JP2011045052A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust density in a monochromatic image of a certain color in a color image, such as, densifying a corresponding part on the monochromatic image by intensifying a specific color in a color document. <P>SOLUTION: In an image processing apparatus configured to convert an RGB signal obtained by reading a color image to a monochromatic signal to provide a monochromatic image, a color conversion part 13 includes a table, wherein parameters for performing conversion to monochromatic signal values in response to respective stages of the RGB signal are respectively set. The image processor includes a user interface 13a, allowing a density adjustment value of the monochromatic image to be input thereto at least for a part of each of a plurality of preset hues. The image processing apparatus, further, includes a matrix for calculating the parameters from density adjustment values, prepared on the basis of the plurality of preset hues and input by the user interface, values of the respective stages of the RGB signal, and a coefficient values set by each hue basis. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  Embodiments described herein relate generally to an image processing apparatus that obtains a monochrome image by converting an RGB signal obtained by reading a color image into a monochrome signal.

  In general, some copiers and the like output a color original as a monochrome image. In this case, a color original is read with an RGB signal, converted into a monochrome signal, and given to the print engine, thereby outputting a good monochrome image.

  Conventionally, as a method of converting an RGB signal into a monochrome signal, a method of reproducing the brightness of a color image using the saturation information of the color signal (for example, see Patent Document 1) is known. In this method, when a color image is converted into a black and white image, each color area can be distinguished from the converted black and white image. Areas having the same pixel value in the color image are labeled, Gray scale data is created for the brightness component obtained from the area based on the total number of labels and the input / output characteristics of the image output unit.

JP-A-10-136213

  By the way, when a monochrome image is to be obtained from a color document, the user may want to adjust the brightness (density) for each color. That is, there is a case where a specific color in a color original is emphasized and a corresponding portion on a monochrome image is output darkly, or conversely, a specific color is desired to be displayed lightly in a monochrome image. For example, when a color original is a stamped red mark, and the user wants to display the red mark clearly (darker) in a monochrome image, the user can make the red color in the color image darker in the monochrome image. It is desirable to be able to adjust.

  However, in the above prior art, the user cannot adjust the brightness (density) for each color, and cannot meet the above-mentioned demand.

According to an embodiment of the present invention, there is provided an image processing device for obtaining a monochrome image by converting an RGB signal obtained by reading a color image into a monochrome signal, wherein the monochrome signal value corresponds to each stage of the RGB signal. A table with parameters for converting to
A user interface capable of inputting a density adjustment value in a monochrome image for at least a part of a plurality of preset hues, and a density adjustment value prepared for each of a plurality of preset hues and input by the user interface And a matrix for calculating the parameter from the value of each stage of the RGB signal and the coefficient value set for each hue.

1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the look-up table used by one Embodiment of this invention. It is a figure which shows the hue division threshold value used by one Embodiment of this invention. It is a figure which shows typically the user interface used by one Embodiment of this invention.

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

  FIG. 1 is a block diagram of an image processing apparatus according to this embodiment. The image processing apparatus includes a scanner 11, a signal correction unit 12, a color conversion unit 13, a filter 14, a density adjustment unit 15, a gradation adjustment unit 16, and an engine 17 for monochrome printing.

  The scanner 11 reads a color image from a color document (not shown) with an RGB signal and outputs it. The signal correction unit 11 performs processing such as shading correction (hereinafter referred to as SHD correction), line-to-line correction, and log conversion on the RGB signal input from the scanner 11. These processes are general and well-known in the scanner process. In other words, the SHD correction is a correction for making the scanned data flat because the central portion is brighter than both ends. The inter-line correction is a correction for physically matching the deviations of the R, G, and B signals read at the same time. The log conversion is a process for obtaining a linear signal when viewed in terms of density.

  After such processing, it is input to the color conversion unit 13. The color conversion unit 13 converts an input RGB signal into a monochrome signal and outputs it, and has a user interface 13a. The color conversion unit 13 is a characteristic part in this embodiment, and details thereof will be described later.

  The monochrome signal converted by the color conversion unit 13 is then subjected to filter processing by the filter 14, overall density adjustment processing (TRC) by the density adjustment unit 15, and gradation processing by the gradation adjustment unit 18, and then for printing. It is output to the engine 17.

  The user interface 13a is for adjusting the density of a monochrome image of a color in a color document, and is configured to be able to input density adjustment values for some or all of a plurality of preset hues. That is, the user interface 13a is a menu for adjusting the density of each color (red, green, blue, cyan, magenta, yellow) in the mode for a color document. FIG. 4 is a diagram schematically showing a screen of the user interface 13a on which the user sets the color density. As shown in the figure, an adjustment bar for density adjustment is provided for each color, and when this adjustment bar is moved to the right side, the corresponding color is output darkly in the monochrome image, and when it is moved to the left side, it is lightly output. These density adjustments can be changed simultaneously. As described above, by changing the conversion parameter set in the color conversion unit 13 in accordance with the set value set in the user interface 13a, the density adjustment of each color can be performed.

  Next, the configuration of the color conversion unit 13 will be described with reference to FIG. The color conversion unit 13 has a table in which parameters for converting to a monochrome signal value corresponding to each stage of the RGB signal are set. As this table, the three-dimensional LUT (lookup table) shown in FIG. 2 is used.

  In this LUT, the steps for the respective signal values of the R, G, and B signals are set to 0 to 256, and monochrome signal values corresponding to the steps of the inputted R, G, and B signals are output. That is, it is set to perform color conversion. In FIG. 2, black circles represent representative values, and the R, G, and B axes are divided in 32 increments, but may be in 16 increments. Further, color conversion is performed on the input values of R, G, and B by performing an interpolation operation using a representative value of a black circle.

  The color conversion described above can be performed by setting the monochrome values corresponding to the R, G, and B values of the black circles in the LUT. The parameters set in the LUT of the color conversion unit 13 are calculated and set by the CPU (not shown) using the following data. The data for calculating these color conversion parameters is predetermined data.

RGB to monochrome conversion matrix for each hue (shown by equation (1) below)
-Hue division threshold (th1-th6)
Here, the hue division threshold is data that determines which hue (color) is based on the hue angle obtained from the RGB signals. As shown in FIG. 3, the color space is divided into six hues of red, yellow, green, cyan, blue, and magenta based on the hue division threshold.

上記式（1）において、Ｌｕｔは図２に示したＲＧＢの各代表値（黒丸）に対する値である。よってＲＧＢ代表値を用いて、式（１）によりＲＧＢ→モノクロ変換マトリックス計算を行う事でＬｕｔの値が生成可能となる。 The RGB → monochrome conversion matrix for each hue is a matrix for converting an RGB signal into a monochrome signal, and is a 1 × 10 matrix as shown in the following equation (1). Using these data, parameters for each black circle set in the color conversion unit LUT are calculated.

In the above formula (1), Lut is a value for each representative value (black circle) of RGB shown in FIG. Therefore, the RGB value can be generated by performing RGB → monochrome conversion matrix calculation according to the equation (1) using the RGB representative value.

  Further, β in the equation (1) is a density adjustment coefficient, and is determined by a predetermined relational expression from values set by the user interface 13a for each hue. That is, the density adjustment coefficient β is a coefficient that changes according to a value set by the user interface 13a. The coefficients α1 to α10 are coefficients for converting RGB values into monochrome signals, and six types of count values are set in conjunction with hues (red, green, blue, cyan, magenta, yellow). R, G, and B are the values of each black circle in FIG.

  That is, the matrix represented by the equation (1) is prepared for each of a plurality of preset hues (red, green, blue, cyan, magenta, yellow), and is a coefficient based on the density adjustment value input by the user interface 13a. Parameters are calculated from β, values at each stage of the RGB signal, and coefficient values α1 to α10 set for each hue.

  Here, density adjustment for each hue at the time of RGB → monochrome conversion is realized by repeatedly calculating from RGB = (0,0,0) to (255,255,255) using the above equation (1). . This will be described below.

1. The hue angle is calculated from the RGB representative values. The following formula (2) is used as the calculation formula.
Hue = atan2 (GB, RG) × 180 / π (2)
(This formula (2) is described in accordance with the C language.)
2. Which hue the calculated hue angle Hue corresponds to is determined by the hue division threshold shown in FIG.
3. A density adjustment value (setting value of the user interface 13a) for each hue is acquired, and a density adjustment coefficient β is determined according to the setting value.
4). Based on the determined hue, an RGB-monochrome conversion matrix (formula (1)) in which the coefficient (αl to α10) of the corresponding hue is set is selected, and RGB = (0, 0, 0) as described above. Each Lut is calculated by repeatedly calculating up to (255, 255, 255).
5). When all the calculations are completed, the calculated Lut value is set in the LUT of the color conversion unit 13, and a normal copying operation for obtaining a monochrome image output based on the color original is performed.

  As for the density adjustment coefficient β, for example, when the set value of the user interface 13a is −3, the coefficient of β is 0.7, and when the value is −2, 0 is set according to the density adjustment step. .Change by one. By multiplying this coefficient, when the set value is −3, 255 × 0.7 = 178 and the maximum output value is 178. In the case of +3, 255 × 1.3 = 331. The LUT value indicates 0: white, 255: black. The signal value can be changed in the range of 0 to 255.

  In the above configuration, when setting the red density to be dark in order to make a certain color in the color original, for example, the red color dark as described above, the red adjustment bar of the user interface 13a shown in FIG. Move to the right and set the density adjustment value. Based on this density adjustment value, the density adjustment coefficient β is determined.

  Next, using the RGB → monochrome conversion matrix of Equation (1), calculation is repeatedly performed using representative values (black circles) from RGB = (0, 0, 0) to (255, 255, 255). In this case, it is determined which hue corresponds to the hue angle Hue obtained from Expression (2) from the representative values of RGB based on the hue division threshold shown in FIG. As a result, when corresponding to the red hue, in conjunction with the red hue, the corresponding RGB-monochrome conversion matrix (matrix in which the coefficients α1 to α10 shown in Expression (1) are set to the hue (red)) And the density adjustment coefficient β is applied thereto to obtain Lut. That is, conversion parameters after color adjustment are obtained for each representative value of RGB in which the hue in FIG. 2 is red.

  When all the calculations are completed in this way, the calculated Lut value is set in the LUT of the color conversion unit 13. For example, when the density is adjusted so that the red color is dark, the vermilion portion in the color original is output darkly and clearly in the monochrome image. Of course, contrary to the above description, it is also possible to set a specific hue in a color document to be lightly output in a monochrome image.

  In the above example, the case where the number of colors that can be adjusted by the user and the number of colors held by the parameter is the same has been described. However, the number of colors that can be specified by the user is three (red, green, and blue) The same operation is performed when the number of hues is six. In this case, as one example, the density adjustment coefficient β of the hues of cyan, magenta, and yellow is fixed to 1.0. In this way, the densities of cyan, magenta and yellow do not change. Another example is a method of calculating a specified color and an adjacent color with the same density adjustment coefficient. For example, when the red density is adjusted, the same density adjustment coefficient may be applied to the adjacent yellow and magenta to obtain the LUT value.

  By such a method, even when the number of colors that can be specified by the user is smaller than the number of hues stored as parameters, the color density can be adjusted.

  In the above-described explanation example, the configuration example regarding the case of outputting to a printer has been described. However, a vehicle that applies the same configuration to a network scanner or a FAX is possible.

  By adopting such a configuration, it is possible to adjust the density only for the color selected by the user, and it is possible to perform highly functional image quality adjustment.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Scanner 12 ... Signal correction part 13 ... Color conversion part (it has a table)
13a ... User interface 14 ... Filter 15 ... Density adjustment unit 16 ... Gradation adjustment unit 17 ... Engine for monochrome printing

Claims (3)

An image processing apparatus that obtains a monochrome image by converting a RGB signal obtained by reading a color image into a monochrome signal,
A table in which parameters for converting into a monochrome signal value corresponding to each stage of the RGB signal are set;
A user interface capable of inputting a density adjustment value in a monochrome image for at least some of a plurality of preset hues;
Prepared for each of a plurality of preset hues, and calculates the parameter from the density adjustment value input by the user interface, the value of each stage of the RGB signal, and the coefficient value set for each hue. Matrix,
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the matrix changes a parameter set in the table according to a density adjustment value input from a user interface.   The image processing apparatus according to claim 1, wherein the number of hues whose density can be adjusted by a user interface is equal to or less than the number of hue divisions held by parameters.

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