Image forming apparatus

Abstract

To appropriately set gamma correction characteristics for paper to which a fluorescent whitening agent is added.SOLUTION: The image data acquisition unit 21 acquires first image data obtained by reading the chart on the reference paper and acquires second image data obtained by reading the chart on the target paper. The gradation correction processing unit 22 (a) specifies the gradation characteristic of the target sheet based on the second image data, (b) specifies the correction target range based on the density gradient in the gradation characteristic, and (c) corrects the correction target range in the gradation characteristic of the target sheet based on the gradation characteristic of the reference sheet based on the first image data. The correction characteristic setting unit 23 sets the gamma correction characteristic for the target paper on the basis of the gradation characteristic for the target paper after the correction target range is corrected. The target paper contains a larger amount of the fluorescent brightener than the reference paper.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] One image reading device (a) determines whether a document contains a fluorescent area based on first read image data of the document, (b) if it determines that the document contains a fluorescent area, acquires second read image data of the document by reducing the amount of light received from the document, and (c) corrects the second read image data based on the first read image data to generate processed image data (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-271386 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, fluorescent whitening agents are added to paper, and when the paper is irradiated with light including ultraviolet light, the fluorescent whitening agents emit fluorescence, making the paper appear whiter. As a result, in low-density (high-brightness) gradation areas, the density characteristics (brightness characteristics) tend to saturate, making it difficult to obtain good gradation characteristics.

[0005] It is conceivable to apply the above-mentioned image reading device to such paper, reduce the amount of light received from the document, and correct the obtained read image data to generate processed image data, but because the saturated region in the gradation characteristics differs depending on the paper type due to factors such as the amount of fluorescent whitening agent contained in the paper, it is difficult to set an appropriate amount of reduction in the amount of received light so as to perform appropriate correction for the saturated region. Note that if the reduction amount is unnecessarily large, the amount of correction will be large, and there is a possibility that appropriate correction will not be performed.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to provide an image forming apparatus in which gamma correction characteristics are appropriately set for paper containing a fluorescent whitening agent. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention includes a printing device, an image data acquisition unit that acquires first image data obtained by reading a chart on reference paper printed by the printing device and acquires second image data obtained by reading a chart on target paper printed by the printing device, a gradation correction processing unit that (a) identifies gradation characteristics for the target paper based on the second image data, (b) identifies a correction target range based on a density gradient in the gradation characteristics, and (c) corrects the correction target range of the gradation characteristics for the target paper based on the gradation characteristics for the reference paper based on the first image data, and a correction characteristic setting unit that sets gamma correction characteristics for the target paper based on the gradation characteristics for the target paper after correcting the correction target range. The target paper contains more fluorescent whitening agent than the reference paper. [Effects of the Invention]

[0008] According to the present invention, an image forming apparatus can be obtained in which the gamma correction characteristics for paper containing a fluorescent whitening agent are appropriately set.

[0009] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating the spectral reflectance characteristics of the reference paper and the target paper. [Figure 3]FIG. 3 is a diagram for explaining the correction by the tone correction processing unit 22 in FIG. [Figure 4] FIG. 4 is a flowchart illustrating the operation of the image forming apparatus shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] Fig. 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in Fig. 1 is, for example, a multifunction peripheral. The image forming apparatus shown in Fig. 1 includes an image reading device 11, a printing device 12, an operation panel 13, a communication device 14, a storage device 15, and a controller 16.

[0013] The image reading device 11 is an internal device that optically reads an image of a document placed on a platen glass or a document fed by an automatic document feeder, and generates image data of the read image. In this example, the image reading device 11 generates color image data (RGB data, etc.) of the document image.

[0014] The printing device 12 is an internal device that prints an original image, etc. The printing device 12 performs printing using a plurality of predetermined color materials (ink, toner, etc.) by electrophotography or inkjet printing.

[0015] The operation panel 13 is an internal device located on the top surface of the housing of the image forming apparatus, and includes a display device 13a that displays an operation screen to the user and an input device 13b that accepts user operations. The display device 13a is a liquid crystal display or the like. The input device 13b is a touch panel that, together with the display device 13a, realizes hard keys and soft keys.

[0016] The communication device 14 is a network interface, a short-distance communication interface, or the like, and is an internal device that performs data communication with a terminal device or a server (not shown).

[0017] The storage device 15 is a non-volatile storage device such as a flash memory, and stores data and programs.

[0018] The controller 16 includes a computer having a central processing unit (CPU), read only memory (ROM), random access memory (RAM), etc., an application specific integrated circuit (ASIC), etc., and operates as various processing units. The controller 16 loads programs stored in the ROM or storage device 15 into the RAM and executes them with the CPU, thereby operating as various processing units using software, or as various processing units using hardware such as an ASIC, etc. The controller 16 also controls internal devices to perform various processes.

[0019] Here, the controller 16 operates as an image data acquisition unit 21, a tone correction processing unit 22, a correction characteristic setting unit 23, and an image processing unit 24.

[0020] The image data acquisition unit 21 acquires first image data obtained by reading a chart on a reference paper printed by the printing device 12, and also acquires second image data obtained by reading a chart on a target paper printed by the printing device 12.

[0021] Here, the first image data and the second image data are RGB data. The chart includes a group of patches at a plurality of gradation levels, and is printed based on input data corresponding to the group of patches.

[0022] FIG. 2 is a diagram illustrating the spectral reflectance characteristics of the reference paper and the target paper.

[0023] The target paper contains more fluorescent brightening agent than the reference paper. In this embodiment, the target paper does not contain any fluorescent brightening agent. For example, as shown in FIG. 2, in a specific wavelength range, the amount of reflected light from the target paper (particularly in low-density image areas) is greater than the amount of reflected light from the reference paper due to the fluorescent brightening agent. Therefore, the paper appears whiter, and the density characteristics (brightness characteristics) tend to saturate in low-density (high-brightness) gradation areas.

[0024] The gradation correction processing unit 22 (a) identifies the gradation characteristics for the target paper based on the second image data, (b) identifies the range to be corrected based on the density gradient in the gradation characteristics, and (c) corrects the range to be corrected of the gradation characteristics for the target paper based on the gradation characteristics for the reference paper based on the first image data.

[0025] The gradation characteristics are normalized within a density range from the minimum density to the maximum density, and are expressed within a normalized density range of 0-1.

[0026] In this embodiment, the printing device 12 prints charts on reference paper and target paper using a specific color material from among the multiple colors described above. Therefore, the gradation characteristics for the target paper are the gradation characteristics of this specific color, and the gamma correction characteristics described above are the gamma correction characteristics of this specific color. Here, the specific color is yellow, which easily absorbs light in the fluorescent wavelength range (400-450 nm) of the fluorescent brightener. Note that similar processing may or may not be performed for other color materials (black, cyan, magenta, etc.).

[0027] FIG. 3 is a diagram for explaining the correction by the tone correction processing unit 22 in FIG.

[0028] Specifically, as shown in Fig. 3, the gradation correction processor 22 (a) derives gradation characteristics for the target paper and the reference paper from the image data, and (b) replaces the gradation characteristics for the target paper in the correction target range with the gradation characteristics for the reference paper in the correction target range shifted by a predetermined value. Here, this predetermined value is the difference dD between the density for the reference paper and the density for the target paper at the boundary of the correction target range. Note that the gradation characteristics for the target paper outside the correction target range are not corrected.

[0029] Here, the gradation characteristics are the distribution of density (here, RGB values) relative to the input data values ​​(input values) of the above-mentioned patch group. The RGB values ​​are any of the values ​​of the R channel, G channel, and B channel in the image reading device 11. For example, if the printing device 12 prints using four color materials, cyan, magenta, yellow, and black, the R channel value (R value) read from a chart printed using only cyan of these color materials is used as the RGB value. Similarly, the G channel value (G value) is used as the RGB value for magenta and black, and the B channel value (B value) is used for yellow. Therefore, as shown in FIG. 3, for example, the lower the density of the chart, the closer the color observed as the read image data is to white (the color of the paper itself), and the higher the RGB value.

[0030] The density gradient is the difference in density between two adjacent input values ​​in the tone characteristics shown in FIG.

[0031] The correction characteristic setting unit 23 sets gamma correction characteristics for the target paper based on the gradation characteristics for the target paper after correction of the correction target range.

[0032] The image processing unit 24 performs gamma correction on the image to be printed using the gamma correction characteristics set for the type of paper used in the printing device 12 for printing.

[0033] Next, the operation of the image forming apparatus will be described.

[0034] (a) Setting the gamma correction characteristics of the target paper

[0035] FIG. 4 is a flowchart illustrating the operation of the image forming apparatus shown in FIG.

[0036] First, the controller 16 supplies the image data of the above-mentioned chart to the printing device 12, and the printing device 12 prints the chart on a reference paper and also prints the chart on a target paper based on the image data (CMYK data) (step S1).

[0037] Next, the user operates the input device 13b to cause the image reading device 11 to read images of the reference paper on which the chart is printed and the target paper on which the chart is printed. Then, the image data acquisition unit 21 acquires the read image data (RGB data) of the reference paper and the target paper from the image reading device 11 (step S2).

[0038] The gradation correction processing unit 22 identifies the gradation characteristics of the target paper based on the read image data of the target paper, and identifies the range to be corrected based on the density gradient in the gradation characteristics (step S3).

[0039] Then, the gradation correction processing unit 22 corrects the correction target range of the gradation characteristics of the target paper based on the gradation characteristics of the reference paper based on the read image data of the reference paper (step S4).

[0040] Next, the correction characteristic setting unit 23 sets gamma correction characteristics based on the corrected gradation characteristics for the target paper, and stores the gamma correction characteristic data in the storage device 15 in association with the paper type of the target paper (step S5). The gamma correction characteristics are set so that the gradation characteristics after gamma correction become linear.

[0041] (b) Printing user images

[0042] When the controller 16 receives a print job request, the image processing unit 24 performs various image processing operations on the image specified by the print job, and the controller 16 then causes the printing device 12 to print the image after the image processing.

[0043] In this case, in the image processing described above, the gamma correction characteristics corresponding to the paper type specified in the print job request are read from the storage device 15 and used, and the printing device 12 prints the image on paper of that paper type.

[0044] As described above, according to the above embodiment, the image data acquisition unit 21 acquires first image data obtained by reading a chart on reference paper printed by the printing device 12, and acquires second image data obtained by reading a chart on target paper printed by the printing device 12. The gradation correction processing unit 22 (a) identifies gradation characteristics for the target paper based on the second image data, (b) identifies a correction target range based on the density gradient in the gradation characteristics, and (c) corrects the correction target range of the gradation characteristics for the target paper based on the gradation characteristics for the reference paper based on the first image data. The correction characteristic setting unit 23 sets gamma correction characteristics for the target paper based on the gradation characteristics for the target paper after correcting the correction target range. The target paper contains more fluorescent whitening agent than the reference paper.

[0045] As a result, the saturated region in the gradation characteristics caused by the fluorescent whitening agent for the target paper is set as the range to be corrected, and the gradation characteristics of that range to be corrected are appropriately corrected based on the gradation characteristics of the reference paper, so that the gamma correction characteristics for the target paper are appropriately set.

[0046] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, it is intended that such changes and modifications be included within the scope of the claims. [Industrial Applicability]

[0047] The present invention is applicable to, for example, an image forming apparatus. [Explanation of symbols]

[0048] 12 Printing device 21 Image data acquisition unit 22 Gradation correction processing section 23 Correction characteristics setting section

Claims

1. A printing device; an image data acquisition unit that acquires first image data obtained by reading a chart on a reference paper sheet printed by the printing device, and acquires second image data obtained by reading a chart on a target paper sheet printed by the printing device; (a) identifying gradation characteristics for the target paper based on the second image data, (b) identifying a correction target range based on a density gradient in the gradation characteristics, and (c) correcting the correction target range of the gradation characteristics for the target paper based on the gradation characteristics for the reference paper based on the first image data; and a correction characteristic setting unit that sets gamma correction characteristics for the target paper based on the gradation characteristics for the target paper after correction of the correction target range; the target paper contains more optical brightener than the reference paper; An image forming apparatus comprising:

2. 2. The image reading apparatus according to claim 1, wherein the reference paper does not contain a fluorescent whitening agent.

3. 2. The image reading device according to claim 1, wherein the gradation characteristics are normalized within a density range from a minimum density to a maximum density.

4. the printing device prints the chart on the reference paper and the target paper using a colorant of a specific color; the gradation characteristics of the target paper are the gradation characteristics of the specific color, the gamma correction characteristics are gamma correction characteristics of the specific color, the specific color is yellow; 2. The image reading device according to claim 1, wherein:

5. the gradation correction processing unit replaces the gradation characteristics of the target paper in the correction target range with the gradation characteristics of the reference paper in the correction target range shifted by a predetermined value; the predetermined value is a difference between the density of the reference paper and the density of the target paper at the boundary of the correction target range; 2. The image reading device according to claim 1, wherein:

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