JPH0918698A - Image processing unit and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in the image quality and to obtain an output image with high quality by revising a density of an input image and giving an original image in the unit of stripe images and forming each block image divided so that part of the image is overlapped. SOLUTION: An image input section 100 gives an image of a binary bit map form in the unit of lines to a stripe/block conversion buffer 101. The image received in the unit of lines is stored in the stripe/block conversion buffer 101 by a preset prescribed line number, in which stripe divide processing of the image is conducted. The number of lines of the input image received by the buffer 101 is counted and the input/output of the image is controlled by the count. The stripe divide processing is controlled by a block divide address control section 102. Then theimage is divided into block images and stored in a block image buffer 103. The block image by a prescribed block size from a right end of the stripe image is stored in this case by a bit width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and an image processing method, and more particularly to an image processing apparatus and an image processing method for changing the density of an input image and outputting it.

[0002]

2. Description of the Related Art Conventionally, as a pixel density conversion of a digital binary image in a facsimile machine or the like, a binary image is not processed as it is in a bit map form, but a black image (the binary image is composed of white or black). Outline smoothing method for extracting high-quality images by extracting the contours of the case) as vector data (hereinafter referred to as contour vector data), and then subjecting the contour vector data to processing such as scaling and smoothing. Is disclosed in Japanese Patent Application No. 3-345062 (hereinafter referred to as outline processing).

The contour vector data is given by the coordinate data of the start point and the end point, and the scaling according to the pixel density conversion is performed by multiplying the coordinate value by a desired magnification. Furthermore, smoothing is performed on the extracted outline contour coordinate vector with respect to the vector of interest to be smoothed,
This is achieved by redefining the contour coordinate vector of interest again by pattern matching using the length and direction of the contour vector in the vicinity thereof as elements. Examples of smoothing processing include processing such as isolated point / notch division and jaggie (jagged pattern) smoothing.

However, although the outline processing is extremely effective for character / line drawing images, a great effect cannot be expected for general images including photographs and natural images as pseudo halftone images. This is because the minute pixels or thin lines that represent the pseudo halftone image are smoothed by the outline processing, so that the density value of the area changes. Therefore, as a method for solving this problem, the pseudo halftone image area and the character / line drawing image area are discriminated and the conventional SPC is used for the pseudo halftone image area.
(Selective Processing Conversoin) There is a method in which a processed image is selected and an outline processed image is selected for a character / line drawing image. Hereinafter, such a method is referred to as pseudo-halftone correspondence outline processing.

Further, in order to reduce the work memory used for the outline processing and to make the outline processing pipelined, the input image is divided into stripe-shaped stripe images composed of line units, and the stripes are further divided. A method has been proposed in which an image is divided into block images into block images and outline processing is performed in block units (hereinafter referred to as block division processing). In the block division processing, the images processed in block units are then combined with each other and output again as a whole image.

By the way, in the stripe division processing in the outline processing, since the smoothing processing is excessively applied to the divided portions of the image, an image which should not be smoothed originally (for example, a straight line which is an image to be processed has a plurality of stripe images). , Etc.), there is a case where the image quality is deteriorated in the divided portion of the stripe image (for example, unevenness occurs where it should be a straight line).

Therefore, in order to prevent deterioration of image quality due to such stripe processing, marginal portions are assumed at the upper and lower ends of the striped images, and a process of deleting the marginal portion is performed when the stripe images are combined. Is effective (hereinafter referred to as margin processing). As a result, excessive smoothing processing is performed in the marginal portion, and the image of the excessively smoothed portion is deleted when the stripe images are combined, and a good image with little image quality deterioration is obtained.

[0008]

[Outline of the Invention]
The smoothing method was able to realize pixel density conversion of a relatively high quality image at any magnification from low magnification to high magnification. Moreover, by adopting a block division processing method in which an image is divided into blocks and processing is performed in units of each block image, it is possible to significantly reduce the work memory used for the processing.

On the other hand, however, there has been a problem that the image quality deterioration due to the excessive smoothing process accompanying the conventional stripe division process also occurs in the block division process.
For example, by dividing one image into block images, an image continuous in the horizontal direction (long-side direction of the stripe image) across the block images becomes a discontinuous image (terminated image in the divided portion of the image). ), And this portion is subjected to extra smoothing processing according to the smoothing algorithm of the outline processing. In other words, even if an image to which the smoothing process is not applied when originally processed without dividing the image becomes a discontinuous image at the divided part by the block dividing process, the smoothing process is performed on the divided part. Will be. As a result, the continuous image in the horizontal direction becomes an uneven image at the divided portion, or the image is deteriorated such as being rounded, which becomes a cause of hindering the smoothing effect of the outline processing.

The present invention has been made in view of the above problems, and it is possible to prevent the image quality from deteriorating when the pixel density conversion processing is performed in block image units, and to generate a pixel density converted image of good image quality. The purpose is to do.

[0011]

In order to solve the above problems, an image processing apparatus according to the present invention is an image processing apparatus which changes the density of an input image and outputs the image, and the original image is a stripe image unit. Input unit, a block dividing unit that divides each input stripe image into block images so as to partially overlap each other, and a pixel that converts the pixel density of each divided block image according to a set scaling factor. A pixel conversion unit for converting the pixel density in block image units, comprising: a density conversion unit; and an image forming unit that forms an output image by cutting and combining overlapping portions of each block image whose pixel density has been converted. This reduces the memory capacity used for processing, overlaps part of the block image to perform pixel density conversion, and then cuts off the overlapped image part to combine the output images. By, it is possible to prevent deterioration of image quality at the joint portion of the block image to obtain an output image of high quality.

Further, the image processing method according to the present invention is an image processing method for changing the density of an input image and outputting the same, which comprises an input step of inputting an original image in stripe image units and each input stripe image. Block division step for dividing the divided block images so as to partially overlap each other, a pixel density conversion step for converting the pixel density of each divided block image according to a set scaling factor, and each block for which the pixel density has been converted An image forming step of forming an output image by synthesizing while cutting off an overlapping portion of the image, by converting the pixel density in block image units, it is possible to reduce the memory capacity used for processing and Pixel density conversion is performed by overlapping a part of the images, and then the overlapping image parts are cut off and the output images are combined,
Prevents deterioration of image quality in the joint part of block images,
A high-quality output image can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a high image quality pixel density conversion apparatus using an outline smoothing method according to an embodiment of the present invention.
The image input unit 100 supplies a binary bitmap image to the stripe / block conversion buffer 101 line by line. Taking an image that is normally used in a G3 standard facsimile machine as an example, when the input image size is 200 dpi standard reading, the A4 image is 1728 × 11.
The size is about 44 pixels, and in the case of 200 dpi fine reading, the A4 image is about 1728 × 2288 pixels. As described above, the input image is supplied line by line to the stripe / block conversion buffer 101,
In the above example, the input image is composed of 1728 pixels (bit) per line.

An image input line by line is stored and held in the stripe / block conversion buffer 101 for a predetermined number of lines set in advance, and the stripe division processing (excluding margin processing) of the image is performed here. Is given.
The stripe division processing of the input image is realized by counting the number of lines of the input image captured in the stripe / block conversion buffer 101 and controlling the input / output of the image by the counted value. The stripe division process is
It is controlled by a block division address control unit 102 described later.

Stripe / block conversion buffer 101
Then, the stripe image stored in the block image is divided into block images under the control of the block division address control means 102 and stored in the block image buffer 103.

FIG. 3 is a schematic diagram of a stripe image and a block image in the stripe / block conversion buffer 101. In the figure, 301 is a block image. The stripe width corresponds to the number of lines in the input image. Further, the block size corresponds to the number of columns forming the block image. Considering good image quality, it is preferable to secure a stripe width of about 8 lines, and it is preferable to set the block size to about 10 pixels in consideration of image quality and the capacity of the work memory. Note that the stripe images are actually divided so as to overlap each other in the vicinity of the division, but here, in order to facilitate understanding of the operation of the entire apparatus, the stripe image will be simply divided.

A line image corresponding to a predetermined stripe width is input, and the stripe / block conversion buffer 101 is input.
After the stripe image is stored in, the block image of a predetermined block size from the right end of the stripe image,
Parallel data is transferred to and stored in the block image buffer 103 with a bit width corresponding to the stripe width. In addition, 1
Reference numeral 15 (FIG. 1) is a parallel image transfer bus, which has a bus width corresponding to the stripe width of a stripe image, and in the case of this example, is composed of an 8-bit bus. The parallel data transfer of the block image is to transfer the image data included in the same column of the stripe image in a parallel data form.

Stripe / block conversion buffer 101
The block division address control unit 102 performs the timing control of the image transfer for each line for each line, the series of timing control when dividing the stripe image into a predetermined block size, and the like. That is, the block division address control unit 102 counts the number of lines of the image when dividing the image into stripes, counts the number of transfer columns of the stripe image when dividing into blocks, and based on the count value, performs the stripe division processing. And timing and address signals for block division processing are generated.

Stripe / block conversion buffer 101
Image data supplied from the block image buffer 1
A block image is formed by sequentially accumulating in 03. The block image accumulated in the block image buffer 103 is subjected to scaling processing in the pixel density conversion unit 120, then output in pixel units from the pixel selection unit 108, and accumulated and held in the block / stripe conversion buffer 109.

FIG. 4 is a diagram schematically showing an image flow in the pixel density conversion device. The images input line by line are sequentially accumulated in the stripe / block conversion buffer 101, and the stripe conversion buffer 101 divides the stripe image into blocks when the input of the image corresponding to the stripe width (for example, 8 lines) is completed. It is output to the pixel density conversion unit 120. Reference numerals 401 to 404 in the figure respectively denote block images. In FIG. 4,
For convenience of explanation, the stripe image is divided into four block images. For example, a stripe image having 1728 pixels in one line has a block size of 10
When a block is divided into pixels, it is divided into 173 block images.

The block division is sequentially transferred in parallel from the right end of the stripe image and supplied to the pixel density conversion unit 120. In FIG. 4, block images 404 and 40 are shown.
3, 402, 401 are transferred in this order, and the block division is completed by transferring 401.

In the example shown in FIG. 4, the block image 4
03 has been subjected to pixel density conversion processing in the pixel density conversion unit 120, and the block image 404 has been subjected to pixel density conversion processing and is stored in the block / stripe conversion buffer 109 in pixel units. At this time, the block images 404 are sequentially accumulated from the right end of the block / stripe conversion buffer 109.

Details of the block division processing will be described below. FIG. 5 shows the stripe / block conversion buffer 1
It is a figure explaining the division process in 01. Applying pseudo-halftone compatible outline processing to block images,
As described above, the image quality is deteriorated due to excessive smoothing processing at the end (divided portion) of the block image.

Therefore, in order to prevent the above-mentioned image quality deterioration, the stripe image is divided so that a part of the block image overlaps in the vicinity of the boundary between one block image and the block images adjacent thereto. This process has the same meaning as the margin process for the stripe image described above, and by cutting off the edge (periphery) of the block image with degraded image quality, the image quality is degraded by block division leaving a good image portion. Is to prevent. Therefore,
In the overlapping division processing of the block image, the image portion to be cut off is overlapped in advance and included in the block image and divided (hereinafter, such division processing is referred to as overlapping division processing). The overlapping division processing of block images will be described below.

The overlapping division processing of the block image is performed from the stripe / block conversion buffer 101 to the pixel density conversion unit 1.
This is achieved by executing parallel data transfer twice for the data of the columns to be overlapped when the image data is transferred in parallel data to 20 and the block division processing is performed.

In FIG. 5, blocks 0 to 3 ...
.. indicates block images obtained by dividing the stripe image, respectively. The hatched portion shows pixels that are divided so as to overlap, and the portion surrounded by a solid line (C
utSize) indicates an effective pixel (other than the margin) of the corresponding block image. Block 0 is beg
Has a block size of in0 to end0, of which 50
Reference numeral 2 indicates a margin image of block 0. This embodiment assumes about 10 pixels (including 502) as a block image. In this case, block 0 can be transferred (divided) by executing the parallel data transfer 10 times.

Next, regarding the block 1, the pixels of the column corresponding to the margin width (the margin image 5 of the block 0)
01 and the overlap image 502 of the block 1 are overlapped with the block 0 and transferred in parallel. As a region (hatched part) that is divided by overlapping,
For example, by setting a column for four pixels, it is possible to suppress image quality deterioration during pixel density conversion. In the image of the margin portion, adjacent block images include the same image.

In the example of FIG. 5, block 1 is beg
Pixels corresponding to the number of columns in1 to end1 are transferred in parallel data. Similarly, block 2 is be
Pixels in columns from gin2 to end2 are transferred in parallel. Similarly, for blocks 3 and onward, the image data of the hatched portion is overlapped and transferred in parallel.

In the following, of the block sizes, the width corresponding to the margin width is the tape size (TapeSize),
In addition, cut size (CutSi
ze) or advance width. The removal of the deteriorated image after the pixel density conversion for the block image subjected to the overlapping division processing will be described later.

Each block image subjected to the overlap division processing as described above is subjected to the above-mentioned pseudo-halftone corresponding outline processing. The block image buffer 103 stores the block image subjected to the overlapping division processing, and the pseudo halftone correspondence outline processing is applied to the block image. That is, the area determination unit 104 determines the area of the block image, and holds the determination result in the area determination result storage buffer 105 in pixel units. The area determination unit 104
It is determined whether the pixels forming the block image are pixels belonging to the pseudo halftone image area or pixels belonging to the character / line drawing image area.

Since the divided block image is subjected to pixel density conversion, the SPC processing unit 106 and the outline processing unit 1
07. The SPC processing is a method of performing pixel density conversion by simply repeatedly drawing or thinning pixels according to the scaling ratio. On the other hand, the outline processing is a method in which the contour portion of the image is extracted as contour vector data and the smoothing / magnifying processing is performed based on this, as described above.

The operation of the outline processing unit 107 will be described below. FIG. 2 is a block diagram showing an example of the internal configuration of the outline processing unit 107. The outline processing unit 107 includes a block image (including a margin image.
Unless otherwise specified, the pixel density conversion is performed in units of the same) and has the following configuration. That is, the outline processing unit 107 converts the outline vector extracting unit 200 that extracts an outline vector from the block image, the outline vector buffer 201 that stores the extracted outline vector data, and the outline vector data held in the outline vector buffer 201 into the outline vector data. On the other hand, the smoothing / scaling unit 202 that performs smoothing / scaling processing, and the contour drawing that performs the contour drawing of the binary image as a previous step of reproducing the binary image based on the smoothed / scaling processed contour vector data. A unit 294, a FIFO (First In First Out) 203 for matching the processing speeds of the smoothing / magnifying unit 202 and the contour drawing unit 204,
The contour drawing unit 204 is provided with a contour drawing buffer 205 for accumulating the binary image generated by the contour drawing unit 204, and a filling unit 206 for filling the inside of the contour image based on the contour drawn image and reproducing a complete binary image.

Next, each block of the outline processing unit 107 will be described in detail.

The contour vector extraction unit 200 extracts the contour line located at the boundary between the black pixel and the white pixel from the input block image as contour vector data. The contour vector data has horizontal and vertical vectors as basic vectors and is extracted in a positional relationship in which black pixels are viewed on the right side of the vector. Data extraction is performed by raster-scanning a matrix window (for example, 3 × 3 matrix window) having a predetermined size and a pixel of interest (3
The contour coordinates located around (the central pixel of the × 3 matrix window) and the connection destination information of the contour coordinates are extracted. When the connection of the extracted contour coordinates extends to an image area of the window that has not been scanned, the connection information of the contour coordinates is temporarily stored in a connection undefined buffer (included in the contour vector extraction unit 200). And is used for the subsequent search for the connection destination of the contour coordinates. Further, when the connection of the extracted contour coordinates crosses the boundary of the block image, the same processing is performed, and the connection information is used when processing the next block image. The contour vector coordinate data extracted as described above is stored in the contour vector buffer 20.
It is accumulated and held at 1.

The contour vector coordinate data has a feature that it always forms a closed loop for an arbitrary image. That is, the contour vector coordinate data output from the contour vector extraction unit 200 always returns to the starting point of the original contour vector data when the connection information is traced. The contour vector coordinate data group extracted from the block image is a set of a plurality of contour vector loops that do not overlap each other.

By the way, the contour vector buffer 201
In the past, since it was necessary to hold all the data extracted from the entire stripe image, and because it was necessary to pipeline the contour vector extraction processing and smoothing / scaling processing, the two-sided buffer format was used. It had to have a very large memory capacity. Specifically, when the data width of the contour vector is 32 bits (including coordinate values and connection information) and the number of typical contour vectors extracted from one stripe image is 4000, the data scale is about 256 kbit. (32 bits × 4k × 2 = 25
6 kbit).

However, in this embodiment, the image to be processed is a block image having a small data scale, and therefore the number of vectors to be extracted is naturally small. For example, when the stripe image is divided into 173 according to the above example, the average number of vectors extracted from the block image is about 24 (4000/173 = 23.1). Therefore, the contour vector buffer 201 is about 1.6k.
It can be set to about 32 bits × 24 × 2 = 1536 bits, and the memory capacity can be reduced to about 0.6% of the conventional memory capacity.

The smoothing / magnifying unit 202 is a processing unit which receives contour vector coordinate data as input and executes smoothing of the contour portion and pixel density conversion.

The smoothing process further includes a first smoothing process and a second smoothing process.
It can be divided into smoothing processing. The first smoothing process is performed by presetting a target vector to be the target of the smoothing process with reference to a plurality of vectors to be connected before and after the target vector, based on the target vector and the length and direction of the reference vector. Matching with the selected pattern and redefining the vector of interest according to the result. Needless to say, the redefinition of the vector pattern and the vector of interest is defined so as to smooth the contour portion of the binary image.

When an image is divided into stripe images or block images, an image that straddles another stripe image or block image is divided at the divided portion of the image. For this reason, excessive smoothing processing may be performed on the divided portions, and image quality may deteriorate. Therefore, the margin width is set so that such image quality deterioration occurs only in the margin image. In addition,
The pixel density conversion process is performed on the contour vector coordinate data that has been subjected to the first smoothing process. The pixel density conversion method is a simple operation of multiplying the coordinate value of the contour vector data by the scaling factor.

The second smoothing process is a process performed on the contour vector coordinate data scaled by the first smoothing process, and is realized by a weighted average calculation of the coordinate values of adjacent contour vectors. It The weighted average calculation is a general mathematical method, and the coordinate data subjected to this processing is redefined so that the coordinate values are regarded as weights and smoothed.

The vector coordinate data smoothed and scaled by the smoothing and scaling unit 202 is processed by a processing speed adjustment FIFO.
It is temporarily stored in 203, and then the contour contour drawing unit 20.
4 is supplied. The smoothed / scaled contour vector data is reproduced as a contour image of a binary bitmap by passing through the contour drawing unit 204. For contour drawing, for example, the inclination of the contour vector to be drawn is obtained in advance from the start point / end point coordinates of the vector, and the pixels in the main scanning direction are sequentially displaced in pixel units based on the inclination, while the displacement position in the sub scanning direction is set. It is possible to realize by performing the processing (dot drawing) on all contour vectors.

The contour drawing data is stored in the contour drawing buffer 20.
Played on 5. Therefore, the contour drawing buffer 205 needs to secure a capacity corresponding to the image size reproduced at one time, that is, the image size after the pixel density conversion of the block image. Conventionally, since a series of processes has been performed in stripe image units, assuming, for example, that the pixel density conversion magnification is 3 times in the main scanning direction, 3 times in the sub scanning direction, and the stripe width is 8 lines (of which the margin width is 4 lines), The contour drawing buffer 205 requires a capacity of 63 kbit (1728 bit × 3 × 4 lines × 3 = 62208 bit). However, if the image is divided into blocks and processed as in the present embodiment, for example, when the block size is 10 pixels,
About 360 bits (10 bits × 3 × 4 lines × 3 = 3
60 bits) is sufficient.

2 reproduced on the contour drawing buffer 205
The value contour image outputs the final outline processed image by filling the inside of the contour with black pixels. The filling processing inside the contour is performed by the filling unit 206.
Specifically, the contour image stored in the contour drawing buffer 205 is raster-scanned in the main scanning direction, and an exclusive OR operation is performed on the pixel values of two adjacent pixels (the pixel to be scanned and the pixel previously scanned). It is possible to fill the inside of the contour image by replacing the pixel to be scanned with the calculation result. Therefore, the filling unit 206 is composed of a latch circuit that holds the pixel value of one of the two adjacent pixels (the pixel value that was previously scanned) and the exclusive OR circuit.

For example, when white pixels (pixel values are 0) are adjacent to each other, the output is a white pixel, and as a result, pixel value replacement is not performed. When a black pixel (pixel value is 1) is scanned next to a white pixel, the output becomes a black pixel, and in this case also, the pixel value is not replaced. On the other hand, when a white pixel is scanned next to a black pixel, the output is a black pixel, so the white pixel is replaced by the black pixel,
Even if the next pixel is a white pixel, a black pixel is output again.
Therefore, when the black pixel is scanned after the white pixel, as long as the pixel scanned after that is the white pixel, the pixel is replaced by the black pixel, and the replacement by the black pixel is performed until the black pixel is scanned again. On the other hand, when there is only one black pixel in one line of the block image, the pixel value after the replacement at the right end of the block image is held until the next block image is processed to match the block images. To take.

Note that this filling algorithm cannot be applied when a part of the contour drawing image is a horizontal line and when it is a one-pixel protrusion (dent), and each requires special processing. The pattern that is the target of special processing detects the contour shape by pattern matching, and applies a special pattern to this. The filling unit 206 also includes these processing mechanisms.

The block image outline-processed as described above is output in the form of a block image as a smoothing process and pixel density conversion process image, and the pixel selecting unit 108
Is supplied to.

Each block image subjected to the pixel density conversion processing by the SPC processing unit 106 and the outline processing unit 107 is supplied to the pixel selection unit 108 in pixel units. The pixel selection unit 108 refers to the result of the area determination performed by the area determination unit 104 in advance, and refers to the SPC processing unit 10
6 or the pixel by the outline processing unit 107 is selected and output. That is, when the area determination result is the pixel belonging to the pseudo halftone area, the pixel output from the SPC processing unit 106 is selected, while the character
If the pixel belongs to the line drawing area, the pixel output from the outline processing unit 107 is selected.

The region determination result is stored in the region determination result storage buffer 105 for the entire block image and is referred to in pixel units. At this time, the output image of the SPC processing unit 106 or the outline processing unit 107 has been subjected to the pixel density conversion, while the determination result stored in the region determination result storage buffer 105 is for the block image before the pixel density conversion. The pixel density of the target pixel that reflects the result is different. Therefore, when the area determination result is applied to the pixel selection unit 108, the pixel density of the determination result is also converted by using the SPC processing unit 112 to match the pixel density of the target pixel. The SPC processing unit 112
The basic configuration of is similar to that of the SPC processing unit 106.

The pixel selection unit 108 selectively outputs the output pixel of either the SPC processing unit 106 or the outline processing unit 107, and the pixels thus selected and output are sequentially accumulated and held in the block / stripe conversion buffer 109. The images processed in block units in this way are sequentially held in the block / stripe conversion buffer 109, the block images are combined, and reproduced again as a stripe image.

The block image combining process is performed in accordance with the process of accumulating the selected pixels in the block / stripe conversion buffer 109, and the control is performed by the block combination address control unit 110. Then, the overlapped image is overlapped with the block image combining process, and the deteriorated image is removed.

FIG. 6 is a diagram for schematically explaining the margin processing after the pixel density conversion. The block image after the pixel density conversion has a size obtained by multiplying the block image before conversion by a desired magnification. That is, the cut width (advance width) after pixel density conversion is CutSize ′, the tape width (overlap width) is TapeSize ′, and the pixel density conversion magnification is mag. Then, it becomes as follows. CutSize ′ = CutSize × mag. (Equation 1) TapeSize ′ = TapeSize × mag. (Equation 2) As shown in the figure, the block image after the scaling is overlapped at both ends of the block as a margin image (hatched portion), and the same pixels as other adjacent block images are displayed. It is held (block images at both ends of the stripe image are only on one side). Therefore, when the overlapping image is cut off in the margin processing, the image cutting may be performed at both ends of the block image after the pixel density conversion. This image excision means excision of the image of the column corresponding to the margin image. The images (block 0 ', block 1', block 2 '...) The margins of which have been cut off are sequentially combined to generate a stripe image.

Specifically, the overlap processing of the block image is performed when the block image is accumulated in the block / stripe conversion buffer 109. That is, the block image (including the margin image) that has undergone the pseudo-halftone-compatible outline processing is output from the pixel selection unit 108 in pixel units. The output pixels are accumulated / held in the block / stripe conversion buffer 109, and the accumulation address is controlled by the block combination address control unit 110.

The control of the storage address is performed, for example, in the period in which the pixel selection unit 108 supplies the pixels corresponding to the marginal image to the block / stripe conversion buffer 109, the storage address is stopped from being changed and the same address is controlled. In a period in which the images are redundantly stored and a valid image (a block image other than the margin image) is supplied, the storage address may be sequentially changed to an appropriate value and stored. Further, the pixel selection unit 108 may be configured to prohibit accumulation of pixels in the block / stripe conversion buffer 109 while the pixels corresponding to the margin image are being output. Except for the block images at both ends of the striped image, the block images have marginal images at both ends. In each case, the marginal images of each block image can be cut off by the same control as above.

Further, the block combination address control unit 110
The storage address is calculated by calculating the cut width (advance width) and the tape width (margin width) from (Equation 1) and (Equation 2), respectively, and further calculating the stripe width after pixel density conversion (before conversion). Multiply the stripe width by the factor).

The block image processed in block image units as described above is reproduced in the block / stripe conversion buffer 109 as a binary stripe image after pixel density conversion without deterioration in image quality. The reproduced stripe image is output according to the specifications of the image output unit 111. The image output unit is, for example, a laser beam printer (LBP) or the like. In this case, it is desirable to output the image in line units. Further, in the case of an ink discharge type printer, since a plurality of lines are printed at once, it is desirable to output a plurality of lines in parallel from the image output from the block / stripe conversion buffer 109.

In the above example, it is necessary to centrally control the memory address and the like as represented by the block division address control unit 102 and the block combination address control unit 110, which is performed by the CPU. And a memory for holding the control program thereof and the like (not shown). Needless to say, it can be configured as hardware.

As described above, even for block images,
As in the case of the stripe processing, it is possible to apply the margin processing, and it is possible to prevent the deterioration of the image quality that occurs during the outline processing even at the connection portion of the block images. As a result, even when a small work memory is used, the pixel density conversion by the outline smoothing method is useful, and a high-quality output image can be obtained.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is implemented by supplying a program to a system or an apparatus. In this case, the storage medium storing the program according to the present invention constitutes the present invention. Then, by reading the program into the system or device from the storage medium, the system or device operates in a predetermined manner.

[0060]

As described above, according to the present invention, it is possible to prevent the image quality from deteriorating when the pixel density conversion is performed in units of blocks, and to generate a pixel density converted image with a good image quality.

[0061]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a high image quality pixel density conversion apparatus using an outline smoothing method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of an internal configuration of an outline processing unit 107.

FIG. 3 is a schematic diagram of a stripe image and a block image in a stripe / block conversion buffer.

FIG. 4 is a diagram schematically showing an image flow in a pixel density conversion device.

FIG. 5 is a diagram illustrating overlap division processing in a stripe / block conversion buffer.

FIG. 6 is a diagram schematically illustrating a margin process after pixel density conversion.

Claims (14)

[Claims] 1. An image processing apparatus for changing the density of an input image and outputting the same, wherein an input means for inputting an original image in stripe image units and a block so that each input stripe image is partially overlapped. Block division means for dividing the image into pixels, pixel density conversion means for converting the pixel density of each divided block image according to the set scaling factor, and combining while cutting out the overlapping portions of the block images with pixel density conversion And an image forming unit that forms an output image. 2. The pixel density conversion means, a contour vector extraction means for extracting a contour vector of each divided block image, a smoothing for smoothing the extracted contour vector of each block image, and a smoothing for scaling with the scaling factor. The image processing apparatus according to claim 1, further comprising: a scaling unit. 3. The pixel density conversion means is a simple scaling means for scaling each divided block image by repeatedly drawing or thinning out the pixels forming the block image according to the scaling ratio. An area determining unit that determines whether or not the pixel belongs to a pseudo-halftone area; and if the pixel belongs to a pseudo-halftone area, an image that is simply scaled by the simple scaling unit is A selection unit that selects an image smoothed and scaled by the smoothing and scaling unit and supplies the image to the image forming unit when the image does not belong to the pseudo halftone region. 2. The image processing device according to 2. 4. The block dividing means includes a stripe image storage means for temporarily storing each input stripe image, and a sequential column unit corresponding to the number of columns of each block image for dividing each stored stripe image. Read to
Read control means for time-divisionally dividing each block image,
At the time of reading, for some columns, a read control unit that controls reading so as to overlap with columns that form an adjacent block image, and an image read from the stripe image storage unit is used to convert the pixel density. 4. The image processing apparatus according to claim 1, further comprising: a block image holding unit that temporarily holds the block image unit. 5. The stripe image synthesizing means for synthesizing each block image of which the pixel density has been converted, sequentially storing the block images of which pixel densities have been converted in a predetermined area while discarding the overlapping portion, and synthesizing the respective stripe images after pixel density conversion. The image processing apparatus according to claim 4, further comprising: 6. The image processing apparatus according to claim 1, further comprising an output unit that outputs the formed output image. 7. The image processing apparatus according to claim 6, wherein the output unit is a printer. 8. An image processing method for changing the density of an input image and outputting the image, wherein an input step of inputting an original image in stripe image units and a block so that each input stripe image is partially overlapped. Block division process to divide into image, pixel density conversion process to convert the pixel density of each divided block image according to the set scaling factor, and combine while cutting the overlapping part of each block image with pixel density conversion And an image forming step of forming an output image, the image processing method comprising: 9. The pixel density converting step includes: a contour vector extracting step of extracting a contour vector of each divided block image; and a smoothing step of smoothing the extracted contour vector of each block image and scaling with the scaling factor. The image processing method according to claim 8, further comprising: a scaling step. 10. The pixel density conversion step is a simple scaling step of scaling each divided block image by repeatedly drawing or thinning out pixels constituting the block image according to the scaling ratio. A region determining step of determining whether or not the pixel belongs to a pseudo halftone region, and if the pixel belongs to a pseudo halftone region, an image that is simply scaled by the simple scaling process is If the image does not belong to the pseudo halftone region, a selecting step of selecting an image smoothed / scaled by the smoothing / scaling step and supplying the selected image to the image forming step is further included. 9. The image processing method described in 9. 11. The block dividing step comprises a stripe image storing step of temporarily storing each input stripe image, and a sequential column unit for each stored stripe image corresponding to the number of columns of each block image to be divided. Read to
A readout control step of time-sharing each block image,
At the time of the reading, a reading control process is performed in which some columns are read so as to be overlapped with columns that form an adjacent block image, and the read image is temporarily stored in block image units for conversion of pixel density. The image processing method according to any one of claims 8 to 10, further comprising: a block image holding step of holding the image selectively. 12. The stripe image synthesizing step of synthesizing the block images of which the pixel densities are converted, sequentially storing the block images of which the pixel densities are converted in a predetermined area while arranging the stripe images after the pixel densities conversion, in the image forming step. The image processing method according to claim 11, further comprising: 13. The method according to claim 8, further comprising an output step of outputting the formed output image.
The image processing method according to any one of 1. 14. The image processing method according to claim 13, wherein the output step outputs the formed output image to a printer.