JP2006074274A - Image processor and method for correcting image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of efficiently performing smoothing correction for a registration-corrected image without increasing the number of matching patterns necessary for the smoothing correction. <P>SOLUTION: The image processor comprises a registration correction part 12 for correcting the positional deviation of an image, a second resolution conversion part 13 for correcting the resolution of the image so as to reduce it, and a smoothing part 14 for performing the smoothing correction of the resolution-converted image. Since resolution conversion is applied to the registration-corrected image and the image having the small number of pixels is smoothed, the number of matching patterns necessary for smoothing correction is not increased and the smoothing correction can be efficiently performed. Since the smoothing correction is applied to the registration-corrected image, an image in which edge disturbance due to registration correction is corrected can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image correction method for performing smoothing processing for smoothing edges of an input image and registration correction for an output image.

  Smoothing is known as a process for smoothly correcting an image composed of straight lines / curves such as characters and line drawings without jaggedness. There are various smoothing methods. As a typical example, pattern matching is performed between image data read by a scanner or the like and a known pattern. If a matching known pattern exists, the corresponding smoothing is performed. The processed pattern is output.

  In the tandem type image forming apparatus, a plurality of image forming units are used to form one image. Variations in the dimensions and mounting positions of the components constituting the image forming unit, the eccentricity of the rotational drive member such as the photosensitive drum, the moving speed of the image forming surface of the member carrying the image such as the photosensitive drum (in the sub-scanning direction) Image displacement and size variations (hereinafter collectively referred to as registration misalignment) due to causes such as variations in the movement speed along the line) and positional shifts of the respective components due to temperature changes inside the apparatus. If the registration error is a color image, it is visually recognized as a color error (color registration error). For this reason, registration correction (hereinafter referred to as registration correction) for aligning images formed by the image forming units of the respective colors is performed.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for correcting an image forming position based on image data obtained by smoothing an image edge, a side registration correction amount, and a magnification correction amount.

  Patent Document 2 discloses a technique for performing smoothing correction on a step portion of an image generated by registration correction.

JP 2001-208990 A JP 2001-245156 A

  However, when the registration correction is performed on the image after the smoothing correction is performed, the smoothing correction and the registration correction are performed independently, so that the edge portion of the smoothed image is disturbed. Patent Document 1 cannot solve this problem.

  In Patent Document 2, smoothing correction is performed only on the image of the registration correction portion, and smoothing is not performed on the entire image.

  In order to perform smoothing by pattern matching on the entire image after the registration correction, it is necessary to prepare a large number of matching patterns in order to specify a smoothing target. For this reason, problems such as the time required for the smoothing process taking place and the use amount of the memory for recording the matching pattern increase.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image processing apparatus and an image correction method capable of performing smoothing correction with a small number of matching patterns on the entire image after registration correction. To do.

  In order to achieve the above object, an image processing apparatus according to the present invention lowers the resolution of a registration correction unit that performs registration correction for correcting image misregistration, and the image after the registration correction. The image forming apparatus includes a resolution converting unit that performs correction and a smoothing correcting unit that performs smoothing correction on an image after resolution conversion.

  In the present invention, resolution conversion is performed on an image after registration correction, and smoothing is performed on an image with a small number of pixels. Therefore, the number of matching patterns necessary for smoothing correction is not increased, and smoothing correction is efficiently performed. Can be done automatically. In addition, since the smoothing correction is performed on the image after the registration correction, it is possible to obtain an image in which the edge disturbance due to the registration correction is corrected.

  The image processing apparatus further includes an output selection unit that selects and outputs the image after the smoothing correction in the area subjected to the smoothing correction, and selectively outputs the image after the registration correction in the other area. It is good to have.

  Since the image after registration correction is output to an area where smoothing is not performed, an image closer to the input image can be output.

In the image processing apparatus, the resolution conversion unit may determine the density of the pixel after conversion including the density of peripheral pixels of the plurality of pixels when converting the plurality of pixels before conversion into one pixel.
Therefore, the resolution conversion of the image can be performed with high accuracy.

  In the image processing apparatus, the smoothing correction unit may perform the smoothing correction by pattern matching between an input image and a registered matching pattern.

  By performing the smoothing correction by pattern matching, the smoothing correction can be performed with high accuracy. Further, by using pattern matching for the smoothing correction of the present invention, it is possible to prevent an increase in the number of patterns required for the matching pattern.

  The image correction method of the present invention includes a step of performing registration correction for correcting image misregistration, a step of performing correction for lowering the resolution of the image after the registration correction, and a step after resolution conversion Applying smoothing correction to the image.

  In the present invention, resolution conversion is performed on an image after registration correction, and smoothing is performed on an image with a small number of pixels. Therefore, the number of matching patterns necessary for smoothing correction is not increased, and smoothing correction is efficiently performed. Can be done automatically. In addition, since the smoothing correction is performed on the image after the registration correction, it is possible to obtain an image in which the edge disturbance due to the registration correction is corrected.

  The present invention can efficiently perform smoothing correction on an image after registration correction without increasing the number of matching patterns necessary for smoothing correction.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the present embodiment will be described with reference to FIG. In FIG. 1, a document 2 placed on a document table 1 is R (red) and G (green) by an image scanner including a color CCD sensor 3 via a scanning optical system including a light source and a scanning mirror. , B (blue) analog image signals. The analog image signals of R, G, and B read by the color CCD sensor 3 are converted into Y (yellow), M (magenta), C (cyan), and K (black) image images by the image processing unit 4. Image data of each color is sequentially output to ROS (Raster Output Scanner) 7C, 7M, 7Y, 7K of the forming units 5C, 5M, 5Y, 5K, and emitted from these ROS 7C, 7M, 7Y, 7K according to the image data. Laser beams are scanned and exposed on the surfaces of the respective photoconductive drums 6C, 6M, 6Y, and 6K to form electrostatic latent images. The electrostatic latent images formed on the photosensitive drums 6C, 6M, 6Y, and 6K are developed as toner images of respective colors Y, M, C, and K by the developing devices 8C, 8M, 8Y, and 8K, respectively.

  Further, the misregistration amount measuring unit 9 shown in FIG. 1 calculates the misregistration amounts of the C, M, Y, and K color images forming the image. There are various methods for measuring the amount of misalignment by the misalignment measuring unit 9. For example, as shown in FIG. 2, a registration deviation measurement pattern P is formed over the entire circumference of the transfer belt 50, and this registration deviation measurement pattern P is repeated at a predetermined timing by the positional deviation measurement unit 9 (see FIG. 1). Sampling. From the sampling data obtained in this way, for example, the registration deviation amount of each color (yellow, magenta, cyan) with reference to black is detected, and these are divided by the number of samplings to calculate the average registration deviation amount R. Registration correction is performed based on the deviation amount R. The displacement amount measured by the displacement amount measuring unit 9 is sent to the control unit 10.

  Next, the configuration of the image processing unit 4 will be described with reference to FIG. As shown in FIG. 3, the image processing unit 4 includes a control unit 10, a first resolution conversion unit 11, a registration correction unit 12, a second resolution conversion unit 13, a smoothing unit 14, and an output selection unit 15. Have. The control unit 10 controls each unit. Further, a registration correction correction amount is determined from the positional shift amount measured by the positional shift amount measurement unit 9 and notified to the registration correction unit 12.

  The first resolution conversion unit 11 performs resolution conversion on the input image and outputs a high-resolution image. One pixel of the input image is converted into a number of pixels having a predetermined resolution.

  As illustrated in FIG. 4, the registration correction unit 12 includes a main scanning registration correction unit 21, a line buffer memory 22, and a sub-scanning registration correction unit 23.

  The main scanning registration correction unit 21 receives the output image of the first resolution conversion unit 11, performs registration correction in the main scanning direction, and outputs the corrected image to the line buffer 22. The main scanning registration correction unit 21 receives the main scanning registration correction amount from the control unit 10. The control unit 10 outputs the registration correction amount in the main scanning direction based on the positional deviation amount to the main scanning registration correction unit 21. When the image data for one line is input, the main scanning registration correction unit 21 inserts and thins out pixels according to the main scanning registration correction amount notified from the control unit 10 and stores the corrected image data in the line buffer. Accumulate in memory 22. The line buffer memory 22 stores image data for a plurality of lines.

  A sub-scanning registration correction amount from the control unit 10 is input to the sub-scanning registration correction unit 23. The sub-scanning registration correction unit 23 starts reading image data from the line buffer memory 22 when image data for a plurality of lines is accumulated in the line buffer memory 22. The sub-scanning registration correction unit 23 reads the same line (or part of the line) twice (insertion processing) or reads the line (or part of the line) according to the sub-scanning registration correction amount notified from the control unit 10. By skipping reading and reading out the next line (or part of the line) (thinning-out process), registration correction is performed, and image data after registration correction for one line is output to the outside. FIG. 6 shows an image after resolution conversion and registration correction are performed on the input image shown in FIG. In the image after the registration correction shown in FIG. 6, pixels are inserted in a predetermined region in the image. Note that circles shown in FIG. 6 indicate positions where pixels are inserted.

  The second resolution conversion unit 13 performs resolution conversion on the image after registration correction, and outputs a low resolution (equivalent to the input image) image. The second resolution conversion unit 13 converts a predetermined number of pixels in the main scanning direction and the sub-scanning direction into one pixel. For example, when 2400 dpi is converted to 600 dpi, the high-resolution 4 × 4 pixels shown in FIG. 7A are converted into one pixel with a low resolution. Further, the second resolution conversion unit 13 determines a plurality of pixels before the resolution conversion based on the density, and determines the density of the pixel after the conversion. That is, it is determined whether the pixel of interest after conversion is a white image or a black image. The determination area is an area larger than the area that becomes one pixel after resolution conversion. If one pixel after resolution conversion is a 4 × 4 area before conversion, for example, density determination is performed with 5 × 5 pixels shown in FIG. 7B larger than 4 × 4. FIG. 7C continuously shows the determination area where the density determination is performed. As shown in FIG. 7C, the area for determining density overlaps one line at a time in the main scanning direction and the sub-scanning direction. The density determination area for resolution conversion is not limited to that shown in FIG. 7B, and may be a determination area as shown in FIG. 8, for example.

  The smoothing unit 14 performs pattern matching between the input image and a known matching pattern recorded in a memory (not shown), and outputs a pattern subjected to smoothing processing in advance when there is a matching pattern that matches. To do. 9 and 10 show examples of matching patterns and output patterns. FIG. 9 shows a matching pattern and an output pattern in the main scanning direction, and FIG. 10 shows a matching pattern and an output pattern in the sub-scanning direction. With the central pixel of the 5 × 5 matrix as the target pixel, when the arrangement of the white image and the black image around the target pixel matches the matching pattern shown in the figure, the target pixel is corrected to the corresponding output pattern. 9 and 10 may be a white image or a black image. FIG. 11 shows an area determined as a smoothing correction target area by pattern matching, and FIG. 12 shows an image after smoothing correction by the matching pattern.

  The output selection unit 15 receives the image after the registration correction from the registration correction unit 12 and the image subjected to the smoothing correction from the smoothing unit 14. The output selection unit 15 inputs these images and selectively outputs the images. That is, as shown in FIG. 13, the smoothed image from the smoothing unit 14 is output for the image of the area on which the smoothing correction has been performed. For images in other regions, an image that has undergone registration correction by the registration correction unit 12 is output. In FIG. 13, the area printed in black is indicated by diagonal lines in order to display the area using the smoothed image in an easy-to-understand manner.

  As described above, in this embodiment, an image obtained by performing the smoothing correction on the image after the registration correction is output to the smoothing correction target area, and an image after the registration correction is output to the other areas. Since the smoothing correction is performed on the image after the registration correction, an image in which edge disturbance due to the registration correction is corrected can be obtained. In addition, since resolution conversion is performed on the image after registration correction and smoothing is performed on an image with a small number of pixels, matching can be performed with a small number of patterns. In addition, since the image after the registration correction is output to an area where smoothing is not performed, an image closer to the input image can be output.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows the structure of an image processing apparatus. It is a figure for demonstrating the measuring method of positional offset amount. It is a figure which shows the structure of an image process part. It is a figure which shows the structure of a registration correction | amendment part. It is a figure which shows an example of an input image. It is a figure which shows the image which carried out the registration correction | amendment with respect to the input image. It is a figure which shows the determination area | region for resolution conversion. It is a figure which shows the determination area | region for resolution conversion. It is a figure which shows a matching pattern. It is a figure which shows a matching pattern. It is a figure which shows the area | region determined as the object area | region of smoothing correction | amendment by pattern matching. It is a figure which shows the image after the smoothing correction | amendment by a matching pattern. It is a figure which shows the image after the image process by the image process part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Original stand 2 Original 3 Color CCD sensor 4 Image processing part 5C, 5M, 5Y, 5K Image forming unit 6C, 6M, 6Y, 6K Photosensitive drum 7C, 7M, 7Y, 7K ROS
8C, 8M, 8Y, 8K Developer 9 Position shift amount measurement unit 10 Control unit 11 First resolution conversion unit 12 Registration correction unit 13 Second resolution conversion unit 14 Smoothing unit 15 Output selection unit 21 Main scanning registration correction unit 22 Line buffer Memory 23 Sub-scanning registration correction unit

Claims (5)

Registration correction means for performing registration correction for correcting image misalignment;
Resolution conversion means for performing correction to lower the resolution of the image after the registration correction;
An image processing apparatus comprising smoothing correction means for performing smoothing correction on an image after resolution conversion.   2. The output selection means for selecting and outputting the image after smoothing correction in an area subjected to smoothing correction, and selecting and outputting the image after registration correction in another area. The image processing apparatus described.   3. The resolution conversion unit, when converting a plurality of pixels before conversion into one pixel, determines a density of a pixel after conversion including a density of peripheral pixels of the plurality of pixels. Image processing apparatus.   The image processing apparatus according to claim 1, wherein the smoothing correction unit performs the smoothing correction by pattern matching between an input image and a registered matching pattern. A step of performing registration correction for correcting image displacement;
Correcting the registration-corrected image to reduce the resolution of the image;
And a step of performing smoothing correction on the image after resolution conversion.

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