JP4158128B2 - Image processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus such as a laser beam printer, and more particularly to a technique for improving image quality.
[0002]
[Prior art]
A conventional apparatus refers to a pixel of interest and its surrounding area as described in, for example, Japanese Patent Laid-Open No. 2-112966 and compares it with a pattern written in advance in a ROM. When the pattern matches, the light beam modulation signal is output to correct the size and position of the target pixel to be printed, and smoothing is performed.
[0003]
[Problems to be solved by the invention]
However, the above prior art does not take into consideration the fluctuation of the light beam spot diameter due to the main scanning image surface curvature or the like in the optical system of the laser beam printer, and the beam on the main scanning on the photosensitive member of the pixel to be printed. There is a problem that the effect of smoothing changes depending on the spot irradiation position.
[0004]
The above problem will be described below with reference to the drawings.
[0005]
2 is a diagram showing an optical system of a laser beam printer. In FIG. 2, 21 is a light emitting element such as a semiconductor laser, 29 is a collimating lens, 22 is a rotary polygon mirror for deflecting light, and 23 is equiangular scanning. Fθ lens 24 for correcting the light from the rotated polygonal mirror 22 to constant speed scanning on the photosensitive member 25, a beam detection sensor for detecting a light beam and outputting a beam detect signal 26 indicating the start of the line , 25 is a photoconductor, 27 is a cross-sectional shape of a light beam converged on the photoconductor 25 at a point x1, 28 is a cross-sectional shape of a light beam converged on the photoconductor 25 at a point x2, 210 is a scanning line, and 211 is Fθ. A focal locus 212 of the laser light after passing through the lens 23 indicates a deviation between the focal point at a certain point and the surface of the photosensitive member 25.
[0006]
In FIG. 2, the laser light emitted from the light emitting element 21 is converted into a plane wave by the collimator lens 29, further deflected by the rotary polygon mirror 22, and incident on the Fθ lens 23. At this time, as shown in the focal locus 211, a focus shift occurs on the scanning line. For example, in FIG. 2, the point x1 is when the light beam is completely focused on the photoconductor 25, and x2 is as shown at 212 because the light beam is focused farther than the surface of the photoconductor 25. The light converges on the photosensitive member 25 slightly before the focal point. It is assumed that the diameter of the spot in the main scanning direction of the light beam converged on the photosensitive member 25 at the point x1 is wx and the diameter of the spot in the sub scanning direction is wy. At this time, at a point x2 that converges on the photosensitive member 25 just before the focal point of the light beam as in 212, the spot diameter of the light beam is the same in both the main scanning direction and the sub-scanning direction as shown in 28. It spreads by about 10%, and becomes 1.1 wx in the main scanning direction and 1.1 wy in the sub scanning direction. At this time, the light intensity is constant, and when the light intensity is constant and the light spot diameter is widened, the peak of the exposure intensity decreases.
[0007]
Further, FIG. 3 is defined by about 1 / 1.6 of the normal spot diameter using a light beam such that wx = 1.6p and wy = 1.6p when the scanning line interval is p. FIG. 5 is a diagram showing an exposure intensity distribution on a photosensitive member when one pixel representing a minimum resolution is printed. A light beam on / off signal 31 is irradiated with a light beam while this signal is “H”. In this case, the irradiation width is p. 32 is an exposure intensity distribution at point x1 in FIG. 2, 33 is an exposure intensity distribution at point x2 in FIG. 2, 34 is a development threshold value, and an area having an exposure intensity higher than this threshold value is printed at the development portion. Image. Since the exposure intensity distribution 32 at the point x1 and the exposure intensity distribution 33 at the point x2 have almost the same width on the threshold 34, there is almost no difference in the printed image.
[0008]
However, in the above-described prior art (Japanese Patent Laid-Open No. 2-112966), the received binary image signal is smoothed by the smoothing unit, and the emission time of the light beam is controlled within a unit of one pixel. In such a case, for example, when printing a minute pixel of 30% width of one pixel, it is as shown in FIG.
[0009]
FIG. 4 shows the exposure intensity distribution on the photosensitive member when 0.3 dot printing is performed using the light beam such that wx = 1.6p and wy = 1.6p where the scanning line interval is p. 41 is a light beam on / off signal, and the light beam is irradiated while this signal is “H”. In this case, the irradiation width is 30% of p. 42 is an exposure intensity distribution at point x1 in FIG. 2, 43 is an exposure intensity distribution at point x2 in FIG. 2, 34 is a development threshold value, and an area where the exposure intensity is higher than this threshold value is printed at the development portion. Image. In such a case, the exposure intensity distribution 42 at the point x1 has a peak exposure intensity exceeding the threshold value, so that fine pixels are printed, whereas the exposure intensity distribution 43 at the point x2 has an exposure intensity peak. Since the threshold value is not reached, nothing is printed, a so-called pixel omission problem occurs, leading to a reduction in image quality.
[0010]
As a solution to this problem, it is conceivable to measure the curvature of field in advance and control the irradiation intensity of the light beam based on the measurement result.
[0011]
However, the above solution solves the problem shown in FIG. 4, but a new problem occurs. FIG. 5 is a diagram showing an example of the non-printing with a width p between black pixels using a light beam such that wx = 1.6p and wy = 1.6p when the scanning line interval is p. The exposure intensity distribution on the photoconductor when forming a region is shown. In FIG. 5, 51 is a light beam on / off signal. While this signal is “H”, the light beam is irradiated. In this case, the signal is such that the non-irradiation width is p. 52 is an exposure intensity distribution at a point x1 in FIG. 2, 53 is an exposure intensity distribution subjected to a process for increasing the exposure intensity at a point x2 in FIG. 2, and 34 is a development threshold value. The area where the image is strong is printed at the developing unit to form an image. In such a case, since the exposure intensity distribution 52 at the point x1 falls below the threshold value in the non-irradiated area, a non-printing area is formed between the pixels, whereas the exposure intensity at the point x2. Since the exposure intensity distribution 53 subjected to the process of increasing the exposure intensity is subjected to the process of increasing the exposure intensity, the exposure intensity does not fall below the threshold value in the non-irradiated area, and the non-printed area between the pixels is not formed, so-called collapse. Occurs.
[0012]
As another solution, it is conceivable to increase the accuracy of the optical system so as to minimize the curvature of field, but this is not practical because the number of mechanical parts increases and the cost increases.
[0013]
An object of the present invention is to eliminate the above-described problems, perform optimal control according to the position on the scanning line in the main scanning direction of the fine pixel to be printed and the print pattern, and to prevent defects such as pixel breakage and collapse. An object of the present invention is to provide an image processing apparatus capable of providing a quality image.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention relates to a photosensitive pixel, a light source, an optical unit that irradiates the photosensitive member with a light beam emitted from the light source, and a pixel of interest with respect to an input image signal. A smoothing circuit that outputs a smoothing signal for correcting the size and position of the target pixel when the pattern matches the pattern prepared in advance and matches the pattern, and the light beam. Detecting a position of the photoconductor on scanning and outputting a detected position signal, and based on the smoothing signal and the position signal, irradiation time of the light beam and / or emission intensity has a light beam modulation signal generator for outputting a light beam modulated signal for controlling said light beam modulation signal generator comprises a look-up table, the smoothing signal Serial target pixel and the surrounding area data thereof, and said position signal, and input as an address for the same look-up table, reads the pattern selection signal written in the address, the smoothing signal, the position signal However, the light beam irradiated onto the photoconductor is divided and output depending on whether the light beam is focused on the photoconductor or an area other than the area. An image processing apparatus is assumed.
The light beam modulation signal generation unit may be an image processing device that generates a pattern selection signal having a larger number of bits than the smoothing signal from the smoothing signal and the position signal.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0016]
FIG. 6 shows a system configuration diagram of the printer.
[0017]
In the figure, 61 is a printer controller that controls the entire system, 62 is an image processing apparatus that performs processing such as smoothing to improve image quality, and 63 is a laser printer that actually performs printing.
[0018]
The printer controller 61 receives a control signal 67 from a computer (not shown) and controls the image processing apparatus 62 according to the control signal 67. The printer controller 61 outputs a binary image signal 14 which is defined by about 1.6 times the spot diameter of the normal light beam and indicates the presence or absence of a pixel representing the minimum resolution in synchronization with the reference pixel clock 15. The image processing device 62 performs processing such as smoothing on the input binary image signal 14, and then outputs a light beam modulation signal 19 that modulates the light beam emission time and / or intensity to the laser printer 63. To do. The laser printer 63 outputs a beam detect signal 16 indicating the start of the line output from the beam detection sensor 24 to the printer controller 61 and the image processing device 62.
[0019]
Next, details of the internal configuration of the image processing apparatus 62 will be described with reference to FIG.
[0020]
11 is a smoothing circuit for performing a smoothing process , 12 is a position detection circuit on the scanning line, and 13 is a light beam modulation signal generation circuit.
[0021]
Smoothing circuit 11 is input to the binary image signal 14 from the printer controller 61 performs smoothing for processing. In the known smoothing circuit used in the present embodiment, the pixel of interest and its surrounding area are referred to and compared with a pattern previously written in the ROM. When the pattern matches, the smoothing signal 17 is output to correct the size and position of the target pixel to be printed.
[0022]
The output smoothing signal is 3 bits here, but this can be any number of bits.
[0023]
The smoothing signal 17 is input to the light beam modulation signal generation circuit 13.
Next, an embodiment of the position detection circuit 12 on the light beam scanning line is shown in FIG.
[0024]
In FIG. 7, reference numeral 71 denotes a dot counter that counts the reference clock, and 72 denotes an area counter that counts the output of the dot counter 71.
[0025]
FIG. 8 is a timing chart showing the operation of the circuit of FIG.
[0026]
In FIG. 8, 16 is a beam detect signal output from the beam detection sensor 24, 81 is a print start signal indicating the start position of the print area, 76 is a signal obtained by inverting the beam detect signal 16, and is called a counter clear signal. Reference numeral 15 is a reference pixel clock, 82 is a count output of the dot counter 71, 75 is a carry signal of the dot counter 71 and is referred to as an area signal, 18 is a count output of the area counter 72, and becomes a position signal 18 on the light beam scanning line.
[0027]
The dot counter 71 is set to “0” when the counter clear signal 76 is at a low level. When the reference pixel clock 15 is input, the dot counter 71 counts up at the rising edge (82). The signal for clearing the counter is not limited to the beam detect signal 16, but is always at the same position before the light beam reaches the print area for each line in the sub-scanning direction, such as an inverted signal of the print start signal 81. As long as it is a signal output at
[0028]
In this case, since a 4-bit counter is used as the dot counter 71, each time the reference pixel clock 15 is counted by 16 dots, an area signal 75 as a carry signal is output and the count output 72 is returned to "0". The dot counter 71 repeats the above operation until the counter clear signal 76 is next input and cleared. The dot counter 71 is a counter for simplifying the light beam modulation signal generation circuit 13. In this embodiment, 16 dots are used as one area.
[0029]
The area counter 72 is set to “0” at the rising edge of the counter clear signal 76. When the area signal 75 is input, the area counter 72 counts up at the rising edge and outputs the position signal 18 on the light beam scanning line. The area counter 72 repeats the above operation until the counter clear signal 76 is next input and cleared. The signal for clearing the counter is not limited to the beam detect signal 16, but is always at the same position before the light beam reaches the print area for each line in the sub-scanning direction, such as an inverted signal of the print start signal 81. As long as it is a signal output at The number of stages of the area counter 72 may be determined according to the resolution, the count area width, and the number of stages of the dot counter 71. For example, if the width from the output of the beam detect signal 16 at a resolution of 240 dpi to the end of printing one line is 40 cm and the number of stages of the dot counter 61 is 4 bits (countable number 16), the pixels included between them are about 3780 dots. Since the area is 16 dots and 1 area, 3780/16 = 236.25 and 237 areas and log 2237 = 7.89, the area counter 72 may be an 8-bit counter.
[0030]
Here, if the number of stages of the dot counter 71 is set to be small, the light beam modulation signal generation circuit 13 needs a large scale, but fine control is possible. Of course, the dot counter 71 may not be provided. In that case, the number of stages of the area counter 72 may be determined according to the resolution and the counting area width. For example, if the width from the output of the beam detect signal 16 at the resolution of 240 dpi to the end of one line printing is 40 cm, the pixels included in the interval are about 3780 dots, and log 23780 = 11.88. That's fine. Then, depending on the scale of the light beam modulation signal generation circuit 13, all the bits of the output of the area counter 72 or the upper bits are used as the position signal 18 on the light beam scanning line, which is the same as when the dot counter is used. An effect is obtained.
[0031]
The output of the area counter 72 is input to the light beam modulation signal generation circuit 13 as the position signal 18 on the light beam scanning line.
[0032]
Next, the configuration of the light beam modulation signal generation circuit 13 will be described with reference to FIG. In this example, the smoothing circuit 11 refers to a pixel of interest and its surrounding area, for example, a 5 × 5 dot area, and compares it with a pattern to be smoothed previously written in the ROM. When the pattern matches the pattern to be smoothed, a smoothing signal 17 is output to correct the size and position of the target pixel to be printed.
[0033]
While smoothing the signal output is shall be the 3-bit in this case, which of course may be any number of bits.
[0034]
When the smoothing signal 17 and the light beam scanning line position signal 18 are input as the address signal of the lookup table ROM 91, the lookup table ROM 91 outputs the 4-bit data previously written at the address as the pattern selection signal 92. .
[0035]
Here, the pattern selection signal 92 output from the lookup table ROM 91 of FIG. 9 is 4 bits, but any number of bits may be used. However, setting the number of bits smaller than the smoothing signal 17 is meaningless.
[0036]
In this example, the lookup table uses a ROM, but instead, a RAM may be used to read pattern selection data when the printer is powered on. Further, it can be configured using a logic circuit without using a memory.
[0037]
The pattern selection signal 92 is input as a select signal of the light beam modulation signal selection selector 94. The light beam modulation signal selector 94 is formed by the fine pixel forming circuit 93, selects a signal corresponding to the pattern signal 92 from the inputted fine pixel signal 95, and outputs it as the light beam modulation signal 19. In this embodiment, since the pattern selection signal 92 is 4 bits, 16 types of fine pixel signals are input.
[0038]
Further, the functions of the smoothing circuit 11 and the light beam modulation signal generation circuit 13 can be integrated to simplify the circuit. FIG. 10 shows an example in which the smoothing circuit 11 and the light beam modulation signal generation circuit 13 are combined.
[0039]
In the figure, 101 is a line buffer for five lines, 102 is a 5 × 5 matrix register, and 103 is a lookup table ROM.
[0040]
The line buffer 101 stores the binary image signal 14 input from the printer controller 61 for five lines and outputs it to the matrix register 102 for each line. When the 25-bit 5 × 5 pattern data 105 indicating the 5 × 5 dot data of the matrix register 102 and the light beam scanning line position signal 18 are input to the lookup table ROM 103 as the address signal, the address is previously stored in the address. The written 4-bit data is output as the pattern selection signal 92. FIG. 11 is a diagram illustrating an example of the value of the smoothing signal 17 and a pattern corresponding thereto. In this example, one dot is divided into 10 fine pixels. For example, when the smoothing signal 17 is 2, printing is performed by replacing the dots to be recorded with a pattern that prints a 30% area from the left of one dot. When the smoothing signal 17 is 0, the corresponding pattern is through, which means that there is no need for smoothing. This means that printing dots are output without being processed.
[0041]
FIG. 12 is a view of the photosensitive member 25 as viewed from above, and 121 indicates a print area.
[0042]
An area in the print area 121 where the focus is relatively on the photoconductor 25 is A1, and the other area is A2.
[0043]
Here, the region A1 is a region including the point x1 in FIG. 2, and the region A2 is a region including the point x2 in FIG.
[0044]
FIG. 13 is a table obtained by dividing the correspondence table shown in FIG. 11 depending on whether the region indicated by the position signal 18 on the light beam scanning line is in the region A1 or A2 shown in FIG. In FIG. 11, for example, when the smoothing signal 17 is 2, printing is performed by replacing the dots to be recorded with a pattern that prints a 30% area from the right of one dot. As mentioned above, it has the problem shown in 4.
[0045]
Therefore, when the area indicated by the position signal 18 on the light beam scanning line indicates A1, a pattern that prints 30% of the area from the right of the dot, and the area indicated by the position signal 58 on the light beam scanning line indicates A2. When printing, a pattern that prints 40% of the area from the right of the dot is printed. The effect of this is shown in FIG.
[0046]
In FIG. 14, a pattern corresponding to the smoothing signal 17 = 2 is printed in FIG. 13 using a light beam such that wx = 1.6p and wy = 1.6p when the scanning line interval is p. FIG. 14 is a diagram showing the exposure intensity distribution on the photoconductor, in which 141 is a light beam on / off signal in the area A1, and the light beam is irradiated while this signal is “H”. In this case, the irradiation width is 30% of p. Reference numeral 142 denotes a light beam on / off signal in the area A2, and the light beam is irradiated while this signal is "H". In this case, the irradiation width is 40% of p. Reference numeral 143 denotes an exposure intensity distribution at a point x1 included in the area A1, 144 denotes an exposure intensity distribution at a point x2 included in the area A2, and 34 denotes a development threshold. An area having an exposure intensity higher than the threshold is shown in FIG. The image is printed at the development unit.
[0047]
As can be seen from the comparison between 143 and 144 in FIG. 14, the difference in exposure intensity distribution between 143 and 144 is almost eliminated by the processing shown in this embodiment. As a result, the problem as shown in FIG. 4 is solved.
[0048]
Further, in the present embodiment, the light beam is modulated only when a fine pixel for which field curvature is a problem is printed, so the problem as shown in FIG. 5 does not occur.
[0049]
FIG. 15 shows a case where a non-printing area having a width p is formed between black pixels using a light beam such that wx = 1.6p and wy = 1.6p, where the scanning line interval is p. Is a light beam on / off signal 51, and the light beam is irradiated while this signal is "H". In this case, the signal is such that the non-irradiation width is p. 52 is an exposure intensity distribution at point x1 in FIG. 2, 153 is an exposure intensity distribution at point x2 in FIG. 2, 34 is a development threshold value, and an area where the exposure intensity is higher than this threshold value is printed at the development portion. Image. Since the exposure intensity distribution 52 at the point x1 and the exposure intensity distribution 153 at the point x2 have almost the same width on the threshold value 34, there is almost no difference in the printed image, and the problem shown in FIG. It will be resolved.
[0050]
In this example, the area is divided into only two for simplicity, but finer control can be performed if more areas are divided.
[0051]
In this example, for the sake of simplicity, the light beam modulation signal 19 performs only pulse width modulation to control only the light emission time. However, the light beam modulation signal 19 modulates the light emission intensity. It may be a signal, or a signal that controls both the light emission time and light emission intensity. In either case, control may be performed in the same procedure as in this embodiment.
[0052]
【The invention's effect】
By performing optimal control in accordance with the position on the scanning line in the main scanning direction of the fine pixel to be printed and the printing pattern, it is possible to provide a high-quality image free from defects such as pixel omission and collapse.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of the present invention.
FIG. 2 is a schematic diagram of an optical system of a laser beam printer.
FIG. 3 is a diagram illustrating an exposure intensity distribution on a photoreceptor when printing one dot.
FIG. 4 is a diagram showing an exposure intensity distribution on a photoconductor when 0.3 dot printing is performed.
FIG. 5 is a diagram showing an exposure intensity distribution on a photoreceptor when correction according to a conventional example is performed.
FIG. 6 is a system configuration diagram of a printer.
FIG. 7 is a diagram showing an embodiment of a position detection circuit on a scanning line according to the present invention.
FIG. 8 is a timing chart of the position detection circuit on the scanning line according to the present invention.
FIG. 9 is a diagram showing an example of a light beam modulation signal generation circuit of the present invention.
FIG. 10 is a diagram showing another example of the light beam modulation signal generation circuit of the present invention.
FIG. 11 is a correspondence table between a smoothing signal and an output signal.
FIG. 12 is an example of area division on a photoreceptor.
FIG. 13 is a correspondence table between a smoothing signal and signals output for divided areas.
FIG. 14 is a diagram showing an exposure intensity distribution on a photoreceptor when the present invention is applied.
FIG. 15 is another view showing the exposure intensity distribution on the photoreceptor when the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Smoothing circuit, 12 ... Scan line position detection circuit, 13 ... Light beam modulation signal generation circuit, 14 ... Binary image signal, 15 ... Reference pixel clock, 16 ... Beam detect signal, 17 ... Smoothing signal, 18 ... Light Position signal on beam scanning line, 19: light beam modulation signal, 21: light emitting element, 22: rotating polygon mirror, 23: fθ lens, 24: beam detection sensor, 25: photoconductor.

Claims (2)

A photoreceptor,
A light source, and an optical unit that irradiates the photosensitive member with a light beam emitted from the light source;
The input image signal is referred to the target pixel and its surrounding area, compared with a pattern prepared in advance, and when it matches the pattern, smoothing is performed to correct the size and position of the target pixel. A smoothing circuit for outputting a signal;
A position detection unit that detects a position of the light beam on scanning of the photosensitive member and outputs a detected position signal;
Based on the smoothing signal and the position signal, a light beam modulation signal generation unit that outputs a light beam modulation signal for controlling the irradiation time or emission intensity of the light beam or both,
The light beam modulation signal generation unit includes a look-up table, and inputs the smoothing signal as the address of the pixel of interest and the surrounding area data and the position signal to the same look-up table. Read the pattern selection signal written in
The smoothing signal is divided according to whether the position signal indicates either a region where the light beam irradiated onto the photoconductor is in focus or a region other than the region. An image processing apparatus characterized by being output . The image processing apparatus according to claim 1.
The light beam modulation signal generation unit is an image processing apparatus that generates a pattern selection signal having a larger number of bits than the smoothing signal from the smoothing signal and the position signal.

Images