JPH10229493A - Image area based resolution conversion processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a highly precise halftone area by deciding whether every pixel belongs to an edge area and then modulating and outputting a pulse after the selection of a resolution conversion processing method, corresponding to the edge pixels or non-edge pixels. SOLUTION: A color signal selected by a selector 105 is inputted to an edge pattern decision means 106. The edge decision result that decides whether the pixel signals belong to an edge part or a non-edge part is outputted together with a pattern number which identifies an edge pattern. Based on the outputted result, a selector 110 selects one of conversion value which are outputted from a character/line drawing smoothing means 108 or a halftone table conversion means 109. Then a selector 111 selects and outputs one of pulse start point control flags, which are outputted from the means 108 or 109. A pulse width modulator 112 converts an image signal into the corresponding pulse width and sends this converted signal to a printer engine 113.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image output apparatus, and more particularly to a laser printer which converts an image density information value into a print dot area and outputs the result.

[0002]

2. Description of the Related Art When an image is printed by a device having an output resolution higher than that of an original image, there is a method of outputting a character / line drawing area with high definition by smoothing processing. For example,
In the graphic processing device disclosed in Japanese Patent Application Laid-Open No. 4-260981, several types of patterns are prepared in advance, and a pixel matching the pattern, that is, an edge portion is found and a smoothing process is performed to realize high image quality of a character / line drawing area. ing.

[0003]

However, in the above-mentioned method, a high quality image can be realized by smoothing processing for a character / line drawing area. However, for a pixel which does not match a pattern, that is, for a non-edge portion, an input is performed. Since the image was printed with the same resolution, a high-definition image could not be obtained.

[0004]

Means for solving the above-mentioned problems are as follows. Judgment means for judging whether each pixel constituting one page of image information belongs to an edge area, and means for performing resolution conversion corresponding to the edge pixel. Means for performing resolution conversion corresponding to non-edge pixels, and means for selecting one of two types of resolution conversion processing according to the determination result of the determination means, and then uniformly outputting pulse width modulation. Can be solved.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a color laser printer system which is an output device of a computer as an example of an image processing apparatus equipped with the present invention. PC101
Denotes a host computer, which outputs color information of one pixel as R (red), G (green), and B (blue) color signals as an image output. The color laser printer 102 is a mechanism for printing image information sent from the PC 101 on recording paper. The image memory 103 is a memory for storing each color signal for one page of image data to be printed. A color converter 104 is a color material C for printing image information represented by R, G, and B on recording paper.
(Cyan), M (magenta), Y (yellow), and K (black) color signals. This can be realized, for example, by forming a conversion table with a semiconductor memory, inputting R, G, B color signals as addresses and outputting C, M, Y, K color signals after color conversion as data. Selector 105
Is a function of sequentially switching and outputting the image information C, M, Y, K in units of one page, and can be realized by a selector of a logic circuit. The edge pattern determination 106 is a function of inputting image information for each pixel and outputting an edge pattern number of a target pixel. The line memories 107a and 107b have a function of delaying the input pixel information by one main scanning line. This can be realized, for example, by a semiconductor memory. The character / line drawing smoothing function 108 performs a resolution conversion process when the pixel of interest is determined to be an edge portion. The halftone table conversion 109 is a function for performing resolution conversion processing when the pixel of interest is determined to be a non-edge portion. The selector 110 has a function of selecting and outputting one of two resolution conversion processes input by the edge pattern number output from the edge pattern determination 106. This can be realized by a selector which is a logic circuit. The selector 111 has a function of selecting and outputting one of two pulse start point control flags input based on the edge pattern number output from the edge pattern determination 106. This can be realized by a selector which is a logic circuit. The pulse width modulation 112 has a function of converting an image signal value for each pixel into a pulse width corresponding to the signal value. A specific embodiment will be described with reference to FIG. The printer engine 113 is means for attaching a dye corresponding to each color signal to recording paper. This can be realized by, for example, a printing mechanism of a laser printer, and the density is expressed by changing the size of the printing dot according to the output pulse width of the pulse width modulation 112 and printing. That is, PW
By changing the amount of the color material attached to the print area of one pixel in accordance with the pulse width of the M output, the density of the color is expressed.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described. The PC 101 transfers, to the image memory 103, image data that is separated into R, G, and B for one page to be printed out by the printer engine 113. Next, R, G, B are sent from the image memory 103 to the color conversion unit 104 pixel by pixel.
An image signal is input and converted into C, M, Y, and K color component signals. The selector 105 selects a signal for one color from C, M, Y, and K for each page. Next, the color signal selected by the selector 105 is input to the edge pattern determination 106, and an edge determination result for determining whether the pixel signal of interest belongs to an edge portion or a non-edge portion and an edge pattern are identified. Output the pattern number. Next, in accordance with the edge determination result, the selector 110 selects one of the conversion values output from the character / line drawing smoothing 108 or the halftone table conversion 109,
The selector 111 selects and outputs one of the pulse start point control flags output from the character / line drawing smoothing 108 or the halftone table conversion 109. The pulse width modulation 112 converts the image signal into a corresponding pulse width and sends the signal to the printer engine 113. The printer engine 113 changes the amount of color material attached to one pixel in accordance with the pulse width output from the pulse width modulation 112 and prints on a recording sheet. The above process is performed for four colors in one page unit, and finally, a print result is output.

FIG. 2 shows edge pattern determination 1 in FIG.
06 shows an example. Comparison 201, 20
Reference numeral 2203 denotes a function of outputting 1 if the input image signal is larger than a certain threshold, 0 if the input image signal is smaller than the threshold, and outputting the input signal as it is otherwise. This can be realized by a comparator which is a logic circuit. The latches 207a to 207i are means for storing a color component signal in units of one pixel.
To 207d to 207f to 207g to i constitute a shift register for three pixels in the main scanning direction. These can be realized by flip-flops that are logic elements. The pattern table 208 is means for judging which edge pattern the pixel of 207e which is the smoothing processing target pixel corresponds to from the value of each latch, and outputting a corresponding number according to the edge pattern. This can be realized, for example, by configuring a conversion table with a semiconductor memory, inputting the value of each latch to an address, and using the corresponding value as output data.

Next, the operation of the edge pattern judgment 106 will be described. In comparisons 201, 202, and 203, the input signal is binarized based on thresholds output from thresholds 204, 205, and 206, and is changed to a value that can be compared with an edge pattern stored in pattern table 208, and then latched. Enter a value for. Latches 207a-d, 207f-
i contains a color component signal of eight pixels adjacent to the pixel of the latch 207e to be smoothed. The pattern table 208 compares the values of the latches of these nine pixels with an edge pattern composed of 3 × 3 pixels prepared in advance, and determines whether the latch 207 is a pixel to be smoothed.
Output the edge pattern number of e.

FIG. 3 shows the pattern table 20 in FIG.
8 shows an example of a pattern 8 and a pixel state after smoothing. In the figure, the numeral next to P indicates the pattern number, the white square indicates 0 after the comparison processing, the black square indicates 1, and the hatching indicates an arbitrary state. P0 is a number when no pattern matches. The upper side of the arrow is an edge pattern composed of a total of nine pixels adjacent to the pixel to be smoothed described in the edge pattern determination 106, and the pixel to be smoothed at the center indicates a state before smoothing. . These edge patterns are compared with the values of the respective latches, and if they match the pattern, the smoothing processing target pixel is changed to a state as shown below the arrow.

FIG. 4A shows an embodiment of the character / line drawing smoothing 108 in FIG. FIG.
In (a), a pulse width table 401 for character / line drawing
Is a function of outputting a value to an even line and an odd line in accordance with a pattern number when doubling the resolution in the sub-scanning direction. This can be realized by inputting the output pattern number and the counter value of the sub-scanning counter 403, and using the converted value as output data. The pulse start point table 402 has a function of outputting a signal specifying whether the table value of the line table grows from the left side or the right side in one pixel.
This can be realized by configuring the conversion table with a semiconductor memory in the same manner as the line table. The sub-scanning counter 403 is a 1-bit counter, and counts up by one at the start of image processing for one main scanning line, and performs a counting operation in a two-line cycle from 0 to 1. The count value identifies whether the line is an even line or an odd line. This can be realized by a flip-flop which is a logic element.

Next, the operation of the character / line drawing smoothing 108 will be described. Character / line drawing pulse width table 40
To 1 is input the pattern number output from the edge pattern determination 106 and the counter value output from the sub-scanning counter 403. When the counter value is 0, the pulse width table for even lines is used. When the counter value is 1, Selects and outputs a pulse width table for odd lines. The pulse start point table 402 receives the pattern number output from the edge pattern determination 106 and the counter value from the sub-scanning counter 403. If the counter value is 0, the pulse start point table for even lines is used. If the counter value is 1, Selects and outputs a pulse start point table for odd lines.

FIG. 4B shows an embodiment of the character / line drawing pulse width table 401 in FIG. 4A. In the figure, a sub-scanning counter value of 0 indicates an even line, and a sub scanning counter value of 1 indicates an odd line. FIG.
FIG. 4C shows the pulse starting point table 402 in FIG.
1 shows an embodiment of the present invention. In the figure, a sub-scanning counter value of 0 indicates an even line, and a sub scanning counter value of 1 indicates an odd line.

FIG. 5A shows an embodiment of the halftone table conversion 109 in FIG. FIG. 5 (a)
, The halftone pulse width table 501 has a function of outputting a value to an even line and an odd line in accordance with the signal value of an input image signal when doubling the resolution in the sub-scanning direction.
This can be realized, for example, by forming a conversion table with a semiconductor memory, inputting the image signal value and the counter value of the sub-scanning counter 502 into an address, and using the converted value as output data. The sub-scanning counter 502 is the same as that in FIG. The constant pulse start point 503 is a function of fixing the pulse start point control flag to 0, and can be realized by storing a value in a register formed of a logic circuit.

Next, the operation of the halftone table conversion 109 will be described. The image signal and the counter value output from the sub-scanning counter 502 are input to the halftone pulse width table 501. If the counter value is 0, the pulse width table for even lines is used. Select the pulse width table for output. The constant pulse start point 503 outputs a fixed pulse value of 0 so that the output pulse always grows from the left side in one pixel.

FIG. 5B shows one embodiment of the halftone pulse width table in FIG. 5A. In the figure, when the sub-scanning counter value is 0, the even-numbered line is 1
Indicates an odd line.

FIG. 6 shows an embodiment of the pulse width modulation 112. The D / A 601 has a function of converting an input 4-bit digital signal into an analog signal and outputting the analog signal. This can be realized by a general D / A converter. The sawtooth wave generation A 602 has a function of generating a voltage so that the voltage linearly rises in proportion to the elapse of time when the pixel clock is 1 and resets to the ground level when the pixel clock is 0. . This can be achieved by a combination of capacitors, resistors and operational amplifiers. The sawtooth wave generation B 603 has a function of generating a voltage such that the voltage linearly decreases in proportion to the elapse of time when the pixel clock is 1 and is set to a high level while the pixel clock is 0. . This can be achieved by a combination of capacitors, resistors and operational amplifiers.
The selector 604 has a function of selecting and outputting one of two sawtooth wave outputs input by a pulse start point control flag. This can be realized by a selector which is a logic circuit. The comparison 605 outputs 1 when the upper input voltage is higher than the lower input voltage, and outputs 0 otherwise. This can be achieved with an operational amplifier.

Next, the operation of the pulse width modulation 112 will be described. FIGS. 7A and 7B show operation waveforms of the pulse width modulation 111. FIG. First, a 4-bit digital signal is converted into an analog signal by the D / A 601,
Enter Next, one of the two sawtooth waves is selected by the selector 605 according to the value of the pulse start point control flag,
Enter 05. The comparator 605 compares these two inputs, and outputs 1 when the output of the D / A 601 is larger than the sawtooth voltage output from the selector 604. as a result,
An output whose pulse width changes in proportion to the input image signal is obtained.

[0018]

According to the present invention, not only the image quality of the character / line drawing area of the image but also the definition of the halftone area can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system configuration example in which the present invention is mounted.

FIG. 2 is a block diagram of an embodiment of edge pattern determination.

FIG. 3 is an explanatory diagram of an embodiment of a pattern table.

FIG. 4 is an explanatory diagram of an embodiment of character / line drawing smoothing.

FIG. 5 is an explanatory diagram of an embodiment of halftone table conversion.

FIG. 6 is a block diagram of an embodiment of pulse width modulation.

FIG. 7 is an explanatory diagram of an example of an operation waveform of pulse width modulation.

[Explanation of symbols]

101: personal computer, 102: color laser printer, 103: image memory, 104: color conversion, 1
05: selection, 106: edge pattern determination, 107a,
b: line memory, 108: line drawing / character smoothing,
109: halftone table conversion; 110, 111: selector; 112: pulse width modulation; 113: printer engine.

Claims (1)

[Claims] An output device capable of outputting at a resolution higher than that of an original image and capable of expressing shading by changing the size of a print dot formed in one pixel. Edge pattern determination means for performing pattern matching with a previously prepared pattern table by binarizing the grayscale signal of a certain threshold value and extracting edge pattern determination candidates, first processing means for performing smoothing processing,
A second processing unit that divides one pixel in the sub-scanning direction into a plurality of sub-scanning directions and outputs different values from the divided pixels according to an input signal value; And a selecting unit for selecting any one of the image processing of the second unit and the image processing unit.