Image processing device, image processing method, image processing system, and program

Abstract

To perform processing to quantize signal values of image data to a low bit number in a simpler manner while inhibiting deterioration of image quality.SOLUTION: An image processing apparatus acquires image data whose color information is defined by signal values of a first bit number for each of color components; acquires first information indicating a maximum value and a minimum value of the signal values for each of the color components in the image data acquired; performs quantization to quantize the signal values for each of the color components in the image data acquired into signal values of a second bit number which is smaller than the first bit number on the basis of the first information; and in order to restore the signal values in the quantized image data to signal values of a third bit number greater than the second bit number, transmits the quantized image data and second information indicating a maximum value and a minimum value of the signal values for each of the color components in the image data acquired.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to techniques for quantizing signal values ​​of image data. [Background technology]

[0002] There are methods for compressing data by quantizing the signal values ​​of image data to a low number of bits.

[0003] Patent Document 1 describes a method for quantizing the signal value of image data to a low bit number while suppressing loss of information amount of the image data. In Patent Document 1, parameters for separating an input image into two regions, a dark image region and a light image region, are set, and a grayscale map is generated in accordance with the set parameters, indicating whether each pixel of the input image belongs to the dark image region or the light image region. Then, based on the grayscale map and the number of quantization bits, the signal value of each pixel of the input image is quantized by a quantization method corresponding to the region to which the pixel belongs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-278889 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, a printing device may receive image data to be printed that has been RIP-processed and color-converted by an external image processing device, and print based on the received image data. In order to efficiently transmit and receive image data, the image data may be transmitted after reducing the amount of data transmission by quantizing the signal values ​​of the image data to a low bit number. In this case, the process of quantizing to a signal value with a low bit number needs to be performed by the image processing device. It is preferable that the image processing device executes the quantization process in a simpler manner that suppresses deterioration of image quality.

[0006] However, the method of Patent Document 1 requires the image processing device to perform complex processing such as generating a gray-scale map, determining a quantization method for each pixel of the input image data based on the gray-scale map, and quantizing the signal value for each pixel to a low bit rate. [Means for solving the problem]

[0007] The image processing device disclosed herein is characterized by having a first acquisition means for acquiring image data whose color information is defined by an N-bit signal value for each color component, a second acquisition means for acquiring data range information indicating the maximum and minimum values ​​of the signal value for each color component in the image data acquired by the first acquisition means, a quantization means for quantizing the signal value for each color component in the image data acquired by the first acquisition means to a signal value of M bits (N>M) based on the data range information acquired by the second acquisition means, and a transmission means for transmitting the quantized image data and data range information corresponding to the image data acquired by the first acquisition means in order to convert the signal value in the quantized image data to a signal value of L bits (L>M). Effect of the Invention

[0008] According to the technology of the present disclosure, the process of quantizing the signal values ​​of image data to a lower number of bits so as to suppress deterioration of image quality can be performed in a simpler manner. [Brief description of the drawings]

[0009] [Figure 1] A diagram showing the size of the color gamut for each color space. [Diagram 2] A conceptual diagram of a color management system. [Diagram 3] 1 is a diagram for explaining conversion parameters included in an ICC profile. [Figure 4] 11 is a diagram showing an example of a correspondence relationship between an input device-dependent signal value and an output device-dependent signal value after color conversion; [Diagram 5]FIG. 2 is a diagram illustrating the internal configuration of a printing apparatus. [Figure 6] FIG. 2 is a block diagram illustrating the control configuration of the image processing apparatus and the printing apparatus. [Figure 7] FIG. 2 is a diagram showing a printing sequence in the printing system. [Figure 8] FIG. 4 is a diagram showing detailed steps of a transfer data quantization process. [Figure 9] FIG. 13 is a graph showing data range information and a one-dimensional LUT for quantization. [Figure 10] FIG. 11 is a diagram for explaining the process of a transfer data quantization step. [Figure 11] FIG. 4 is a diagram showing detailed steps of a received data restoration process. [Figure 12] A graph showing a 1D LUT for restoration. [Figure 13] FIG. 2 is a diagram showing a printing sequence in the printing system. [Figure 14] FIG. 13 is a diagram showing an overall color setting UI screen. [Figure 15] FIG. 13 is a diagram illustrating a UI screen for determining conversion parameters of a Destination Profile. [Figure 16] FIG. 4 is a diagram showing a sequence of a display process in the display system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the technology of the present disclosure will be described with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the technology of the present disclosure is not limited to the configurations shown in the drawings.

[0011] <First embodiment> In the field of commercial and industrial printing, there are printing devices capable of reproducing a wide color gamut. In such printing devices, in addition to the process color inks cyan (C), magenta (M), yellow (Y), and black (K), special color inks are used to achieve color reproduction in a wide color gamut. Special color inks are, for example, inks such as orange (O), green (G), and blue (B).

[0012] For offset printing, "offset printing standards" that comply with ISO 12647-2 have been established. For example, JananColor is used as the standard in Japan, SWAP and GRACoL in North America, and Euroscale in Europe, all of which comply with ISO standards. These standards stipulate standard paper, standard ink, and standard measurement values ​​for solid colors, and define the method of color reproduction in ICC profiles. Also, ISO / PAS 15339-2 standardizes common color reproduction that is independent of the printing process, and specifies dot area percentages (CMYK%) and colorimetric values ​​(CIE L * a * b * The data set is called Characterized Reference Printing Condition (CRPC), and there are seven types available depending on the size of the color space.

[0013] Figure 1 shows the CIE L * a * b * Color space a * b * This is a diagram in which values ​​corresponding to the outermost boundary of the reproducible color gamut of the following three color spaces are plotted on a plane. In Fig. 1, the outermost boundary of the color gamut of the AdobeRGB color space is shown by a dashed line. The outermost boundary of the reproducible color gamut when offset printing is performed in the CMYK color space of CRPC5 defined in ISO / PAS 15339-2 is shown by a dotted line. The outermost boundary of the reproducible color gamut of an inkjet printer that uses special inks of orange, green, and blue in addition to CMYK is shown by a solid line. CRPC5 is a typical target for publishing printing. As shown in Fig. 1, the reproducible color gamut of offset printing is smaller than that of the AdobeRGB color space. The reproducible color gamut of an inkjet printer equipped with special inks of orange, green, and blue is larger than that of offset printing, and is approaching the gamut of the AdobeRGB color space.

[0014] In commercial and industrial printing systems, it is common to use a color management system (hereafter referred to as CMS) that uses ICC profiles as a means of approximating the colors of the input original image data to the colors of the printed matter that is output.

[0015] 2 is a diagram showing the concept of a CMS. An input device 200 is an input device such as a digital camera, a scanner, a monitor, or a PC. Signal values ​​(hereinafter simply referred to as signal values) of each color component constituting a color, which is color information in image data output from the input device 200, are input to a color management module (hereinafter referred to as CMM) 210. The signal values ​​output from the input device 200 are signal values ​​dependent on the input device 200.

[0016] The Source Profile 211 is configured as an ICC profile that includes conversion parameters for converting input device-dependent signal values ​​to device-independent color space signal values. The input device-dependent signal values ​​are converted to PCS212 signal values, which are device-independent color space signal values, by the conversion parameters linked to the Input Device 200 included in the Source Profile 211 in the CMM 210. The device-independent color space, PCS212, includes the CIE L * a * b * color space, or the CIE XYZ color space is used.

[0017] The Destination Profile 213 is configured as an ICC profile including conversion parameters for converting signal values ​​in a device-independent color space into output device-dependent signal values. The signal values ​​of the PCS 212 are converted from device-independent signal values ​​to output device-dependent signal values ​​by the conversion parameters linked to the Output Device 220 in the Destination Profile 213. Then, image data in which color information is defined by the converted signal values ​​is transmitted to the Output Device 220.

[0018] When the output device is a printing device such as an inkjet printer, the output device-dependent signal values ​​are expressed by the signal values ​​of each channel (each color component) of CMYK corresponding to the ink type. When the output device is a printer, the conversion parameters included in Destination Profile 213 are created so that the maximum possible value of the output device-dependent signal value is the signal value that deposits ink at the maximum output of the output device.

[0019] FIG. 3 is a diagram for explaining the conversion parameters included in the ICC profile that constitutes Destination Profile 213. The ICC profile that constitutes Destination Profile 213 includes, as conversion parameters, a color conversion table (LUT) for converting device-independent signal values ​​to output device-dependent signal values. Also included as conversion parameters is a color conversion table for converting output device-dependent signal values ​​to device-independent signal values. FIG. 3 shows a color conversion LUT for converting device-dependent signal values ​​to output device-independent signal values. In FIG. 3, each signal value of CMYK, which is an output device-dependent signal value, is a 16-bit signal value (maximum possible value = 65535) that corresponds to the reproducible color gamut of an inkjet printer that uses special color inks. Also, in FIG. 3, the device-independent signal value is L * a * b * are the signal values ​​of

[0020] The primary colors green, cyan, blue, magenta, red, and yellow correspond to the vertices of the gamut (reproducible color range) of the CMYK color space shown in Figure 1. The combinations of CMYK signal values ​​in Figure 3 correspond to the colors picked up at equal intervals on the outermost edge of the reproducible color gamut.

[0021] The primary colors green, cyan, blue, magenta, red, and yellow, which correspond to the vertices of the reproducible color gamut, have signal values ​​expressed as percentages as follows: Yellow (C,M,Y,K)=(0,0,100%,0) Green (C,M,Y,K)=(100%,0,100%,0) Cyan (C,M,Y,K)=(100%,0,0,0) Blue (C,M,Y,K)=(100%,100%,0,0) Magenta (C,M,Y,K)=(0,100%,0,0) Red (C,M,Y,K)=(0,100%,100%,0) As shown in Figure 3, the combination of signal values ​​that indicates the outermost colors corresponding to the lines connecting the vertices of the reproducible color gamut is 65535, which is the maximum value that the signal values ​​of any of the CMYK channels can take.

[0022] The reproducible color gamut of a printer that does not use spot color inks is, for example, the same as the gamut range of the CRPC5 CMYK color space as shown by the dotted line in Figure 1. Therefore, when such a printer prints based on image data created with highly saturated colors in the CRPC5 CMYK color space, inks are used to reproduce colors at maximum output. When the signal values ​​of such original image data are color-converted into 16-bit signal values, the maximum value of the output device-dependent signal value after color conversion becomes close to 65535, which is the maximum possible value, and the minimum value becomes close to 0, which is the minimum possible value. In other words, the signal value is converted into an output device-dependent signal value such that the data range from the maximum value to the minimum value of the signal value is close to the full range. On the other hand, since the reproducible color gamut of an inkjet printer that uses spot color inks is wide, the output device-dependent signal value corresponding to an inkjet printer that uses spot color inks may not be close to the full range.

[0023] FIG. 4(a) is a diagram showing an example of the correspondence between input device-dependent signal values ​​and output device-dependent signal values ​​after the signal values ​​are color-converted by CMS. In the Input column 401 in FIG. 4(a), signal values ​​in the CMYK color space of CPRC5 are held as 16-bit input device-dependent signal values. In the Output column 402, a combination (color) of 16-bit output device-dependent signal values ​​after color conversion corresponding to the combination (color) of signal values ​​held in the column 401 is held. The output device-dependent signal values ​​in FIG. 4(a) are CMYK signal values ​​corresponding to the color gamut that can be reproduced by an inkjet printer using special color inks. When printing based on original image data created in the CMYK color space of CPRC5 is performed by an inkjet printer using special color inks, the inkjet printer can reproduce the colors of the original image data without relying on maximum output. That is, as shown in FIG. 4(a), the maximum value of the output device-dependent signal value after color conversion is not the maximum possible value of 16 bits, ie, 65535.

[0024] Column 403 in Fig. 4(a) holds values ​​obtained by expressing the 16-bit signal values ​​in column 402 as a percentage. In percentage representation, the signal value is expressed with the maximum possible value of the signal value being 100%. That is, in the case of 16 bits, a value of 65535 is expressed as 100%.

[0025] FIG. 4(b) is a diagram showing the data range (maximum and minimum values) of the signal values ​​of each color component after color conversion in column 403. As shown in FIG. 4(a), the signal values ​​of the Y channel (Y color component) in column 403 show that the maximum value is 71.76% and the minimum value is 3.53%. The Range (%) in FIG. 4(b) holds the difference between the maximum and minimum signal values ​​of each channel of CMYK. It can be seen that only 68.24% of the full range (100%) of the signal values ​​of the Y channel after conversion to output device-dependent signal values ​​is used. This shows that an inkjet printer capable of reproducing a wide color gamut can reproduce the colors of image data in the CMYK color space of CRPC5, which has a narrow color gamut, even if it does not output ink to correspond to the full range signal values ​​of each channel of CMYK.

[0026] [About the printing system] In this embodiment, a printing system for commercial and industrial printing will be described as an example. The printing system includes an image processing device and a printing device. The printing system of this embodiment is a system for directly opening an original image file and printing. Alternatively, the printing system is a commercial printing system in which a print management application such as a workflow RIP generates a print job based on an original image file, and receives the print job and prints.

[0027] [Printing device hardware configuration] FIG. 5 is a diagram for explaining the internal configuration of a printing device 510 included in the printing system of this embodiment. As an example, the printing device 510 will be explained as a line printer that prints on a recording medium (also called a medium) in one pass. The medium will be explained as a rolled continuous sheet. The printing device 510 has each unit of a continuous sheet supply unit 500, a printing unit 501, an ink supply unit 502, a drying unit 503, a reading unit 504, and a sheet discharge unit 505. The continuous sheet is transported by a transport mechanism having a roller pair, a belt, etc. along a continuous sheet transport path 508 shown by a dashed line in FIG. 5, and is processed by each unit.

[0028] The continuous sheet supply unit 500 stores a continuous sheet wound in a roll shape, and supplies the continuous sheet to a conveying path 508 .

[0029] Print unit 501 has a print head and a plurality of transport rollers that transport the continuous sheet. The print head prints an image on the transported continuous sheet. The print head will be described as a print head that prints by an inkjet method. The ink used for printing is seven colors (CMYKOGB), including four colors (CMYK) of cyan, magenta, yellow, and black, plus three spot colors (OGB) of orange, green, and blue. The inkjet printing method is a well-known technology, and detailed description will be omitted.

[0030] The print head is, for example, a line-type print head in which an inkjet nozzle row is formed in a range covering the maximum width of the continuous sheet expected to be used. The print head has a plurality of print heads corresponding to a plurality of inks arranged in parallel along the conveying direction (x direction) of the continuous sheet. As a method of ejecting ink by the inkjet method, a method using a heating element, a method using a piezoelectric element, a method using an electrostatic element, a method using a MEMS element, etc. can be adopted. Ink of each color is supplied to the print head from an ink supply unit 502 through each ink tube. In addition, the print head moves in the up and down direction (z direction) to perform a capping operation. It also moves in the vertical direction (y direction). It is equipped with a mechanism for performing this operation and a motor for driving it.

[0031] The drying unit 503 is a unit that heats the sheet printed by the printing unit 501 to quickly dry the applied ink. The drying unit 503 also includes a conveyor belt and conveyor rollers for sending the sheet to the next process.

[0032] The reading unit 504 performs processing for reading the test pattern for maintenance of the print head printed by the printing unit 501 .

[0033] The sheet discharge unit 505 includes a winding device that winds up the printed and dried medium in a roll and discharges it.

[0034] [Printing system control configuration] 6 is a block diagram for explaining the control configuration of the image processing device 600 and the printing device 510 included in the printing system of this embodiment. First, the image processing device 600 will be explained. The image processing device 600 is a device that receives original image data including a PDL drawing command from an input device, performs RIP processing on the received original image data, and performs color conversion to signal values ​​of an output device-dependent color space by CMS as shown in Fig. 2. In addition, the image processing device 600 transfers print instructions, necessary information, and data to the printing device 510.

[0035] The printing device 510 converts the bitmap image data, in which the color values ​​of each pixel are represented by output device-dependent signal values, sent from the image processing device 600 into a data format for printing, and prints on a medium based on the data obtained by the conversion. Data transfer between the image processing device 600 and the printing device 510 is performed via an interface such as a network, USB, or local bus.

[0036] As shown in FIG. 6, the image processing device 600 includes a UI unit 601 , a working memory 602 , a data input / output unit 603 , a calculation unit 604 , and a large-capacity storage unit 605 .

[0037] The UI unit 601 has, for example, input devices (operation unit) such as a keyboard and a mouse, and an output device (display unit) such as a liquid crystal display. The UI unit 601 may be configured with a touch panel or the like that also has input and output functions. The UI unit 601 has a user interface function that allows the user to perform various inputs including color settings, and displays information required by the user.

[0038] The mass storage unit 605 is configured by an HDD or SSD, and stores and manages software such as the OS and system programs, as well as various setting values ​​and data such as parameters required for various processes.

[0039] The calculation unit 604 is composed of a CPU, a GPU, etc., and executes software stored in the mass storage unit 605 by using the working memory 602.

[0040] The data input / output unit 603 is an interface for inputting print jobs and transferring data to the printing device 510 .

[0041] The functions (functional units) for executing each process (step) described later are realized by the calculation unit 604 executing a predetermined program to instruct each unit in the image processing device 600 and transmit information. For example, the function of performing CMS processing (color conversion processing) using the ICC profile shown in FIG. 2 is also realized by the calculation unit 604 processing, but is not limited to this. Other hardware such as a GPU (Graphics Processing Unit) or an FPGA (Field Programmable Gate Array) for accelerating calculations may be used. The functional units may be realized by cooperation between software and hardware such as a dedicated IC, or some or all of the functions may be realized only by hardware.

[0042] 6 is a block diagram for explaining the control configuration of the printing device 510. The printing device 510 has a data transfer unit 611, a print control unit 612, an image processing unit 613, a large-capacity storage unit 614, a print engine 615, and a printing device control unit 616.

[0043] The printing device control unit 616 is a unit that controls the entire printing device 510. The printing device control unit 616 has a CPU, a memory, a controller 617 equipped with various I / O interfaces, and a power supply (not shown). The operation of the printing device 510 is controlled based on commands from the controller 617 included in the printing device control unit 616, or an information processing device 507 (see FIG. 5), such as a host computer, connected to the controller 617 via an I / O interface. Although FIG. 5 shows an example of a configuration in which the information processing device 507 exists outside the printing device 510, the information processing device 507 may exist inside the printing device 510.

[0044] The data transfer unit 611 receives a print job output from the image processing device 600. The print job includes document image data, print setting information, color space information (information on the device-dependent color space after color conversion and its area), etc. The received document image data is image data that has been converted by the image processing device 600 into bitmap data, signal values ​​have been converted into output device-dependent signal values, and the signal values ​​have been quantized to a lower bit rate in order to compress the data.

[0045] Of the received print job, the data transfer unit 611 sends document image data to the image processing unit 613 and sends print setting information to the print control unit 612 .

[0046] The print control unit 612 controls the operation of the print engine 615 according to the print setting information. The print engine 615 is composed of a print head that ejects ink, a supply system that supplies ink to the print head, and the like, and executes an ink ejection operation according to image data that has been subjected to a series of image processes in the image processing unit 613. In the printing system shown in FIG. 6, the image processing device 600 and the printing device 510 are configured as independent devices, but the image processing device 600 may be included in the printing device 510, for example.

[0047] As shown in Fig. 6, image processing such as color conversion may be performed in an image processing device 600 separate from the printing device 510. For example, in commercial and industrial printing, it is rare for a single vendor to design the entire system, and as shown in Fig. 6, the printing device 510 is typically connected to existing external systems and workflow software.

[0048] From the viewpoint of maintaining accuracy, it is desirable that the signal value of the document image data is transmitted from the image processing device 600 to the printing device 510 as it is with a high bit. However, when transmitting image data with a high bit signal value, the amount of transmitted data increases, and it takes time to transmit, making it impossible to output at a high speed. In particular, for commercial and industrial printing, not being able to output at a high speed can be problematic because it reduces productivity. For this reason, it is possible to use a communication device capable of high-speed data transfer, but this would incur a burden for introducing the communication device. Therefore, when transmitting image data with a high bit signal value between devices, it is common to quantize the signal value of the image data to a low bit signal value before transmitting the image data.

[0049] When quantizing a high-bit signal value to a low-bit signal value, for example, a conversion including a bit shift may be performed, such as simply converting a 32-bit or more fixed-point format to a 16-bit or 8-bit integer type. In this case, the number of gradations in the image may be reduced due to bit loss. As a result, details in the dark and highlight areas of the image may be lost, deteriorating the image quality. If an attempt is made to quantize to a low-bit signal value so as not to reduce the number of gradations, the processing becomes complicated, and it may be difficult to make an existing image processing device perform such processing. Therefore, in this embodiment, a method of quantizing to a low-bit signal value so as not to reduce the number of gradations using a simpler method will be described.

[0050] [Printing system sequence] 7 is a diagram showing a print sequence in the printing system of this embodiment. In this embodiment, a print job is input to the image processing device 600. The document image data included in the print job is PDL image data. The document image data includes a command to draw an object with color information in an RGB work color space in which the signal value of each RGB channel is a luminance signal value. Alternatively, the document image data includes a command to draw an object with color information in a CMYK work color space defined by the ink usage amount of CMYK.

[0051] First, the process executed by the image processing device 600 will be described. Each process (step) described below will be described as being performed by the calculation unit 604 instructing each unit in the image processing device 600 and transmitting information. For example, the processing of each process performed in the image processing device 600 in Fig. 6 is performed by the calculation unit 604 expanding program code stored in the mass storage unit 605 into the working memory 602 and executing it. Also, some or all of the functions of the processes in Fig. 6 may be realized by hardware such as ASIC or electronic circuits.

[0052] In the rendering process 700, the calculation unit 604 interprets the PDL of the document image data included in the print job and performs rendering processing. Then, the calculation unit 604 converts the document image data into bitmap document image data. After the rendering process 700, a color conversion process 701 is performed.

[0053] In the color conversion step 701, the calculation unit 604 performs color conversion using the conversion parameters as described in FIG. 2 on the RGB signal values ​​or CMYK signal values, which are pixel values ​​of each pixel of the original image data to be color converted and which have been processed in the rendering step 700. The ICC profile for each color space including the conversion parameters is stored in the mass storage unit 605. Based on the information on the input device-dependent signal values ​​and the information on the output device-dependent signal values ​​specified via the UI unit 601, the calculation unit 604 acquires the ICC profile used for color conversion from the mass storage unit 605. As a result of the color conversion step 701, the signal values ​​representing the color of the target object in the original image data are converted to signal values ​​dependent on the output device. For example, as shown in FIG. 4, conversion is performed from the signal values ​​of the CMYK color space of CRPC5 to signal values ​​corresponding to the reproducible color gamut of the inkjet printer.

[0054] In commercial and industrial printing, the printed matter obtained by printing device 510 is often the final product. For this reason, in order to maintain the image quality of the printed matter, the color conversion process 701 in the image processing device 600 will be described as a process of converting the color into a high-bit signal value that is greater than the high resolution 8 bits. The color conversion process 701 can also be said to be a process of acquiring image data whose color information is defined by high-bit signal values.

[0055] The image data after being converted into high-bit signal values ​​has a large volume. Therefore, in the transfer data quantization step 702, quantization is performed to compress the data volume of the document image data in order to transmit the document image data to the printing device 510. In this embodiment, the signal values ​​of the document image data after the color conversion step 701 are quantized from signal values ​​defined by high bits (e.g., 16 bits) to signal values ​​defined by low bits (e.g., 8 bits).

[0056] In a transmission step 704, the calculation unit 604 transmits the document image data whose signal values ​​have been quantized to 8 bits and data range information of the signal values, which will be described later, to the printing device 510. The details of the transfer data quantization step 702 and the data range acquisition step 703 will be described later.

[0057] Next, the steps executed by the printing device 510 will be described. The processes of each step executed by the printing device 510 shown in Fig. 7 are executed by the controller 617 by expanding the program code stored in the storage unit into the RAM and executing it. In addition, some or all of the functions of the steps in Fig. 7 may be realized by hardware such as an ASIC or an electronic circuit. Some or all of the steps in Fig. 7 may be executed by the image processing unit 613, for example.

[0058] In a receiving step 711, the controller 617 receives the document image data, the signal values ​​of which have been quantized to 8 bits, and the data range information of the signal values, transmitted from the image processing device 600.

[0059] In the received data restoration step 712, the controller 617 performs processing to restore the signal values ​​of the original image data to the number of processing bits in the printing device 510. The number of processing bits in the printing device 510 is a number of bits larger than the number of processing bits in the transfer data quantization step 702, and is assumed to be 16 bits in the following explanation. The controller 617 performs restoration so that the data range of the signal values ​​of the original image data after the color conversion step 701 and the data range after the processing in the received data restoration step 712 are relatively the same. The received data restoration step 712 will be described in detail later.

[0060] In the color separation process 713, the controller 617 converts the CMYK signal values ​​restored to 16 bits into signal values ​​for each color component corresponding to each ink of CMYK, G, and B corresponding to the ink colors used in the printing device 510. This color conversion process is performed by referring to a four-dimensional lookup table (four-dimensional LUT) in which CMYK signal values ​​and CMYK, G, and B signal values ​​are associated with each other and stored in advance in the mass storage unit 614. Specifically, the CMYK signal values ​​are converted into CMYK, G, and B signal values ​​associated with each other by the four-dimensional LUT.

[0061] In the gradation correction process 714, the controller 617 acquires the CMYKOGB signal values ​​obtained in the color separation process 713. Then, in the gradation correction process 714, the controller 617 performs a linear conversion for each ink so that the density expressed on the medium can maintain a linear relationship with the input signal value. This linear conversion is performed by referring to a one-dimensional LUT for each ink that is pre-stored in the mass storage unit 614. As described above, the signal value conversion processes performed in the color conversion process 701, the color separation process 713, and the gradation correction process 714 are all performed on 16-bit multi-value signals. The multi-value data that has been subjected to the gradation correction is passed to the quantization process 715.

[0062] In a quantization step 715, the controller 617 converts the multi-value data that has been subjected to gradation correction into binary data for each ink, in which a dot is printed with a "1" and a dot is not printed with a "0".

[0063] The controller 617 sends the binary data obtained as a result of the quantization process 715 to the print engine 615. Then, in a printing process 716, the controller 617 causes the print head included in the print engine 615 to eject ink in accordance with the binary data, and prints an image corresponding to the document image data on a medium.

[0064] [About the transmission data quantization process] Next, the details of the transfer data quantization step 702 and the data range acquisition step 703 will be described. In the transfer data quantization step 702 of this embodiment, quantization is performed to reduce the signal value to a lower bit using data range information indicating the data range of the signal value after color conversion in the color conversion step 701. The data range information is data indicating the maximum and minimum values ​​of the signal value of the number of bits after color conversion in the color conversion step 701. In the following description, it is assumed that in the color conversion step 701, the signal value of the original image data is converted to a 16-bit signal value of CMYK.

[0065] In the data range acquisition step 703, the calculation unit 604 performs processing for acquiring data range information. In the data range acquisition step 703 of this embodiment, the minimum and maximum actual signal values ​​of each channel are acquired from the data distribution of 16-bit signal values ​​of each channel (each color component) of CMYK in the original image data obtained by color conversion in the color conversion step 701. For example, the calculation unit 604 acquires the maximum and minimum signal values ​​of the C channel in the original image data by checking the signal values ​​of the C channel for all pixels of the bitmap original image data. In a similar manner, the calculation unit 604 acquires the maximum and minimum signal values ​​of the M channel, the maximum and minimum signal values ​​of the Y channel, and the maximum and minimum signal values ​​of the K channel. Data range information indicating the minimum and maximum signal values ​​of each channel of CMYK of the original image data after the color conversion step 701 is output to the transfer data quantization step 702.

[0066] 8 is a diagram showing detailed steps of the transfer data quantization step 702. The transfer data quantization step 702 includes a one-dimensional LUT generation step 801 and a quantization step 800.

[0067] In the one-dimensional LUT generating step 801 , the calculation unit 604 obtains data range information indicating the minimum and maximum values ​​of each of the CMYK channels obtained in the data range obtaining step 703 .

[0068] 9(a) is a diagram showing an example of data range information, showing an example of the maximum and minimum values ​​of 16-bit signal values ​​for each channel of CMYK. In the case of 16 bits, the maximum possible value of a signal value is 65535, but the maximum signal value of actual document image data may be smaller than 65535, and the minimum actual signal value may be larger than 0. For this reason, as mentioned above, signal values ​​in the full range from 0 to 65535 may not be used in document image data.

[0069] In a one-dimensional LUT generating step 801, the calculation unit 604 generates a one-dimensional LUT for quantization for each channel of CMYK. That is, a one-dimensional LUT for quantization corresponding to each of the four channels (four color components) of CMYK is generated.

[0070] 9(b) to (e) are graphs showing one-dimensional LUTs for quantization of each channel of CMYK that are generated when the data range information shown in FIG. 9(a) is acquired.

[0071] The generated one-dimensional LUT for quantization is a one-dimensional LUT in which the input is a 16-bit signal value which is the signal value of the current document image data, and the output is an 8-bit signal value which is the number of processing bits in the transfer data quantization step 702. In the one-dimensional LUT generation step 801, the correspondence is performed so that the minimum value of the 16-bit signal value indicated by the data range information is converted to 0 which is the minimum value that an 8-bit signal value can take. Also, the correspondence is performed so that the maximum value of the 16-bit signal value indicated by the data range information is converted to 255 which is the maximum value that an 8-bit signal value can take. Signal values ​​between the maximum value and the minimum value indicated by the data range information are linearly expanded and associated with 8-bit signal values ​​to generate the one-dimensional LUT for quantization.

[0072] FIG. 9(b) is a graph showing the quantization one-dimensional LUT corresponding to the cyan (C) channel. As shown in FIG. 9(a), the maximum value of the 16-bit signal value of the C channel of the original image data after color conversion by the color conversion process 701 is 48640. Therefore, the quantization one-dimensional LUT is generated so that the input 48640 is converted to 255 as an 8-bit signal value. Similarly, the minimum value of the 16-bit signal value of the C channel is 2560, and the quantization one-dimensional LUT is generated so that the input 2560 is converted to 0 as an 8-bit signal value. Therefore, the quantization one-dimensional LUT is generated so that 2560 to 48640 out of the full 16-bit range of 0 to 65535 is converted to the full 8-bit range. Therefore, the range of possible values ​​of the input signal value corresponding to the output signal value of 1 can be narrowed.

[0073] In the quantization process 800, the calculation unit 604 quantizes the signal values ​​of each CMYK channel, which are the pixel values ​​of each pixel of the original image data after the color conversion process 701, using a one-dimensional LUT for quantization corresponding to each channel, and converts them into signal values ​​compressed to 8 bits.

[0074] FIG. 10 is a diagram for simply explaining the processing of the transfer data quantization step 702. FIG. 10(a) shows an image indicated by the original image data before being quantized to a low-bit signal value. That is, it is a diagram of an image in which color information is defined by a 16-bit signal value. In FIG. 10(a), for simplicity, it is assumed that the color of the original image data is expressed by a signal value of one channel. When the signal value is expressed as a percentage, it is assumed that the color information of the background color is defined by a signal value (density) of 0% in the original image data after the color conversion step 701. Similarly, it is assumed that the color information of object 1001 is defined by a signal value (density) of 10%, object 1002 is defined by a signal value (density) of 30%, and object 1003 is defined by a signal value (density) of 50%. In addition, an object 1004 is arranged in which a gradation is expressed in 256 gradations using signal values ​​from 0% to 50%.

[0075] Fig. 10(b) is a graph showing the one-dimensional LUT for quantization generated in the one-dimensional LUT generation step 801. When the data range acquisition step 703 is performed on the image in Fig. 10(a), 32768, which corresponds to 50% in percentage, is acquired as the maximum signal value, and 0, which corresponds to 0%, is acquired as the minimum signal value.

[0076] When the calculation unit 604 generates a one-dimensional LUT for quantization using the maximum and minimum values ​​of this 16-bit signal value, an LUT is generated that outputs 255, the maximum possible 8-bit value, when 32768 is input as a 16-bit signal value.

[0077] Fig. 10(c) is a diagram of an image represented by image data obtained by quantizing the 16-bit signal value of the image data corresponding to the image shown in Fig. 10(a) to an 8-bit signal value by the method of this embodiment. The data range of the signal value in the image data corresponding to the image in Fig. 10(c) is expanded from 0 to 50% before quantization to 0 to 100% in percentage representation. The object 1004 in Fig. 10(c) in which the gradation is expressed is expressed from the minimum possible value of 0% (0) to the maximum possible value of 100% (255) in 8 bits. Since the data range is expanded during quantization, the number of gradations of the gradation of the object 1004 in Fig. 10(c) is maintained at 256 gradations before quantization.

[0078] As a comparative example, suppose that a one-dimensional LUT for quantization is generated so that when 65535, the maximum possible value of 16 bits, is input, 255, the maximum possible value of 8 bits, is output, and when 0 is input, 0 is output. Then, suppose that a 16-bit signal value is quantized to an 8-bit signal value using the one-dimensional LUT for quantization. In this case, the 16-bit signal value 0% (0) to 100% (65535) is quantized to correspond to an 8-bit signal value 0% (0) to 100% (255). The 256-level gradation expressed by 16-bit signal values ​​0% (0) to 50% (32768) in the input image has a gradation number of 128, half of 256, after quantization to 8 bits by the method of the comparative example. Therefore, according to the quantization of this embodiment, data can be compressed while suppressing deterioration in the number of levels compared to the method of the comparative example.

[0079] In this embodiment, quantization to a low bit rate can be performed using a one-dimensional LUT. The one-dimensional LUT can also be generated by acquiring the maximum and minimum signal values ​​after the color conversion process 701. This eliminates the need for complex processing such as determining a quantization method for each pixel, making it possible to compress data using a simpler method while suppressing deterioration in the number of gradations.

[0080] Then, in a transmission step 704, the calculation unit 604 transmits the document image data, whose signal values ​​have been quantized to 8 bits, to the printing device 510. Furthermore, the calculation unit 604 transmits data range information used to generate the one-dimensional LUT for quantization as shown in Fig. 9(a) to the printing device 510 as one piece of print setting information.

[0081] [About the received data restoration process] 11 is a diagram showing detailed steps of the received data restoration step 712 in the printing device 510. The received data restoration step 712 includes a one-dimensional LUT generation step 1101 and a restoration step 1100.

[0082] In the one-dimensional LUT generation step 1101, the controller 617 acquires data range information of the signal values ​​before quantization of each channel included in the print setting information transmitted from the image processing device 600. For example, data range information indicating the maximum and minimum values ​​of the signal values ​​before quantization by the transfer data quantization step 702 as shown in Fig. 9(a) is acquired.

[0083] In the one-dimensional LUT generation step 1101, the controller 617 generates a one-dimensional LUT for restoration for each channel of CMYK. That is, one-dimensional LUTs for restoration corresponding to each of the four channels (four color components) of CMYK are generated. The one-dimensional LUT for restoration is a one-dimensional LUT in which the input is a signal value of the number of processing bits in the transfer data quantization step 702 (signal value of the received original image data), and the output is a signal value of the number of processing bits in the received data restoration step 712. In the following description, it is assumed that the number of processing bits in the color conversion step 701 is 16 bits. It is also assumed that the number of processing bits in the transfer data quantization step 702 is 8 bits. It is also assumed that the number of processing bits in the received data restoration step 712 is 16 bits. That is, it is assumed that in the reception step 711, original image data of 8-bit signal values ​​and data range information indicating information of 16-bit signal values ​​are received.

[0084] In the one-dimensional LUT generation step 1101, the controller 617 performs correspondence so that 0, which is the minimum value that an 8-bit signal value can take, is converted to the minimum value of a 16-bit signal value indicated by the data range information transmitted from the image processing device 600. Also, the controller 617 performs correspondence so that 255, which is the maximum value that an 8-bit signal value can take, is converted to the maximum value of a 16-bit signal value indicated by the data range information. Then, the controller 617 performs correspondence so that values ​​between the maximum value and the minimum value are linearly expanded to generate a one-dimensional LUT for restoration. That is, a one-dimensional LUT for restoration is generated so that 8-bit signal values ​​of 0 to 255 in each channel of CMYK are returned to the data range of each channel of CMYK before the transfer data quantization step 702.

[0085] 12(a) to 12(d) are graphs showing the restoration one-dimensional LUTs for each of the CMYK channels generated in the one-dimensional LUT generating step 1101 when the data range information shown in FIG. 9 is acquired.

[0086] Fig. 12(a) is a graph showing a one-dimensional restoration LUT corresponding to the cyan (C) channel. As shown in Fig. 9(a), the maximum value of the 16-bit signal value of the C channel of the original image data after color conversion by the color conversion process 701, which is the maximum value indicated by the data range information, is 48640. Therefore, the one-dimensional restoration LUT is generated so that 255, which is the maximum value that an 8-bit signal value can take, is converted to 48640. Similarly, the minimum value of the 16-bit signal value of the C channel is 2560, and the one-dimensional restoration LUT is generated so that 0 is converted to 2560 as an 8-bit signal value.

[0087] The number of processing bits in the received data restoration step 712 may differ from the number of bits corresponding to the maximum and minimum values ​​indicated by the data range information. In this case, in the one-dimensional LUT generation step 1101, the controller 617 performs processing to convert the maximum and minimum values ​​indicated by the data range information into the number of processing bits in the received data restoration step 712. For example, if the number of bits in the data range information is 16 bits and the number of processing bits in the received data restoration step 712 is 12 bits, the number of bits is converted by substituting the maximum or minimum value of the data range information using the following formula.

[0088] 12-bit signal value = (16-bit signal value / 65535) x 4095 Then, in the one-dimensional LUT generation step 1101, correspondence is performed so that the minimum value (0) that an 8-bit signal value can take is converted into the minimum value of a 12-bit signal value indicated by the data range information. Also, correspondence is performed so that the maximum value (255) that an 8-bit signal value can take is converted into the maximum value of a 12-bit signal value. Then, a one-dimensional LUT for restoration is generated, in which the input is an 8-bit signal value and the output is a 12-bit signal value.

[0089] As mentioned above, Fig. 10(c) shows image data in which color information is defined by 8-bit signal values ​​before restoration processing. Fig. 10(d) shows a one-dimensional LUT for restoration generated from a data range of the signal values ​​before quantization from a minimum value of 0% (0) to a maximum value of 50% (32768).

[0090] In the restoration step 1100, the controller 617 inputs the signal value of each pixel of the original image data before the restoration process into a one-dimensional restoration LUT to perform a process of restoring the signal value quantized to a low bit. As a result, the signal value compressed to 8 bits is restored to a 16-bit signal value. As a result of the restoration step 1100, the original image data sent from the image processing device 600 is restored to image data showing an image whose color information is defined by a 16-bit signal value as shown in Fig. 10(a). In the restoration step 1100, the 8-bit signal value is linearly converted to a 16-bit signal value in the original data range, so the number of gradations before the restoration process is restored while being preserved.

[0091] As described above, in this embodiment, the minimum and maximum signal values ​​of each high-bit channel are associated with the minimum and maximum possible low-bit values, respectively, and the values ​​between them are linearly expanded and associated to generate a one-dimensional LUT. Then, based on the generated one-dimensional LUT, the signal value with a high bit number is converted to a low-bit signal value. In this way, according to this embodiment, quantization is performed using a one-dimensional LUT, so that a high-bit signal value can be quantized to a low-bit signal value in a simple manner while suppressing the influence of bit dropping. In addition, in the restoration process of converting a low-bit signal value to a high-bit signal value, the restoration process is performed so that the data range of the signal value returns to the state before quantization. Therefore, it is possible to restore to high-bit image data while suppressing the deterioration of the number of gradations due to quantization to low bits. Therefore, according to this embodiment, even an existing image processing device can perform a quantization process appropriately.

[0092] According to this embodiment, when image data in a narrow color gamut is compressed by bit-number conversion and transmitted to an image output device capable of color reproduction in a wide color gamut, data compression can be performed in a simpler manner that suppresses deterioration of gradation reproducibility due to bit-number conversion. In particular, when the data range of the original image data after color conversion by CMS is narrow (the maximum signal value is small or the minimum signal value is large), it is possible to suppress a decrease in the number of gradations due to bit-number conversion.

[0093] In the above description, the number of processing bits in the color conversion step 701 is 16 bits, the number of processing bits in the transfer data quantization step 702 is 8 bits, and the number of processing bits in the received data restoration step 712 is 16 bits, but these numbers of processing bits are merely examples. If the number of processing bits in the color conversion step 701 is N bits, the number of processing bits in the transfer data quantization step 702 is M bits, and the number of processing bits in the received data restoration step 712 is L bits, then it is sufficient that the relationship N>M and L>M holds. For example, N bits may be 10 bits, M bits may be 8 bits, and L bits may be 16 bits, or N bits may be 16 bits, M bits may be 8 bits, and L bits may be 12 bits.

[0094] Furthermore, the data range information transmitted to the printing device 510 in the transmission step 704 of the image processing device 600 may be information indicating the maximum and minimum values ​​of the signal values ​​before quantization in the transfer data quantization step 702. That is, the data range information transmitted in the transmission step 704 may be information different from the data range information used to generate the one-dimensional LUT for quantization in the one-dimensional LUT generation step 801. For example, in the transmission step 704, the one-dimensional LUT for quantization used in the transfer data quantization step 702 may be transmitted to the printing device 510 as data range information. In that case, in the received data restoration step 712 of the printing device 510, the minimum and maximum signal values ​​may be obtained from the shape of the quantized one-dimensional LUT to generate the one-dimensional LUT for restoration.

[0095] <Second embodiment> In the first embodiment, a method for obtaining data range information indicating maximum and minimum signal values ​​by checking the signal values ​​of each pixel in the document image data after color conversion has been described. In the present embodiment, a method for obtaining data range information by a different method will be described.

[0096] Fig. 13 is a diagram showing a print sequence in the print system of this embodiment. The same steps as those in the first embodiment are given the same reference numerals and the description will be omitted. As shown in Fig. 2, in a color conversion step 701 by CMS, a signal value dependent on an input device is converted into a signal value dependent on an output device by a source profile and a destination profile. In a data range acquisition step 1301 of this embodiment, conversion parameters used in the color conversion in the color conversion step 701 are acquired from the source profile and the destination profile. Then, in the data range acquisition step 1301, the maximum and minimum signal values ​​for each color component are calculated using the acquired conversion parameters, and data range information before quantization of the document image data is acquired.

[0097] Fig. 14 is a diagram showing an overall color setting UI screen displayed on the UI unit 601 of the image processing device 600. The settings related to the Source Profile shown in Fig. 2 are made based on the contents selected by the user via the overall color setting UI screen 1400. In the overall color setting UI screen 1400, the color space of the object in the document image data is set.

[0098] The "RGB source" pull-down 1401 on the overall color setting UI screen 1400 is used by the user to select a detailed color space when color information is specified in RGB in the original image data. For example, when a detailed color space is not specified in the original image data, the user selects a detailed color space using the pull-down 1401. As shown in Fig. 2, the Source Profile includes an ICC profile for each color space, so the color space selected by the user is used to determine which ICC profile to use.

[0099] For example, when sRGB is selected from the pull-down menu 1401, the RGB signal values ​​in the document image data are considered to be defined in the sRGB color space, and the corresponding ICC profile is acquired. In the color conversion process 701, color conversion processing to a device-independent color space is performed using the acquired ICC profile.

[0100] The "RGB rendering intent" pull-down 1402 selects the gamut compression method used when color-converting RGB signal values. Commonly known compression methods are "Perceptual", "Saturation", "Relative Colorimetric", and "Absolute Colorimetric", and these four types can be specified in this embodiment as well.

[0101] The ICC profile for each color space contains a color transformation table (LUT) for each compression method (rendering intent). Therefore, the compression method selected by the user is used to determine which color transformation LUT to use.

[0102] Similarly, a "CMYK source" pull-down 1403 is used to select a detailed color space when signal values ​​are specified in CMYK in the original image data. Like the pull-down 1401, a color space is selected from the pull-down 1403 when a detailed color space is not specified in the original image data. Like the pull-down 1402, a "CMYK rendering intent" pull-down 1404 also selects a compression method when color information of the original image data is specified by CMYK signal values.

[0103] The "Grayscale source" pull-down 1405 is used to select a detailed color space when the detailed color space of the original image is not specified. The "Grayscale rendering intent" pull-down 1406, like the pull-down 1402, selects a compression method when the detailed color space is not specified.

[0104] 15 is a diagram for explaining a UI screen for determining conversion parameters in a Destination Profile, which is displayed on the UI unit 601 of the image processing device 600. The Destination Profile is set and saved in association with a recording medium (hereinafter, referred to as "media"), such as paper, used in the printing device 510.

[0105] 15(a) is a UI screen for displaying the types of media used in the printing device 510 and accepting selection by the user. A menu bar 1501 includes five types of buttons. By pressing a button, the user can instruct the addition of new media, editing registered media, deleting registered media, importing media via a file, and exporting registered media via a file.

[0106] A media settings screen 1510 shown in Fig. 15(b) is displayed when the "Add" or "Edit" button on menu bar 1501 is pressed. The user enters the name of the type of media into text box 1511 displaying "Name" in media settings screen 1510. The user enters the weight per unit area of ​​the media into text box 1512 displaying "Weight". A pull-down menu 1513 displaying "Coating" includes candidates for the type of coating on the media surface, and the user selects the type of coating for the media from among the candidates.

[0107] When the Browse button 1515 is pressed, a dialog (not shown) containing a list of ICC profiles corresponding to the Destination Profile is displayed. When the user selects an arbitrary ICC profile, the ICC profile corresponding to the Destination Profile used in the color conversion process 701 is displayed in the "Output Profile" text box 1514. When the OK button 1516 is pressed, the conversion parameters used for color conversion are determined from the ICC profile displayed in the text box 1514.

[0108] In this way, an ICC profile for converting input device-dependent signal values ​​to device-independent signal values ​​used in the color conversion process 701 is determined based on the contents specified on the UI screen 1400 for overall color setting in Fig. 14 and the UI screen in Fig. 15. Furthermore, an ICC profile for converting device-independent signal values ​​to output device-dependent signal values ​​is determined. Then, from the determined ICC parameters, conversion parameters used for color conversion in the color conversion process 701 are determined.

[0109] In the data range acquisition step 1301 of this embodiment, the calculation unit 604 acquires conversion parameters determined based on the user's selection. In addition, in the data range acquisition step 1301, the calculation unit 604 extracts signal values ​​arbitrarily sampled from within the possible data ranges of the RGB, CMYK, and Grayscale signal values ​​of the input document image data. Then, the calculation unit 604 performs color conversion on the extracted signal values ​​using the acquired conversion parameters. In the data range acquisition step 1301, the calculation unit 604 determines the minimum and maximum values ​​of each channel from the signal values ​​output as a result of the color conversion, and acquires the determined maximum and minimum values ​​of each channel as data range information.

[0110] For example, in the case of an object whose color information is defined by the signal values ​​of each CMYK channel, 11 signal values ​​are extracted from each channel in 10% increments from the signal values ​​of 0% to 100% of each channel. Then, 11 x 11 x 11 x 11 = 14641 colors are input to the conversion parameters and color conversion is performed for each color. The minimum and maximum values ​​of each CMYK channel are determined from the signal values ​​indicating the colors output as a result of the color conversion, and the determined maximum and minimum values ​​of each CMYK channel are obtained as data range information.

[0111] For example, assume that the color space specified as the color information of an object in the document image data included in the print job is the CMYK color space of CRPC5. In this case, as shown in column 401 of FIG. 4(a), a combination (color) of sampled signal values ​​from among the possible values ​​of the signal values ​​of each channel (each color component) of CMYK is extracted. Then, the combination (color) of sampled signal values ​​stored in column 401 is color converted using conversion parameters, and converted into a combination (color) of signal values ​​in an output device-dependent color space as shown in column 402. The maximum and minimum values ​​are determined from the signal values ​​of each channel constituting the converted color, i.e., the signal values ​​stored in each CMYK column in column 402, and are acquired as data range information.

[0112] Similarly, for objects whose color information is defined by RGB and Grayscale signal values, signal values ​​are extracted at any sampling interval and signal values ​​after color conversion are calculated. If it is known in advance that the original image data is either RGB, CMYK, or Grayscale, it is better to determine the maximum and minimum values ​​from the calculation results of only the data type of that original image data.

[0113] Note that a plurality of one-dimensional LUTs, which are parameters used in the transfer data quantization step 702 and the received data restoration step 712, may be generated in advance based on the respective conversion parameters corresponding to the media information and the color setting information. As described above, since the maximum and minimum values ​​of the signal value after color conversion can be determined from the conversion parameters, a one-dimensional LUT for quantization and a one-dimensional LUT for restoration can be generated in advance for each conversion parameter.

[0114] The one-dimensional LUT for quantization generated in advance is stored in the mass storage unit 605 of the image processing device 600 in association with the conversion parameters used for generation. Also, the one-dimensional LUT for restoration generated in advance is stored in the mass storage unit 614 of the printing device 510.

[0115] For example, if a one-dimensional LUT for quantization has been generated in advance, the transfer data quantization step 702 acquires the conversion parameters used in the color conversion step 701 by the above-mentioned method. Then, the transfer data quantization step 702 may acquire a one-dimensional LUT for quantization stored in association with the acquired conversion parameters from among the one-dimensional LUTs for quantization generated in advance, and perform a process of quantizing to a low-bit signal value. In this way, the conversion parameters may be used as data range information indicating the maximum and minimum values ​​of the signal value after color conversion.

[0116] <Third embodiment> In the above-described embodiment, the image output device that outputs an image based on image data whose signal values ​​are quantized to low bits is described as a printing device, but the image output device is not limited to a printing device. For example, the image output device may be an HDR display device having an HDR display that is a display device capable of reproducing a wide color gamut. Therefore, in this embodiment, a method will be described in which an HDR display device receives image data whose signal values ​​are quantized to low bits and displays an image based on image data obtained by restoring the signal values.

[0117] 16 is a diagram showing a sequence of display processing in a display system for displaying an image based on image data in which color information is defined by a high-bit signal value on a display (display unit). The display system of this embodiment includes an image processing device 1600 and an HDR display device 1610. The hardware configuration of the image processing device 1600 is similar to that of the image processing device 600.

[0118] The steps executed by the image processing device 1600 will be described. The image data input to the image processing device 1600 is bitmap image data, and the color information of each pixel is defined by RGB luminance signal values. Therefore, unlike the image processing device 600, the image processing device 1600 does not include a step corresponding to the rendering step 700.

[0119] In color conversion process 1601, a process of color conversion is performed by using a color management method to convert the signal value of each pixel of the input image data so that the colors are displayed correctly on the HDR display device 1610. As in color conversion process 701, color conversion in color conversion process 1601 is performed using an ICC profile as shown in Fig. 2. It is assumed that the color conversion in color conversion process 1601 is performed with a processing bit count of 16 bits. Therefore, it is assumed that the signal values ​​of each RGB channel in each pixel in the image data obtained as a result of color conversion process 1601 are 16-bit signal values.

[0120] Image data having 16-bit signal values, which is image data color-converted in the color conversion step 1601 , is output to a transfer data quantization step 1602 and a data range acquisition step 1603 .

[0121] In the data range acquisition step 1603, processing similar to that in the data range acquisition step 703 in Fig. 7 or the data range acquisition step 1301 in Fig. 13 is performed. In addition, in the transfer data quantization step 1602, processing similar to that in the transfer data quantization step 702 in Fig. 7 is performed.

[0122] As a result of the quantization by the transfer data quantization step 1602, the signal value of the image data is converted to a bit number lower than 16 bits (for example, 8 bits). In the transmission step 1604, the image data with the signal value quantized to a low bit is transmitted to the HDR display device 1610.

[0123] Next, the steps executed by the HDR display device 1610 will be described. The HDR display device 1610 has a control unit including a CPU, ROM, RAM, etc., and the processing of each step executed by the HDR display device 1610 shown in FIG. 16 is executed, for example, by the CPU expanding program code stored in the ROM into the RAM and executing it. Alternatively, some or all of the functions of the steps may be realized by hardware such as an ASIC or electronic circuit. In the receiving step 1611, the document image data, whose signal values ​​have been quantized to a low bit (for example, 8 bits), and the data range information of the color-converted signal values, transmitted from the image processing device 600, are received.

[0124] In the received data restoration step 1612, the same processing as in the received data restoration step 712 is performed. That is, processing is performed to restore the signal value of the image data to the number of processing bits (for example, 16 bits) in the HDR display device 1610.

[0125] In the display step 1605, the display engine displays the image based on the image data whose RGB signal values ​​have been restored to 16 bits. As described above, according to this embodiment, when transmitting image data from a PC to a display after quantizing a signal value to a low bit, it is possible to reduce the influence of information loss caused when quantizing the signal value to a low bit. For example, when image data in which the distribution of low-contrast, low-saturation colors is limited to a narrow color gamut is compressed by bit-number conversion and then displayed on an external HDR display capable of reproducing images in a wide color gamut, data compression can be performed that suppresses deterioration of gradation reproducibility.

[0126] <Other embodiments> In the above-described embodiment, the transfer data quantization step does not have to be performed after the color conversion step. Alternatively, for example, the one-dimensional LUT for quantization generated in the one-dimensional LUT generation step 801 may be incorporated into the conversion parameters used in the color conversion step 701, so that quantization to low bits may be performed in the color conversion step 701. For example, if the Destination Profile has a one-dimensional LUT for conversion to an output device-dependent signal value, the color conversion step 701 may perform a process of combining the one-dimensional LUT and the one-dimensional LUT for quantization generated in the one-dimensional LUT generation step 801. Then, the signal value may be converted using the one-dimensional LUT combined in the color conversion step 701, so that conversion to an output device-dependent signal value and quantization to low bits may be performed.

[0127] The present disclosure can also be realized by a process in which a program for implementing one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0128] The disclosure of the above-described embodiment includes the following configurations.

[0129] (Configuration 1) a first acquisition means for acquiring image data in which color information is defined by an N-bit signal value for each color component; a second acquisition means for acquiring data range information indicating maximum and minimum signal values ​​for each of the color components in the image data acquired by the first acquisition means; a quantization means for quantizing the signal value for each color component in the image data acquired by the first acquisition means to a signal value of M bits (N>M) based on the data range information acquired by the second acquisition means; A transmitting means for transmitting the quantized image data and data range information corresponding to the image data acquired by the first acquiring means in order to convert the signal value in the quantized image data into a signal value of L bits (L>M); 13. An image processing device comprising:

[0130] (Configuration 2) The quantization means quantizing the signal value for each color component in the image data acquired by the first acquisition means such that the maximum value is the maximum value that the M bits can take and the minimum value is the minimum value that the M bits can take. 2. The image processing device according to claim 1,

[0131] (Configuration 3) The maximum value is associated with a maximum value that the M bits can take, the minimum value is associated with a minimum value that the M bits can take, and the relationship between the values ​​between the maximum value and the minimum value and the value of the M bits is linearly expanded to correspond to each other, a generation unit for generating a lookup table for each of the color components, the lookup table outputting the M-bit signal value corresponding to the N-bit signal value input thereto; The quantization means performs the quantization using the lookup table. 3. The image processing device according to configuration 2.

[0132] (Configuration 4) The data range information acquired by the second acquisition means is data range information indicating maximum and minimum values ​​for each color component among signal values ​​for all pixels of the image data acquired by the first acquisition means. 4. The image processing device according to any one of configurations 1 to 3.

[0133] (Configuration 5) The image data acquired by the first acquisition means is Image data obtained as a result of color conversion processing that converts the signal values ​​of the image data to be processed into the N-bit signal values ​​for each color component. 4. The image processing device according to any one of configurations 1 to 3.

[0134] (Configuration 6) The data range information acquired by the second acquisition means is data range information generated based on conversion parameters used in the color conversion process. 6. The image processing device according to configuration 5.

[0135] (Configuration 7) The data range information acquired by the second acquisition means is is data range information indicating the maximum and minimum values ​​for each color component of signal values ​​obtained by converting sampled signal values ​​corresponding to the image data to be processed into the M bits using the conversion parameters. 7. The image processing device according to configuration 6,

[0136] (Configuration 8) a generating means for generating a parameter used when the quantization means performs quantization based on the transformation parameter in advance; a storage means for storing the parameters generated by the generating means in association with the corresponding transformation parameters; and The quantization means acquires parameters associated with the conversion parameters used in the color conversion process from the parameters stored in the storage means, and performs the quantization using the acquired parameters. 8. The image processing device according to configuration 6 or 7.

[0137] (Configuration 9) In the color conversion process, a signal value of the image data to be processed is converted so as to become image data in a color space capable of reproducing a color gamut wider than the reproducible color gamut in the color space of the image data to be processed. 9. The image processing device according to any one of configurations 5 to 8.

[0138] (Configuration 10) The transmitting means is The lookup table used by the quantization means for quantization is transmitted as data range information related to the image data acquired by the first acquisition means. 4. The image processing device according to configuration 3.

[0139] (Configuration 11) 11. The image processing device according to any one of configurations 1 to 10, wherein the N bits and the L bits are the same number of bits.

[0140] (Configuration 12) A receiving means for receiving the quantized image data transmitted from the image processing device according to any one of configurations 1 to 11 and data range information corresponding to the image data acquired by the first acquiring means; a conversion means for converting the signal value of the quantized image data into the L-bit signal value based on the received data range information; an output means for outputting an image based on the image data converted into the L-bit signal value; 1. An image output device comprising:

[0141] (Configuration 13) the image output device is a printing device, The output means outputs an image by printing an image based on the image data converted into the L-bit signal value on a recording medium. 13. The image output device according to claim 12,

[0142] (Configuration 14) An image processing device according to any one of configurations 1 to 11, 14. The image output device according to claim 12 or 13, A system comprising:

[0143] (Configuration 15) A first acquisition step of acquiring image data in which color information is defined by an N-bit signal value for each color component; a second acquisition step of acquiring data range information indicating maximum and minimum signal values ​​for each of the color components in the image data acquired by the first acquisition step; a quantization step of quantizing the signal value for each color component in the image data acquired in the first acquisition step into a signal value of M bits (N>M) based on the data range information acquired in the second acquisition step; a transmitting step of transmitting the quantized image data and data range information related to the image data acquired by the first acquiring step in order to convert a signal value in the quantized image data into a signal value of L bits (L>M); 13. An image processing method comprising:

[0144] (Configuration 16) 12. A program for causing a computer to execute each of the means of the image processing device according to any one of configurations 1 to 11. [Explanation of symbols]

[0145] 600 Image Processing Device 701 Color conversion process 702 Transmission data quantization process 703 Data range acquisition process 704 Transmission process

Claims

1. A first acquisition means for acquiring image data in which color information is defined by N-bit signal values ​​for each color component, A second acquisition means for acquiring data range information indicating the maximum and minimum signal values ​​for each color component in the image data acquired by the first acquisition means, A quantization means that, based on the data range information acquired by the second acquisition means, quantizes the signal value for each color component in the image data acquired by the first acquisition means to an M-bit (N > M) signal value, A transmission means for transmitting the quantized image data and data range information corresponding to the image data acquired by the first acquisition means, in order to convert the signal values ​​in the quantized image data into L-bit (L > M) signal values, It has, The quantization means is The signal values ​​for each color component in the image data acquired by the first acquisition means are quantized such that the maximum value is the maximum value that the M bits can take, and the minimum value is the minimum value that the M bits can take. An image processing apparatus characterized by the following:

2. The system further includes a generation means for generating a lookup table for each color component, which outputs the M-bit signal value corresponding to the input N-bit signal value by associating the maximum value with the maximum possible value of the M bits, associating the minimum value with the minimum possible value of the M bits, and linearly extending the relationship between the value between the maximum and minimum values ​​and the value of the M bits. The quantization means performs the quantization using the lookup table. The image processing apparatus according to feature 1.

3. The data range information acquired by the second acquisition means is data range information that shows the maximum and minimum values ​​for each color component among the signal values ​​of all pixels in the image data acquired by the first acquisition means. The image processing apparatus according to feature 1.

4. The image data acquired by the first acquisition means is This is image data obtained as a result of a color conversion process that converts the signal values ​​of the image data to be processed into the N-bit signal values ​​for each of the color components. The image processing apparatus according to feature 1.

5. The data range information acquired by the second acquisition means is data range information generated based on the conversion parameters used in the color conversion process. The image processing apparatus according to feature 4.

6. The data range information acquired by the second acquisition means is: This data range information indicates the maximum and minimum values ​​for each color component of the signal values ​​obtained by converting the sampled signal values ​​corresponding to the image data to be processed into M bits using the conversion parameter, which are then converted to M bits using the conversion parameter. The image processing apparatus according to feature 5.

7. A generation means that generates in advance the parameters used by the quantization means when performing quantization based on the conversion parameters, A storage means for storing the parameters generated by the generation means in association with the corresponding conversion parameters, It further possesses, The quantization means obtains parameters associated with the conversion parameters used in the color conversion process from the parameters stored in the storage means, and performs the quantization using the obtained parameters. The image processing apparatus according to feature 5.

8. In the color conversion process, the signal values ​​of the image data to be processed are converted so that the image data becomes image data in a color space that can reproduce a wider color gamut than the color gamut that can reproduce in the color space of the image data to be processed. The image processing apparatus according to feature 4.

9. The aforementioned transmission means is The lookup table used by the quantization means during quantization is transmitted as data range information relating to the image data acquired by the first acquisition means. The image processing apparatus according to claim 2.

10. The N bits and the L bits have the same number of bits. The image processing apparatus according to feature 1.

11. A receiving means that receives the quantized image data transmitted from the transmitting means and data range information corresponding to the image data acquired by the first acquisition means. A conversion means for converting the signal value of the quantized image data to the L-bit signal value based on the received data range information, An output means that outputs an image based on the image data converted to the L-bit signal value, The image processing apparatus according to claim 1, characterized by having the following features.

12. The aforementioned image processing apparatus is a printing apparatus, The output means outputs an image by printing an image based on the image data converted to the L-bit signal value onto a recording medium. The image processing apparatus according to feature 11.

13. A first acquisition step involves acquiring image data in which color information is defined by N-bit signal values ​​for each color component, A second acquisition step involves acquiring data range information that indicates the maximum and minimum signal values ​​for each color component in the image data acquired by the first acquisition step, A quantization step is performed to quantize the signal values ​​for each color component in the image data acquired in the first acquisition step to M-bit (N > M) signal values, based on the data range information acquired in the second acquisition step. A transmission step that transmits the quantized image data and data range information corresponding to the image data acquired in the first acquisition step in order to convert the signal values ​​in the quantized image data into L-bit (L > M) signal values. It has, In the aforementioned quantization step, The signal values ​​for each color component in the image data acquired by the first acquisition step are quantized such that the maximum value is the maximum value that the M bits can take, and the minimum value is the minimum value that the M bits can take. An image processing method characterized by the following:

14. A first acquisition means for acquiring image data in which color information is defined by N-bit signal values ​​for each color component, A second acquisition means for acquiring data range information indicating the maximum and minimum signal values ​​for each color component in the acquired image data, A quantization means that quantizes the signal value for each color component in the acquired image data to an M-bit (N > M) signal value based on the acquired data range information, The system includes a transmission means for transmitting the quantized image data and data range information corresponding to the acquired image data, in order to convert the signal values ​​in the quantized image data into L-bit (L > M) signal values. An image processing system characterized by the following:

15. A program for causing a computer to execute each means of the image processing apparatus described in any one of claims 1 to 12.

Images