JP3111734B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer and an LED.
The present invention relates to a technology of reproducing an image based on an image signal by performing line scanning such as an electrophotographic printer such as an LED printer using an array head and a CRT, and particularly smoothing jaggies at edges of characters and the like, Further, the present invention relates to an image processing apparatus for sufficiently reproducing thin lines and isolated dots to improve the image quality of a reproduced image, and correcting the tone characteristics of a pseudo halftone image to ideal characteristics.

[0002]

2. Description of the Related Art There are two conventional methods for improving image quality by smoothing edges of an image reproduced on a printer or a CRT. The first method is to generate image data at a higher resolution, and to increase the resolution of the image reproducing device in accordance with the higher resolution.

However, in this method, the memory capacity for storing the image data when generating the image data is increased and the cost is increased. Further, in order to increase the resolution of the image reproducing apparatus, the required accuracy of the exposure system is increased, and the cost is increased.

A second method is the "PIECE-WISE PRINT IMAGE ENHANCEMENT FOR DOT" invented by Tung et al.
U.S. Pat. No. 4,846,641 entitled "MATRIX PRINTERS" (Peace-wise Print Image Enhancement for Dot Matrix Printers).
It was released on July 11, 989.

Hereinafter, an image processing apparatus using the second method will be described with reference to the drawings.

FIG. 33 is a block diagram of a conventional image processing apparatus for performing edge smoothing. The raster-scanned bitmap image signal 100 is input to the pixel window scanning circuit 101. Pixel window scanning circuit 1
Reference numeral 01 includes a line buffer memory for performing line delay and a shift register for performing pixel delay. The pixel window scanning circuit 101 sets M
It outputs data 102 of × N pixels. The data 102 of M × N pixels is input to the pattern matching and correction image signal generating means 103. The pattern matching and correction image signal generation circuit 103 compares a plurality of predetermined patterns with the input M × N pixel data, and activates the pattern match signal 106 when any of the patterns matches. . When the pattern matching signal 106 is active, the pattern matching and corrected image signal generation circuit 103 outputs the corrected center pixel data 105.

The corrected central pixel data 105 and the uncorrected central pixel data 104 are input to the selector 107. When the pattern match signal 106 is active, the selector 107 outputs the corrected central pixel data 105
Select The output 108 of the selector is used as a modulation signal of the semiconductor laser of the laser printer.

[0008] How the edge is smoothed in the above-mentioned conventional image processing apparatus will be described below.

When the edge smoothing processing is not performed,
The laser modulation signal for the input image data shown in FIG. 34A is as shown by the solid line in FIG. Even when considering that the spot shape of the laser beam is a circle, the reproduced image is as shown in FIG.

When performing the edge smoothing process, A, B, C, D, and D in FIG.
The E and F pixels are detected and the laser modulation signal is corrected. For example, a template pattern as shown in FIG. 35 is compared with data of 9 × 9 pixels whose central pixel is a processing target pixel. In FIG. 35, shaded pixels are don't care pixels for comparison, hatched pixels are exposed pixels, and white pixels are non-exposed pixels. If they match, as shown in FIG. 36, the central pixel data is replaced with data that turns on the laser for one half pixel on the right side from the data for turning off the laser for one pixel. The template pattern of FIG.
When the pixel E in FIG. FIG.
A plurality of types of template patterns are prepared, and when they match the template, the center pixel data is replaced so as to eliminate jaggies. For example, the center pixel data is replaced so as to obtain a laser drive signal as shown by a dotted line in FIG. At this time, the reproduced image is as shown in FIG. 34D, jaggies are reduced, and a high-resolution image can be obtained.

[0011]

However, in the above-described edge smoothing method, when an isolated dot or a thin line having a width of one dot is reproduced, the exposure spot has a broad profile such as a Gaussian distribution. Thin or thin isolated dots cannot be reliably reproduced. Alternatively, it is necessary to increase the exposure energy in order to reproduce a fine line or an isolated dot. Therefore, there is a problem that the reproduced font image becomes thick and the font image is crushed.

Furthermore, since the exposure energy density of an exposure pixel per pixel cannot be increased by the edge smoothing process as compared with the case where the smoothing process is not performed, there is a problem that a sufficient edge smoothing effect cannot be obtained.

Further, when the input image data is a pseudo halftone image, the edge smoothing method has a drawback that a pseudo contour or moire is generated or a gradation characteristic is impaired. As a conventional method for eliminating the disadvantage of the edge smoothing process for the pseudo halftone image, the edge smoothing process is prohibited by manual setting or the effect of the edge smoothing can be reduced. However, with this method, when the font image and the pseudo halftone image are mixed in the input image data, sufficient edge smoothing cannot be performed.

Further, since the pseudo halftone image simulates the halftone by the density of black dots, the image density (or reflectance) reproduced by the printer should have a linear relationship with the black dot density. . However, it is difficult for a normal printer to reproduce a high-quality halftone image because the relationship between black dot density and reproduced image density is non-linear.

[0015]

In order to solve the above-mentioned problems, an image processing apparatus according to the present invention comprises a method for temporarily storing pixels to be processed of input binary image data representing image pixels and non-image pixels and a plurality of peripheral pixels. Temporary storage means for temporarily storing the data, and converting the input pixels into N fine pixels in the main scanning or sub-scanning direction by referring to the pixel data stored in the temporary storage means. Edge smoothing means for smoothing edges of the image data, average density calculating means for calculating an average density using some of pixels to be processed and some peripheral pixels stored in the storage means, and inputting based on the average density A correcting unit that corrects the binary image data and outputs a plurality of fine pixels; and a region of dense image pixels or a region of dense non-image pixels among the pixels stored in the storage unit. And a selector for selecting the output of the edge smoothing means when a dense image area is detected by the determination means, and selecting the output of the correction means when not detecting the dense image area. Further, the edge smoothing means includes means for matching a plurality of predetermined pattern images with the temporarily stored input image pattern and a plurality of predetermined patterns, and a pixel to be processed is an image pixel.
Means for generating N fine pixel data including M (<N) image fine pixels out of N fine pixels when the pattern and the temporarily stored input image do not match;
When at least one of the patterns matches the temporarily stored input image, a means for generating N fine pixel data determined in advance corresponding to the predetermined pattern is provided. Do

[0016]

According to the method described above, the image processing apparatus of the present invention faithfully reproduces an isolated dot or a thin line having a width of one dot, and does not make the reproduced font image thick or crushed.

Further, even when the input image data is a pseudo halftone image, the gradation reproduction characteristics can be improved without generating a pseudo contour or moire. Furthermore, even when the font image and the pseudo halftone image are mixed in the input image data, the edge smoothing process for the font image and the process for improving the tone reproducibility for the pseudo halftone image can be compatible.

[0018]

FIG. 1 is a schematic block diagram of a recording unit of a laser printer for reproducing an image based on an image signal processed by a first embodiment of the image processing apparatus of the present invention. The modulated laser light from the semiconductor laser 31 is collimated by the collimator lens 45. Next, the laser light is reflected by the rotating polygon mirror 46, fθ corrected by the fθ lens 47, and scans the photosensitive drum 48.
The photosensitive drum 48 rotates in the direction of the arrow in the figure. An electrostatic latent image is formed on the photosensitive drum 48. Based on the electrostatic latent image on the photosensitive drum 48, an image is formed on recording paper by a well-known electrophotographic method. Pin photodiode 3
0 is provided near the scanning start position of one line of the laser beam, and detects the line scanning timing of the laser beam.

FIG. 2 is a schematic block diagram of a first embodiment of the image processing apparatus of the present invention. The line-scanned image data 11 is input to the pixel window scanning circuit 12 in synchronization with the rising edge of the pixel clock CLK22. The line enable signal LEN_21 is an active low signal indicating a valid period between one line of image data, and is input to the pixel window scanning circuit 12. The pixel window scanning circuit 12 outputs image data 13 of 7 × 7 pixels whose central pixel is a pixel to be processed. The pixel window scanning circuit will be described later.

The edge smoothing circuit 14 has a 7 × 7
Pixel image data 13 is input. The edge smoothing circuit 14 converts input data of one central pixel into eight pieces of fine pixel data 15 and outputs them in parallel. The edge smoothing circuit 14 determines the edge of the reproduced image based on the center pixel and its surrounding pixel data so that the edge of the reproduced image is smooth, the thin line is not thickened or thinned, or the isolated dot is not erased or collapsed. To generate eight pieces of fine pixel data 15. The details of the edge smoothing circuit 14 will be described later.

The average density calculation circuit 24 receives data of 16 pixels including the pixel to be processed among the outputs of 49 pixels of the pixel window scanning circuit 12. FIG. 37 shows pixels input to the average density calculation circuit. The hatched pixels are the pixels input to the average density calculation circuit. * Pixels are pixels to be processed. The average density calculation circuit 12 calculates and outputs the number of black pixels among the 16 input pixels. The number of black pixels takes a value from 0 to 16, but 16 is rounded down to 15 and the average density signal 25 is output as a 4-bit value.

The correction circuit 26 receives only the pixel data to be processed among the outputs of the average density signal 25 and the 49 pixels of the pixel window scanning circuit 12. The correction circuit 26
The pixel data to be processed is divided into eight fine pixels, and the correction signal 2
7 is output in parallel. The correction circuit 26 determines the number of black fine pixels among the eight fine pixels based on the value of the average density signal 25 and the pixel data to be processed. Correction circuit 2
Details of 6 will be described later.

The output of 49 pixels of the pixel window scanning circuit 12 is input to the determination circuit 28. Discrimination circuit 28
Determines whether there is a dense white or black area in the 7 × 7 pixel window. The determination circuit 28 outputs a high-level determination signal 29 when there is a dense area. Discrimination circuit 2
Details of 8 will be described later.

The selector 41 selects one of the eight pixel data 15 output from the edge smoothing circuit 14 and the eight pixel data 27 output from the correction circuit and outputs the pixel data 42. I do. When the discrimination signal 29 is at the high level, the selector 41 outputs the eight fine pixel data 1 output from the edge smoothing circuit 14.
5 is selected and output.

The parallel-serial conversion circuit 16 converts the eight pieces of fine pixel data 42 input in parallel into a serial data string, and outputs a laser modulation signal 17. The parallel-serial conversion circuit 16 outputs the pixel clock CLK.
The laser modulation signal 17 is output in synchronization with a clock MCLK 23 having a period of 1/8 of 22. The parallel-serial conversion circuit 16 will be described later. Laser modulation signal 1
Reference numeral 7 is connected to a semiconductor laser drive circuit of a laser printer (not shown).

With the configuration shown in FIG. 2, the discrimination circuit discriminates whether a pixel to be processed is included in a pseudo halftone image area or a binary image area such as a font image, and enables edge smoothing processing. And whether to enable the correction process for pseudo-halftones, so that even if the input image data contains both font images and pseudo-halftone images, edge smoothing and pseudo-halftone images Can be performed at the same time.

FIG. 3 is a block diagram of the pixel window scanning circuit 12. Pixel window scanning circuit 1 using FIG.
The operation of No. 2 will be described. The line buffer memory 51 is a buffer memory for inputting and outputting data having a 7-bit width. An inverted line enable signal LEN_ is input to the read reset terminal and the write reset terminal of the line buffer memory 51. The inverted pixel clock CLK is input to the read clock terminal and the write clock terminal of the line buffer memory 51. The line enable L is provided to the read enable terminal and the write enable terminal of the line buffer memory 51.
EN_21 is input.

Image data 11 is input to a data input terminal I0 of the line buffer memory 51, and an image signal delayed by one line is output to a data output terminal O0. The image signal delayed by one line from the data output terminal O0 is input to the data input terminal I1, and an image signal delayed by two lines with respect to the image data 11 is output to the data output terminal O1. Similarly, the data output terminal O
An image signal delayed by 2 lines is output by 3 lines, O3 by 4 lines, O4 by 5 lines, O5 by 6 lines, and O6 by 7 lines. 7-bit wide latches 52-58
Latches the line-delayed image signal output from the line buffer 51 and delays it by one pixel. With the above-described configuration, the pixel window scanning circuit 12 has a 7 ×
The image data 13 consisting of 49 pixels in the 7-pixel window is output.

Before describing the edge smoothing circuit 14, the exposure energy distribution of the laser beam spot will be described. FIG. 4 is a diagram showing an exposure energy distribution of a laser beam. Usually, the laser beam diameter w is designed to be about 1.3 times the resolution of the image data 11. For example, when the resolution of the image data 11 is 300 dpi, the laser beam diameter w is about 110 μm. When the semiconductor laser is driven directly by the image signal 11 when the image data 11 is the data shown in FIG. 5, the image shown in FIG. 6 is reproduced by the laser printer. As can be seen from FIG.
A jaggy at dpi has occurred.

In order to eliminate jaggies determined by the resolution of the image signal 11, the edge smoothing circuit 14 generates fine pixels divided into 1/8 in the main scanning direction and performs edge smoothing. In the edge smoothing circuit 14, the number of exposure pixels (black pixels) that do not need to be corrected is 8 as shown in FIG.
The micro pixel data 15 for exposing the center four micro pixels out of the micro pixels is generated.

(1) Example of Edge Smoothing Process in the Main Scanning Direction FIG. 8 is an enlarged view of a portion A of the image data 11 shown in FIG. The operation of the edge smoothing circuit 14 will be described by taking the image data of the portion B in FIG. 8 as an example.

FIG. 9 shows a template pattern for performing pattern matching with a pixel in a pixel window having a central pixel as a pixel to be processed, and fine pixel data generated when matching with each template pattern. In the template pattern, hatched pixels are exposed pixels, white pixels are unexposed pixels, and shaded pixels are pixels unrelated to matching. In the drawing of the fine pixel data, hatched fine pixels indicate exposure fine pixels. Considering that the laser beam is a circle having a diameter about 1.3 times as large as one pixel, an image exposed and reproduced by the generated fine pixel data is as shown in FIG. 8C, and edges are smoothed.

The feature here is the case of generating a fine pixel as shown in FIG. Exposed pixels that do not require correction generate fine pixel data so as to expose four fine pixels. In the case of FIG. 9E, the exposure time per pixel is longer than the exposure pixel that is not corrected. As described above, since the exposure pixel that is not corrected is converted into four exposure fine pixels,
The degree of freedom for correction is large.

(2) Example of edge smoothing processing in the sub-scanning method FIG. 10 is an enlarged view of a portion D of the image data 11 shown in FIG. The operation of the edge smoothing circuit 14 will be described by taking the image data of the portion E in FIG. 10 as an example.

FIGS. 11 and 12 show template patterns for performing pattern matching with pixels in a pixel window whose central pixel is a pixel to be processed, and fine pixel data generated when matching with each template pattern. . By exposing with the generated fine pixel data, the reproduced image is as shown in F of FIG.
Edges are smoothed.

The characteristic feature here is that FIG.
This is the case of the fine pixel generation of (c) and (f) of FIG. Exposed pixels that do not require correction generate fine pixel data so as to expose four fine pixels. In the case of generating these fine pixels, the exposure time per pixel becomes longer than the exposure pixels that are not corrected. In this way, since the exposure pixel that is not corrected is converted into four exposure fine pixels, the exposure energy per pixel in the case of correction can be made larger or smaller than the pixel that does not correct the exposure energy, and the degree of freedom of correction by generating the fine pixel is large. .

(3) Example of Edge Smoothing Process for Fine Line in Sub-scanning Direction FIG. 13 shows image data of a fine line in the sub-scanning direction having a width of one pixel. The operation of the edge smoothing circuit 14 will be described using the image data of FIG. 13 as an example.

FIG. 14 shows a template pattern for performing pattern matching with a pixel in a pixel window having a central pixel as a pixel to be processed, and fine pixel data generated when matching with each template pattern.
Although not shown in FIG. 14, the fine pixel generation pattern obtained by inverting the template pattern of FIG. 14 up, down, left, and right and inverting the left and right of the fine pixel data is also used for pattern matching.

In the case of matching both the template patterns (b) and (e), the matching with the template pattern (b) has priority. Further, when matching is performed with both the template patterns (c) and (f), the matching with the template pattern (c) is prioritized. Matching with the template pattern (g) has the lowest priority.

By exposing with the fine pixel data generated in this way, the edge can be smoothed and a thin line can be reproduced without blurring or interruption. Exposure pixels that do not need to be corrected generate fine pixel data so that four fine pixels are exposed. On the other hand, in the case of correction by generating these fine pixels, the exposure time per pixel must be corrected. The exposure position is shifted by 25% in order to eliminate jaggies while increasing the exposure pixel by 25%.
For example, according to the processing of the matching patterns (b) and (c), the exposure position is shifted to the right by four fine pixels (corresponding to 1/2 pixel), and five fine pixels are continuously exposed. In the edge smoothing method, the exposure energy per pixel could not be made larger than the exposure pixel whose exposure energy was not corrected. For this reason, the exposure energy must be increased more than necessary so that the thin line is not blurred, so that the font image or the like is crushed or fat.

(4) Example of Edge Smoothing Process of Fine Line in Main Scanning Direction FIG. 15 shows image data of a fine line in the main scanning direction having a width of one pixel. The operation of the edge smoothing circuit 14 will be described using the image data of FIG. 15 as an example.

FIG. 16 shows a template pattern for performing pattern matching with a pixel in a pixel window having a central pixel as a pixel to be processed, and fine pixel data generated when matching with each template pattern.
Although not shown in FIG. 16, a template pattern obtained by inverting the template pattern of FIG.

By exposing with the fine pixel data generated in this way, the edge can be smoothed and a thin line can be reproduced without blurring or interruption. An exposure fine pixel is added in order to eliminate blurring and interruption of fine lines and reduce jaggies. For example, by the processing of the matching pattern (a), the image data that was not exposed in the original image data becomes fine pixel data that exposes two fine pixels, thereby reducing jaggy. FIG.
By the generation of the fine pixels in FIG. 6D, the exposure energy is increased by 25% as compared with the exposure pixels that are not subjected to the correction, and the blur of the fine line is prevented.

(5) Processing of Thin Line in Oblique Direction FIG. 17 shows a template pattern for performing pattern matching with a pixel in a pixel window whose central pixel is a pixel to be processed, and is generated when matching with each template pattern is performed. FIG.

By exposing with the fine pixel data generated in this way, the uncorrected exposure image data is converted into four fine pixel data, whereas it is included in a thin line of one pixel width in the oblique direction. Since a pixel is converted into six consecutive fine pixels, the exposure energy per pixel is increased by 50%. In contrast to the exposure pixels included in the fine line in the main scanning direction or the sub-scanning direction, the pixels included in the diagonal thin line have a long distance between adjacent exposure pixels. Will be blurred.

(6) Processing of Isolated Point FIG. 18 shows a template pattern for performing pattern matching with a pixel in a pixel window whose central pixel is a pixel to be processed, and fine pixels generated when the template pattern is matched. Show data.

The exposure image data which is not corrected is converted into four fine pixel data, whereas the isolated exposure pixel is converted into eight continuous fine pixels, so that the exposure energy per pixel is increased by 100%. Become. Since isolated exposure pixels do not have adjacent exposure pixels, isolated points cannot be reproduced unless the exposure energy is sufficiently increased in this way.

(7) Processing of Inverted Fine Line and Isolated Point FIG. 19 shows an example of inverted fine pixel image data of one pixel width. As shown in FIG. 19, most of the peripheral pixels are exposed pixels, and fine lines formed by non-exposed pixels are formed. Such a thin line is called an inverted thin line. Similarly, a peripheral pixel is an exposed pixel, and an isolated point formed by one isolated non-exposed pixel is called an inverted isolated point.

In the case of an inverted fine line or an isolated point, a reproduced image is blackened due to leakage of exposure energy to a non-exposed pixel position due to peripheral exposed pixels. FIG. 20 shows an example of a template pattern for performing pattern matching with a pixel in a pixel window having a central pixel as a pixel to be processed, and micropixel data generated when matching with the template pattern. In order to prevent the reproduced image from being collapsed, the exposure pixels near the inverted fine line and the exposure pixels adjacent to the inverted isolated point are detected by matching with the template pattern, and the two fine pixels shown in FIG. 20 are generated. Therefore, the exposure energy of the exposed pixel adjacent to the inverted fine line or the inverted isolated point can be reduced by 50%, and the inverted fine line or the inverted isolated point can be reproduced without being crushed.

Actually, matching with the input image data is performed using many template patterns other than those shown in the figure, and eight fine pixels are generated per pixel. The matching process between the template pattern and the input image data and the generation of eight fine pixels can be represented by a truth table having 49 inputs and 8 outputs. The input of the truth table may include don't care. By using the logic synthesis software, the processing of the edge smoothing circuit 14 represented by a truth table can be realized by a combination of AND and OR gates after logical compression.

A first embodiment of the correction circuit 26 in FIG. 2 will be described. When the pixel to be processed is a white pixel (non-exposed pixel), the correction circuit 26 sets all eight output fine pixels 27 as white fine pixels. When the pixel to be processed is a black pixel (exposed pixel), the correction circuit 26 converts a predetermined number of pixels into black fine pixels based on the value of the average density signal 25 and outputs the result. FIG. 38 shows the relationship between the value of the average density signal 25 and the eight fine pixels output by the correction circuit 26. In the output fine pixel diagram of FIG. 38, hatching indicates black fine pixels. Since the average density signal is a 4-bit signal, FIG. 38 shows a truth table having five inputs and eight outputs. FIG. 39 is a block diagram of a first embodiment of the correction circuit 26. A combination logic circuit of the correction circuit 26 shown in FIG. 39 can be designed from the truth table by a logic synthesis method.

When a pseudo halftone image is reproduced in an electrophotographic printer, isolated black dots are difficult to reproduce, so that a low-density image with many isolated black dots is reproduced with lower density. In addition, since an isolated missing image is easily broken, a high-density image having many isolated missing images is reproduced with a higher density. However, the correction circuit increases the number of black fine pixels for black pixels in the low-density image area compared to the medium-density image, and decreases the number of black fine pixels for black pixels in the high-density image area than the medium-density image area. As a result, the black dot density of the image data and the reproduced image density can be corrected in a linear relationship.

Next, a description will be given of a second embodiment of the correction circuit 26 in FIG. FIG. 40 shows the second circuit of the correction circuit 26.
FIG. 4 is a block diagram of an embodiment of FIG. The randomizer 42 outputs a random signal 43 which becomes high level with an average probability of に for each pixel. In addition, the randomizer 42 generates a random signal 4 which becomes high level with an average probability of 1/3 for each pixel.
4 and a random signal 45 which goes high with an average probability of 1/4. Combinational logic circuit 46 of FIG.
Table 1 shows the input / output relationship.

[0054]

[Table 1]

In Table 1, a to h are the same as the output fine pixels a to h in FIG. As can be seen from Table 1, for example, when the pixel to be processed is black and the value of the average density signal is 4, the number of black fine pixels of the output fine pixels is 5, with a probability of 1/2.
It becomes 4 with a probability of 1/2. By giving the transition characteristic to the change in the number of black fine pixels per pixel with respect to the value of the average density signal in this way, it is possible to prevent false contours of a reproduced image on a printer. In Table 1, when the value of the average density 25 is 4, 6, 7, 10, 11, 13, and 14, the number of black fine pixels changes according to the output signal of the randomizer 42, and the characteristics change to fine pixels. Has characteristics.

Next, the determination circuit 28 of FIG. 2 will be described. The output of 49 pixels of the pixel window scanning circuit 12 is input to the determination circuit 28. The determination circuit 28 outputs a high-level determination signal 29 when white and black pixels are mixed in all the 3 × 3 pixel windows included in the 7 × 7 pixel window centered on the pixel to be processed. FIG.
The hatched pixels of 7 are centered on the pixel to be processed.
It is an example of a 3 × 3 pixel window included in a × 7 pixel window. There are a total of 25 3 × 3 pixel windows included in the 7 × 7 pixel window. When at least one 3 × 3 pixel window in which the pixels in the 3 × 3 window are all black pixels or all white pixels is present, the determination signal 29 is at a low level. That is, that the determination signal 29 is at the low level means that the dense area of the white pixels or the black pixels is 7 ×
This indicates that the detection was performed within the 7-pixel window.

In the input image signal subjected to the pseudo halftone processing using the error diffusion method or the like, black pixels or white pixels are diffused. Therefore, when the input pixel subjected to the pseudo halftone processing is the pixel to be processed, the determination signal 29 becomes low level. When the input image signal is a character or a blank character, the determination signal 29 is at a high level because there is always a dense area of black or white pixels around the pixel to be processed. As described above, when the determination signal 29 is at the high level, it indicates that the pixel to be processed is not a pixel included in the pseudo halftone image. When the determination signal 29 is at a low level,
This indicates that the pixel to be processed is a pixel included in the pseudo halftone image. When the pixel to be processed is a character image that is not included in the pseudo halftone image, the selector 41 in FIG. 2 outputs the fine pixel data 15 output from the edge smoothing circuit to the pixel in which the pixel to be processed is included in the pseudo halftone image. In this case, the correction signal 27 is selected.

The parallel-serial converter 1 in FIG.
Operation 6 will be described with reference to the drawings. FIG.
FIG. 3 is a block diagram of a serial converter 16. FIG. 22 is a timing chart of the parallel-serial converter of FIG.
The shift register 61 has an asynchronous 8-bit parallel load input and serial output function. D-flip-flop 6
3 delays and inverts the pixel clock CLK22 by a half cycle of MCLK23. NAND gate 62 is connected to CL
A parallel load signal 6 which is a low pulse signal having a time width of a half cycle of the MCLK 23 from the rising edge to K22.
5 is output. To the 8-bit parallel load input terminals A to H of the shift register 61, eight micro pixel data 42 from the selector 41 are input. The shift register 61 stores the eight fine pixel data 42 synchronized with the pixel clock 22.
Is output as a laser modulation signal 17 in synchronization with the MCLK 23 having a frequency eight times the pixel clock.

FIG. 23 is a schematic configuration diagram of a recording unit of an LED printer that reproduces an image based on an image signal processed by the image processing apparatus according to the second embodiment of the present invention. LE
The light from the D array 231 is
And scans on the photosensitive drum 248. The photoconductor drum 248 rotates in the direction of the arrow in the figure. An electrostatic latent image is formed on the photosensitive drum 248. Photoconductor drum 24
On the basis of the electrostatic latent image on the image 8, an image is formed on a recording sheet by a known electrophotographic method.

FIG. 24 is a schematic block diagram of a second embodiment of the image processing apparatus of the present invention. The line-scanned image data 311 is input to the pixel window scanning circuit 312 in synchronization with the rising edge of the pixel clock CLK322. The line enable signal LEN_321 is an active low signal indicating a valid period between one line of image data, and is input to the pixel window scanning circuit 312. Master line enable signal MLEN_323
Means that the pixel window scanning circuit 312 outputs image data 313
Is an active-low signal indicating a valid period between one line when the signal is output. Line enable signal LEN_3
FIG. 25 shows a timing chart of 21 and the master line enable MLEN_323. As can be seen from FIG.
MLEN_ becomes active eight times during one period of LEN_. One active time is LEN_ and MLE
The same applies to N_.

The pixel window scanning circuit 312 outputs image data 313 of 7 × 7 pixels with the central pixel as a pixel to be processed. The pixel window scanning circuit will be described later.

The circuit block 314 is exactly the same as the circuit block A shown in FIG.

The line selector 316 sequentially switches the eight pieces of fine pixel data 42 input in parallel for each line exposure of the LED, and outputs LED exposure data 317. The LED array performs eight line exposures during one line cycle of the input image data. The line selector 316 will be described later. The LED exposure data 317 is connected to an LED array driving circuit of an LED printer (not shown).

FIG. 26 is a block diagram of the pixel window scanning circuit 312. The operation of the pixel window scanning circuit 312 will be described with reference to FIG. The line buffer memory 351 is a buffer memory that inputs and outputs 7-bit data. An inverted line enable signal LEN_ is input to a write reset terminal of the line buffer memory 351, and an inverted master line enable signal MLEN_ is input to a read reset terminal. A line enable signal LEN_321 is input to a write enable terminal of the line buffer memory 351 and a master line enable signal MLEN_323 is input to a read enable terminal. An inverted pixel clock is input to a read clock terminal and a write clock terminal of the line buffer memory 351.

Image data 311 is input to the data input terminal I0 of the line buffer memory 351 and an image signal delayed by one line is output to the data output terminal O0. The image signal delayed by one line from the data output terminal O0 is input to the data input terminal I1, and an image signal delayed by two lines with respect to the image data 11 is output to the data output terminal O1. Similarly, data output terminal O2 has three lines, O3 has four lines, and O4 has five lines.
An image signal delayed by 6 lines is output to O5, and an image signal delayed by 7 lines is output to O6. 7-bit wide latches 52-5
Reference numeral 8 latches the line-delayed image signal output from the line buffer 351 and delays it by one pixel. The read enable terminal of the line buffer memory 351 receives MLEN when one line of the input image signal 311 is input.
_ Will output the same data eight times. With the configuration shown above, the pixel window scanning circuit 312
Is 49 image data 313 in a 7 × 7 pixel window
Is output.

In the first embodiment, a laser printer is used as a printer for reproducing an image. Therefore, one pixel data is divided into eight fine pixels in the main scanning direction. In the second embodiment, an LED printer is used. Therefore, eight fine pixels divided in the sub-scanning direction are generated from one pixel data. Therefore, the operation of the edge smoothing circuit is different only in that the relationship between the main scanning direction and the sub-scanning direction is reversed. FIG. 27 shows each pixel of the image data 13 of the 7 × 7 pixel window in FIG. By inputting the image data sequence shown in FIG. 27 to the pixel shown in FIG. 28 and changing it to the circuit block A314 in FIG. 24, the circuit block A in FIG. 2 and the circuit block A314 in FIG. I understand that it is good. The operation of the circuit block A314 is the same as that of the first embodiment shown in FIG.

The line selector 316 in FIG. 24 will be described with reference to FIG. FIG. 29 is a block diagram of the line selector 316. FIG. 30 is a timing chart of the line selector shown in FIG. The latch 330 latches eight pieces of fine pixel data 42 at the rise of the pixel clock CLK322. The D flip-flop 332 delays and inverts the master line enable MLEN_323 by one pixel clock. Counter 333
Is a 3-bit binary counter with a synchronous clear input. The line enable LEN_321 is input to the clear input of the counter 333. The counter 333 is
It is cleared by LEN_331 and counts up from 0 to 7 by the output signal of the D-flip-flop.
The selector 331 is an 8to1 selector, and the latch 33
Eight micropixel data output from 0 are input. The selector 331 selects one of the eight inputs and outputs the LED exposure data 317 according to the output value of the counter 333.

As can be seen from the above description, the pixel window scanning circuit 312 has the line enable LEN_32
Until 1 becomes the next active state, the same pixel window data 313 is output for eight line scans of the master line enable MLEN_323. Circuit block A31
4 also has the same fine pixel data 42 for the scanning of MLEN_8 lines.
Is output. In accordance with the master line enable MLEN_323, the line selector 316 receives eight micropixel data 42
Are sequentially selected, and LED exposure data for eight lines is output. That is, based on one line of input image data, 8
Obtain exposure data for the line. Using the exposure data for the eight lines, the LED array divides one line into eight lines for exposure.

Even when an LED printer is used as a printer for image reproduction in place of a laser printer as in the second embodiment, the edge smoothing effect and the reproduction of fine lines and isolated points can be obtained as in the first embodiment. And the gradation of the pseudo halftone image can be improved.

FIG. 31 is a schematic block diagram of a third embodiment of the image processing apparatus according to the present invention. The output mode switching signal MODE424 is a signal for setting the type of a printer for reproducing image data. Mode switching signal 4
24 is set to a high level when a laser printer is used, and set to a low level when an LED printer is used. The line-scanned image data 411 is input to the pixel window scanning circuit 412 in synchronization with the rising edge of the pixel clock CLK422. The line enable signal LEN_421 is an active-low signal indicating a valid period between one line of the image data 411, and is input to the pixel window scanning circuit 412. The master line enable signal MLEN_423 is an active-low signal indicating a valid period between one line when the pixel window scanning circuit 412 outputs the image data 413. When the LED printer is used, the master line enable signal MLEN_423 and the MLEN_ in the second embodiment are used. Is the same. When a laser printer is used as the output printer, MLEN_423 inputs the same signal as line enable LEN_421. The pixel window scanning circuit 412 outputs image data 413 of 7 × 7 pixels whose central pixel is a pixel to be processed. The configuration of the pixel window scanning circuit 413 is the same as that of the pixel window scanning circuit 312 in the second embodiment shown in FIG.

The data arrangement select circuit 425 has 7 ×
Image data 413 of 49 pixels in a 7-pixel window is input. When the mode switching signal MODE 424 is at a high level, the data arrangement selection circuit 425 outputs data in a 7 × 7 pixel data arrangement (FIG. 27) as in the first embodiment. When MODE 424 is at the low level, the data is output in the data arrangement (FIG. 28) as in the second embodiment. The data arrangement select circuit outputs the mode switching signal MODE4
The image data 426 of 7 × 7 pixels is output in a data arrangement determined by H.24.

The circuit block A 414 is exactly the same as the circuit block A in FIG. The circuit block A414 has 7
Image data 426 of × 7 pixels is input. The circuit block A414 converts the input data of one central pixel into eight fine pixel data 42 and outputs them in parallel.

FIG. 32 is a block diagram of the output switching circuit 416. The parallel-serial conversion circuit 501 is the first
Is the same as the parallel-serial conversion circuit 16 in the embodiment of FIG.
2 is converted into a serial data string, and a laser modulation signal 50
3 is output. The line selector 502 is the same as the line selector 316 in the second embodiment, and sequentially switches the eight pieces of fine pixel data 42 input in parallel for each line exposure of the LED array to obtain the LED exposure data 504.
Is output. The selector 505 outputs the mode signal MODE42
When 4 is at a high level, the laser modulation signal 507 is selected.
LED exposure data 504 when ODE 424 is at low level
Is selected, and data 417 is output. The data 417 is connected to a laser drive circuit or an LED array drive circuit (not shown). When using a laser printer,
That is, when MODE 424 is at a high level, the output switching circuit 416 has LEN_421 and MLEN_4
You do not need to enter 23. When an LED printer is used, that is, when the MODE 424 is at a low level, it is not necessary to input the MCLK 427 to the output switching circuit 416.

By setting the mode signal MODE424, the image processing apparatus shown in the third embodiment can use either a laser printer or an LED printer to reproduce an image. This is particularly advantageous when the image processing apparatus of the third embodiment is configured by an LSI.

In the above embodiment, the case where an LED printer is used has been described. However, the same effect can be obtained when a printer using an array-like image writing head such as a liquid crystal shutter array or a thermal head is used.

In the embodiment, a printer is used as an image reproducing device. However, a similar effect can be obtained when a CRT is used.

[0077]

As described above, by using the image processing apparatus of the present invention, isolated dots and thin lines having a width of 1 dot can be faithfully reproduced, and the reproduced font image can be prevented from becoming thick or crushed. The above edge smoothing effect can be obtained. Further, even when the input image data is a pseudo halftone image, the gradation reproduction characteristics can be improved without generating a pseudo contour or moire. Furthermore, even when the font image and the pseudo halftone image are mixed in the input image data, the edge smoothing process for the font image and the process for improving the tone reproducibility for the pseudo halftone image can be compatible.

Further, as a printer for reproducing an image, either a laser beam printer or an LED printer can be used.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a recording unit of a laser beam printer.

FIG. 2 is a schematic block diagram of a first embodiment of the image processing apparatus of the present invention.

FIG. 3 is a block diagram of a pixel window scanning circuit 12 in FIG. 2;

FIG. 4 is an exposure energy distribution diagram of a laser beam.

FIG. 5 is a diagram showing an example of image data 11;

6 is an image obtained by reproducing the image data shown in FIG. 5 by a laser printer as it is.

FIG. 7 is a diagram of fine pixel data generated for an exposure pixel that does not need to be corrected;

8 is an enlarged view of a portion A of the image data of FIG.

FIG. 9 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 10 is an enlarged view of a portion D of the image data of FIG. 5;

FIG. 11 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 12 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 13 is a diagram of image data of a thin line in the sub-scanning direction having a width of one pixel.

FIG. 14 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 15 is a diagram of image data of a fine line in the main scanning direction having a width of one pixel.

16 is an image signal compression / expansion circuit 817 in FIG.
Block diagram of

FIG. 17 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 18 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 19 is a diagram illustrating an example of image data of a reversed thin line having a width of one pixel;

FIG. 20 is a diagram of a template pattern for pattern matching and generated fine pixels.

FIG. 21 is a block diagram of a parallel-serial converter 16;

FIG. 22 is a timing chart of the parallel-serial converter of FIG. 21;

FIG. 23 is a schematic configuration diagram of a recording unit of the LED printer.

FIG. 24 is a schematic block diagram of a second embodiment of the image processing apparatus of the present invention.

FIG. 25 is a timing chart of a line enable signal LEN_321 and a master line enable MLEN_323.

FIG. 26 is a block diagram of a pixel window scanning circuit 312.

FIG. 27 is a diagram in which each pixel of the image data 13 of the 7 × 7 pixel window in FIG. 2 is numbered;

FIG. 28 is a diagram showing an arrangement of pixels input to a block A314 in FIG. 24;

FIG. 29 is a block diagram of a line selector 316.

30 is a timing chart of the line selector shown in FIG. 29;

FIG. 31 is a schematic block diagram of a third embodiment of the image processing apparatus of the present invention.

FIG. 32 is a block diagram of an output switching circuit 416.

FIG. 33 is a block diagram of a conventional image processing apparatus that performs edge smoothing.

FIG. 34 is a diagram of edge smoothing processing.

FIG. 35 is a diagram of a template pattern.

FIG. 36 is a diagram of image data to be replaced;

FIG. 37 is a diagram showing pixels input to the average density calculation circuit 24;

FIG. 38 is a view showing the relationship between the value of the average density signal 25 and eight fine pixels output by the correction circuit 26;

FIG. 39 is a block diagram of a first embodiment of the correction circuit 26;

FIG. 40 is a block diagram of a second embodiment of the correction circuit 26;

FIG. 41 is a diagram showing an example of a 3 × 3 pixel window included in a 7 × 7 pixel window centered on a pixel to be processed;

[Explanation of symbols]

 11 Image Data 13 7 × 7 Pixel Window Data 14 Edge Smoothing Circuit 17 Laser Modulation Signal 24 Average Density Calculation Circuit 26 Correction Circuit 28 Discrimination Circuit 31 Semiconductor Laser 41 Selector 45 Collimator Lens 46 Polygon Mirror 47 fθ Lens 48 Photosensitive Drum 51 Line Buffer 100 image data 107 selector 231 LED array 245 rod lens array

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (16)

(57) [Claims] 1. Temporary storage means for temporarily storing pixels to be processed of input binary image data representing image pixels and non-image pixels and a plurality of peripheral pixels, and refer to pixel data stored in the temporary storage means. Edge smoothing means for converting an input pixel to be processed into N fine pixels in the main scanning or sub-scanning direction to smooth edges of the binary image data, and processing to be stored in the storage means. Average density calculating means for calculating an average density using a pixel and some of the peripheral pixels; correcting means for correcting input binary image data based on the average density to output a plurality of fine pixels; Determining means for determining whether there is a dense image pixel area or a dense non-image pixel area in the pixels stored in the memory; and detecting the dense image area by the determining means. An image processing apparatus comprising: a selector for selecting an output of the edge smoothing means when the detection is performed, and selecting an output of the correction means when the detection is not performed. 2. An edge smoothing means for matching a plurality of predetermined pattern images with the temporarily stored input image pattern and a plurality of predetermined patterns, wherein a pixel to be processed is an image pixel. Means for generating N fine pixel data including M (<N) image fine pixels of the N fine pixels when the pattern and the temporarily stored input image do not match; 2. The apparatus according to claim 1, further comprising: means for generating, when at least one pattern matches the temporarily stored input image, N pieces of fine pixel data determined in advance corresponding to the predetermined pattern. An image processing apparatus according to claim 1. 3. An image processing apparatus according to claim 1, wherein the average density calculating means calculates the number of pixels to be processed and the number of image pixels included in predetermined peripheral pixels. 4. The image processing apparatus according to claim 1, wherein the average density calculating means calculates the number of image pixels in pixels included in a P × Q pixel area including a pixel to be processed. . 5. The correcting means divides an input pixel into N fine pixels and changes the number of image fine pixels among the N fine pixels based on the input image data and the average density value. The image processing apparatus according to claim 1. 6. A correcting means comprising a probability signal generating means for outputting a signal of 1 or 0 at a predetermined probability for each input pixel, dividing the input pixel into N fine pixels, 2. The image processing apparatus according to claim 1, wherein the number of image fine pixels among the N fine pixels is changed based on the average density value and the average density value. 7. When a pixel to be processed is an image pixel and a thin line and an isolated dot pixel are detected by matching with a predetermined pattern, L larger than M
3. The method according to claim 2, wherein the generating unit generates a plurality of fine pixel data.
An image processing apparatus according to claim 1. 8. When a pixel to be processed is detected as an image pixel and adjacent to a thin line formed by non-image pixels and an isolated non-image pixel by pattern matching, the I fine pixels smaller than M are detected. The image processing apparatus according to claim 2, wherein the apparatus generates data. 9. An exposure device for image formation, wherein the exposure device performs a raster scan by deflecting a laser beam output from a semiconductor laser based on a plurality of fine pixels output from the selector. 2. The image processing apparatus according to claim 1, wherein a light emission time corresponding to one pixel of the laser is exposed by dividing the light by N. 10. An exposure device for forming an image, wherein the exposure device uses an array print head in which light emitting elements are arranged in an array, and corresponds to one pixel based on a plurality of fine pixels output by the selector. 3. The image processing apparatus according to claim 2, wherein a line to be exposed is divided into N times and exposed. 11. A first mode in which a plurality of fine pixels output by a selector are serially output, and a second mode in which a plurality of fine pixels output by the selector are sequentially output one by one for each line. The image processing apparatus according to claim 1, wherein: 12. Temporary storage means for temporarily storing pixels to be processed of input binary image data representing image pixels and non-image pixels and a plurality of peripheral pixels, and pixels to be processed stored in said storage means. And average density calculating means for calculating an average density using some of the peripheral pixels, and converting the input binary image data into N fine pixels in the main scanning or sub scanning direction based on the average density. Correction means for determining whether the pixel to be processed is a pixel subjected to pseudo halftone processing, and when the determination means determines that the pixel is a pixel subjected to pseudo halftone processing, the correction is performed. An image processing apparatus wherein an input image signal is corrected by means. 13. The image processing apparatus according to claim 12, wherein the average density calculation means calculates the number of pixels to be processed and the number of image pixels included in predetermined peripheral pixels. 14. The image processing apparatus according to claim 12, wherein the average density calculating means calculates the number of image pixels in pixels included in a P × Q pixel area including a pixel to be processed. . 15. The correction means divides an input pixel into N fine pixels and calculates N based on input image data and the average density value.
13. The image processing apparatus according to claim 12, wherein the number of image fine pixels among the fine pixels is changed. 16. A correction means comprising a probability signal generating means for outputting a signal of 1 or 0 at a predetermined probability for each input pixel, dividing the input pixel into N fine pixels, and 13. The image processing apparatus according to claim 12, wherein the number of image fine pixels among the N fine pixels is changed based on the average density value and the average density value.