JP2008153742A - Image recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is adaptable to higher density of recording resolution and is free from the degradation of thin-line reproducibility. <P>SOLUTION: Pattern matching (c) using a detection pattern of one (lateral) pixel by four (longitudinal) pixels is performed for a lateral line (a) of interest with a 2-pixel width and an oblique line (a) of interest to make line width corrections. Further, luminance modulation is performed in addition to the line width corrections so that one pixel is made high in luminance, thereby correcting the quantity of light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus. In particular, the present invention relates to an electrophotographic image forming apparatus used in, for example, a copying machine, a printer, a facsimile, a plate making system, and the like.

  As high-speed and high-quality image forming apparatuses, copying machines and laser beam printers that employ an electrophotographic method are known. In recent years, as digital contents have become common in offices and homes, the demand for higher image quality of these electrophotographic image recording apparatuses has further increased, and the recording resolution has become higher, such as 1200 dpi, 2400 dpi, and 3600 dpi. Progressing.

  An electrophotographic image recording apparatus irradiates an image carrier with light by a laser beam or the like, and an image is recorded by the amount of light irradiated at that time. From a binary image such as a character, a photograph or the like is recorded. Any image up to an image including a halftone can be formed.

  Specifically, a dither method, a density pattern method, or the like can be used as a method for reproducing a halftone, and a good output image can be obtained by outputting multiple values for each pixel.

  As a method for converting the multi-value data at this time into an irradiation light amount, a light amount control method combining a pulse width modulation method (PWM), a power modulation method (PM), or a combination thereof has been proposed.

  In addition, with recent demands for higher recording resolution and higher image quality, it has become a challenge to achieve good dot reproducibility in the highlight region, and various techniques have been proposed.

  The following is disclosed as an image forming apparatus using laser power modulation means.

  Patent Document 1 describes an image recording apparatus including a pulse width modulation unit and a laser power control unit. The pulse width modulation means controls the drive signal pulse width of the semiconductor laser based on predetermined bit image data of the plurality of bits of image data. The laser power control means controls the drive signal amplitude of the semiconductor laser based on the image data of other bits among the plurality of bits of image data.

  Patent Document 2 describes an image output device that includes output mode switching means for switching the number of output gradations per dot by an input control signal in an image output device that performs pulse width modulation simultaneously with light intensity modulation. ing.

  Patent Document 3 discloses a technique for realizing smoothness of an image at low density by increasing the number of bits of power modulation only in a low density area when controlling the exposure amount by a combination of power modulation and pulse width modulation. Is described.

  Patent Documents 4 and 5 describe techniques for improving the reproducibility of minute dots by providing an overshoot of exposure intensity at the light output rising portion of a semiconductor laser when an a-Si photosensitive member is used. Has been.

  Patent Document 6 describes a technique in which an overshoot is generated in a laser light output waveform for each light emitting point of a semiconductor laser, and the light intensity at the rising edge of laser light emission is made stronger than that in steady light emission.

Japanese Patent No. 2698099 JP-A-9-116750 JP 2001-130050 A JP 2002-361922 A JP 2002-361925 A JP 2003-266663 A

  As described above, various correction techniques have been proposed for the highlight area, but reproducibility has not been improved for high-density areas with repeated high-density thin lines and small-point characters, and is isolated. The reproducibility of fine lines and isolated dots is not sufficient.

  In particular, when the recording resolution is increased, such as 2400 dpi and 3600 dpi, there is a case where the fine line reproducibility is reduced as compared with the case where recording is performed at a low density, and the correspondence to such a case cannot be realized. .

  An object of the present invention is to provide an image forming apparatus that can cope with an increase in recording resolution and does not deteriorate fine line reproducibility.

  In one embodiment of the present invention for achieving the above object, an output image is formed on a recording medium based on a latent image formed by exposing and scanning an image carrier with light from a light emitting element driven in accordance with an input image. In the image forming apparatus, thinning means for thinning the attention line of the input image, and luminance correction means for correcting the light emission intensity of the light emitting element and increasing the intensity of the thinned attention line. It is provided with.

  Here, the line of interest can be determined using a filtering process. The attention line can be determined using pattern matching. The target line is detected using a detection pattern composed of n pixels arranged in a direction perpendicular to the length direction of the line, and the detected line of interest is arranged in the vertical direction. It is possible to correct the light emission intensity of the light emitting element for pixels excluding at least one of the pixels smaller than the n pixels by thinning by replacing with a replacement pattern composed of pixels smaller than the pixels. Further, the image processing apparatus may further include a determination unit that determines a character part of the input image, and the attention line may be determined for the determined character part. In addition, the width of the target line can be reduced to a width corresponding to 0 pixels or narrower.

  According to the present invention, in an image recording apparatus that outputs at a high recording resolution, an attention line of an input image is thinned, and an emission intensity of a light emitting element is increased with respect to the attention line. It is possible to improve the reproducibility of isolated thin lines and repeated high-density thin lines in an image, and to realize high-definition characters and fine lines.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus to which the present invention can be applied. The image forming apparatus includes a photosensitive drum 11 as an image carrier and a charging unit 12, an image exposure unit 17, a developing unit 19, a developing roller 13, a transfer unit 14, a fixing unit 15, and a cleaning unit 16 disposed around the photosensitive drum 11. An electrophotographic recording apparatus.

  The photosensitive drum 11 can be of a function separation type having a two-layer structure such as a charge generation layer and a charge transport layer, or a single layer type with a conductive support substrate as the lowermost layer.

  The charging unit 12 is a corona charging method using a corona charger composed of a wire and an electric field control grid, and roller charging is performed by applying a direct current or a superimposed bias of direct current and alternating current to a charging roller in contact with the image carrier. A method etc. can be used.

  The image exposure unit 17 for exposure scanning includes a scanner type using a semiconductor laser, an LED that performs image exposure via a SELFOC lens that is a condensing device, an EL element, and a plasma light emitting element. Other optical systems can be used.

  As the developing unit 19, a magnetic one-component non-contact developing method, a magnetic contact developing method, a non-magnetic one-component non-contact developing method, a non-magnetic one-component contact developing method, or a two-component developing method is used. can do. In the magnetic single component non-contact development method, magnetic toner is conveyed by a magnetic force, and is developed in a non-contact manner on the image carrier in a development nip. In the magnetic contact development method, development processing is performed by bringing the image carrier into contact with the development nip. The non-magnetic one-component non-contact developing method is a method in which non-magnetic toner is regulated and charged by a blade, conveyed while being carried by a developing sleeve, and the toner is developed in a non-contact manner in a developing nip. The non-magnetic single component contact development method is a development process in which the image carrier is brought into contact with the development nip. In the two-component development method, non-magnetic toner is similarly mixed with a carrier that is magnetic powder, and is also conveyed to the development nip by the development sleeve to perform development processing.

  As the transfer unit 14, a transfer method using an electric force or a mechanical force can be used. As a method of transferring using an electric force, a corona transfer method in which a DC bias having a polarity opposite to the toner charging polarity is applied by a corona wire, or a roller is brought into contact with the toner to reverse the polarity. It is possible to use a roller transfer type that applies the above bias.

  As the fixing unit 15, a recording paper as a recording medium is passed through the joint of two opposing rollers, and a toner is fixed to the recording material by heat or pressure, or a recording material using a non-contact heater or lamp. It is possible to use a system in which toner is fixed by heating. It is also possible to use a belt-like unit as a unit for sandwiching the recording material and fix it by applying heat or pressure.

  FIG. 2 is a diagram showing details of a scanner type image exposure unit using a semiconductor laser used in the apparatus of FIG.

  As shown in FIG. 2, the image exposure unit 17 that is a scanning optical system includes a semiconductor laser 21, a polygon mirror 24 that rotates at high speed, and an f-θ lens 25. For example, the semiconductor laser 21 blinks the laser light based on the laser drive signal from the semiconductor laser drive control unit 20 based on the image data input through the image processing unit 10 (FIG. 1) including the CCD line sensor. The laser beam emitted from the semiconductor laser 21 is made substantially parallel light by the collimator lens 22 and is condensed on the polygon mirror 24 by the cylindrical lens 23. Then, the light is reflected and deflected on the polygon mirror 24 rotating at a constant speed, passes through the f-θ lens group 25, is again polarized by the folding mirror 18, and is imaged in a spot shape on the photosensitive drum 11. Scanning is performed at a constant speed in the scanning direction 28). Reference numeral 26 denotes a folding mirror position, and reference numeral 27 denotes an image plane of the photosensitive drum 11.

  The semiconductor laser drive control unit 20 includes a CPU, a ROM, and a RAM. The CPU performs data correction, character image determination, and laser drive control, which will be described later in detail. The ROM stores CPU control programs and various control data. The RAM defines work areas and various tables used by the CPU when executing control.

  Here, various methods can be used as the halftone processing method for the input image. The image processing methods most commonly used are a dither method and a density pattern method. In the dither method, when one pixel of a read input signal is output in correspondence with one pixel for binary recording, one pixel is turned on or off based on m × m threshold data.

  The pulse width of the laser emission at this time is controlled by gradation, but the emission position at that time is “center”, “left”, “right” in the pixel, and the influence of the pixel position in the matrix pattern and peripheral pixels. Can be set in consideration of

  Furthermore, using an error diffusion method or an image forming method using a blue noise mask is also suitable for high-definition image output realized in this embodiment.

  The engine resolution can be applied to any engine resolution such as 400 dpi, 600 dpi, 1200 dpi, 2400 dpi, and 3600 dpi. However, when the resolution becomes high such as 1200 dpi, 2400 dpi, 3600 dpi, etc., the laser spot diameter tends to become larger with respect to the recording density. For this reason, as described above, the fine line reproducibility is often reduced as compared with the case of recording at a low density, and the application of the present invention in a high-resolution engine is more suitable because the effect is more likely to appear.

  Since it is difficult to correct within one pixel at high resolution, and because of the high resolution, the image clock frequency becomes high and the necessity for correction increases, the application of the present invention to a high resolution engine is more preferable.

  Next, with reference to FIG. 3 and FIG. 4, the current state and problems of the laser scanning pattern in the present embodiment, which are problems when realizing formation of a high-definition latent image, will be described.

  FIG. 3A shows image data and a three-dimensional and two-dimensional light amount distribution when a thin line corresponding to one line of 1200 dpi is drawn using a data resolution of 1200 dpi. FIG. 3B shows image data and three-dimensional and two-dimensional light quantity distributions when a fine line corresponding to one line of 1200 dpi is drawn with two lines using a data resolution of 2400 dpi. Comparing both cases, it can be understood that the contrast of the light amount distribution is lower when the image is drawn with two lines of 2400 dpi (FIG. 3B). In both cases, the integrated light quantity is the same, so when the same optical spot shape is used, the laser power is halved, the scan position is shifted twice, and the scan is performed twice (FIG. 3 (a)). In comparison, it can be understood that the distribution of the amount of light formed is broadened and the fine line reproducibility is lowered.

  FIG. 4A illustrates image data and three-dimensional and two-dimensional light quantity distributions when a repetitive line pattern corresponding to one line to one space of 1200 dpi is drawn using a data resolution of 1200 dpi. FIG. 4B shows image data and a three-dimensional and two-dimensional light amount distribution when a line pattern corresponding to one line to one space of 1200 dpi is drawn with two lines using a data resolution of 2400 dpi. .

  Comparing both cases, as in the case of drawing one line, it can be seen that the contrast of the light amount distribution is lower when the image is drawn with two lines of 2400 dpi (FIG. 4B). Furthermore, when the high-density pattern is repeated, the image drawing with two lines raises the light intensity distribution level of the portion corresponding to the space, thereby lowering the contrast more than the isolated line in FIG. It can be understood that it becomes prominent.

  In view of the above problems, in the embodiment of the present invention, as shown in FIG. 5 to FIG. 8, the semiconductor laser drive control unit 20 is a thin line with respect to the attention line of the input image according to the input image data from the image processing unit 10. Processing and brightness correction processing are performed together. The amount of light that is short enough to adjust the line width by thinning processing is interpolated by increasing the brightness of the thin line by luminance modulation. By such processing according to the present embodiment, high-definition fine line reproduction and good fine line reproduction can be realized even in a high-density repetitive pattern, and the reproducibility of small point characters can also be improved.

  In this case, a known pattern matching technique, an edge / thin line part extraction technique using a filter process, and a character part detection technique using a character flag are used to determine a pixel that performs luminance modulation on the line width and laser power. be able to. Alternatively, it is possible to use a technique in which they are combined.

  Depending on the pattern size used for pattern matching at this time, the filter size used for filter processing, etc., it is possible to adapt from an extra fine line of about one line to a line width of about several lines. Further, by devising the pattern type and number of pattern matching, the present invention can be applied not only to a simple line pattern but also to an image part having a complicated shape such as a character part. Furthermore, it is more preferable to implement the present invention using a laser driving device having a plurality of luminance modulation levels.

(Embodiment 1)
In the present embodiment, as shown in FIGS. 5A and 5B, 1 (horizontal) × 4 (vertical) shown in FIG. 5C is applied to the horizontal attention line and the diagonal attention line of 2 pixels width. Pattern matching based on the pixel detection pattern is performed on the target line to correct the line width. Further, luminance modulation is performed in addition to line width correction so as to increase the luminance of 1 pixel.

  The semiconductor laser drive control unit 20 binarizes the input image, performs pattern matching based on the detection pattern stored in the ROM or the like, and replaces 2 pixels arranged vertically in the line of interest with a 1-pixel width replacement pattern. Further, the luminance modulation processing is performed so as to drive the semiconductor laser 21 by increasing the luminance of one pixel of the replacement pattern so that the light quantity is not insufficient by this replacement, and the semiconductor laser drive control unit 20 outputs the result. Therefore, as shown in FIGS. 5A and 5B, the vertical 3 pixels of the input image are made vertical 2 pixels in the output image and are thinned. For example, the upper one of the two pixels (in the figure, The dark pixel) is subjected to luminance modulation to correct the shortage of light.

  Here, the pattern matching method used in the present invention will be described with reference to FIG.

  The detection pattern shown in FIG. 5C is sequentially adapted to each pixel of the input image data, and when the ON / OFF of the pattern in the detection pixel matches, the replacement pattern shown in FIG. Converted. In this manner, the detection pattern is sequentially applied to each pixel, and the pixel is thinned and the laser power is increased in brightness by using a predetermined replacement pattern when they match. As the detection pattern at this time, one in the horizontal direction as shown in FIG. 6 or a combination of vertical and horizontal is used. Alternatively, a two-dimensional pattern can be used. As shown in FIG. 7, it is also possible to correct a wider line pattern by increasing the size of the detection pattern.

  Regarding the brightness level of the modulated laser power at this time, it is preferable that the integrated exposure amount before correction and the integrated exposure amount after correction are substantially equal. For example, when a line pattern composed of two pixels is thinned and a line pattern is composed of one pixel, the luminance modulation level of the laser power is approximately doubled so that the integrated exposure amount is substantially equal before and after correction. It is preferable to make it. It is also preferable to implement the present invention by using a laser drive device having a plurality of luminance modulation levels, setting the laser power after the change in advance in multiple stages, and fine-tuning appropriately according to the conditions of surrounding pixels. is there. As a range of fine adjustment at this time, it is possible to obtain a desired line width image in a range of 0.8 to 1.2 times the integrated exposure amount before correction according to the conditions of the peripheral pixels.

FIG. 6 shows a case where the line of interest and the detection pattern are perpendicular to those of FIG.
A detection pattern of 4 (horizontal) × 1 (vertical) pixel rotated 90 degrees as shown in FIG. 6C provides a replacement pattern of 1 pixel width for the vertical attention line of 2 pixels width, and the replacement pattern 1 pixel of the pixel is subjected to luminance modulation in order to correct the shortage of light.

  In the above embodiment, the present invention is applied to an isolated line image. However, the example shown in FIG. 7 is obtained by performing thinning and luminance modulation by pattern matching similar to the above for repeated lines in the horizontal direction. is there.

  Note that if a character image is determined from the input image and a target line is determined for the character image portion, the same thinning and luminance modulation as described above can be performed for the small-point character. The character image can be determined by, for example, well-known black character determination after shading correction, black correction, splicing processing, and MTF correction to a signal obtained by binarizing the signal from the sensor. This is an example and does not limit the present invention.

  The set value of the laser power of the “intensity modulation pixel” selected by pattern matching can be adjusted in consideration of the device characteristics and usage environment. In this embodiment, an example in which one type of pattern matching is applied vertically and horizontally is shown, but a plurality of patterns may be used for pattern matching at this time. Further, the laser power setting of the “intensity modulation pixel” is also multi-stage in the intensity modulation, and can be appropriately changed according to each pattern used for pattern matching.

  As described above, according to the present embodiment, the emission intensity of the light-emitting element is corrected to increase the intensity for any line of interest for small-point characters, isolated thin lines, and high-density repeated thin lines. As a result, the problems of the conventional example were solved and good fine line reproducibility could be realized. In other words, thinning of the line width and high brightness of the laser power are performed at the same time, preventing a decrease in the contrast of the light amount distribution due to the overlap of the laser spots, and good thin line reproducibility without causing a shortage of the light amount. Can be realized.

(Embodiment 2)
In this embodiment, as shown in FIGS. 8A and 8B, 1 (horizontal) × 5 (vertical) shown in FIG. 8C is applied to the horizontal attention line and the diagonal attention line of 3 pixels width. Pattern matching based on the pixel detection pattern is performed on the target line to correct the line width. Further, luminance modulation is performed in addition to line width correction so as to increase the luminance of 1 pixel.

  This embodiment is an example using a detection pattern having a width wider than that of the first embodiment, and can be extended to a target line having a different 90-degree orientation as well as a repeated high-density thin line as in the first embodiment. In addition, the detection pattern can be applied up to a 10-pixel-wide attention line with a maximum 10-pixel width, and in any case, as in the first embodiment, all of small-point characters, isolated thin lines, and high-density repeated thin lines are good. Fine reproducibility can be realized. Since the maximum detection pattern width is 10 pixels, it can be made narrower.

  The effects of the above embodiments are shown in the following table in comparison with the prior art.

(Other embodiments)
As described above, the present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.) but also to an apparatus composed of a single device (for example, a copying machine, a facsimile machine). May be.

  In addition, a program code of software for realizing the functions of the embodiment is provided in an apparatus or a computer in the system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiments. What is implemented by operating the various devices in accordance with a program stored in a computer (CPU or MPU) of the system or apparatus supplied is also included in the scope of the present invention.

  Further, in this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, a storage storing the program code The medium constitutes the present invention.

  As a storage medium for storing the program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) in which the program code is running on the computer, or other application software, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.

  Further, after the supplied program code is stored in a memory provided in a function expansion board of a computer or a function expansion unit connected to the computer, a CPU provided in the function expansion board or function storage unit based on an instruction of the program code However, it is needless to say that the present invention also includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

1 is a configuration diagram illustrating a schematic configuration of an image forming apparatus to which the present invention can be applied. It is a figure explaining the scanner type image exposure unit using the semiconductor laser used for the image forming apparatus of FIG. It is a figure explaining the subject of a prior art. It is a figure explaining the subject of a prior art. It is a figure explaining Embodiment 1 of this invention. It is a figure explaining Embodiment 1 of this invention. It is a figure explaining Embodiment 1 of this invention. It is a figure explaining Embodiment 2 of this invention.

Explanation of symbols

11 Image carrier 12 Charging unit 13 Developing roller 14 Transfer unit 15 Fixing unit 16 Cleaning unit 17 Image exposure unit 18 Folding mirror 19 Developing unit 20 Semiconductor laser drive controller 21 Semiconductor laser 22 Collimator lens 23 Cylindrical lens 24 Polygon mirror 25 f− θ lens 26 Folding mirror position 27 Image surface 28 of photosensitive drum Scanning direction

Claims (6)

In an image forming apparatus for forming an output image on a recording medium based on a latent image formed by exposing and scanning an image carrier with light from a light emitting element driven according to an input image,
A thinning means for thinning a target line of the input image; and
An image forming apparatus comprising: a luminance correction unit that corrects the light emission intensity of the light emitting element to increase the intensity of the thinned line of interest.   The image forming apparatus according to claim 1, wherein the line of interest is determined using a filter process.   The image forming apparatus according to claim 1, wherein the line of interest is determined using pattern matching. The target line is detected using a detection pattern composed of n pixels arranged in a direction perpendicular to the length direction of the line, and the detected line of interest is detected from the n pixels arranged in the vertical direction. Is replaced with a replacement pattern consisting of a small number of pixels and thinned.
The image forming apparatus according to claim 3, wherein the light emission intensity of the light emitting element is corrected for pixels excluding at least one of the pixels smaller than the n pixels. A determination means for determining a character portion of the input image;
The image forming apparatus according to claim 1, wherein the attention line is determined for the determined character portion.   The image forming apparatus according to claim 1, wherein the line of interest has a width corresponding to 10 pixels or narrower.

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