JP2006035810A - Laser printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser printer which records dots of different sizes in image recording, and makes edge smoothing in a sub-scanning direction as well as that in a main-scanning direction. <P>SOLUTION: Dots of different sizes are made recordable by switching an amount of laser, and further when a pixel whose edge part needs to be corrected by a pattern matching processing is detected, the edge smoothing in the sub-scanning direction is made by using larger-sized dots than those of recording pixels used for ordinary gradation reproduction, depending on an edge image pattern. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser printer that can record dots of different sizes when performing image recording.

  In general, an image output apparatus such as a printer, a copier, or a facsimile records an image formed of a dot pattern as an output image on a recording medium such as paper based on input image information. Usually, since these dots are arranged on a square lattice with a certain resolution, a state called jaggy occurs in the shaded portion of the outline of characters or figures, and the image quality may be lowered. In order to avoid this state, it is sufficient to increase the resolution. However, if the resolution is increased, the amount of data increases, and the amount and time for processing increase accordingly.

  Therefore, conventionally, a technique called edge smoothing is used to extract only the necessary part, and the part is smoothed by interpolating dots at a higher resolution than the normal resolution, thereby improving the image quality. ing.

  FIG. 3 shows a schematic diagram of a conventional edge smoothing effect in a laser printer. FIG. 3A shows an example in the case where the edge smoothing process is not performed. FIG. 3-B shows an example in which the conventional edge smoothing process is applied to this. As is well known, in laser printers, when an image (electrostatic latent image) is generally formed on a photosensitive member by laser scanning, image formation is performed in units of dots based on a dot clock. When the pixel to be detected is detected, the edge part of the recorded image is smoothed by changing the exposure time as shown in FIG. This suppresses the occurrence of jaggies and improves the image quality. As shown in FIG. 3, the edge of the recorded image subjected to the edge smoothing process shown in FIG. 3-B becomes smoother than the edge of the recorded image not subjected to the edge smoothing process shown in FIG. The deviation from the straight line is small.

  However, the edge smoothing process for controlling the general laser exposure time as described above is effective only in the main scanning direction and not effective in the sub-scanning direction. Therefore, a measure for smoothing processing in the sub-scanning direction has been proposed. (For example, see Patent Documents 1 and 2.)

Japanese Patent Laid-Open No. 4-163099 JP-A-8-27110

  An object of the present invention is to provide an edge smoothing processing method in the sub-scanning direction by a simpler method as compared with the prior art.

  In the present invention, it is possible to record dots of different sizes by switching the laser light quantity, and when a pixel that requires correction of the edge portion is detected by pattern matching processing, the normal pixel pattern of the edge is used. A dot having a size larger than the dot size of a recording pixel used for gradation reproduction is used.

  According to the present invention, in addition to edge smoothing processing in the main scanning direction that is common in laser printers, smoothing processing can be performed in the sub-scanning direction, and a high-quality printing result can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 4 shows a block diagram of this embodiment. A printer 401 is connected to a host 402 and includes a printer engine 404 and a printer control device 403. Print data sent from the host 402 is input to the control unit 405 of the printer control device 403 and sent to the input buffer 407. The data sent to the input buffer 407 is sent to the storage apparatus 408 according to an instruction from the host 402 and temporarily stored. Thereafter, the data is sent to the image processing unit 406 or directly sent to the image processing unit 406. Data sent from the storage device 408 or the input buffer 407 to the image processing unit is first processed by the color conversion processing unit 409 of the image processing unit 406. The color conversion processing unit 409 converts the data of the transmitted pixels into data of 256 gradations and 8 bits for each color of CMYK. Then, the data is sent to the gradation processing unit 410 and the ternarization determination processing unit 411, and in the case of binary data for each color of CMYK, it is converted to 255 and 0 and similarly to the gradation processing unit 410 and the ternarization determination processing unit 411 send. Here, the 256 gradation data and 8 bit data are data having a higher density as the value is larger.

  The gradation processing unit 410 performs gradation processing for converting the received pixel data into a value of the number of gradations that can be printed by the printer for each color by using a dither method, error diffusion method, and the like. Are output to the selector 413 as pixel gradation data. In this embodiment, the result after gradation processing is simply expressed by 1 bit for the sake of simplicity. If 0, the dot is printed, and if it is 1, the dot is not printed.

  The edge smoothing process is performed in parallel with the gradation process for each color in the same way as the gradation process, and the process is performed by the ternary determination processing unit 411 and the edge detection processing unit 412.

  The pixel classification data generation processing performed by the ternarization determination processing unit 411 will be described. The ternarization determination processing unit 411 classifies the edge detection pixels into three types based on the pixel values from the multivalued image data, and generates classification data. The types of pixels to be classified may not be three types. An algorithm of the ternarization determination process performed by the ternarization determination processing unit 411 is shown in FIG. In the ternary determination process, the pixel is classified into three types, a high density pixel, a low density pixel, and a halftone pixel, depending on the pixel value. If the pixel value is larger than the threshold value B, the pixel is classified as a high density pixel. If the pixel value is smaller than the threshold value W, the pixel is classified as a low density pixel. In this way, the number of patterns required for the pattern matching process can be reduced by ternizing the multi-gradation data.

  The edge detection processing performed by the edge detection processing processing unit 412 will be described. The edge detection process is performed by comparing the pattern of the classification data of a plurality of pixels with a pixel pattern for edge detection registered in advance. Here, as an example, a pixel pattern for edge detection will be described as a 5 × 5 square.

  FIG. 6 shows an example of a 5 × 5 pixel block. Pixel n is a target pixel to be smoothed, and 25 pixels of a to z pixels for 5 pixels in the X direction and 5 lines in the Y direction including pixel n are referred to. The reference pixel block does not necessarily have to be a square as shown in FIG. 7A, and does not have to be a rectangular area as shown in FIG. 7B.

  FIGS. 8A and 8B show examples of patterns for detecting edges. As shown in this example, the edge detection pattern does not distinguish between halftone pixels and low density pixels. FIG. 8C shows an example of a pattern used for detecting the inside of a solid used in the correction value generation process. As shown in FIG. 8C, it is not always necessary to refer to all pixels even in the reference pixel block, and there may be non-reference pixels. Using these detection patterns, if the pattern of the ternarization determination result matches these patterns and there are no halftone pixels in the reference pixels in the reference pixel block, the pattern is enlarged according to the pattern. Correction pixels, reduction correction pixels, and solid internal pixels are used, and if they do not match any of the patterns, correction data is sent to the selector 413 as non-correction pixels. Here, only one stage is set for each of the enlargement correction pixel and the reduction correction pixel, but there may be a plurality of stages. In this embodiment, the value 2 is assigned to the reduction correction pixel, and the value 3 is assigned to the enlargement correction pixel. By doing so, the value of the gradation processing result and the value after correction can be handled in the same way. For solid internal pixels and uncorrected pixels that are not corrected, 0 is output to the selector 414 as correction data.

  The selector 413 receives the gradation data output from the gradation processing unit 410 and the correction data output from the edge detection processing unit 412. If the correction data value is 0, the selector 413 selects the gradation data as the correction data value. If is other than 0, the correction data is output to the output buffer 414 as print data. Further, when the smoothing process is not performed, the gradation data can be output as it is regardless of the value of the correction data according to an instruction from the control unit.

The output buffer 414 outputs data to the printer engine 404 according to an instruction from the control unit 405. The printer engine 404 sends the received data to the laser drive unit 415. A laser light quantity control circuit 416 and a light emission time control circuit 417 are mounted on the laser drive unit, and laser drive control is performed by a combination of these. In the present embodiment, the laser light amount control circuit 416 controls the laser light amount at the time of light emission in two steps of the standard light amount and the maximum light amount, and the light emission time control circuit 417 sets the laser light emission time to 1 dot time and 1/2 dot time. It shall be controlled in two stages. That is, the following control is specifically performed by the above combination.
-When the received data is 0: The laser is not emitted (dots are not printed).
-When the received data is 1, light is emitted with the standard light quantity for one dot time.
When the received data is 2: Light is emitted with a standard light amount for 1/2 dot time.
-When the received data is 3, light is emitted with the maximum amount of light for one dot time.

  2-A and 2-B are schematic diagrams of the original image and multi-valued data after color conversion, and FIGS. 2-C and 2-D show gradation data and correction data after gradation processing, respectively. FIG. 2E shows a schematic diagram of print data synthesized by the selector. FIG. 1A shows an image of a printed image on the medium when the edge smoothing corresponding to FIG. 2-C is not performed, and FIG. 1B shows the case where the edge smoothing corresponding to FIG. 2-E is performed. Shows an image of a printed image on the medium. A dotted line is a virtual grid line of the interval of the printing resolution d, and a thick line is an ideal straight line corresponding to the original image. As shown in FIG. 1-B, by performing the edge smoothing processing of the present embodiment, as compared with the case where the processing is not performed as in FIG. 1-A, not only in the conventional main scanning direction but also in the sub-scanning direction. Also, edge smoothing can be performed, which can improve the print quality.

The schematic diagram which shows the effect of the edge smoothing of this invention. The schematic diagram which shows the system of the edge smoothing of this invention. The schematic diagram which shows the effect of the conventional edge smoothing. The block diagram which shows embodiment of this invention. The flowchart which shows the algorithm which classifies multi-value image data in embodiment of this invention. FIG. 6 is a diagram illustrating a pixel range to be referred to when performing pattern matching processing in the embodiment of the present invention. The figure explaining the range of the pixel referred when performing a pattern matching process. The figure which shows the example of the pattern which detects an edge and a solid internal pixel in embodiment of this invention.

Explanation of symbols

401: printer 402: host 403: printer control device 404: printer engine 405: control unit 406: image processing unit 407: input buffer 408: storage device 409: color conversion processing unit 410: gradation processing unit 411: ternary determination Processing unit 412: Edge detection processing unit 413: Selector 414: Output buffer 415: Laser drive unit 416: Laser light quantity control circuit 417: Light emission time control circuit

Claims (4)

  In laser printers that can record dots of different sizes by switching the amount of laser light when performing image recording, use dots of a size larger than the dot size of the recording pixels used for normal gradation reproduction. A laser printer characterized in that edge smoothing in both the scanning direction and the sub-scanning direction can be processed.   Generate pixel classification data for edge detection from multivalued image data based on pixel values, perform edge detection by pattern matching using this pixel classification data, and correct the size of the recorded dots The laser printer according to claim 1, further comprising an image processing device that performs detection.   2. The laser according to claim 1, further comprising an image processing device configured to generate classification data by classifying into three types of pixels when generating classification data of pixels for edge detection from multi-valued image data based on pixel values. Printer. An image processing apparatus that corrects the size of a recording dot around an edge pixel by pattern matching using the information of the pixel that is detected according to claim 2 or 3 to correct the size of the recording pixel. Item 1. A laser printer according to item 1.

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