Image processing device
The image processing apparatus corrects image data in fluorescent regions to enhance gradation reproduction on paper with fluorescent whitening agents by identifying and adjusting for spectral reflectance differences, improving reading accuracy and reducing scan time.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KYOCERA DOCUMENT SOLUTIONS INC
- Filing Date
- 2024-12-05
- Publication Date
- 2026-06-17
AI Technical Summary
Existing image reading devices struggle to accurately reproduce gradation on paper containing fluorescent whitening agents due to saturation of spectral reflectance, particularly affecting yellow coloring materials, leading to increased scan times and reduced accuracy.
An image processing apparatus that generates image data using a yellow colorant, identifies fluorescent regions based on B channel data, and corrects first image data in these regions using G or R channel data, accounting for differences at the boundary between fluorescent and non-fluorescent regions.
Improves gradation reproduction on paper with fluorescent whitening agents by correcting image data, eliminating density steps, and normalizing density across blank and solid image areas, thereby enhancing reading accuracy.
Smart Images
Figure 2026098427000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to an image processing apparatus.
Background Art
[0002] Copy paper (hereinafter referred to as "paper") added with a fluorescent whitening agent is known. The fluorescent whitening agent absorbs ultraviolet light and emits bluish-white visible light (fluorescence) with a wavelength of 400 to 450 nm. That is, since the paper added with the fluorescent whitening agent emits fluorescence in addition to normal reflected light, there is an effect that the white paper portion of the paper looks whiter. However, when a document using paper containing a fluorescent whitening agent is read by an optical document reading device, the spectral reflectance of the white paper portion becomes saturated, so it becomes difficult to detect a low-density image, and gradation cannot be reproduced. In particular, since the absorption spectrum of the yellow coloring material coincides with the wavelength range of the fluorescence, it becomes more difficult to detect than other coloring materials.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] As a technique to improve the gradation of the fluorescent region, for example, Patent Document 1 proposes that if the RGB values obtained from scanning the original document are saturated, it is determined that a fluorescent region exists in the original document, and a second scan is performed under conditions where the light reception amount is set lower than the first scan, and gamma generation is performed in the region where the RGB values are not saturated. However, since the amount of fluorescent whitening agent differs depending on the type of paper, the degree of saturation in the fluorescent region also differs depending on the type of paper. Therefore, with the configuration of Patent Document 1, the light reception amount in the second scan must be significantly reduced, and the required correction amount becomes large, raising concerns about a deterioration in accuracy. To set the light reception amount according to the type of paper, a method of searching for the optimal value while gradually reducing the light reception amount can be considered, but this method increases the number of scans, thus increasing the working time.
[0005] In consideration of the above circumstances, the present invention aims to improve the gradation when reading an image formed on paper containing a fluorescent whitening agent. [Means for solving the problem]
[0006] To solve the above problems, the image processing apparatus according to the present invention comprises: generation means for generating image data obtained by converting reflected light from an original having an image using a yellow colorant into density; identification means for identifying a fluorescent region based on a first image data corresponding to the B channel of the generated image data; and correction means for correcting the first image data in the fluorescent region using a second image data corresponding to the G channel or R channel of the generated image data.
[0007] The correction means may correct the first image data in the fluorescent region using the difference between the first image data and the second image data at the boundary between the fluorescent region and the non-fluorescent region.
[0008] The generation means may generate the image data by normalizing the density within a range that includes the blank area and the solid image area. [Effects of the Invention]
[0009] According to the present invention, it is possible to improve the gradation when reading an image formed on paper containing a fluorescent whitening agent. [Brief explanation of the drawing]
[0010] [Figure 1] This is a perspective view showing the external appearance of an image forming system according to one embodiment of the present invention. [Figure 2] This is a schematic front view showing the configuration of a document transport device and a document reading device according to one embodiment of the present invention. [Figure 3] This is a schematic right-side view showing the configuration of a printing apparatus according to one embodiment of the present invention. [Figure 4] This is a block diagram showing the functional configuration of an image processing apparatus according to one embodiment of the present invention. [Figure 5] This is a flowchart illustrating the process performed by an image processing device according to one embodiment of the present invention. [Figure 6] This figure shows the relationship between input values and concentration in one embodiment of the present invention. [Figure 7] This figure shows the spectral reflectance of paper that does not contain fluorescent whitening agents. [Figure 8] This figure shows the spectral reflectance of paper containing a fluorescent whitening agent. [Figure 9] This figure shows the relationship between input values and density in a conventional image reading device. [Modes for carrying out the invention]
[0011] Hereinafter, an image forming system 100 according to one embodiment of the present invention will be described with reference to the drawings.
[0012] Figure 1 is a perspective view showing the external appearance of the image forming system 100. Figure 2 is a schematic front view showing the configuration of the document transport device 120 and the document reading device 110. Figure 3 is a schematic right side view showing the configuration of the printing device 1. In each figure, U, Lo, L, R, Fr, and Rr indicate top, bottom, left, right, front, and back, respectively. Note that these directions are defined only for the sake of explanation.
[0013] The image forming system 100 (see Figure 1) comprises a printing device 1, a document reading device 110, and a document transport device 120. The document reading device 110 is located above the printing device 1, and the document transport device 120 is located above the document reading device 110. The document transport device 120 transports the document via the reading position of the document reading device 110. The document reading device 110 is a flatbed image scanner that reads the document and generates image data. The printing device 1 forms an image on a sheet S based on the image data.
[0014] [Printing device] The printing device 1 (see Figure 3) comprises a rectangular parallelepiped main housing 3. Inside the lower part of the main housing 3, there is a paper feed cassette 4 in which the sheets S are stored, and a paper feed roller 5 that feeds the sheets S backward from the paper feed cassette 4. Above the paper feed cassette 4, there is an imaging device 6 that forms a toner image using an electrophotographic method, and above and behind the imaging device 6, there is a fixing device 7 that fixes the toner image onto the sheet S. Above the fixing device 7, there is an discharge roller 8 that discharges the sheet S with the toner image fixed on it, and an discharge tray 9 on which the discharged sheets S are stacked.
[0015] Inside the main body housing 3, a conveyance path 10 is provided that extends from the paper feed roller 5 through the image forming device 6 and the fixing device 7 to the discharge roller 8. The conveyance path 10 is mainly formed by plate-like members facing each other with a gap for the sheet S to pass through, and conveyance rollers 17 for sandwiching and conveying the sheet S are provided at multiple locations in the conveyance direction Y. A registration roller 18 is provided upstream of the image forming device 6 in the conveyance direction Y. To the right of the fixing device 7, a reverse conveyance path 10R is provided. The reverse conveyance path 10R branches off from the conveyance path 10 at a branch point located downstream of the fixing device 7 in the conveyance direction Y and merges into the conveyance path 10 at a merging point located upstream of the registration roller 18 in the conveyance direction Y.
[0016] The image forming device 6 includes four image forming units 6U and an intermediate transfer unit 15. The image forming unit 6U includes a photosensitive drum 11 whose potential changes upon irradiation with light, a charging device 12 for charging the photosensitive drum 11, an exposure device 13 for emitting laser light according to image data, a developing device 14 for supplying toner to the photosensitive drum 11, and a cleaning device 16 for removing the toner remaining on the photosensitive drum 11. The intermediate transfer unit 15 includes an endless intermediate transfer belt 15B wound around a driving roller 15D and a driven roller 15N, a primary transfer roller 151 that faces the inner peripheral surface of the intermediate transfer belt 15B at a position corresponding to the photosensitive drum 11 and generates a primary transfer bias, and a secondary transfer roller 152 that faces the outer peripheral surface of the intermediate transfer belt 15B at a position corresponding to the driving roller 15D and generates a secondary transfer bias. A toner container 20 for supplying toner to the developing device 14 is connected to the developing device 14. The image forming device 6 forms a color image by overlapping four-color toner images on the intermediate transfer belt 15B. Note that the printing device 1 may include two, three, or five or more image forming units 6U. <000009The original document reading device 110 (see FIG. 2) includes a rectangular parallelepiped housing 30, a first carriage 32 having a light source 32A and a reflecting mirror 32B, a second carriage 33 having two reflecting mirrors 33A and 33B, a lens 34A for imaging light, an imaging device 34 for converting the imaged light into image data, and a contact glass 31 on which the original document is placed. The contact glass 31 is provided on the upper surface of the housing 30.
[0018] [Original document conveying device] The original document conveying device 120 (see FIG. 2) includes a generally rectangular bottom plate 35 formed in a flat shape. The rear end portion of the bottom plate 35 is connected via a hinge (not shown) to a portion behind the contact glass 31 on the upper surface of the housing 30, and the bottom plate 35 can be opened and closed about the hinge. The bottom plate 35 has the function of supporting each part of the original document conveying device 120 and the function of pressing the original document on the contact glass 31.
[0019] <0000The control unit 2 comprises an arithmetic unit and a memory unit (not shown). The arithmetic unit is, for example, a CPU (Central Processing Unit). The memory unit includes a storage medium such as ROM (Read Only Memory), RAM (Random Access Memory), or EEPROM (Electrically Erasable Programmable Read Only Memory). The arithmetic unit performs various processes by reading and executing the control program stored in the memory unit. Note that the control unit 2 may be implemented using only integrated circuits without the use of software.
[0021] [Display operation section] A display and operation unit 19 is provided on the front side of the document scanning device 110. The display and operation unit 19 includes a display panel, a touch panel superimposed on the display surface of the display panel, and a keypad. The control unit 2 displays a screen on the display panel showing the operation menu and status of the printing device 1 and the document scanning device 110, and controls each part of the printing device 1 and the document scanning device 110 in accordance with operations detected by the touch panel and keypad.
[0022] [Operation] The basic operation of the image forming system 100 is as follows: When a user places a document on the upper surface of the contact glass 31 and instructs the document reader 110 to read it, the first carriage 32 moves to the right at a speed V, and in conjunction with this, the second carriage 33 moves to the right at a speed V / 2. During this time, the light source 31A of the first carriage 32 illuminates the document with light, and the reflected light from the document is reflected by the reflector 32B of the first carriage 32 and the reflectors 33A and 33B of the second carriage 33, guided to the lens 34A, and formed on the image sensor 34 to be converted into an image signal. The image signal is output to the control unit 2 of the printing device 1 and converted into image data.
[0023] Meanwhile, when a user places a document in the paper tray 36 and instructs the document reader 110 to read it, the document feeder 40 feeds the document one sheet at a time into the transport path 39. The document is transported along the transport path 39 and discharged into the output tray 37 via the opening 35A. During this time, the light source 32A of the first carriage 32 shines light onto the document through the opening 35A, and the reflected light from the document is reflected by the reflector 32B of the first carriage 32 and the reflectors 33A, 33B of the second carriage 33, guided to the lens 34A, and formed into an image on the image sensor 34 and converted into an image signal. The image signal is output to the control unit 2 of the printing device 1 and converted into image data.
[0024] In the printing apparatus 1, the paper feed roller 5 feeds the sheet S from the paper feed cassette 4 to the transport path 10, the registration roller 18, whose rotation has stopped, corrects the orientation of the sheet S, and the registration roller 18 feeds the sheet S to the image-making apparatus 6 at a predetermined timing. In the image-making apparatus 6, the charging device 12 charges the photoreceptor drum 11 to a predetermined potential, the exposure device 13 writes a latent image to the photoreceptor drum 11, the developing device 14 develops the latent image using toner supplied from the toner container 20 to form a toner image, the primary transfer roller 151 transfers the toner image to the intermediate transfer belt 15B, and the secondary transfer roller 152 transfers the toner image to the sheet S.
[0025] Next, the fixing device 7 holds the sheet S and transports it while melting the toner image, thereby fixing the toner image to the sheet S, and the discharge roller 8 discharges the sheet S into the discharge tray 9. In the case of double-sided printing, the sheet S with the toner image fixed to the first side is sent to the transport path 10 via the inversion transport path 10R, thereby transferring the toner image to the second side.
[0026] [Image processing device] Figure 7 shows the spectral reflectance of paper without a fluorescent whitening agent. Figure 8 shows the spectral reflectance of paper containing a fluorescent whitening agent. The horizontal axis represents wavelength [nm], and the vertical axis represents spectral reflectance (dimensionless). The spectral reflectance is shown when white light is shone on an image formed using yellow toner. The image density is shown in five levels, with the lowest density being the white area where no toner is on the paper, and the highest density being a solid image where the paper is completely filled with toner.
[0027] The phenomenon of reduced spectral reflectance due to absorption of the 400 to 500 nm wavelength range by yellow toner is common to both paper containing and not containing fluorescent whitening agents. However, in the case of paper without fluorescent whitening agents (see Figure 7), the spectral reflectance of the white area in the 400 to 450 nm wavelength range is about 0.8, whereas in paper containing fluorescent whitening agents (see Figure 8), as a result of the addition of fluorescence, a peak in spectral reflectance appears around 440 nm, and the peak value in the white area is about 1.1. Therefore, if dots are formed at a low density on paper containing fluorescent whitening agents, the spectral reflectance decreases only slightly, and the dots become undetectable.
[0028] Figure 9 shows the relationship between input value and density in a conventional image reading device. The input value on the horizontal axis (dimensionless) is the gradation value shown by the image data. The density on the vertical axis (dimensionless) is the reciprocal of the spectral reflectance. The density was determined from the spectral reflectance in the B channel (peak wavelength 460 nm) and G channel (peak wavelength 540 nm) of the image sensor 34. In the G channel, since there is a density gradient in the entire range of the input value, gradation reproduction is possible even in the low density range. On the other hand, in the B channel, the density gradient becomes flat in the low density range where the input value is approximately 3.5 or less, so gradation reproduction becomes impossible. Therefore, in this embodiment, the gradation performance is improved by the configuration shown below.
[0029] First (step S01), the control unit 2 reads the document with the document reader 110. Next (step S02), the control unit 2 (generation means 51) generates a first image data Vb corresponding to the B channel of the image sensor 34 and a second image data Vg corresponding to the G channel.
[0030] Next (step S03), the control unit 2 determines whether or not there is a region in the first image data Vb where the density gradient Sb is less than the threshold Cb. If the density gradient Sb is less than the threshold Cb, it means that there is a fluorescence region in channel B in Figure 9 where the density is constant. If there is a region where the density gradient Sb is less than the threshold Cb (step S03: YES), the control unit 2 proceeds to step S04. If there is no region where the density gradient Sb is less than the threshold Cb (step S03: NO), the control unit 2 proceeds to step S08.
[0031] Next (step S04), the control unit 2 determines whether the density gradient Sg of the second image data Vg is greater than the threshold Cg in the region where the density gradient Sb of the first image data Vb is less than the threshold Cb. A density gradient Sg greater than the threshold Cg means that there is a significant density change. If the density gradient Sg is greater than the threshold Cg (step S04: YES), the control unit 2 proceeds to step S05. If the density gradient Sg is not greater than the threshold Cg (step S04: NO), the control unit 2 proceeds to step S08.
[0032] Next (step S05), the control unit 2 (identification means 52) identifies the fluorescence region. Specifically, it identifies the range of input values (see Figure 6) in which the determination in step S03 is YES and the determination in step S04 is YES as the fluorescence region. The fluorescence region becomes the range to be corrected.
[0033] Next (step S06), the control unit 2 (correction means 53) calculates the correction amount within the fluorescent region. Specifically, it calculates the difference ΔEd between the first image data Vbd and the second image data Vgd at the boundary between the fluorescent region and the non-fluorescent region.
[0034] Next (step S07), the control unit 2 (correction means 53) corrects the first image data Vb in the fluorescence region using the second image data Vg. Specifically, it replaces the first image data Vb in the fluorescence region with a value obtained by adding ΔEd to the second image data Vg.
[0035] On the other hand, in step S08, since there is no fluorescent region, the control unit 2 outputs the first image data Vb without correction.
[0036] Finally (step S09), the control unit 2 generates and updates the gamma using the corrected first image data.
[0037] The image processing apparatus according to the embodiment described above includes a generation means 51 that generates image data by converting reflected light from an original document having an image using a yellow colorant into density, a identification means 52 that identifies a fluorescent region based on a first image data corresponding to the B channel of the generated image data, and a correction means 53 that corrects the first image data in the fluorescent region using a second image data corresponding to the G channel or R channel of the generated image data. With this configuration, it is possible to improve the gradation when reading an image formed on paper containing a fluorescent whitening agent.
[0038] Furthermore, according to the image processing apparatus of this embodiment, the correction means 53 corrects the first image data in the fluorescent region using the difference between the first image data Vbd and the second image data Vgd at the boundary between the fluorescent region and the non-fluorescent region. With this configuration, it is possible to eliminate the density step caused by the difference between the first image data and the second image data at the boundary between the fluorescent region and the non-fluorescent region.
[0039] Furthermore, according to the image processing apparatus of this embodiment, the generation means 51 generates image data by normalizing the density within a range that includes both the blank area and the solid image area. This configuration makes it possible to avoid the effects of variations in RGB values due to the paper. [Explanation of symbols]
[0040] 51 Generation Methods 52 Specific methods 53 Correction Methods
Claims
1. A generation means for generating image data by converting reflected light from an original document containing an image with a yellow colorant into density, A means for identifying a fluorescent region based on a first image data corresponding to the B channel among the generated image data, An image processing apparatus comprising: a correction means for correcting the first image data in the fluorescence region using a second image data corresponding to the G channel or R channel from the generated image data.
2. The image processing apparatus according to claim 1, characterized in that the correction means corrects the first image data in the fluorescent region using the difference between the first image data and the second image data at the boundary between the fluorescent region and the non-fluorescent region.
3. The image processing apparatus according to claim 1 or 2, characterized in that the generation means generates the image data by normalizing the density in a range that includes a blank area and a solid image area.