Image forming apparatus, program, and image forming method

Abstract

To eliminate the need to hold a color conversion lookup table for every image data and prevent excessive correction due to color matching to a specific image, thereby simplifying the procedure for density adjustment.SOLUTION: An image forming apparatus comprises: an image reading unit that reads a first output object to be an example and a second output object output by the image forming apparatus; a correction data holding unit that holds a color conversion lookup table used for color conversion of the RGB colorimetric system into the CMYK colorimetric system; and a color conversion correction unit that corrects the color conversion lookup table. The color conversion correction unit executes correction of the color conversion lookup table based on the number of pixels and the amount of change for every hue by using information on the reading of the first output object, and corrects the corrected color conversion lookup table again by using information on the reading of the second output object.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a program, and an image forming method. [Background technology]

[0002] 2. Description of the Related Art Conventionally, when printing from a newly purchased image forming apparatus such as a printer, fine density adjustments may be manually performed in order to obtain the same color tone as that of the printer that was previously used.

[0003] Furthermore, Patent Document 1 discloses a technique for scanning a model output and performing parameter correction to make the printer output of an RGB image in a memory card closer to the model color in order to make the printer output closer to the model color. Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the conventional technology, it is necessary to extract features and calculate correction parameters for each RGB image to be color converted, which causes problems such as cumbersome parameter management and an increase in memory space.In addition, with the conventional technology, even though the means for reading image data are different, the read RGB values ​​are not corrected, so there is a problem that it is not possible to judge overcorrection, etc.

[0005] The present invention has been made in consideration of the above, and aims to simplify the density adjustment procedure by eliminating the need to maintain a color conversion lookup table for each image data and by preventing over-correction due to matching colors to a specific image. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present invention provides an image forming apparatus comprising an image reading unit that reads a first output object that serves as a model and a second output object output by the image forming apparatus, a correction data storage unit that stores a color conversion lookup table used when color converting an RGB color system to a CMYK color system, and a color conversion correction unit that corrects the color conversion lookup table, wherein the color conversion correction unit uses read information of the first output object to correct the color conversion lookup table based on the number of pixels and the amount of change for each hue, and uses read information of the second output object to re-correct the corrected color conversion lookup table. Effect of the Invention

[0007] According to the present invention, it is not necessary to store a color conversion lookup table for each image data, and by preventing over-correction due to matching colors to a specific image, it is possible to simplify the density adjustment procedure. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of a functional configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a flowchart showing an outline of the flow of the correction process for the color conversion lookup table. [Diagram 3] FIG. 3 is a conceptual diagram showing a three-dimensional lookup table. [Figure 4] FIG. 4 is a flowchart showing in detail the flow of the correction process for the color conversion lookup table. [Diagram 5] FIG. 5 is a diagram showing an example of RGB distribution when output samples of an image forming apparatus before replacement and an image forming apparatus after replacement are read by an image reading unit. [Figure 6] FIG. 6 is a block diagram showing an example of a hardware configuration when the image processing and formation according to the present embodiment is applied to a multifunction peripheral. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of an image forming apparatus, a program, and an image forming method will be described in detail with reference to the attached drawings. An example in which an image forming apparatus according to the present embodiment is applied to a multifunction machine will be described below. This embodiment describes a process for making the print result of a newly purchased image forming apparatus after replacement have the same color tone as that of the image forming apparatus used up until now before replacement.

[0010] Fig. 1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to an embodiment. As shown in Fig. 1, a client PC 2 is connected to the image forming apparatus 1. The client PC 2 outputs RGB color image data 2b to the image forming apparatus 1 via a printer driver 2a. The printer driver 2a adds information such as the resolution when printing the image data 2b to the image forming apparatus 1 and outputs the image data 2b to the image forming apparatus 1.

[0011] As shown in FIG. 1, the image forming apparatus 1 includes an image processing section 10, an image forming section 20, and an image reading section 30.

[0012] The image processing unit 10 performs various processes such as color conversion, density conversion, and gradation processing on the image data 2 b input from the client PC 2 , and outputs the processed image data to the image forming unit 20 .

[0013] The image forming unit 20 is mainly composed of a printer, and forms an image of each color corresponding to the image data of each color on a recording medium based on the image data of each color of CMYK processed by the image processing unit 10. The image forming unit 20 also forms a sample image on a recording medium (for example, a printing paper or a transfer belt, etc.) based on the image data of each color of CMYK processed by the image processing unit 10, and outputs the recording medium on which the sample image has been formed (output sample) to a reading window where the image reading unit 30 performs image reading.

[0014] The image reading unit 30 is mainly composed of a scanner, reads a recording medium (output sample) on which a sample image is formed, and outputs the read image data to the image processing unit 10.

[0015] Then, the image processing unit 10 uses a recording medium (output sample) on which the sample image input from the image reading unit 30 is formed to perform a correction process for a color conversion lookup table (LUT) T, which will be described later.

[0016] Next, the function of the image processing unit 10 will be described in more detail. As shown in Fig. 1, the image processing unit 10 includes a color conversion processing unit 11, a density conversion processing unit 12, a gradation processing unit 13, and a color conversion correction unit 14. A color conversion lookup table T is stored in a correction data holding unit 144, which is a storage means of the color conversion correction unit 14.

[0017] The color conversion lookup table T is a three-dimensional lookup table that stores parameters used when converting RGB data (RGB color system) into CMYK data (CMYK color system).

[0018] The color conversion processing unit 11 performs color conversion processing on the image data 2b of each color of RGB input from the client PC 2, converting it into image data of each color of CMYK, using a color conversion lookup table T in the correction data storage unit 144 in the color conversion correction unit 14. Specifically, the color conversion processing unit 11 performs color conversion such that the color tone of the monitor display of the client PC 2 is reproduced using the color materials of the image forming device 1.

[0019] The density conversion processing unit 12 performs density conversion processing on the image data after the color conversion processing. More specifically, the density conversion processing unit 12 performs density conversion for each color of CMYK of the image data input from the color conversion processing unit 11. More specifically, the density conversion processing unit 12 performs density conversion that absorbs individual differences of the image forming apparatus 1.

[0020] The gradation processing unit 13 converts the image data of each color of CMYK after density conversion processing into image data with a number of gradations according to the gradation processing capability of the image forming unit 20. Specifically, the gradation processing unit 13 determines the dot arrangement during image formation and sends it to the image forming unit 20.

[0021] The color conversion correction unit 14 performs a correction process for the color conversion lookup table T using data of the output sample of the image forming apparatus 1 before replacement and the output sample of the image forming apparatus 1 after replacement, which are read by the image reading unit 30.

[0022] Next, a more detailed description will be given of the function of the color conversion correction unit 14. As shown in Fig. 1, the color conversion correction unit 14 includes a data processing unit 142, a correction data generation unit 143, and a correction data storage unit 144 that stores the above-mentioned color conversion lookup table T.

[0023] The data processing unit 142 analyzes the data of the output sample of the image forming apparatus 1 before replacement and the output sample of the image forming apparatus 1 after replacement, which are read by the image reading unit 30 .

[0024] The correction data generation unit 143 changes and modifies the color conversion lookup table T based on the analysis by the data processing unit 142 , and stores the changed and modified color conversion lookup table T in the correction data holding unit 144 .

[0025] Next, the correction process of the color conversion lookup table T in the image forming apparatus 1 will be described in detail.

[0026] FIG. 2 is a flowchart showing an outline of the flow of the correction process for the color conversion lookup table T.

[0027] As shown in FIG. 2, first, the image reading unit 30 scans and reads a sample output (first output as a model) of the image forming device before replacement and a sample output (second output) of the image forming device 1 after replacement (step S1).

[0028] Next, data processing unit 142 extracts non-character areas from the scanned data (step S2). More specifically, since character areas, like black characters, tend to have a large amount of change relative to paper white and strong edges, data processing unit 142 extracts character and non-character areas according to this tendency.

[0029] Next, after extracting the non-character region, the data processing unit 142 performs a smoothing process on the pixels of the scan data (step S3). More specifically, the data processing unit 142 performs the smoothing process in order to reduce the influence of noise during reading.

[0030] Next, after the smoothing process, the correction data generation unit 143 maps the pixel values ​​(RGB values: first feature) of the scan data of the output sample of the image forming device before replacement and the pixel values ​​(RGB values: second feature) of the scan data of the output sample of the image forming device 1 after replacement to a three-dimensional lookup table (3D-LUT) (step S4), and grasps the distribution of the input pixel values ​​for each hue (step S5).

[0031] FIG. 3 is a conceptual diagram showing a three-dimensional lookup table (3D-LUT). As shown in FIG. 3(a), when the 3D-LUT is based on the RGB color space, it is configured as a solid body with three-dimensional axes in the R, G, and B directions. When RGB is each 8 bits, the color R=G=B=0 represents black, and R=G=B=255 represents white. Also, the 3D-LUT can reduce the amount of data by using the lattice points when equally dividing every arbitrary value of 2 or more as representative points, and values ​​that are not on the lattice points can be calculated by interpolation.

[0032] As shown in Fig. 3(b), the lines connecting white to R, G, B, C, M, Y, and the lines connecting R, G, B, C, M, Y, and black represent the R, G, B, C, M, Y color systems, and the hue can be grasped by plotting any RGB value on the 3D-LUT. In Fig. 3(b), it is also possible to set a hue reference point between R and Y to increase the number of hue divisions.

[0033] Next, the correction data generating unit 143 calculates differences and the like from the distribution of input pixel values ​​for each hue before the replacement and the distribution of input pixel values ​​for each hue after the replacement, and corrects the color conversion lookup table T held in the image forming apparatus 1 after the replacement (step S6). Note that while the color conversion lookup table T is configured as a 3D-LUT, the 3D-LUT used in step S4 is used to grasp the distribution of pixel values ​​and calculate differences, and is different from the color conversion lookup table T.

[0034] Next, a detailed description will be given of the color conversion lookup table correction process performed by the correction data generating unit 143. Here, Fig. 4 is a flowchart showing in detail the flow of the color conversion lookup table correction process.

[0035] As shown in FIG. 4, first, the correction data generating unit 143 checks whether or not this is the first time that the color conversion lookup table T is corrected (step S11).

[0036] If this is the first time the color conversion lookup table T is corrected (Yes in step S11), the correction data generation unit 143 checks whether the number of pixels around a 3D-LUT lattice point of any hue is equal to or greater than a threshold (step S12).

[0037] If the number of pixels around a 3D-LUT lattice point of any hue is equal to or greater than a threshold value (Yes in step S12), the correction data generation unit 143 increases the amount of correction for the color conversion lookup table T (initial color conversion lookup table T) held in the replaced image forming device 1 (step S13), and corrects the color conversion lookup table T (step S14).

[0038] In addition, if the number of pixels around a 3D-LUT lattice point of any hue is less than a threshold value (No in step S12), the correction data generation unit 143 reduces the amount of correction for the color conversion lookup table T (initial color conversion lookup table T) held in the replaced image forming device 1 (step S15), and corrects the color conversion lookup table T (step S14).

[0039] The greater the number of pixels to be targeted, the more reliable the information can be considered, so the correction data generation unit 143 performs control so that the greater the number of pixels to be targeted, the greater the amount of correction is, in order to bring the color closer to that of the image forming device before replacement.

[0040] On the other hand, if the correction of the color conversion lookup table T is not the first time (No in step S11), the correction data generation unit 143 checks whether the input data includes a new hue (uncorrected) (step S16).

[0041] If the input data includes a new (uncorrected) hue (Yes in step S16), the correction data generating unit 143 determines the amount of correction according to the threshold determination of the number of pixels in step S12.

[0042] If the input data does not include a new (uncorrected) hue (No in step S16), the correction data generation unit 143 determines whether or not correction is required for the target hue in the updated color conversion lookup table T.

[0043] Specifically, the correction data generator 143 calculates the difference between the initial color conversion lookup table T and the updated color conversion lookup table T (step S17).

[0044] If the difference is greater than the predetermined value (Yes in step S18), the correction data generator 143 considers that the correction that has already been performed is already sufficient, and ends the process without correcting the color conversion lookup table T. This makes it possible to grasp the degree of change in the target hue, thereby preventing overcorrection.

[0045] If the difference is smaller than the predetermined value (No in step S18), the correction data generating unit 143 checks whether the number of pixels around the 3D-LUT lattice point of any hue is equal to or greater than a threshold value (step S19).

[0046] If the number of pixels around a 3D-LUT lattice point of any hue is equal to or greater than a threshold (Yes in step S19), the correction data generation unit 143 increases the amount of correction from the updated color conversion lookup table T (step S20). In this way, the reason why the amount of correction from the updated color conversion lookup table T is increased when the number of pixels around a 3D-LUT lattice point of any hue is equal to or greater than a threshold is because the newly acquired data is considered to be more reliable. This makes it possible to increase the accuracy of the color conversion lookup table T when the number of references is large.

[0047] On the other hand, if the number of pixels around the 3D-LUT grid point of any hue is less than the threshold value (No in step S19), the correction data generation unit 143 reduces the amount of correction from the updated color conversion lookup table T (step S21). This makes it possible to prevent overcorrection when the number of references is small.

[0048] Fig. 5 is a diagram showing an example of RGB distribution when output samples of the image forming apparatus before replacement and the image forming apparatus 1 after replacement are read by the image reading unit 30. Fig. 5(a) shows an example of RGB distribution when an output sample of the image forming apparatus before replacement is read by the image reading unit 30. Fig. 5(b) shows an example of RGB distribution when an output sample of the image forming apparatus 1 after replacement is read by the image reading unit 30. As shown in Fig. 5, since the image forming apparatus before replacement has a distribution in the direction of larger R values, it can be seen that the color conversion lookup table T of the image forming apparatus 1 after replacement also needs to be corrected in the direction of increasing the R output value.

[0049] Thus, according to this embodiment, when printing results of a newly purchased, post-replacement image forming apparatus 1 need to have the same color tone as the image forming apparatus previously in use, it is not necessary to store a color conversion lookup table for each image data, and over-correction caused by matching colors to a specific image is prevented, thereby simplifying the density adjustment procedure.

[0050] More specifically, when correcting the color conversion lookup table T of the image forming apparatus 1, the scanner read information of an arbitrary image (output sample) is used to perform correction based on the number of pixels and the amount of change for each hue, and the scanner read information of another image (output sample) is used to re-correct the corrected color conversion lookup table T. This makes it possible to generate the color conversion lookup table T without extracting features and calculating correction parameters for each RGB image to be color converted, and to prevent overcorrection caused by specializing it to a specific RGB image.

[0051] FIG. 6 is a block diagram showing an example of a hardware configuration when the image forming apparatus 1 according to the present embodiment is applied to a multifunction peripheral. As shown in this figure, this multifunction peripheral is configured by connecting a controller 110 and an engine unit (Engine) 160 via a PCI (Peripheral Component Interconnect) bus. The controller 110 is a controller that controls the entire multifunction peripheral and controls drawing, communication, and input from an operation unit (not shown). The engine unit 160 is a printer engine that can be connected to a PCI bus, and is, for example, a black-and-white plotter, a one-drum color plotter, a four-drum color plotter, a scanner, or a fax unit. The engine unit 160 includes an image processing unit such as error diffusion and gamma conversion in addition to a so-called engine unit such as a plotter.

[0052] The controller 110 has a CPU 111, a north bridge (NB) 113, a system memory (MEM-P) 112, a south bridge (SB) 114, a local memory (MEM-C) 117, an ASIC (Application Specific Integrated Circuit) 116, and a hard disk drive (HDD) 118, with the north bridge (NB) 113 and the ASIC 116 connected via an AGP (Accelerated Graphics Port) bus 115. The MEM-P 112 further has a ROM (Read Only Memory) 112a and a RAM (Random Access Memory) 112b.

[0053] The CPU 111 performs overall control of the multifunction device, and has a chip set consisting of the NB 113, the MEM-P 112, and the SB 114, and is connected to other devices via this chip set.

[0054] The NB 113 is a bridge for connecting the CPU 111 with the MEM-P 112, the SB 114, and the AGP 115, and includes a memory controller for controlling reading and writing to the MEM-P 112, a PCI master, and an AGP target.

[0055] MEM-P112 is a system memory used as a memory for storing programs and data, a memory for expanding programs and data, a memory for printer drawing, etc., and is composed of ROM 112a and RAM 112b. ROM 112a is a read-only memory used as a memory for storing programs and data, and RAM 112b is a writable and readable memory used as a memory for expanding programs and data, a memory for printer drawing, etc.

[0056] The SB 114 is a bridge for connecting the NB 113 to PCI devices and peripheral devices. The SB 114 is connected to the NB 113 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

[0057] The ASIC 116 is an IC (Integrated Circuit) for image processing purposes having hardware elements for image processing, and serves as a bridge connecting the AGP 115, the PCI bus, the HDD 118, and the MEM-C 117. The ASIC 116 includes a PCI target and an AGP master, an arbiter (ARB) that is the core of the ASIC 116, a memory controller that controls the MEM-C 117, a plurality of DMACs (Direct Memory Access Controllers) that rotate image data using hardware logic, and a PCI unit that transfers data between the engine unit 160 and the ASIC 116 via the PCI bus. The ASIC 116 is connected to an FCU (Fax Control Unit) 130, a USB (Universal Serial Bus) 140, and an IEEE1394 (the Institute of Electrical and Electronics Engineers 1394) interface 150 via the PCI bus. The operation display unit 120 is directly connected to the ASIC 116.

[0058] The MEM-C 117 is a local memory used as an image buffer for copying and a code buffer, and the HDD (Hard Disk Drive) 118 is a storage for storing image data, programs, font data, and forms.

[0059] AGP115 is a bus interface for graphics accelerator cards proposed to speed up graphics processing, and it accelerates graphics accelerator cards by directly accessing the MEM-P112 at high throughput.

[0060] The program executed by the image forming apparatus 1 of this embodiment is provided in a state where it is pre-installed in a ROM or the like. The program executed by the image forming apparatus 1 of this embodiment may be provided by being recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a digital versatile disk (DVD) in the form of a file in an installable or executable format.

[0061] Furthermore, the program executed by the image forming apparatus 1 of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Also, the program executed by the image forming apparatus 1 of the present embodiment may be provided or distributed via a network such as the Internet.

[0062] The program executed by the image forming apparatus 1 of this embodiment has a modular structure including each part of the image processing unit 10 described above (color conversion processing unit 11, density conversion processing unit 12, gradation processing unit 13, color conversion correction unit 14), and in terms of actual hardware, the CPU (processor) reads the program from the ROM and executes it, loading each part mentioned above onto the main memory device, and the color conversion processing unit 11, density conversion processing unit 12, gradation processing unit 13, and color conversion correction unit 14 are generated on the main memory device.

[0063] In the above embodiment, the image forming apparatus 1 of the present invention has been described as being applied to a multifunction device having at least a printer function (image forming unit 20) and a scanner function (image reading unit 30) among the copy function, printer function, scanner function and facsimile function. However, the image forming apparatus can be applied to any image forming device having a printer function and a scanner function, such as a copier, printer, facsimile machine, etc. [Explanation of symbols]

[0064] 1. Image forming device 14 Color conversion correction section 30 Image reading unit 144 Correction data storage unit T Color conversion lookup table [Prior art documents] [Patent documents]

[0065] [Patent Document 1] Patent No. 4793356

Claims

1. In an image forming apparatus, an image reading unit that reads a first output object as a model and a second output object output by the image forming apparatus; a correction data storage unit that stores a color conversion lookup table used when converting colors from an RGB color system to a CMYK color system; a color conversion correction unit that corrects the color conversion lookup table; Equipped with the color conversion correction unit corrects the color conversion lookup table based on the number of pixels and the amount of change for each hue using the read information of the first output object, and re-corrects the corrected color conversion lookup table using the read information of the second output object; An image forming apparatus comprising:

2. The color conversion correction unit acquiring a first feature amount from read information of the first output object; projecting the first feature amount onto a three-dimensional lookup table, and determining an amount of correction for the initial color conversion lookup table by determining a threshold value for the number of pixels around a lattice point of the three-dimensional lookup table for an arbitrary hue; 2. The image forming apparatus according to claim 1,

3. The color conversion correction unit When the read information of the second output object input after the correction of the color conversion lookup table includes an uncorrected hue, a correction amount for the color conversion lookup table is determined by a threshold judgment of the number of pixels.

3. The image forming apparatus according to claim 2,

4. The color conversion correction unit If the read information of the second output object input after the correction of the color conversion lookup table does not include an uncorrected hue, a difference between the initial color conversion lookup table and the updated color conversion lookup table is calculated; determining whether to correct the color conversion lookup table based on the difference; 3. The image forming apparatus according to claim 2,

5. The color conversion correction unit If the difference is greater than a predetermined value, the color conversion lookup table is not changed.

5. The image forming apparatus according to claim 4.

6. The color conversion correction unit acquiring a first feature amount from read information of the first output object; acquiring a second feature amount from read information of the second output product; If the difference is smaller than a predetermined value, the first feature amount and the second feature amount are projected onto a three-dimensional lookup table, and a threshold determination is made of the number of pixels around a lattice point of the three-dimensional lookup table for an arbitrary hue.

5. The image forming apparatus according to claim 4.

7. When the difference is equal to or greater than a threshold value, the color conversion correction unit increases a correction amount for the color conversion lookup table.

7. The image forming apparatus according to claim 6,

8. When the difference is less than the threshold value, the color conversion correction unit reduces the amount of correction for the color conversion lookup table.

7. The image forming apparatus according to claim 6,

9. A computer that controls an image forming apparatus, an image reading unit that reads a first output object as a model and a second output object output by the image forming apparatus; a correction data storage unit that stores a color conversion lookup table used when converting colors from an RGB color system to a CMYK color system; a color conversion correction unit that corrects the color conversion lookup table; Function as a the color conversion correction unit corrects the color conversion lookup table based on the number of pixels and the amount of change for each hue using the read information of the first output object, and re-corrects the corrected color conversion lookup table using the read information of the second output object; A program characterized by.

10. 1. An image forming method in an image forming apparatus that holds a color conversion lookup table used for color conversion from an RGB color system to a CMYK color system, comprising: an image reading step of reading a first output object as a model and a second output object output by the image forming apparatus; a color conversion correction step of correcting the color conversion lookup table; Including, the color conversion correction step includes correcting the color conversion lookup table based on the number of pixels and the amount of change for each hue using read information of the first output object, and re-correcting the corrected color conversion lookup table using read information of the second output object; An image forming method comprising the steps of:

Images