit 3 Halftone dot pattern storage unit 4 Halftone dot pattern output unit 5 Halftone dot pattern pasting unit

Claims (3)

[Claims] 1. A gradation image halftone dot processing apparatus for converting a gradation image into a halftone dot image corresponding to the gradation level, comprising: a pixel extracting section for extracting a pixel group of a specific region from the gradation image. A gradation level calculation unit for calculating an address corresponding to the gradation level of the pixel group; a halftone dot pattern storage unit for storing a pattern of a halftone dot group corresponding to the gradation level of the pixel group; A halftone dot pattern output unit for taking out a pattern of a corresponding halftone dot group from the halftone dot pattern storage unit at the address calculated by the level calculation unit and outputting it as a halftone dot pattern of the pixel group. Tonal image halftone processing device. 2. The pixel extracting unit superimposes the mask pattern having a size corresponding to a specific region on the gradation image, validates the pixels in the region of the mask pattern, and invalidates the remaining pixels. 2. The gradation image halftone dot processing apparatus according to claim 1, further comprising: an extraction unit for extracting a pixel group in a specific area. 3. A halftone dot pattern pasting unit for creating a halftone dot image corresponding to a gradation image by overwriting the halftone dot pattern output from the halftone dot pattern output unit on an unprocessed portion of the halftone dot image. The gradation image halftone dot processing apparatus according to claim 1 or 2, characterized in that.