KR0161247B1 - Mtf correcting method of image input apparatus - Google Patents

Abstract

The present invention relates to an adaptive MTF correction method of an image input apparatus that adaptively processes an MTF correction filter according to characteristics of an input image, and scans and reads one line of image data of a window according to the start of scanning. A second step (21 22) of storing the required number of pixel lines in the MTF correction memory: determining whether the storage of the pixel lines required for correction is completed in the MTF correction memory, and configuring block units of a predetermined size; Otherwise scanning (23, 24) while continuing to increase the line; A third step (25) of judging the area for each block according to the image characteristic after performing said step; A fourth step (26) of performing MTF correction filtering on each block area in which the image characteristic is determined; A fifth step 27 of outputting and ending the image after performing the above step is provided.

Description

Adaptive MTF Correction Method of Image Input Device

1 is a schematic view showing the configuration of a general image pressure device.

2 is a block diagram of a conventional MTF correction filter.

3 is a flowchart illustrating an embodiment of an adaptive MTF correction method of an image input apparatus according to the present invention.

4 is an exemplary block diagram of an MTF correction memory.

5 is a detailed flowchart for determining image characteristics of each block.

6 is a flowchart of processing for performing MTF correction filtering on image characteristics of each block.

7 to 9 are block diagrams of filters employed in the adaptive MTF correction method according to the present invention for filtering each block.

The present invention relates to a method for MTF correction for an input image scanned in an image forming apparatus provided in an office equipment such as a copy machine, a facsimile machine, and the like, and in particular, an image input apparatus for adaptively processing an MTF correction filter according to characteristics of each input image. The present invention relates to an adaptive modulation transfer function (MTF) correction method.

In general, the image input device reads the lens 1 for reducing the reflected image irradiated with the light source lamp as shown in FIG. 1 and the image incident through the lens 1 to be converted into an electrical signal. A charge coupled device (hereinafter referred to as a charge coupled device (CCD)) 2, an A / D converter 3 for converting analog data which is an electrical signal of the CCD 2 into digital data, and the A / An MTF correction memory 4 for storing the signal output from the D converter 3 for correction by a modulation transfer function, and a center for image processing of the image data stored in the MTF correction memory 4 according to a pre-built processing method. And a central controller 5 for controlling the overall operation to store the stored image data in the image storage memory 6 or output the printed image to the printer 8 for printing.

Here, the radiant image is changed depending on the process of changing the analog signal of the CCD reading the original image into a digital signal or the amount of light entering the CCD (2). In particular, deterioration may occur due to optical factors such as the lens (1). In this case, it can be seen that the image signal is generally blurred and the reproducibility of the copy image is reduced.

Therefore, MTF correction is performed on an image input to the CCD to obtain a clearer image. Conventionally, MTF correction is performed on an optical system such as a lens and a mirror by using an MTF correction filter as shown in FIG. 2 to MTF correction an input image. MTF degradation due to degradation and spatial frequency mismatch of CCD image sensor was corrected.

However, the input image in the image pressure device exists in various forms such as a text, a photo, and a dot and has different signal characteristics. For example, the MTF correction filter with the edge enhancement dimension has different characteristics for each image signal such as a photographic image having a small change in density of the image, a background, and a binary image of a character region having a large change in density. There is a problem in that there is a limit in expressing high quality images.

Accordingly, the present invention has been devised to solve the above problems, and is an adaptive type of image input apparatus capable of reproducing high-quality images by processing with a suitable MTF correction filter for each signal characteristic having various characteristics. Its purpose is to provide an MTF correction method.

In order to achieve the above object, the present invention includes a first step of scanning by reading one line of the image data of the window according to the start of scanning, and storing a predetermined number of pixel lines necessary for correction in the MTF correction memory; A second step of determining whether or not the storage of the pixel line required for correction is completed in the MTF correction memory and configuring a block unit having a predetermined size; otherwise, continuously scanning while increasing the line; A third step of judging the area for each block according to the image characteristic after performing said step; A fourth step of performing MTF correction filtering on each block area in which the image characteristic is determined; A fifth step of outputting and terminating the image after performing the step is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings of FIG. 3.

3 is a flowchart illustrating an embodiment of an adaptive MTF correction method of an image input apparatus according to the present invention, FIG. 4 is an example of an image block of an MTF correction memory, and FIG. 5 is used to determine image characteristics of each block. 6 is a process flow chart for performing MTF correction filtering on the image characteristics of each block, and FIGS. 7 to 9 are filters used for the adaptive MTF correction method according to the present invention to filter each block. 7 is a block diagram of a smoothing filter, FIG. 8 is a block diagram of an MTF correction right angle filter, and FIG. 9 is a block diagram of an MTF correction diagonal filter.

In the adaptive MTF correction method according to the present invention, in the system block of the image pressure device shown in FIG. 2, the characteristic of the image is a block unit of a predetermined number of horizontal x vertical pixel lines among the image data stored in the MTF correction memory 4. The MTF correction is performed according to the characteristics of each image by filtering and classifying the pixels in the respective blocks, and the method for performing MTF correction will now be described.

As shown in FIG. 3, in accordance with the start of scanning, one line of image data of the window is scanned and read, and a predetermined number of pixel lines necessary for correction are stored in the MTF correction memory. 6-line images are stored in the MTF correction memory so as to be easily divided. (21, 22)

In addition, if the storage is completed by determining whether 6 lines of images are stored in the MTF correction memory, a block unit having a predetermined size for image data of 6 lines is configured. Otherwise, scanning is performed while increasing the lines to the MTF correction memory. Save it. (23, 24)

Then, after performing the above step, the process of determining the area of each block according to the image characteristic is performed.

Here, the determination processing step for each block performs a detailed process as shown in FIG. 5, which will be described below.

The processing lines are set to the predetermined number N of pixels in the scanned annular data lines equally in the horizontal and vertical directions. In this embodiment, four processing lines in the horizontal x vertical (in the case of N = 4) and the upper and lower sides 2 A block unit consisting of two lines as a reference line is inputted. (51)

After determining the maximum value Lmax of the luminance in the block and the minimum value Lmin of the luminance, an error value Ldif, which is a difference therebetween, is determined to determine the image characteristics in the block.

Here, the error value Ldif is a change amount of luminance in a block, and the parameter K for determining a background and a photographic region having a small change characteristic and a region of a binary image such as a photograph and a dot having a large change in luminance. Becomes

By using this parameter K, it is determined whether the error value Ldif is greater than the threshold, and if it is large, it is determined as a binary image area, and if it is small, it is determined as a background and photo area and separated. (53)

After the above process, it is determined whether or not the luminance minimum value Lmin is greater than the luminance threshold value Lth in the background and photo areas, and when 0 is determined, 0 is assigned to the region judgment (RJ) RAM. If it is determined as a photo area, the process of assigning 1 to the area determination RAM is performed. (54 to 56)

In addition, for the area determined as a binary image, first, the horizontal change (HC) value and the vertical change (VC) value are respectively calculated to determine whether the value is larger than the parameter (K). If the value is equal to or greater than K, the process determines that the halftone region is assigned to the region determination RAM, and the other region is determined to be the character region, and 3 is assigned to the region determination RAM.

Here, HC and VC represent the number of change point pixels in the horizontal direction and the number of change point pixels in the vertical direction when binarized to 1/2 of the maximum luminance.

The dot region generates more pixels than the binary image of the character region, and there are many variations in image, term, left, and right. Thus, the dot region and the character region are distinguished using these characteristics.

When the above detailed processing is performed, the MTF correction filtering is performed on the determined blocks, and then the image is output and terminated.

MTF correction filtering for each block is described in detail with reference to FIG.

It is determined whether the image block stored in the MTF correction memory is assigned to the area determination RAM as 0 (71). If it is 0, it is determined as the background area, and if it is not 0, it is determined whether it is assigned to 1 in the area determination RAM.

As shown in FIG. 7, if the area assigned to the area determination RAM is zero, the coarse signal in the background is smoothed by processing using a peripheral pixel and a 3 × 3 smoothing filter that averages pixel average values. Remove the noise signal. (72)

If it is determined that the image block is allocated to the area determination RAM as 1 (73), the image block corresponds to the photograph area, so that the block is made by using the MTF general correction filter as shown in FIG. 2 to improve the overall contrast. Each pixel in the filter is filtered (74), and if it is not 1, it is determined whether or not it is assigned to 2 in the next region determination RAM.

In the process of determining whether 2 is assigned to the area determination RAM, this value corresponds to a halftone area, and the halftone area has a high frequency characteristic in an oblique direction, and thus the diagonal line as shown in FIG. The MTF correction slant filter with low frequency attenuation characteristic in the direction is used for the correction process to suppress the generation of moire due to MTF deterioration.

In addition, if it is determined in the process of determining whether the area determination RAM is assigned to 2, the area determination RAM is assigned to 3 and is determined to be a character area. Since the characteristics of the character region have high frequency characteristics in the main and sub-scanning directions, the attenuation characteristics of the main and sub-scans as shown in FIG. 8 are relatively low, and correction processing is performed using an MTF-corrected right angle filter with high reproducibility of characters. Perform the process. (77)

As described above, when the background area, the picture area, the halftone area, and the text area are each filtered by a corresponding filter suitable for their characteristics, the luminance (Li) of the horizontal side among the first pixels Lij of the block is convolutionally calculated. If the value is larger than the number N of pixels in the block, it is determined that i = 1, and if it is small, the filtering is continued while increasing the number of pixels horizontally.

When i = 1 is corrected, it is determined whether the value obtained by convolution of the vertical brightness Lj is larger than the block pixel number N, and if it is large, the process is corrected to j = 1, and if it is small, the number of pixels is increased to the vertical side. Increase the to continue filtering.

As described above, the present invention, which is subjected to MTF correction processing, reproduces the characteristics of each image well so that a high resolution image quality can be obtained, and the image is added later, that is, half tone, since the area is determined in the preprocessing step of the image processing. Processing, and even when the resolution is converted, efficient image processing can be performed by using the area determination value of the block.

Claims (3)

In the MTF correction method which is applied to an image input device that scans and reads an image of an original, the MTF correction method for correcting image data values of a charge coupled device, wherein scanning is performed by scanning one line of image data of a window according to the start of scanning. First steps (21, 22) of storing a predetermined number of pixel lines in the MTF correction memory: determining whether the storage of pixel lines necessary for correction is completed in the MTF correction memory, and if so, constitutes a block unit having a predetermined size. A second step (23, 24) of scanning while increasing the line otherwise; a third step (25) of judging the area for each block according to the image characteristic after performing the step; A fourth step (26) of performing MTF correction filtering on each block area for which the image characteristic is determined; and a fifth step (27) of outputting and terminating the image after performing the step. Adaptive MTF Correction Method. The method of claim 1, wherein the third step sets the processing line to the predetermined number N of horizontally and vertically, respectively, among the scanned image data lines, and configures a block unit using the upper and lower lines as reference lines. Inputting the first process 51; A second step (52) of determining the image characteristics in the block by obtaining the maximum value (Lmin) of the luminance in the block and the minimum value (Lmin) of the luminance, and then obtaining an error value (Ldif) which is a difference between them; A third step (53) of determining whether the error value Ldif is greater than a threshold value after performing the second step and determining a binary image area if it is large, and determining and separating it into a background and a photograph area if it is small; Determining whether the luminance minimum value Lmin is greater than the luminance threshold value Lth in the background and photo areas, and if the value is small, assigns 0 to the area determination RAM, and if it is small, assigns 1 to the area determination RAM. Processes 54 to 56; And calculating a horizontal change (HC) and a vertical change (VC) value for the region determined as the binary image, and determining whether the value is greater than the parameter (K). And a fifth process (57 to 60) for determining that it is a halftone region and assigning 2 to the region determination RAM if it is equal to or greater than (K), and allocating 3 to the region determination RAM for determining the character region. Adaptive MTF Correction Method of Image Input Device. The method as claimed in claim 1, wherein the fourth step determines whether the image block stored in the MTF correction memory is assigned to the area determining RAM as 0 and if it is determined that the background block is assigned to 0, using a smoothing filter. A first process (71 to 73) for processing and determining whether or not to assign 1 to the area determination RAM if it is not 0; If it is determined in the first step that the picture block is assigned to the area determination RAM as 1, the MTF general correction filter is used to filter each pixel in the block. If not, the image block is assigned to the area determination RAM 2 as the next step. A second process (74, 75) of judging whether it has been done; A third step (76) of performing a correction process using an MTF correction diagonal filter when it is determined that the halftone region assigned to 2 in the area determination RAM in the second step; And a fourth step 92 of performing a correction process using an MTF correction orthogonal filter when it is determined that the character area allocated to the area determination RAM is 3 in the second step. .