JP4883613B2 - 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 having a color material save mode for outputting color material consumption more than usual, and relates to a technique suitable for, for example, a printer or a multifunction peripheral.

  In addition to the normal output mode that generates and outputs a high-quality image, there is a printer as a device that includes a color material save mode that saves and outputs color material consumption more than usual. The color material save mode is used when the image quality is not important, for example, when checking the layout of the output image.

  Conventional methods for saving color material consumption include a method of density conversion, a method of taking a logical product of a dither image and a thinning pattern, a method of performing pulse width modulation and writing light amount control, and the like. Since all of these methods output with the image density lowered, the image quality is inferior to that in the normal output mode. However, even in the color material saving mode, there is a demand for maintaining the readability without degrading the image quality, particularly for a highly important character image.

  The devices of Patent Documents 1 and 2 maintain character readability by switching color material saving for each image attribute. The color material saving of the character object is hardly performed (or not performed at all), and the color material saving is reliably performed on the object other than the character, so that the color material consumption can be saved while maintaining the readability of the character.

JP 2004-167755 A JP 2001-34118 A JP 2004-194091 A

  However, these methods of switching processing between the character area and other areas maintain the readability of the character completely for white characters (characters written in white on a background with a density other than white). Not. In other words, since the color material is surely saved in the background portion other than the white characters, the contrast between the white characters and the background image is lowered, making it difficult to read.

  FIG. 1A shows an image in which white characters on a black background are output in the normal output mode, and FIG. 1B shows a background image in which only the density of the white characters is stored (originally white, meaningless). Is a dithered image output after saving the color material. Thus, in the conventional color material saving method, the readability of white characters is degraded.

  Therefore, in the apparatus of Patent Document 3, in the case of a white character, the background and the character density are reversed and output. That is, when a white character image on a black background is output in the color material save mode, it is converted to a black character image on a white background and output. By this processing, it is possible to maintain readability without reducing the contrast of the outline characters and to save the color material consumption. However, the change between the original image and the output image is so large that the layout cannot be confirmed sufficiently.

The present invention has been made in view of the above problems,
The object of the present invention is to reproduce the image without saving the color material on the outer periphery of the negative character or by replacing the inner periphery of the negative character with the background color, maintain the readability of the white character, and improve the impression of the original image. An object of the present invention is to provide an image processing apparatus, an image processing method, a program, and a recording medium that realize a color material saving mode that does not change significantly.

The present invention provides an image processing apparatus having a mode that does not save color material consumption (hereinafter referred to as a first mode) and a mode that saves color material consumption (hereinafter referred to as a second mode) when outputting an image. The first determination means for determining whether or not the attribute of the target pixel constituting the image is a character, and when the character pixel and the non-character pixel are mixed in a predetermined area including the target pixel, Second determination means for determining a pixel as a character edge; and third determination means for determining whether the pixel of interest is a character outer periphery or a character inner periphery based on the determination results of the first and second determination means; Fourth determination means for determining the density of the target pixel, and fifth determination means for determining whether the target pixel is the outer periphery or the inner periphery of the negative character based on the determination results of the third and fourth determination means. Conversion means for converting the inner periphery of the negative character into a high density background color; When the second mode is set, the first mode is set by disabling the set second mode for the inner periphery of the negative character converted to the high-density background color. And a processing means for executing the set second mode is provided on the outer periphery of the negative character .

  According to the present invention, when color material saving is set, the color material consumption is not saved on the outer periphery of the negative character, so that the color material save is maintained without changing the impression of the original while maintaining the readability even with the white character. A mode can be realized. In addition, the conventional color material saving process can be performed on the color ground black characters that are positive characters, and the conventional image quality can be maintained.

  According to the present invention, when the color material save is set, the inner periphery of the negative character is replaced with the color of the background image, so that the color material save is maintained without changing the impression of the document while maintaining the readability even with the white character. A mode can be realized. Further, the conventional color material saving process can be performed on the white ground black characters and the color ground black characters which are positive characters, and the conventional image quality can be maintained.

  According to the present invention, the “replacement of the background image with the color” is realized by the expansion process, and thus can be realized with a relatively simple configuration.

  According to the present invention, when the character density is higher than a preset value, it is determined as a positive character. Therefore, even for a negative character having a relatively high character density, a color material saved image that does not change the impression of the original image as much as possible. Can be generated.

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

Example 1:
FIG. 2 shows a block diagram of Embodiment 1 of the present invention. The printer output command sent from the application 10 is converted into a drawing command by the printer driver 11, and the rasterizer 13 creates a bitmap RGB image from the drawing command. In the application 10, the user can select and instruct the output mode of the normal output mode or the color material save mode. The instructed output mode is recorded in the header of the RGB image so that it can be referred to later.

  The command conversion unit 12 reads the object information from the drawing command and creates an attribute image. The attribute image is composed of characters, thin lines, graphics, and image attributes. The line memory 14 temporarily stores rgb signals for several lines. This is for securing a reference area for determining the image feature for saving the color material and for synchronizing the calculated image feature with the rgb signal.

  The blocks from the reference area cutout unit 15 to the negative / positive determination unit 19 are processing portions that perform determination of image characteristics for color material saving. As an image feature, a negative / positive determination unit 19 outputs a determination result as to which of the following areas the pixel of interest belongs: “positive character inner periphery / positive character outer periphery / negative character inner periphery / negative character outer periphery / other”. Details will be described later. The color conversion unit 20 performs conversion from the rgb signal to the c′m′y ′ signal, and the black generation / under color removal unit 21 converts the signal into cmyk. The γ correction unit 22 performs a one-dimensional LUT conversion for correcting the γ characteristic of the printer. In the present invention, the γ correction unit 22 performs the color material saving process when the color material is saved. The γ table (one-dimensional LUT) is switched according to the image feature “positive character inner periphery / positive character outer periphery / negative character inner periphery / negative character outer periphery / others” for color material saving. Details of the γ correction will be described later. After the γ correction, the pseudo halftone processing unit 23 performs dither processing, and the printer 24 outputs the recording paper.

FIG. 3 is a block diagram of the line memory 14, the reference area cutout unit 15, the density determination unit 16, and the edge determination unit 17.
<< Line memory 14, reference area cutout 15 >>
The line memory 14 includes a line memory for three signals r, g, and b and a line memory for attribute images. An example of the r signal will be described. It has a line memory 1-1 that temporarily stores the image signal of the previous line and a line memory 1-2 that temporarily stores the image signal of the previous line. The r signal for three lines can be referred to together with the current input line. In the reference area cutout 15, 3 × 3 pixels r11 to r33 (the target pixel is r22) are cut out.

<< Density determination unit 16 >>
The density calculation unit 160 converts the rgb signal of 3 × 3 pixels into a density signal for each pixel. An explanation will be given by taking the target pixel as an example. Here, the density signal d22 is converted by the conversion formula (1).
d22 = 255− (r22 + 2 × g22 + b22) Formula (1)
In r22, g22, and b22, 0 is black, 255 is white, and the density d22 is 0, white, and 255, black. The density-related determining unit 161 determines that the pixel is on the “high density side” when both of the following expressions (2) and (3) hold. That is, when the density changes within 3 × 3 pixels and is not flat (equation (2)), and the target pixel is the highest density pixel within 3 × 3 pixels (equation (3)), “high” “Density side” is determined, and other cases are determined as “others”.

Max (d11, d12, d13, d21, d22, d23, d31, d32, d33) ≠ Min (d11, d12, d13, d21, d22, d23, d31, d32, d33) Equation (2)
Max (d11, d12, d13, d21, d22, d23, d31, d32, d33) = d22 Formula (3)

<< Edge Detection Unit 17 >>
A “character edge” is detected with reference to an attribute image of 3 × 3 pixels. In the character pixel counting unit 170, the attribute counts the number of pixels of characters. The non-character pixel counting unit 171 counts the number of pixels whose attributes are not characters. In the character / non-character mixing determination unit 172, the result of the character pixel counting unit 170 is not 0 (“the result is not 0” means that the number of pixels of the attribute is 1 in 3 × 3 pixels as a result of counting. In addition, the result of the non-character pixel counting unit 171 is not 0 (“the result is not 0” means that the number of pixels other than characters is 1 in 3 × 3 pixels as a result of counting. In the case of the above, it is determined that the target pixel is a “character edge”. If any of them is 0, it is determined as “others”. Thereby, the character edge part in which a character and a non-character are mixed can be detected.

<< Character Outer / Inner Perimeter Determination Unit 18 >>
FIG. 4 is an operation flowchart of the character outer / inner periphery determination unit 18. From the “character edge / other” that is the output result of the edge detector 17 and the attribute of the pixel of interest (“genus 22” in FIG. 3),
-If the character edge and the attribute is a character,
・ If the character edge and the attribute is not a character,
・ If it is not a character edge,
Is determined.

  Whether or not it is a character edge is an output result of the edge detection unit 17. If it is a character edge, “1” is output as a result, and if it is not a character edge, “0” is output as a result. Whether or not the attribute is a character is described as object information in a drawing command sent from the printer driver. The object information is held as an attribute image through the command conversion unit 12 and the rasterizer 13. For example, it is assumed that the attribute image is represented by a binary image, and a signal of “1” is assigned if it is a character and “0” is assigned if it is not a character. In the above, “a character edge and an attribute is a character” is a case where both the result of the edge detection unit 17 in the pixel of interest and the attribute of the pixel of interest are “1”, and are obtained by a logical product operation of both. It is done. “A character edge and an attribute is not a character” is a case where the result of the edge detection unit 17 at the target pixel is “1” and the attribute of the target pixel is “0”. It can be obtained by calculation. The above “and” means logical product operation, and “not” means inversion of the signal.

<< Negative / Positive Judgment Unit 19 >>
FIG. 5 is an operation flowchart of the negative / positive determination unit 19. From “character inner periphery / character outer periphery / others” which is the output result of the character outer periphery / inner periphery determination unit 18 and “high density side / others” which is the output result of the density determination unit 16,
・ In the case of the inner circumference of the character and the high density side, the “positive character inner circumference”
・ If the inner circumference of the character is not on the high density side, the inner circumference of the negative character
・ If the outer periphery of the character is on the high density side, the outer periphery of the negative character
・ If the character is outside and not on the high density side, “Positive character”,
・ If the character is not inside or outside the character,
Is determined.

  Whether it is the character outer periphery, the character inner periphery or the other is the output result of the character outer periphery / inner periphery determination unit 18. Here, “11” is output as a result when the character is outside the character, “10” is output as a result when the character is inside the character, and “00” is output as a result when the character is neither the character outer periphery nor the character inner periphery. Shall be output.

  Whether it is on the high concentration side is an output result of the concentration determination unit 16. If it is on the high concentration side, “1” is output as a result, and if it is not on the high concentration side, “0” is output as a result. In the above description, “when the character is on the inner periphery and on the high density side” means that the character outer periphery / inner periphery determination result at the target pixel is “10” and the density determination result at the target pixel is “1”. In this case, a logical product operation is performed on the character outer / inner periphery determination result at the target pixel and “11”, whether the result is “10”, the density determination result at the target pixel and the logic of “1”. It is obtained by performing a product operation and calculating whether or not the result is “1”. In the above, “in the case of character inner periphery and not on the high density side” means that the character outer periphery / inner periphery determination result at the target pixel is “10” and the density determination result at the target pixel is “0”. This is a case where a logical product operation of the character outer / inner periphery determination result at the target pixel and “11” is performed, whether the result is “10”, the density determination result at the target pixel and “1”. It is obtained by performing an AND operation and calculating whether or not the result is “0”. In the above, “in the case of the character outer periphery and on the high density side” means that the character outer periphery / inner periphery determination result at the target pixel is “11” and the density determination result at the target pixel is “1”. This is a case where a logical product operation of the character outer / inner periphery determination result at the target pixel and “11” is performed and whether the result is “11”, the density determination result at the target pixel and “1”. This is obtained by performing an AND operation and calculating whether or not the result is “1”. In the above, “when the character is outside and not on the high density side” means that the character outer / inner periphery determination result at the target pixel is “11” and the density determination result at the target pixel is “0”. This is a logical product operation of the character outer / inner periphery determination result at the target pixel and “11”, and whether the result is “11”, the density determination result at the target pixel and the logic of “1”. It is obtained by performing a product operation and calculating whether or not the result is “0”. “Neither character inner periphery nor character outer periphery” means that the character outer periphery / inner periphery determination result at the target pixel is “00”, and the character outer periphery / inner periphery determination result at the target pixel is “11”. Is obtained by calculating whether or not the result is “00”.

  A positive character is a character having a high density with respect to the background, and a negative character is a character having a low density with respect to the background. Therefore, "Positive character inner periphery" and "Positive character outer periphery" are the character side edge of the positive character and the positive character background side edge, and "Negative character inner periphery" and "Negative character outer periphery" are the characters of the negative character. It is also the side edge and the background edge of the negative character.

  FIG. 6 is a diagram showing the results of edge detection (b), density determination (c), and negative / positive determination (d) in the case of a black character image on white. FIG. 7 is a diagram showing the results of edge detection (b), density determination (c), and negative / positive determination (d) in the case of a black ground white character image (a). In either case of edge detection (b), the inside and outside of the character are detected as character edges one dot at a time.

  In the density determination (c), the black pixel portion of the character edge portion is determined as the high density side. In the case of the black ground character (a) in FIG. 6, the inner circumference is one dot inside the character, and in the case of the black ground white character (a) in FIG.

  In negative / positive determination (d), as shown in FIGS. 6 and 7, “positive character inner periphery”, “positive character outer periphery”, “negative character inner periphery”, and “negative character outer periphery” are identified.

Next, γ correction in the color material save mode will be described.
<< γ correction section 22 >>
FIG. 8 shows an example of the γ table. For the normal output γ table, a color material saving γ table as shown in FIG.

  FIG. 9 shows processing switching for each image feature in the γ correction unit 22. When the output mode described in the header of the image is the normal output mode, the normal output γ table is always used.

  When the output mode is the color material save mode, the “positive character outer”, “negative character inner” or “other” pixel is selected according to the negative / positive determination result, which is the image feature detected for color material saving. The color material saving γ table is applied to the color material saving process to enable the color material saving process. For the pixels of “positive character inner periphery” or “negative character outer periphery”, the color material saving process is invalidated by applying the normal output γ table.

  FIG. 10 shows an image (b) obtained by performing the color material saving process (γ correction in the color material save mode) of the present embodiment on the white ground black character image (a). Since the color material saving process becomes invalid in the positive character inner periphery shown in (b), the density of the positive character inner periphery is preserved, and the readability is maintained.

  FIG. 11 shows an image (b) obtained by performing the color material saving process of the present embodiment on the black ground white character image (a). Since the color material saving process becomes invalid at the outer periphery of the negative character shown in (b), the density is preserved even at the outer periphery of the negative character, and the readability is maintained.

  As described above, according to the present embodiment, by disabling the color material save at the outer periphery of the negative character, the color material save mode that maintains the readability of the outline character and does not greatly change the impression of the original image is realized. The image as shown in FIG. 1C is reproduced.

  In this embodiment, the gamma correction is performed so as to invalidate the color material save at the outer periphery of the negative character, but a gamma table that reduces the degree of saving of the color material consumption even if it is not invalidated is used. An effect close to this can be expected.

Example 2:
According to the first embodiment, the density of the outer periphery of a character is always preserved for a negative character having a higher density in the background than in the character. By the way, the negative character is not only a white character but also a character having a certain density. For negative characters with relatively high character density, storing the character inner periphery rather than storing the character outer periphery may not impair the impression (character color and character thickness) of the document.

  FIG. 12 is a block diagram of the second embodiment. In the second embodiment, a correction unit 25 is added to the configuration of the first embodiment. The density determination unit 16 outputs the determination result of “high density side / others” as in the first embodiment, and at the same time, in the present embodiment, the minimum density value Min (d11, d12, d13, d21 in 3 × 3 pixels). , D22, d23, d31, d32, d33) are also output. The correction unit 25 corrects the result of the negative / positive determination unit 19 to reverse the negative / positive determination result based on the minimum density value.

FIG. 13 is an operation flowchart of the correction unit 25. Input the negative / positive determination result and the minimum density value (the minimum density value corresponds to the character density in negative characters).
-If the negative character inner circumference and the minimum density value is larger than the predetermined value Th, the judgment result is changed to "Positive character inner circumference".
-If the negative character outer periphery and the density minimum value is larger than the predetermined value Th, the determination result is changed to "positive character outer periphery".
・ In other cases, there is no change in the judgment result.
And The predetermined value Th is preferably set based on a level that the minimum readability can be secured if the character density is Th even if the background of the negative character is replaced with white.

  FIG. 14 shows an image (b) obtained by performing the color material saving process of the present embodiment on the black ground gray character image (a). When the density of the gray character is larger than Th, the judgment is changed from the inner periphery of the negative character to the inner periphery of the positive character, and as shown in FIG. More color information can be left.

  As described above, according to the present exemplary embodiment, the same effect as that of the first exemplary embodiment is exhibited for white characters, and the impression of the original image is not changed as much as possible even for negative characters having a relatively high character density. Color material save image can be generated.

Example 3:
In Example 1, the density of the outer periphery of the character is stored for the negative character, so that the density of the character outline is stored and the readability is maintained. In this embodiment, a method for replacing the inner periphery of a character with a background color is presented as another means for maintaining the readability by storing the character outline information of the negative character.

FIG. 15 is a block diagram of the third embodiment. In the third embodiment, an expansion unit 26 and a selector 27 are added to the first embodiment. The expansion unit 26 expands the high density pixel. In accordance with Equations (4) to (6), each pixel rgb is replaced with the minimum value in 3 × 3 pixels (the pixel value of the darkest pixel in 3 × 3 pixels).
R22 = Min (r11, r12, r13, r21, r22, r23, r31, r32, r33) Equation (4)
G22 = Min (g11, g12, g13, g21, g22, g23, g31, g32, g33) Equation (5)
B22 = Min (g11, g12, g13, g21, g22, g23, g31, g32, g33) Equation (6)
Then, depending on the determination result of the negative / positive determination unit 19, the selector 27 selects either the unexpanded rgb signal or the expanded RGB signal and transmits it to the process after color conversion. When the negative / positive determination unit 19 determines and outputs a negative, the selector 27 selects the expanded RGB signal.

  FIG. 16 shows processing switching in accordance with image characteristics in the selector 27 and the γ correction unit 22. When the color material save mode is set, the expansion processing is enabled only for the inner periphery of the negative character (selects the expanded RGB signal by the selector 27), and the γ correction unit 22 sets the color when “character inner periphery” regardless of the negative / positive. Disable material save processing. In the case of “character outer circumference” and “others”, the color material saving process is enabled.

  FIG. 17 shows an image (c) obtained by performing the color material saving process of the present embodiment on the black ground white character image (a). The black pixel portion is expanded by expansion processing, and one dot inside the character is replaced with a black pixel (b). Further, as shown in (c), the color material other than the inner periphery of the negative character is saved as a background color. The density of the inner periphery of the negative character replaced with is saved, and the readability is maintained.

  As described above, according to the present embodiment, by replacing the inner periphery of the negative character with the background color, it is possible to realize the color material save mode that maintains the readability of the white character and does not greatly change the impression of the original image. it can.

  The present invention also supplies a storage medium storing software program codes for realizing the processing procedures and functions of the above-described embodiments to a system or apparatus, and a computer (CPU or MPU) of the system or apparatus stores the storage medium. This can also be achieved by reading and executing the program code stored in. In this case, the program code itself read from the storage medium realizes the processing procedures and functions of the above-described embodiment. As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a magnetic tape, 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 processing procedure of the above-described embodiment is realized, but also an OS (operating system) running on the computer based on the instruction of the program code. Includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing. 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. This includes 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.

It is a figure explaining the conventional toner save and the toner save of this invention. 1 shows a block diagram of Embodiment 1 of the present invention. The block diagram of a line memory, a reference area cutout part, a density | concentration determination part, and an edge determination part is shown. It is an operation | movement flowchart of a character outer periphery / inner periphery determination part. It is an operation | movement flowchart of a negative / positive determination part. The results of edge detection, density determination, and negative / positive determination in the case of a white ground black character image are shown. The results of edge detection, density determination, and negative / positive determination for a black ground white character image are shown. An example of a γ table is shown. The process switching for each image feature in the γ correction unit is shown. The image which performed the color material save process (gamma correction at the time of a color material save mode) of Example 1 with respect to a white ground black character image is shown. The image which performed the color material save process of Example 1 with respect to the black ground white character image is shown. The block diagram of Example 2 of this invention is shown. It is an operation | movement flowchart of a correction | amendment part. The image which performed the color material save process of Example 2 with respect to a black ground gray character image is shown. The block diagram of Example 3 of this invention is shown. Processing switching according to image characteristics in the selector and the γ correction unit is shown. The image which performed the color material save process of Example 3 with respect to the black ground white character image is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Application 11 Printer driver 12 Command conversion part 13 Rasterizer 14 Line memory 15 Reference area cutout part 16 Density determination part 17 Edge detection part 18 Character outer periphery / inner periphery determination part 19 Negative / positive determination part 20 Color conversion part 21 Black generation / under color removal Unit 22 gamma correction unit 23 pseudo halftone processing unit 24 printer

Claims (5)

When outputting the image mode (hereinafter, a first mode) which does not save the color material consumption and a mode to save color material consumption (hereinafter, a second mode) An image processing apparatus having, First determination means for determining whether or not an attribute of a target pixel constituting the image is a character, and when a character pixel and a non-character pixel are mixed in a predetermined area including the target pixel, A second determination unit that determines whether the target pixel is a character outer periphery or a character inner periphery based on the determination results of the first and second determination units; A fourth determination unit that determines density; a fifth determination unit that determines whether the pixel of interest is an outer periphery or an inner periphery of a negative character based on determination results of the third and fourth determination units; and the negative Conversion means for converting the inner periphery of the character into a high-density background color; When the mode is set, the first mode is executed by disabling the set second mode for the inner periphery of the negative character converted to the high-density background color. An image processing apparatus comprising processing means for executing the set second mode for the outer periphery of the negative character . And the converting means, the image processing apparatus according to claim 1, characterized in that the means for expanding the background color of the high concentration. When outputting the image mode (hereinafter, a first mode) which does not save the color material consumption and a mode to save color material consumption (hereinafter, a second mode) An image processing method having, A first determination step for determining whether an attribute of a target pixel constituting the image is a character; and when a character pixel and a non-character pixel are mixed in a predetermined region including the target pixel, the target pixel is defined as a character edge A third determination step for determining whether the pixel of interest is a character outer periphery or a character inner periphery based on the determination results of the first and second determination steps; and A fourth determination step for determining density, a fifth determination step for determining whether the pixel of interest is an outer periphery or an inner periphery of a negative character based on the determination results of the third and fourth determination steps, and the negative A conversion step of converting the inner periphery of the character into a high density background color; When the mode is set, the first mode is executed by disabling the set second mode for the inner periphery of the negative character converted to the high-density background color. An image processing method comprising a processing step of executing the set second mode for the outer periphery of the negative character . A program for causing a computer to realize the image processing method according to claim 3 . A computer-readable recording medium recording a program for causing a computer to implement the image processing method according to claim 3 .

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