JP2002262089A - Device and method for processing halftone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To process a halftone at high speed by reducing an arithmetic amount. SOLUTION: An inputted image is made into a block by n×n pixel (e.g. 2×2 pixel) and the gradation value of each pixel constituting the block is added. Binarization is performed in the block by adapting a dither matrix, etc., for example, concerning the block where gradation is added. Then a difference between the binarized output gradation value and the inputted gradation adding value is obtained and diffused by a prescribed ratio to another block which exists in the circumference of the block. A dither processing is performed in the block and also the error is diffused by block unit so that the arithmetic amount is reduced to process the halftone at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone processing apparatus and a halftone processing method suitable for performing halftone processing on a multi-tone input image.

[0002]

2. Description of the Related Art For example, in an image output device such as a printer, an image is expressed by two gradations in order to express an image by the presence or absence of a dot. Therefore, in a device such as a printer, each pixel is represented by a plurality of dots, and by changing an on / off pattern of the dots in accordance with a gradation value,
A pseudo continuous tone is realized.

[0003] This halftone expression technique uses halftone (ha
lftone), and as a halftone method, for example, a dither method (dither) or an error diffusion method is known.
In the dither method, the gradation of an input pixel is converted to a density of dots by using a dither matrix or the like.
In the error diffusion method, an error between an input tone of each pixel and a tone value of a halftone cell to be output is calculated, and a difference between an input value and an output value is calculated so that a cumulative error becomes zero. Disperse in. Therefore, the error diffusion method performs more advanced processing than the simple dither method, and the halftone processing accuracy is improved accordingly.

[0004]

As described above, according to the error diffusion method, the density pattern of dots to be allocated to each pixel is determined so that the accumulated error becomes zero. Load increases. In particular, in the case of a color image, it is necessary to perform an operation for each color component of each pixel, so that the CPU burden is large.

[0005] Therefore, aside from the case where a CPU having a high computing capacity and a large amount of memory can be used as in a personal computer or a workstation, for example, an embedded CPU incorporated in a device such as a printer, a digital camera or a scanner. In general, since the calculation capability is low, if the halftone process is performed by the error diffusion method, other processes cannot be performed, and the efficiency of the entire printing process is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a halftone processing apparatus and a halftone processing method capable of performing a halftone processing at high speed.

[0007]

In order to achieve the above-mentioned object, in the present invention, halftone processing is performed using a plurality of halftone algorithms with different processing units.

That is, the halftone processing apparatus of the present invention comprises:
Blocking means for blocking an input image in units of a predetermined plurality of pixels, error diffusion processing means for performing error diffusion in block units, and dither processing means for dithering each error-diffused block in each block. Have.

The blocking means handles the input image in units of a predetermined plurality of pixels. For example, the blocking unit divides the data into blocks with a block size of n × n pixels, and adds and outputs the values of the pixels in the block. Alternatively, the blocking unit may average and output the value of each pixel in the block. The error diffusion processing means performs an error diffusion process on a block basis. That is, the error diffusion processing means distributes an error between an input value (addition value or average value) and an output value of a certain block at a predetermined ratio to other blocks located around the block. The dither processing means performs dither processing in each block by using, for example, a predetermined dither matrix. By performing the error diffusion processing in each block while performing the error diffusion processing in each block, the arithmetic operation required for the error diffusion can be reduced and the halftone processing can be performed at a high speed, although it differs depending on the block size.

Here, the block size can be set so as to be smaller than an edge existing in the input image. In the present invention, since the error diffusion processing is performed in units of blocks composed of a plurality of pixels, if there is an edge narrower than the block size (strong edge), the sharpness of the edges may be lost due to error diffusion in block units. It is.

Therefore, in a preferred embodiment, there is further provided a block size setting means for setting a block size according to the properties of the input image. The characteristics of the input image include, for example, an image of a landscape with few sharp edges, an image mainly composed of text or graphics with many edges, and a resolution of the input image (a low-resolution image or a high-resolution image). ?) And the like.

Further, the block size setting means can set the block size according to the quality of the output image. For example, if the user emphasizes output quality over processing time, set a smaller block size,
When the output quality is not so important, such as in trial printing or thumbnail printing, the block size can be set large.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a printer according to an embodiment of the present invention; FIG.

1. First Embodiment FIGS. 1 to 4 are block diagrams showing a configuration of a printer to which a halftone processing device according to a first embodiment of the present invention is applied.

As will be described later, the printer 1
It comprises a memory card 2, a decoding unit 3, an RGB conversion unit 4, an enlargement / reduction processing unit 5, a CMYK color conversion unit 6, a halftone processing unit 7, and a print engine 8.

For example, a memory card which can be expressed as "original image holding means" is provided in the printer 1 in a detachable manner, and internally stores image data (original image data) photographed by a digital camera or the like. . The memory card 2 includes, for example, JPEG (Joint Photographic Experts Group
A plurality of image data can be stored in a compressed file format such as p) or Exif (Exchangeable Image File Format).

The image data read from the memory card 2 is decoded by the decoding unit 3 and is converted by the RGB conversion unit 4 into image data of the RGB color system. For example, the enlargement / reduction processing unit 5 performs RGB
This is for enlarging or reducing the converted image data to a predetermined magnification. It should be noted that other processing such as rotation may be performed in addition to the enlargement / reduction processing.

The CMYK color conversion unit 6 converts RGB color system image data subjected to designated enlargement processing and the like into CMY color system image data. And CMY
The K-color converted image data is subjected to halftone processing by a halftone processing unit 7 and input to a print engine 8.

The halftone processing section 7 includes a block processing section 11, a dither processing section 12, and an error diffusion processing section 13.

A block processing section 11 as a "blocking means" divides the input multi-grayscale CMYK color image data into blocks of nxn pixels and adds the gradation values of the pixels in the block. And output it.

As will be described later with reference to FIGS. 2 and 3, the dither processing section 12 as "dither processing means"
Dithering is performed for each block by using a dither matrix or the like. The error diffusion processing unit 13 as the “error diffusion means” distributes the error of the dithered block to other blocks existing around the block at a predetermined ratio, so that the accumulated error in the block unit is reduced. The processing is performed so as to be zero.

Next, the halftone processing according to the present embodiment will be described with reference to FIGS.

As shown in FIG. 2A, it is assumed that the image data input to the halftone processing section 7 is composed of pixels a1 to a36 each having a multi-tone value.
The blocking processing unit 11 includes n × n pixels (in the example shown in FIG.
= 2), and a plurality of pixels are divided into blocks. In addition,
Here, the term “blocking” means that the halftone processing is performed in block units. FIG. 2 (b)
As shown in (1), the values of the blocks AS1 to AS9 are obtained by adding the gradation values of the pixels constituting each of the blocks.

As shown in FIG. 3A, each block AS
By applying a dither matrix in which values of Th1 to Th4 are set for each of 1 to AS9, dithering is performed for each block. As a result, the multi-tone image is binarized and pseudo-graded. An error generated when dithering a block is distributed to surrounding blocks so that the accumulated error becomes zero.

FIG. 3B is an example of a process in which numerical values are specifically entered. Here, each pixel of the original image is 0
It is assumed that there are 16 tones of up to 15. As shown on the left side of FIG. 3B, when the value of each pixel constituting a certain image block is 4, 5, 3, and 5, the value obtained by adding these is “17”.

Next, for the added block,
Apply a dither matrix. Here, since four pixels of 16 gradations are added, the gradation value of the block has 64 gradations. Therefore, the value of the dither matrix exists in the range of 0 to 63. As shown on the right side of FIG. 3B, as a result of applying the dither matrix, “1” is set only at a position where a value smaller than the added value “17” is set (a position of the matrix value “12”). , And “0” are set in other portions. This gives 4
One block formed by adding pixels is binarized. Note that the gradation values of the pixels in the block may be averaged. In that case, the value of the dither matrix is limited to the range of 0 to 15.

Here, focusing on the result of the dithering, only one of the four regions is "1", and the others are all "0". If we consider the whole block,
When "1" is set in all four regions, there are 64 gradations. Therefore, when "1" is set in one region, this block is output as binary data with 15 gradations. Can be considered. Since the total gradation value of the entire block is “17”, the difference from the output gradation value “15” is “2”. By distributing the binarization error “2” to the peripheral blocks at a predetermined ratio, the error may be diffused so that the accumulated error becomes zero as a whole.

Then, similarly, for the next block, the gradation values of the four pixels are again summed and dithered.
The error between the input value and the output value is distributed to peripheral blocks.
When this processing is performed over the entire input image, binarized image data for printing is generated. In the above description, the total value of the four pixels is "17", but more precisely, an error distributed from a block dithered earlier than that is added. Here, it should be noted that dithering is performed within a block of four pixels, and error diffusion is performed on a block basis.

Next, the operation of the present embodiment will be described with reference to FIG. Hereinafter, steps are abbreviated as “S”.

First, 1 is calculated from the CMYK color-converted original image.
The pixel data of the block is read (S1), and the gradation value of each pixel is added (S2). Next, this block is dithered by applying a dither matrix or the like (S
3) The output binarized data is held (S
4). Then, an error between the input value (total gradation value of each pixel constituting the block) and the output value (the binarization result of the block) is calculated (S5), and this error is diffused to peripheral blocks at a predetermined ratio. (S6).

It is determined whether the halftone process has been completed for all blocks (S7). If the process has not been completed, the pointer is moved to the next block (S8).
The processes of S1 to S6 described above are repeated. When the entire original image has been binarized, the halftone process ends.

In the present embodiment configured as described above,
Since the halftone processing is performed using a plurality of halftone processing algorithms having different processing units, the following effects are obtained.

First, since dithering is performed in a block of n.times.n pixels and error diffusion is performed in block units, processing is performed by a factor of about n times as large as in the conventional method in which error diffusion is performed in pixel units. Speed can be increased. Therefore, for example, the load on the CPU incorporated in a device such as a printer can be reduced, and the CPU resources can be allocated to other processes by the reduced load.

Second, by setting the block size n to a relatively small value of about 2 to 4, halftone processing can be performed at high speed without causing a significant deterioration in image quality. In particular, for example, when halftoning a relatively low-resolution natural image of about 1 million pixels,
High-speed processing can be performed without deteriorating the quality of an image printed and output. Since there are not so strong edges in the natural image and the resolution is low, there is little possibility that there is an edge with a sharp steepness. In the case of a natural image, unlike text and graphics, the image changes smoothly, so that a resolution of about 200 to 300 dpi is sufficient for practical use. On the other hand, print engine 8
Typically have a print resolution of about 600 dpi. Therefore, even when the halftone processing is performed collectively in a block of 2 × 2 pixels, 30 minutes are required at the input stage of the halftone processing.
A pixel density of 0 dpi or more can be maintained, and there is almost no problem in print quality.

2. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the following embodiments, the same reference numerals are given to the same components as those described above, and description thereof will be omitted. This embodiment is an example of a case where halftone is performed by random dither. In the present embodiment, for convenience of explanation, In00 and In each having 16 gradations are used.
A case where a block including four pixels 01, In10, and In11 is subjected to halftone processing will be described as an example. The output pixels are Out00, Out01, Out10, and Out11.

First, the gradation value of each pixel in the block is added (S11). Next, a random number Rand is obtained (S12),
For example, the value of the obtained random number Rand and the binary number "15"
And the value of the random number Rand is 0 to 15
(S13).

Next, the gradation addition value SUM and the random number R in the block
and is compared (S14). The gradation sum SUM is a random number Rand
In the above case, “1” is set as the value of the output pixel Out00, and an error between the gradation added value SUM and the output value “15” is calculated (S15). On the other hand, the gradation addition value SUM is a random number R
If it is smaller than and, "0" is set as the value of the output pixel Out00 (S16).

Thereafter, similarly, the values of the output pixels Out01 to Out11 are determined (S17 to S31). Finally,
An error generated in each of the output pixels Out00 to Out11 is integrated, and the error is diffused to other blocks located in the vicinity at a predetermined ratio (S32).

In this embodiment configured as described above,
The same effects as in the first embodiment can be obtained.

3. Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. A feature of the present embodiment is that a block size setting unit 21 that sets a block size according to characteristics of an original image, quality of an output image, and the like is provided.

That is, the characteristics of the original image, the quality of the output image, and the like are input to the block size setting unit 21 as “block size setting means”. Here, the characteristics of the original image include, for example, the type of the original image (whether natural image or text or graphic image), the resolution of the original image, and the like. The print quality and print mode include, for example, whether or not test printing is performed, whether or not thumbnail printing is performed, an image enlargement ratio, a specified print resolution, and the like.

As shown in the flowchart of FIG. 7, the block size setting section 21 acquires a print mode, print quality, and the like (S41), and sets an optimal block size (S42).

More specifically, for example, when an image mainly composed of text or graphics is input, the block size n is set small (including n = 1). When a natural image is input, the block size n is set. n can be set larger. Further, for example, in a print mode in which the print quality is not so important, such as test print print and thumbnail list print, the block size n can be set larger. Note that the block size n may be manually set by the user.

In this embodiment configured as described above,
The same effects as in the above embodiments can be obtained. In addition, since the block size can be set according to the characteristics of the original image and the quality of the output image, usability is further improved.

It should be noted that those skilled in the art can make various additions, modifications, combinations, and the like within the scope of the present invention described in the above embodiments.

[0046]

As described above, according to the halftone processing apparatus and the halftone processing method according to the present invention, the amount of calculation can be reduced and the halftone processing can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a block diagram of a printer to which a halftone processing device according to a first embodiment of the present invention is applied.

FIGS. 2A and 2B are explanatory diagrams showing how an original image is divided into blocks. FIG. 2A shows an original image, and FIG. 2B shows a state where the original image is divided into n × n pixels.

FIG. 3 is an explanatory diagram showing a halftone processing method,
FIG. 3A is a diagram illustrating a state where binarization is performed by applying a dither matrix to a block, and FIG. 3B is an explanatory diagram illustrating a general outline of halftone processing by inserting specific numerical values.

FIG. 4 is a flowchart illustrating an outline of a halftone processing method.

FIG. 5 is a flowchart schematically showing a main part of a halftone processing method according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a printer to which a halftone processing device according to a third embodiment of the present invention is applied.

FIG. 7 is a flowchart illustrating an outline of a halftone processing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printer 2 Memory card 3 Decoding part 4 RGB conversion part 5 Enlargement / reduction processing part 6 CMYK color conversion part 7 Halftone processing part 8 Print engine 11 Block processing part 12 Dither processing part 13 Error diffusion processing part 21 Block size setting part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA24 AA26 AA27 AB19 BB01 BB06 BB08 BB18 GA23 5B057 AA11 CA01 CA02 CA08 CA12 CA16 CB01 CB02 CB07 CB12 CB16 CC01 CE13 CE14 CH07 CH08 5C077 LL19 MP01 PP08 NN02 PP01 PQ23 RR21 SS02 TT02

Claims (8)

[Claims] 1. Blocking means for blocking an input image in units of a plurality of predetermined pixels, error diffusion processing means for performing error diffusion in units of blocks, and dithering each of the blocks subjected to error diffusion in each of the blocks. And a dither processing means for processing. 2. The method according to claim 1, wherein the blocking unit converts the input image into n ×
2. The halftone processing apparatus according to claim 1, wherein the halftone processing unit divides into blocks with a block size of n pixels, and adds and outputs the values of the pixels in each block. 3. The method according to claim 1, wherein the blocking unit converts the input image into n ×
2. The halftone processing apparatus according to claim 1, wherein the halftone processing unit divides the data into blocks each having a block size of n pixels, and averages and outputs the values of the pixels. 4. The halftone processing device according to claim 2, wherein the block size is set to be smaller than an edge existing in the input image. 5. The halftone processing apparatus according to claim 2, further comprising a block size setting means for setting the block size according to the properties of an input image. 6. The halftone processing apparatus according to claim 2, further comprising a block size setting unit that sets the block size according to a designated quality of an output image. 7. The method according to claim 1, further comprising: a step of error-diffusing the input image in units of blocks each including a plurality of pixels; and a step of dithering each of the error-diffused blocks in each of the blocks. Halftone processing method. 8. A printer that performs printing based on input image data, a color conversion unit that converts the input image data into CMY colorimetric data, and a halftone process on the color-converted image data. And a printing unit for performing printing based on the generated printing image data, wherein the halftone processing unit converts the input image data into Blocking means for blocking in units of a predetermined plurality of pixels, error diffusion processing means for performing error diffusion in the block units, and dither processing means for dithering each of the error-diffused blocks in each of the blocks. A printer, comprising: