JP6020042B2 - Image processing apparatus, image processing method, program, and recording medium - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, a program, and a recording medium that process an image output in a toner save mode.

  In an image forming apparatus such as a printer, as one function for reducing output cost, there is a toner save mode in which the amount of toner used for image output is reduced and the density of the entire image is reduced (for example, output). , See Patent Document 1).

  Conventionally, when a low density image output using the toner save mode is copied, the density of the image is reduced overall, and there is a possibility that erroneous determination of a character part may occur. In such a case, since the erroneously determined character is processed as a picture instead of a character, coloring occurs, and there is a problem that readability is deteriorated.

The present invention has been made in view of the above problems,
An object of the present invention is to provide an image processing apparatus, an image processing method, a program, and a recording medium that improve the legibility of characters when copying a low-density document output in a toner save mode.

The present invention includes a determination unit image whether it is a toner saving, when the image is determined to be toner saving, a correction means for performing correction processing on the image, the determination Means detects a character edge from the image, detects a dot area around the edge from the image, and detects that the density of the image is less than a predetermined threshold; The most important feature is that it is determined that the toner is saved .

  According to the present invention, when copying a low-density image output in the toner save mode, it is possible to reduce the coloring of the character portion and improve the legibility of the character.

1 shows a configuration of an image processing apparatus according to a first embodiment of the present invention. The structure of a correction process part and a filter process part is shown. FIG. 10 is a diagram illustrating a black generation LUT and a printer γ correction table. The structure of a density | concentration information detection part is shown. The example of a pattern of black character formation is shown. The structure of an edge determination part is shown. The structure of a halftone dot, white background, color, and character edge detector is shown. 2 shows a configuration of an image processing apparatus according to a second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, it is determined whether the image to be copied is a low-density image output in the toner save mode, and when it is determined that the image is output in the toner save mode, the black character processing density is controlled to determine the image. Improve sexiness.

  FIG. 1 shows a configuration of an image processing apparatus according to a first embodiment of the present invention. In FIG. 1, 101 is a density information detection unit, 102 is a character edge detection unit, 103 is a halftone dot determination unit, 104 is a toner save determination unit, and 105 is a correction processing unit.

The toner save determination unit 104 determines that the character portion is a dither pattern (halftone dot) based on the detection result of the character edge detection unit 102 that determines whether the target pixel of the input image is a character edge and the halftone dot determination around the edge. ) And the detection result of the density information detection unit 101 for determining whether or not the density is low by providing a threshold value with the read density. It is determined whether or not the pixel of interest of the image is toner saved.
If the detection result of the character edge detection unit 102 is a black edge and the determination result of the halftone dot determination unit 103 is that there is a halftone dot determination area around the edge, it is determined as a toner save candidate, and the density information of the target pixel If the detection result of the detection unit 101 is a low-density image (original image) that is less than a predetermined threshold value, it is determined that the pixel of interest of the input image is saved with toner.

  Image processing performed by the correction processing unit 105 will be described using the determination result of the toner save determination unit 104. FIG. 2A shows the configuration of the correction processing unit 105, which includes a filter processing unit 201, a printer color correction unit 202, a black processing unit 203, a printer γ correction unit 204, and a gradation processing unit 205.

  FIG. 2B shows the configuration of the filter processing unit. The edge emphasizing unit 302 and the smoothing unit 303 of the filter processing unit 201 respectively perform filter processing on the target pixel, and the synthesis processing unit 304 uses both edge filter processing results to detect the edge detected by the edge amount calculation unit 301. Synthesize based on quantity.

  That is, when the edge amount is large, the composition processing unit 304 performs composition processing so that the ratio of the output result of the edge enhancement unit 302 is large, and when the edge amount is small, the ratio of the output result of the smoothing unit 303 is Composite processing to increase. Normally, the ratio of edge enhancement and smoothing is switched according to the amount of edge, but if it is determined that the toner is saved, the entire image has a low density, so edge enhancement is weak and smoothing is performed. A parameter that increases the intensity of the halftone dots and performs processing to suppress variation in density when the black processing amount is changed.

  In this embodiment, when it is determined that the toner is saved, control is performed to increase the black amount by black processing. In such a case, since the edge portion corresponds to the black processing control, the edge portion is emphasized. As a result, the density balance at the edge portion and other than the edge portion is lost. Therefore, by weakening the edge enhancement, it is possible to suppress the density floating in the portion where the blackening process is performed, and to reduce the density difference (density variation) other than the edge portion, thereby improving the legibility. it can.

  An image storage unit (not shown) stores the image data after filtering and the determination result of the toner save determination unit 104. In the case of copy processing, the once stored image data and toner save determination result are read, and the data is sent to the image processing after the printer color correction unit 202.

  The printer color correction unit 202 converts RGB signals into CMY signals for printer output. The black processing unit 203 performs a process of generating a K signal according to CMY data (black generation) and reducing the amount corresponding to K from CMY (under color removal: UCR). Ink generation and UCR include a method using a calculation formula, a method using a LUT, and the like. In this embodiment, black generation is performed using a LUT, and UCR is performed using a calculation formula.

  FIG. 3A is a diagram for explaining a black generation LUT. In black generation, the minimum value Min (C, M, Y) of C, M, Y (0 is white, 255 is black) is calculated and input to the LUT to obtain an output value. Two ink generation tables for normal characters and a black generation table for toner save determination are prepared in advance, and the black generation table is switched and applied according to the determination result.

  The character black generation table replaces all Min (C, M, Y) with K signals. The black generation table for toner save determination is a table that is slightly inclined from the black generation table for characters.

UCR is performed by the following equation. α is a UCR adjustment parameter.
C = C-α × K
M = M−α × K
Y = Y-α × K
The UCR adjustment parameter is also switched according to the black generation. In the area where the character black generation table is applied, α = 1, and in the area where the toner save black generation table is applied, α = 1.2, for example. By performing these processes, the color of the character part is suppressed and the legibility is improved.

  The printer γ correction unit 204 performs conversion processing using a density conversion table in accordance with the density characteristics of the printer, and the gradation processing unit 205 performs pseudo halftone processing such as dithering and error diffusion.

  FIG. 3B illustrates the printer γ correction table. The printer gamma correction table has a gamma table for increasing the density as compared with a normal printer gamma for toner save determination. Since the image output in the toner save mode has a low density, the character readability can be improved by raising the printer γ and setting the density high.

  According to the present embodiment, the processing can be switched according to the low-density input image output by toner save to increase the image density and suppress the coloring of the character portion, so that the character readability is improved. An output image can be obtained.

  FIG. 4 is a diagram for explaining threshold setting of the maximum density when inputting the toner save image with respect to the read density of the input image. FIG. 4A shows an example of reading densities of a normal output image and a toner save output image. In the toner save mode, since the maximum density at the time of output is regulated, the reading value of the output image is low as shown in the figure. A threshold is provided for the difference between the maximum density of the normal output image and the maximum density of the toner save output image, and it is determined whether or not the input image is output at a low density less than the threshold.

  FIG. 4B shows the configuration of the density information detection unit. The density information is determined by referring to 3 × 3 pixels around the target pixel (3 × 3 pixels are averaged by the averaging unit 401) and determined by the threshold determination unit 402. In the threshold determination, it is determined whether the pixel is a high density pixel or a low density pixel based on the set threshold value. If it is less than the threshold, it is determined as a low density region, and if it is greater than or equal to the threshold, it is determined as a high density region. As shown in FIG. 4A, the density threshold value can be set depending on how much density is dropped by toner save. This threshold setting is variably set according to the image quality mode.

  FIG. 5 shows a pattern example of black character formation during normal output and toner save. Normally, when outputting black characters, the character pattern is output as shown in FIG. 5A unless the density is specified. Further, when outputting in the toner save mode, for example, when the density of the entire output is reduced to 60%, for example, the black character portion is also adjusted to the output density. Therefore, the dither pattern is used to match the density of the black character portion, and the character portion is formed with halftone dots as shown in FIG. The pattern shape varies depending on the dither pattern, but the interval and size of the halftone dot shape are set according to the output density.

FIG. 6A shows the configuration of the edge determination unit. In the ternary circuit 501, the G signal is ternized using two threshold values (th1, th2) in the input image composed of 8 bits for each of RGB. At this time, th1 <th2. 0 is the high density side, 255 is the low density side, and the following settings are used.
0 ≦ G ≦ th1 Black pixel th1 <G <th2 Intermediate pixel th2 ≦ G ≦ 255 White pixel In black pixel pattern matching 502, the black pixel pattern in the 3 × 3 matrix matches any of FIG. 6B. Sometimes the target pixel is determined to be a connected black pixel. Similarly, in the white pixel pattern matching 503, the connected white pixels are determined by checking whether the white pixels match those in FIG.

  The number of connected black pixels and the number of connected white pixels are counted within a 3 × 3 pixel centered on the pixel of interest, and the AND circuit 504 combines both count results to determine whether it is an edge portion. That is, the determination is made using the property that the connected white pixels and the connected black pixels simultaneously exist at a certain density or more in the outline portion of the character.

  FIG. 7A shows the configuration of the halftone dot determination unit. The halftone dot determination uses a method based on peak pixel detection. That is, the peak pixel detection unit 601 determines whether or not the target pixel is a peak point indicating a peak or valley of density change from the density relationship with surrounding pixels. When the density level of the central pixel is higher or lower than all other density levels in the block composed of M × M pixels, it is determined whether or not the peak point is based on the following equation.

Peak detection is performed by the following equation from the peak pixel detection unit (3 × 3) 601.
If M = 3,
| 2m0−m1−m8 | ≧ ΔmTH and
| 2m0−m2−m7 | ≧ ΔmTH and
| 2m0-m3-m6 | ≧ ΔmTH and
| 2m0-m4-m5 | ≧ ΔmTH
That is, the absolute value of the difference between the average value of the two pixel levels at the symmetrical positions ((m1, m8) (m2, m7) (m3, m6) (m4, m5)) and the density of the central pixel across the central pixel m0. When the value is larger than the threshold value ΔmTH, the center pixel is detected as a peak. The blocking unit 602 determines that the block is an active block if at least one peak pixel exists for each 4 × 4 pixel block, and the density correction unit 603 determines the active block in the 5 × 5 block centered on the target block. When the counted value is equal to or greater than a predetermined number, the target block is set as a halftone dot block. Finally, the expansion unit 604 performs expansion processing with 3 × 3 blocks, and attention is paid if at least one halftone dot block exists. Let the block be a halftone dot region.

  Peak pixel detection may be performed for each of the RGB signals, but in the case of simplification, peak detection is performed for the G signal. Then, based on the peak pixel information, it is determined whether the area is a halftone dot area.

  FIG. 7B shows the configuration of the white background determination unit. The binarization unit 701 performs binary determination on whether the pixel is a white pixel or a black pixel. Pattern matching 702 is performed on the determined white pixel, thereby overturning the determination of an isolated white pixel. Specifically, pattern matching is performed with a pattern in which white pixel continuity is observed in four vertical and horizontal diagonal directions. If a pattern is matched, a white pixel is set, and if not matched, a black pixel is set. Next, the expansion unit 703 performs an expansion process of observing surrounding M × M pixels including the target pixel and covering any target pixel with the white pixel if at least one white pixel is included therein. When the surrounding N × N pixels including the target pixel are viewed and there is at least one black pixel, the contraction process is performed to cover the target pixel with the black pixel. An area remaining as a white pixel after the contraction process is a white background determination area.

  FIG. 7C shows the configuration of the color determination unit. The chromatic pixel detection unit 801 detects a pixel corresponding to Max (| RG |, | GB |, | BR |)> th3 (th3 is a predetermined threshold) as a chromatic pixel, and blocks The determination unit 802 determines an active block if at least one chromatic pixel exists for each block of 4 × 4 pixels, and the expansion unit 803 performs expansion processing on a 7 × 7 block, and even one active block is detected. If it exists, the block of interest is set as a chromatic area.

  FIG. 7D shows the configuration of the character edge detection unit. Based on the determination results of the edge determination unit (FIG. 6A), the white background determination unit (FIG. 7B), and the halftone determination unit (FIG. 7A), the white ground character edge determination unit 901 determines the character edge candidate pixel. Determine. If it is an edge, white background, and non-halftone dot, it is determined that it is a character edge candidate pixel.

  The edge determination unit in FIG. 6A detects one dot at a time for each of the inner edge / outer edge as a character edge candidate pixel. A total of 2 dots, one for each of the inner and outer dots, is insufficient for the filter processing. Therefore, the expansion process is performed by the expansion unit (3 × 3) 902, and the result is “character edge”.

  The dilation unit (3 × 3) 902 refers to a 3 × 3 pixel edge candidate pixel centered on the pixel of interest, and if there is at least one character edge candidate pixel, the pixel of interest is a character edge. . In this embodiment, the expansion amount is 3 × 3. The black character / color character determination unit 903 determines from the result of the character edge and the color determination unit that the character edge is a chromatic color and is a “color character edge”, and the character edge and the achromatic color is a “black character edge”. It is determined that

  FIG. 8 shows the configuration of the image processing apparatus according to the second embodiment of the present invention. In the second embodiment, a color determination unit 1004 is further added to the configuration of the first embodiment.

  The toner save determination unit 1005 refers to the determination result of the halftone dot determination unit 1003, the determination result of the character edge detection unit 1002, the determination result of the color determination unit 1004, and the detection result of the density information detection unit 1001. It is determined whether or not the pixel is output in the toner save mode.

  If the result of character edge detection is a black edge and there is a halftone dot determination area around the edge, it is determined as a toner save candidate, and if the density information detection result of the pixel of interest is low density, it is determined that toner is saved. This is the same as in the first embodiment. At this time, if the area determined as a halftone dot is determined to be a chromatic color, the toner save determination unit 1005 determines that the area is not a toner-save image, and the correction processing unit 1006 applies to the area. Does not perform correction processing.

  According to the present invention, a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus is stored in the storage medium. It is also achieved by reading and executing the program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment. As a storage medium for supplying the program code, for example, a hard disk, an optical disk, a magneto-optical disk, a nonvolatile memory card, a ROM, or the like can be used. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on an instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included. Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. A case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is included. Further, the program for realizing the functions and the like of the embodiments of the present invention may be provided from a server by communication via a network.

101 Density Information Detection Unit 102 Character Edge Detection Unit 103 Halftone Determination Unit 104 Toner Save Determination Unit 105 Correction Processing Unit

JP 2007-235583 A

Claims (7)

Determining means for determining whether the image is toner-save;
When the image is determined to be toner saving, and a correction means for performing correction processing on the image,
The determining means detects a character edge from the image, detects a dot area around the edge from the image, and detects that the density of the image is less than a predetermined threshold. An image processing apparatus that determines that an image is saved with toner .   The image processing apparatus according to claim 1, wherein the correction unit performs filter processing that suppresses edge enhancement processing for character edges of the image and emphasizes smoothing processing for halftone dots of the image.   The image processing apparatus according to claim 1, wherein the correction unit performs a black generation process using a black generation table that is higher in black than the black generation for characters.   The image processing apparatus according to claim 1, wherein the correction unit performs γ correction processing for increasing the density of the entire image. A determination step of determining whether the image is toner-save;
When the image is determined to be toner saving, and a correction step of performing correction processing on the image,
In the determination step, when a character edge is detected from the image, a halftone dot region is detected around the edge from the image, and the density of the image is detected to be less than a predetermined threshold, An image processing method comprising: determining that an image is toner saved . A program for causing a computer to realize the image processing method according to claim 5 . A computer-readable recording medium on which a program for causing a computer to implement the image processing method according to claim 5 is recorded.

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