Image processing apparatus, image processing method, and program

Abstract

To form a printed matter more suitable to an observation environment.SOLUTION: An image processing device for generating data for forming an image using ink for forming an irregularity in a recording medium comprises: target image acquisition means which acquires target image data; illumination luminance distribution acquisition means which acquires the illumination luminance distribution in an observation environment for observing the recording medium; observer position acquisition means which acquires the observation position of the recording medium; normal line decision means which decides an irregularity to be applied to the recording medium such that the illumination luminance in the regular reflection direction obtained when observing the recording medium from the observation position becomes the desired brightness; and ink amount decision means which decides an ink amount of each ink.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a technique for forming an image using ink for forming unevenness on a recording medium.

Background Art

[0002] In recent years, metallic ink or glossy ink containing metal particles and capable of imparting metallic luster on a recording medium has been used for printing using a recording device or the like. Further, metallic ink or glossy ink is also used in combination with color ink, and various printing methods for adding metallic luster to high-quality color printing have been proposed.

[0003] In Patent Document 1, the reflection characteristics of a printed matter are divided into diffuse reflection characteristics and specular reflection characteristics, and it is mentioned that the color appears to change due to the brightness of illumination in the normal reflection direction when observing the printed matter even in an environment with the same illuminance. Further, not only color management such as application of a color profile according to a conventional observation environment, but also a technique for selecting a suitable mode based on the difference between diffuse reflection characteristics and specular reflection characteristics depending on an image output mode and generating a printed matter suitable for the observation environment is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The generation of a printed matter suitable for the observation environment is required.

[0006] Therefore, an object of the present invention is to form a printed matter suitable for the observation environment.

Means for Solving the Problems

[0007] An image processing apparatus according to the present invention is an image processing apparatus that generates data for forming an image using ink for forming unevenness on a recording medium, and acquires target image data First an acquisition means, a second acquisition means for acquiring an illumination luminance distribution in an observation environment for observing the recording medium, and an acquisition means for acquiring an observation position of the recording medium Third an acquisition means, and an illumination luminance in the specular reflection direction obtained when observing the recording medium from the observation position Based on determines unevenness to be imparted to the recording medium First a determination means 、 determines the ink amount of each ink Second a determination means, and is characterized by comprising the same.

Effect of the Invention

[0008] According to the present invention, it is possible to form a printed matter more suitable for the observation environment.

Brief Description of the Drawings

[0009]

Figure 1

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Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not necessarily limit the present invention. Also, not all combinations of features described in this embodiment are essential for the solution means of the present invention.

[0011] <<Embodiment 1>> FIG. 1 is a schematic diagram for explaining the angular reflection characteristics of a printed matter using metallic ink. The angular reflection characteristics refer to the characteristics indicating the difference in brightness under different geometric conditions. In patterns (a) to (i) of FIG. 1, the angular reflection characteristics when using different amounts of color ink and metallic ink are shown respectively. Patterns (a) to (i) show that the amount of color ink increases as the arrow goes to the right. Also, the amount of metallic ink increases as the arrow goes down. The dashed arrow indicates the incident light on the printed matter, and the shapes on the printed matter indicate the intensity of the light reflected at each angle from the light incident point. The upper left pattern (a) shows the angular reflection characteristics of the paper white without printing ink. This distribution has less bias such as strong reflection in a specific direction, and the change in brightness is small when viewed from any angle. Pattern (c) shows the angular reflection characteristics when printed using only color ink. Similar to pattern (a), there is less bias for each angle, but the amount of reflection decreases because the color ink absorbs light. On the other hand, pattern (g) shows the angular reflection characteristics when printed using only metallic ink. Metallic ink has high directivity and reflects strong light in the specular reflection direction. Due to such characteristics, the change in brightness when the observation angle is changed by the same amount from the specular reflection light to the diffusion direction is larger for metallic ink than for color ink. Therefore, when observed with the light source reflected, it appears brighter according to the brightness of the light source. However, since there are few diffused components other than the specular reflection direction, it appears dark when the light source is not reflected.

[0012] Both the color ink and the metallic ink can generate intermediate characteristics such as pattern (b) and pattern (d) according to the area gradation. Also, when the color ink and the metallic ink are mixed, characteristics obtained by multiplying the respective angular reflection characteristics can be generated. In practice, even in the case of printing with only color ink, it is common to show slightly stronger reflection in the specular reflection direction compared to other directions. However, since the amount is small compared to the metallic ink, it is omitted for simplicity of explanation. Such differences in angular reflection characteristics are modeled by a Bidirectional Reflectance Distribution Function or the like and can be measured with a commercially available BRDF measuring device.

[0013] Figure 2 is a schematic diagram showing the change in appearance depending on the observation conditions of a printed matter using metallic ink. Figure 2(a) shows the relationship between the angular reflection characteristics shown in Figure 1(g), the light source, and the observation position. Figures 2(b) and 2(c) show the brightness of the figure 103 printed with metallic ink as viewed from different directions. As shown in Figure 2(b), when observed from a direction 102 deviated from the specular reflection direction with respect to the main light source 101, the figure 103 appears dark because little light is reflected in that direction. On the other hand, as shown in Figure 2(c), when observed from a direction 102' that is the specular reflection direction with respect to the main light source 101, the figure 103 appears bright because a lot of light is reflected in that direction. When the observer moves from the direction 102 where the figure 103 appears dark to the direction 102' where the figure 103 appears bright while observing the figure 103, the brightness changes significantly.

[0014] So far, the angular reflection characteristics and their appearance have been explained using a simple light source as an example. In reality, in addition to self-luminous light sources, all kinds of things such as walls, ceilings, or furniture reflect light. Therefore, things other than the light source must also be treated as secondary light sources. In the present embodiment, all directions in the hemisphere centered on the surface normal direction of the printed matter are considered as illumination.

[0015] Next, a method for managing printed matter using metallic ink handled in this embodiment and its observation environment will be described. As described above, since the appearance of the printed matter is affected by the observation environment, the recommended observation environment for the printed matter is defined by the ratio L spec / E of the illumination luminance and illuminance in the specular reflection direction. Hereinafter, the relationship between the brightness of the printed matter and illumination will be described.

[0016] When assuming that the printed matter is a perfect diffusive reflecting surface, its luminance is expressed by the following formula. Lw = E / π ··· Equation (1)

[0017] Here, Lw is the luminance of the perfect diffusive reflecting surface, E is the illuminance, and π is the ratio of the circumference of a circle to its diameter. For a perfect diffusive reflecting surface, since light is diffused omnidirectionally regardless of the incident direction of light, the brightness of the illumination in the specular reflection direction does not need to be considered.

[0018] On the other hand, the brightness of a perfect mirror surface is expressed by the following formula. Lm = L spec ··· Equation (2)

[0019] Here, Lm is the luminance of the perfect mirror surface, and L spec is the illumination luminance in the specular reflection direction. If the printed matter is a perfect mirror surface, the brightness of the reflected illumination becomes the brightness of the printed matter.

[0020] In addition, a general printed matter has properties intermediate between a perfect diffusive reflecting surface and a perfect mirror surface, and its luminance is expressed by the following formula. L = E·ρ diff / π + L spec ·ρ spec ··· Equation (3)

[0021] Here, L is the luminance of the printed matter, E is the illuminance, π is the ratio of the circumference of a circle to its diameter, L spec is the illumination luminance in the specular reflection direction, ρ diff is the reflectance in diffuse reflection, and ρ spec is the reflectance in specular reflection. That is, the brightness of a general printed matter, including those using metallic ink, can be expressed as the sum of the diffuse reflection component and the specular reflection component.

[0022] Generally, the color management of printed matter is often carried out based on the luminance ratio with respect to the white of the paper. This is because the observer perceives the brightness of an object not by the absolute amount of light entering the pupil, but by the luminance ratio with respect to the surrounding brightness. Therefore, when rewriting the appearance of printed matter with the luminance ratio normL, it is expressed by the following formula. normL = L / Lw = ρ diff +L spec ·ρ spec / (E / π) ··· Formula (4)

[0023] This formula is derived from Formula (3) and Formula (1) by regarding the paper white as a perfect diffuse reflection surface. The absolute value of the luminance, which is the brightness of the paper white as seen by the observer, is approximately proportional to the illuminance on the printed matter. This is because the reflection characteristics of the paper white are relatively close to those of a perfect diffuse reflection surface, and the specular reflection component can be almost ignored compared to the diffuse reflection component.

[0024] Among Formula (4), the specular reflection component is L spec ·ρ spec / (E / π), and what changes depending on the observation environment is the illumination luminance L spec in the specular reflection direction and the illuminance E. Therefore, if the ratio of the illumination luminance L spec and the illuminance E is defined, it becomes possible to control the influence of the illumination in the specular reflection direction, that is, the specular reflection component.

[0025] As described above, when using metallic ink, it is possible to obtain images with different appearances by changing the reflected illumination luminance. However, there are cases where it is not possible to obtain the desired appearance of the printed matter when the illumination environment and the observation position are restricted. Specifically, it has been difficult to control the appearance of the printed matter under a plurality of observation conditions.

[0026] Therefore, in the present embodiment, the illumination environment in which the printed matter is displayed and two observation positions are acquired, and in order to obtain the target appearance at each observation position, a printed matter is formed in which the surface normal is controlled by forming unevenness.

[0027] <Hardware Configuration of Image Processing Apparatus 1> FIG. 3 is a diagram showing the hardware configuration of the image processing apparatus 1. The image processing apparatus 1 includes a CPU 301, a ROM 302, a RAM 303, a VC (video card) 304, a general-purpose I / F (interface) 305, a SATA (Serial ATA) I / F 306, and a NIC (network interface card) 307.

[0028] Using the RAM 303 as a work memory, the CPU 301 executes an OS (operating system) or various programs stored in the ROM 302 or an HDD (hard disk drive) 315. Also, the CPU 301 controls each component via the system bus 308. Note that the processing according to the flowchart described later is executed by the CPU 301 after program code stored in the ROM 302 or the HDD 315 is expanded in the RAM 303. A display 317 is connected to the VC (video card) 304. An input device 310 such as a mouse or a keyboard, an illumination device 311 composed of a plurality of light sources, a camera 312, or an image forming apparatus 313 is connected to the general-purpose I / F (interface) 305 via the serial bus 309.

[0029] A general-purpose drive 316 that reads and writes to the HDD 315 or various recording media is connected to the SATA (Serial ATA) I / F 306 via the serial bus 314. The NIC 307 inputs and outputs information to and from an external device. The CPU 301 uses the HDD 315 or various recording media mounted on the general-purpose drive 316 as storage locations for various data. The CPU 301 displays a UI (user interface) screen provided by a program on the display 317 and receives an input such as a user instruction received via the input device 310.

[0030] <Logical Configuration of Image Processing Apparatus 1> FIG. 4 is a diagram showing the logical configuration of the image processing apparatus 1 in the present embodiment. The image processing apparatus 1 includes a target image acquisition unit 401, a color conversion unit 402, an illumination luminance distribution acquisition unit 403, an observer position acquisition unit 404, and a normal vector determination unit 405. Further, the image processing apparatus 1 includes a specular reflection illumination determination unit 406, a metallic ink amount determination unit 407, a color ink amount determination unit 408, a clear ink amount determination unit 409, and an output unit 410.

[0031] The target image acquisition unit 401 acquires first image data and second image data indicating visible target values under different geometric conditions. The color conversion unit 402 converts the color information of the first image data and the second image data into tristimulus values XYZ. The illumination luminance distribution acquisition unit 403 acquires a captured image used for estimating the illumination luminance distribution from the print to the printed matter from the camera 312 installed at the print posting position. The observer position acquisition unit 404 acquires the position of the observer in the captured image acquired by the illumination luminance distribution acquisition unit 403 via an input device 310 or the like.

[0032] The normal vector determination unit 405 outputs normal vector information to the specular reflection illumination determination unit 406 and the clear ink amount determination unit 409. The normal vector information is information for controlling the surface normal for determining the unevenness applied on the printed matter. The specular reflection illumination determination unit 406 determines the illumination luminance in the specular reflection direction from the position of the observer via the print surface normal. The metallic ink amount determination unit 407 determines the metallic ink amount based on the luminance difference between the first image data and the second image data. The color ink amount determination unit 408 determines the color ink amount based on the first image data and the metallic ink amount. The clear ink amount determination unit 409 determines the clear ink amount based on the normal vector information. The output unit 410 outputs the determined metallic ink amount, color ink amount, and clear ink amount to the image forming apparatus 313.

[0033] <Configuration of the image forming apparatus 313> FIG. 5 is a configuration diagram of the image forming apparatus 313. The image forming apparatus 313 in the present embodiment is an inkjet printer that forms a three-dimensional object by performing ink recording on a recording medium. The three-dimensional object is formed of a concavo-convex layer formed by clear ink and an image layer formed by color ink and metallic ink.

[0034] The head cartridge 501 has a recording head including a plurality of ejection ports and an ink tank that supplies ink to the recording head. Further, a connector for receiving signals for driving each ejection port of the recording head is provided. Six types of inks, namely cyan, magenta, yellow, black color inks, metallic ink, and clear ink, are independently provided in the ink tank. The metallic ink has a stronger specular reflection component compared to other inks. The clear ink has a higher solid content concentration such as resin compared to other inks, and unevenness can be formed by depositing the solid content on the recording medium.

[0035] The head cartridge 501 is positioned and mounted on the carriage 502 in an exchangeable manner. The carriage 502 is provided with a connector holder for transmitting drive signals and the like to the head cartridge 501 via a connector. The carriage 502 is capable of reciprocating movement along the guide shaft 503. Specifically, the carriage 502 is driven via a drive mechanism such as a motor pulley 505, a driven pulley 506, and a timing belt 507 using the main scanning motor 504 as a drive source, and its position and movement are controlled. In this embodiment, the movement of the carriage 502 along the guide shaft 503 is referred to as "main scanning", and the movement direction is referred to as the "main scanning direction". A recording medium 508 such as printing paper is placed on an auto sheet feeder (hereinafter, "ASF") 510. During image formation, the pickup roller 512 rotates via a gear by driving the paper feed motor 511, and the recording medium 508 is separated and fed one by one from the ASF 510. Further, the recording medium 508 is conveyed to a recording start position facing the discharge port surface of the head cartridge 501 on the carriage 502 by the rotation of the conveyance roller 509. The conveyance roller 509 is driven via a gear using the line feed (LF) motor 513 as a drive source. The determination as to whether the recording medium 508 has been fed and the determination of the position at the time of paper feeding are made when the recording medium 508 passes through the paper end sensor 514. The head cartridge 501 mounted on the carriage 502 is held such that the discharge port surface protrudes downward from the carriage 502 and is parallel to the recording medium 508. The control unit 520 is composed of a CPU or storage means, etc., receives data for forming the above-described respective layers from the outside, and controls the operations of the respective parts of the image forming apparatus 313 based on the data.

[0036] <Operation of the image forming apparatus 313> Hereinafter, the formation operations of the uneven layer and the image layer in the image forming apparatus 313 having the configuration shown in FIG. 5 will be described. In this embodiment, generally used inkjet paper is used as the recording medium 508.

[0037] First, when the recording medium 508 is conveyed to a predetermined recording start position, the carriage 502 moves on the recording medium 508 along the guide shaft 503, and color ink is ejected from the ejection port of the recording head during the movement. Then, when the carriage 502 moves to one end of the guide shaft 503, the conveyance roller 509 conveys the recording medium 508 by a predetermined amount in a direction perpendicular to the scanning direction of the carriage 502. In the present embodiment, the conveyance of the recording medium 508 is referred to as "paper feed" or "sub-scanning", and this conveyance direction is referred to as "paper feed direction" or "sub-scanning direction". When the conveyance of a predetermined amount of the recording medium 508 is completed, the carriage 502 moves again along the guide shaft 503. In this way, the uneven layer is formed on the recording medium 508 by repeating the scanning by the carriage 502 of the recording head and the paper feed. After the uneven layer is formed, the conveyance roller 509 returns the recording medium 508 to the recording start position. Next, an image layer is formed by recording color ink and metallic ink on the uneven layer in the same process as the formation of the uneven layer.

[0038] FIG. 6 is a schematic diagram showing the representation of an image controlled by the area gradation method. In order to simplify the description, the recording head in the present embodiment is controlled in binary as to whether or not to eject ink droplets. Also, in the present embodiment, it is assumed that the on / off of the ink is controlled for each pixel defined by the output resolution of the image forming apparatus 313, and the state where all the pixels in a unit area are turned on is treated as 100% of the ink recording amount. Note that "on" represents ejecting ink, and "off" represents not ejecting ink. In such a binary printer, in a single pixel, the ink recording amount can only be expressed as 100% or 0%, so intermediate gradations are expressed by a set of a plurality of pixels. In the example shown in FIG. 6, instead of performing intermediate gradation representation at a density of 25% as shown in the lower left of the figure, ink is ejected onto 4 pixels out of 16 pixels (4×4) as shown in the lower right, thereby performing an area-based representation of 25% (4 / 16). The same can be done for other gradations. Note that the total number of pixels for expressing intermediate gradations, the pattern of pixels to be turned on, etc. are not limited to the above example. The pattern of pixels to be turned on can be determined using periodic screen processing or error diffusion processing called halftone dots. Note that the above binarization processing can be extended to multi-valued processing with a plurality of modifiable levels, and this is also applicable to a recording head in which the ink ejection amount is modifiable, and is not limited to binarization.

[0039] In the formation of the concavo-convex layer by the image forming apparatus 313 in the present embodiment, the control of concavo-convexity is performed for each position using the above-described concept of the ink recording amount. When a substantially uniform layer is formed with an ink recording amount of 100% in the formation of the concavo-convex layer, the layer has a certain thickness (height) according to the volume of the ejected ink. For example, when the layer formed with a recording amount of 100% has a height of 2 μm, in order to reproduce a height of 20 μm, the layer may be stacked 10 times. That is, the ink recording amount to be driven into the position where a height of 20 μm is required becomes 1000%.

[0040] FIG. 7 is a diagram for explaining an operation of forming an image layer and a concavo-convex layer by scanning a recording head over a recording medium 508. By main scanning with a carriage 502, a layer is formed over a width L of the recording head, and every time recording of one line is completed, the recording medium 508 is conveyed in a sub-scanning direction by a distance L. To simplify the explanation, it is assumed that the image forming apparatus 313 in the present embodiment can eject only ink up to 100% of the recording amount in one scan, and in the case of forming a layer with a recording amount exceeding 100%, the same area is scanned a plurality of times without conveyance. For example, when the recording amount of the ink to be driven in is a maximum of 500%, the same line is scanned five times. Explaining with reference to FIG. 7, after the area A is scanned five times with the recording head (FIG. 7(a)), the recording medium 508 is conveyed in the sub-scanning direction, and main scanning of the area B is repeated five times (FIG. 7(b)).

[0041] In order to suppress image quality degradation such as periodic unevenness caused by the driving accuracy of the recording head, multi-pass printing, i.e., multiple scans, may be performed even at a recording amount of 100% or less. Examples of two-pass recording are shown in FIGS. 7(c) to 7(e). In this example, the layer is formed by the main scan by the carriage 502 over the width L of the recording head, and every time the recording of one line is completed, the recording medium 508 is conveyed by a distance of L / 2 in the sub-scanning direction. Region A is recorded by the m-th main scan (FIG. 7(c)) and the (m + 1)-th main scan (FIG. 7(d)) of the recording head, and region B is recorded by the (m + 1)-th main scan (FIG. 7(d)) and the (m + 2)-th main scan (FIG. 7(e)) of the recording head. Here, although the operation of two-pass recording has been described, the number of passes for recording can be changed according to the desired accuracy. When performing n-pass recording, for example, every time the recording of one line is completed, the recording medium 508 is conveyed by a distance of L / n in the sub-scanning direction. In this case, even if the recording amount of the ink is 100% or less, the recording head scans the same line of the recording medium n times by dividing it into a plurality of printing patterns to form the uneven layer, the gloss layer, and the image layer. In the present embodiment, in order to prevent confusion between the scan by the multi-pass printing described above and the scan for injecting 100% or more of the ink, the multi-pass printing is not performed, and the multiple scans are described as for laminating the layers. Note that the recording medium 508 is not limited to paper, and various materials can be used as long as they can support the formation of the layer by the recording head.

[0042] <Regarding the shaped object formed on the recording medium> FIG. 8 is a cross-sectional view of a shaped object including a concavo-convex layer and an image layer formed on a recording medium. In the present embodiment, a concavo-convex layer having a height distribution of up to about several tens of μm is formed on the surface of the inkjet glossy paper, and an image layer is formed thereon. Strictly speaking, the image layer also has a height distribution, but its thickness is sufficiently small compared to the concavo-convex layer and its influence on the final concavo-convex shape is negligible, so it can be ignored. FIG. 8(a) is a schematic diagram showing the cross-sectional structure of image data used for printing. The printing resolution of the image forming apparatus is 1200 dpi, and the normal line formed by the concavo-convex layer is formed in units of 4×4 pixels. The width of one unit is about 80 μm, and the height is about 2 μm per layer of the concavo-convex layer. FIG. 8(b) is a cross-sectional view showing the shape of the shaped object obtained by outputting the image data shown in FIG. 8(a). The shaped object 801’ in FIG. 8(b) corresponding to the unit 801 with a maximum concavo-convex of 3 layers in height shown in FIG. 8(a) can form a normal line inclined at about 4 degrees with respect to the vertical direction of the recording medium. Similarly, the shaped object 802’ corresponding to the unit 802 with a maximum concavo-convex of 6 layers in height can form a normal line inclined at about 8 degrees with respect to the vertical direction of the recording medium. Although a two-dimensional cross-sectional view is used for explanation, by inclining also in the depth direction, a unit whose normal line can be controlled in both the x-axis direction and the y-axis direction can be formed. The normal line determination unit 405 stores in advance a plurality of unit shapes that can be created by the image forming apparatus and their normal vector information.

[0043] <Flowchart of the process executed by the image processing apparatus 1> FIG. 9 is a flowchart showing the operation flow of the image processing apparatus 1 of the present embodiment. As described above, in the present embodiment, a method of suitably obtaining illumination light in the specular reflection direction at an arbitrary position by forming concavo-convexities on a printed matter in a state where the brightness of the illumination in the room does not change is explained. The processing in each step of FIG. 9 is performed by the CPU 301 of the image processing apparatus 1 expanding and executing the program code stored in the ROM 302 in the RAM 303. Also, the symbol “S” in the description of each process means that it is a step in the flowchart.

[0044] First, in S901, the target image acquisition unit 401 acquires first image data I1 representing a target appearance under a first geometric condition and second image data I2 representing a target appearance under a second geometric condition, which are formed on a recording medium from an external device such as the HDD 315. The first image data and the second image data record the same subject, but are two target image data in which one has a bright appearance and the other has a dark appearance. The two target image data are selected after determining the degree of difference in brightness between the two images. Here, let the pixel value at the pixel position (x, y) of the first image data be RGB1(x, y). Also, let the pixel value at the pixel position (x, y) of the second image data be RGB2(x, y). The first image data and the second image data are images having color information of 16 bits for each of the R (red), G (green), and B (blue) values, a total of 48 bits per pixel.

[0045] The pixel values of the first image data and the second image data in the present embodiment are RGB values defined in the sRGB space. In addition, RGB images defined in AdobeRGB, which are commonly used, or Lab images corresponding to CIELAB can also be used. Note that the pixel position (x, y) indicates the pixel position in the image when the horizontal coordinate of the pixel is x and the vertical coordinate of the pixel is y.

[0046] In S902, the color conversion unit 402 converts the first image data and the second image data acquired by the target image acquisition unit 401 into tristimulus values XYZ respectively. The color conversion unit 402 converts the pixel values RGB1(x, y) and RGB2(x, y), which are RGB values, into tristimulus values XYZ defined in the CIE1913 XYZ color space. Specifically, based on the following formulas (5) and (6), the converted pixel values XYZ1(x, y) and XYZ2(x, y) are determined.

[0047] R L =degamma(R) G L =degamma(G) ··· Formula (5) B L =degamma(B)

[0048]

Number

[0049] Here, R, G, and B are the R value, G value, and B value that constitute RGB1(x, y) and RGB2(x, y), respectively. The RGB values defined in the sRGB space have gamma characteristics corresponding to the characteristics of a standard display. Degamma is a function that converts this RGB value into the linear RGB values R L , G L , B L to be described later, and the X, Y, and Z values. X, Y, and Z are the X value, Y value, and Z value that constitute XYZ1(x, y) and XYZ2(x, y), respectively. M is a conversion matrix that converts the linear RGB value defined in the sRGB space into the XYZ value defined in the CIE1913 XYZ color space.

[0050] In S903, the illumination luminance distribution acquisition unit 403 acquires the illumination luminance distribution image and illuminance from the camera 312 installed at the print posting position. FIG. 10(a) is a plan view illustrating the positional relationship among the print posting position, the camera 312, and the lighting device 311. The lighting device 311 includes a ceiling light 1011, a stand light 1012, and a floor light 1013. The camera 312 is installed at the print posting position and performs shooting centered on the vertical direction of the printed matter. Note that the information acquired by the illumination luminance distribution acquisition unit 403 assumes the information in the environment where the printed matter is actually displayed. Also, the print display position is the position where the printed matter is planned to be displayed in that environment, and the lighting illuminates with the illuminance assumed during actual observation. These pieces of information may be acquired in S903 from those stored in advance in the ROM 303 or the like.

[0051] FIG. 10(b) is a schematic diagram showing an example of a captured image by the camera 312. The captured image is an image of a semi-circular omnidirectional view that is captured using a fish-eye lens or the like and serves as illumination for the printed matter. Note that the illumination luminance image is obtained by performing gamma conversion on the pixel values of the captured image of the camera 312 so as to be linear with the luminance. At the time of shooting, it is preferable to shoot with an exposure under so that the brightest point of the illumination distribution does not fall outside the dynamic range of the camera 312, or to perform multi-shot shooting to synthesize a high dynamic range image. Further, the illuminance E can be estimated by integrating the values obtained by multiplying the pixel values of each pixel of the captured image by the weights set for each coordinate as distortion correction. In addition, an illuminance meter may be used separately.

[0052] In S904, the observer position acquisition unit 404 presents the illumination luminance distribution image acquired in S903 together with the UI on the display 317, and sets the position of the observer's eyes as the observation position from an input device or the like. In the present embodiment, since two target image data are given in S901, two points p1 and p2 for which the appearances corresponding to the respective target image data are to be realized are arbitrarily specified. In S905, the normal determination unit 405 selects a normal unit that can be formed by the image forming apparatus 313, and inputs the normal vector information thereof to the specular reflection illumination determination unit 406.

[0053] In S906, the specular reflection illumination determination unit 406 determines the illumination luminances Ls1 and Ls2 based on the illumination luminance distribution, the observer position, and the normal vector information. Vectors representing the directions of each pixel position are known from information such as the lens used in the camera 312. From this, a vector representing the specular reflection direction is determined based on the following formula from the vector corresponding to the point p which is the observer position and the normal vector.

[0054]

Equation

[0055] Hereinafter, the arrows of the vectors will be omitted. L represents the vector in the specular reflection direction, E represents the vector corresponding to the point p at the observer position, n represents the normal vector, and E·n represents the inner product of the vectors E and n.

[0056] Here, the relationship between the points p1 and p2 and the specular reflection illumination positions s1 and s2 in FIG. 10(c) is shown. Usually, when the normal vector is the same as the vertical direction of the printed matter, that is, when there is no unevenness on the printed matter, as shown in FIG. 10(c), with the pixel at the center of the printed matter as the center, the position that is point-symmetric to the observer position becomes the specular reflection illumination position.

[0057] On the other hand, the position of the specular reflection illumination with respect to the observer's position changes according to the unevenness (surface normal) formed on the printed surface. FIG. 10(d) shows an example of the specular reflection illumination positions s1' and s2' when the normal vector information input to the specular reflection illumination determination unit 406 is changed. Since the vectors representing the directions of each pixel position are known as described above, the specular reflection illumination positions s1' and s2' can be calculated. Also, the illumination luminances Ls1 and Ls2 at the calculated positions s1' and s2' can be determined from the pixel values of the captured images corresponding to the respective positions.

[0058] In S907, the normal determination unit 405 evaluates the following formula and determines the normal that satisfies the condition. |Y1 - Y2| < |Ls1 - Ls2|·ρ Me_max / (E / π) ··· Formula (8)

[0059] Y1 is the Y value of the first image data determined in S902, Y2 is the Y value of the second image data determined in S902, ρ Me_maxρ is the maximum value of the reflectance of the specular reflection component of the printable metallic ink, E is the illuminance, and π is pi. Here, it is determined whether it is sufficient to reproduce the difference in brightness between the first image data and the second image data in which the illumination luminances Ls1 and Ls2 determined by the normal vector are input. If the above formula cannot be satisfied, even if the metallic ink is printed in the maximum amount, the brightness difference |Y1 - Y2| between the two images cannot be expressed. In that case, return to S906 and repeat the process to search for the normal vector that gives the illumination luminances Ls1 and Ls2 that satisfy the conditions. If the normal vector when the above formula is satisfied can be found, the searched normal vector information may be output to the clear ink amount determination unit 409.

[0060] Note that the order of the normal vector information evaluated in S905 to S907 does not matter, but the priority may be determined in advance based on the ink amount used for unevenness formation or the maximum number of layers related to the printing time. Also, if all candidates for the normal vector do not satisfy the conditions, the user may be notified that there is no solution that meets the conditions.

[0061] In S908, the metallic ink amount determination unit 407 determines the metallic ink amount Me using the reflectance of the specular reflection component. First, the reflectance of the specular reflection component is expressed by the following formula using the normal vector information that satisfies the above formula (8) searched in S906.

[0062]

Equation

[0063] ρ Me is the reflectance of the specular reflection component of the metallic ink for each pixel. The conversion from this reflectance ρ Me to the metallic ink amount Me is performed by using a LUT (look-up table) prepared by measuring these relationships in advance.

[0064] In S909, the color ink amount determination unit 408 determines the CMYK color ink amounts based on XYZ1(x,y), which is the XYZ value of the first image data determined by the color conversion unit 402, and the metallic ink amount Me determined by the metallic ink amount determination unit 407. Note that the XYZ value XYZ2(x,y) of the second image data may be used to determine the color ink amounts. Here, the color ink amounts are determined taking into account the influence of the diffusion color of the previously determined metallic ink. First, the XYZ value XYZ color represented by the color ink is determined by the following formula. XYZ color =XYZ1 / XYZ Me ···Equation (10)

[0065] Here, XYZ Me is the XYZ value representing the diffusion color of the metallic ink. XYZ Me can be determined, for example, by previously holding the relationship between the metallic ink amount and the colorimetric value as a LUT using a 0° / 45° colorimeter excluding the influence of specular reflection light. Also, when a color development model holds that the XYZ value of the printed matter can be obtained by multiplying the XYZ value of the metallic ink and the XYZ value of the color ink, the XYZ value required for the color ink can be obtained by dividing the target value XYZ1 by XYZ Me . This step is performed to adjust the color ink amounts because the brightness of the diffused light decreases due to the amount of metallic ink added. To determine the CMYK color ink amounts from XYZ color , general methods such as using a previously prepared LUT can be used. If the determined XYZ color cannot be reproduced, it may be clipped to be within the reproducible range. Also, a method of adjusting the amount of metallic ink to be within the reproducible range is also conceivable.

[0066] In S910, the clear ink amount determination unit 409 determines the clear ink amount Cl based on the input normal vector information. Since the normal vector is associated with the unit shape that the image forming apparatus 313 can create as described above, it outputs the clear ink amount Cl for creating the unit shape on the front surface of the printed matter. Note that data on the metallic ink amount Me may be received from the metallic ink amount determination unit 407, and the clear ink amount Cl may be generated and output so as to form the unit shape only in the area where the metallic ink is printed.

[0067] In S911, the output unit 410 outputs the metallic ink amount Me determined by the metallic ink amount determination unit 407, the color ink amounts CMYK determined by the color ink amount determination unit 408, and the clear ink amount Cl determined by the clear ink amount determination unit 409 to the image forming apparatus 313.

[0068] As described above, according to this embodiment, it is possible to form a printed matter with a controlled surface normal. Specifically, based on the illumination environment in which the printed matter is displayed, two target images, and two observation positions, it is possible to obtain a printed matter having a surface normal for reproducing the luminance difference between the two images. By controlling the surface normal, it is possible to obtain illumination light in a desired specular reflection direction, so that a favorable appearance of the printed matter can be obtained at two observation positions.

[0069] <<Embodiment 2>> In Embodiment 1, a method for determining the surface normal of a printed matter that can obtain a desired luminance change from two target images and two observation positions for one printed matter was described. In this embodiment, a method for performing a so-called high dynamic range expression for reproducing a color brighter than the paper white from one target image and one observation position will be described. Note that descriptions of parts common to Embodiment 1 will be omitted or simplified, and the following will focus on the differences.

[0070] FIG. 11 is a flowchart showing the operation flow of the image processing apparatus 1 according to the present embodiment. The processing in each step of FIG. 11 is performed by the CPU 301 of the image processing apparatus 1 expanding and executing the program code stored in the ROM 302 in the RAM 303.

[0071] First, in S1101, the target image acquisition unit 401 acquires monochrome 1-channel first image data that is the target image to be formed on a recording medium from an external device such as the HDD 315. In S1102, the color conversion unit 402 converts the first image data acquired by the target image acquisition unit 401 into tristimulus values XYZ and acquires the luminance Y. Here, the luminance Y = 1.0 corresponds to the reflectance of paper white at the illuminance E. The image data has information of a so-called high dynamic range with a luminance Y>1.0.

[0072] In S1103, the illumination luminance distribution acquisition unit 403 acquires an illumination luminance distribution image and illuminance from the camera 312 installed at the print posting position. In S1104, the observer position acquisition unit 404 presents the illumination luminance distribution image acquired in S1103 together with the UI on the display 317 and sets the position p1 of the observer's eye, which is the observation position, from an input device or the like.

[0073] In S1105, the normal vector determination unit 405 determines a normal vector for each unit that forms a normal at each coordinate of the image based on the luminance Y of the target image data and the illumination luminance distribution. Here, if all of the plurality of luminances Y at the corresponding coordinate of the target image data are 1.0 or less, the normal vector is set to be the same as the vertical direction of the printed matter. That is, no unevenness is formed on the printed matter. Further, when a pixel with a luminance Y>1.0 is included, the normal vector is determined with reference to the look-up table shown in FIG. 12.

[0074] FIG. 12 is a LUT showing luminance in the combination of the specular reflection illumination luminance ratio and the amount of metallic ink. Here, E is the illuminance, π is the ratio of a circle's circumference to its diameter, and Ls / (E / π) is the ratio of the specular reflection illumination luminance to the illuminance. The brightness of the metallic ink is determined according to this ratio. For example, in the table shown in FIG. 12, when the maximum value of the luminance required to represent the brightness of the target first image data is Y = 1.75, a normal vector with Ls / (E / π) of 14.0 or more is selected. Also, the amount of metallic ink Me at that time is found to be 1.0. Further, when the maximum value of the required luminance is Y = 1.0, a normal vector with Ls / (E / π) of 8.0 or more is selected. The amount of metallic ink at this time is found to be 0.9 or 1.0. Alternatively, a normal vector with Ls / (E / π) of 14.0 may be selected, and the amount of metallic ink may be determined to be 0.1. Thus, it can be seen that the specular reflection illumination luminance ratio Ls / (E / π) varies depending on the normal vector at the relevant coordinates. Note that the relationship between the normal vector and the specular reflection direction vector can be determined by Equation (7) in the same manner as in Embodiment 1.

[0075] In S1106, the specular reflection illumination determination unit 406 determines the illumination luminance Ls in the specular reflection direction obtained from the determined normal vector. In S1107, the metallic ink amount determination unit 407 determines the amount of metallic ink Me based on the illumination luminance Ls in the specular reflection direction using the look-up table shown in FIG. 12. Note that a general interpolation method for the table may be used.

[0076] In S1108, the color ink amount determination unit 408 determines the black ink amount K based on the target luminance for pixels where the amount of metallic ink Me is 0.0. A table or the like showing the general relationship between the target luminance and the black ink amount K may be used. In S1109, the clear ink amount determination unit 409 determines the clear ink amount Cl based on the input normal vector information. The processes from S1105 to S1109 are repeatedly performed until the processing for all pixels is completed.

[0077] In S1110, the output unit 410 outputs the metallic ink amount Me determined by the metallic ink amount determination unit 407, the black ink amount K determined by the color ink amount determination unit 408, and the clear ink amount Cl determined by the clear ink amount determination unit 409 to the image forming apparatus 313.

[0078] As described above, based on the illumination environment in which the printed matter is displayed, the target image, and one observation position, the surface normal of the printed matter can be controlled, and an appearance of the printed matter including a luminance Y brighter than the paper white can be obtained.

[0079] <<Other Embodiments>> In the above-described embodiment, metallic ink is used as the ink having a bias in the specular reflection characteristics. In addition, the same effect can be obtained by using so-called gloss control ink such as clear ink that improves the smoothness of the printed surface and enhances the specular reflection light, or high refractive index ink that uses a material with a high refractive index to obtain strong specular reflection light.

[0080] Also, in the color ink amount determination step in Embodiment 1, when determining the XYZ values by the color ink, it was described using a color development model by multiplying the XYZ values. It is possible to use other color development models or color development simulations suitable for the image forming apparatus to be used.

[0081] The present invention can also be realized by supplying a program capable of operating one or more functions of the above-described embodiment to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. Further, it can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Description of Reference Numerals

[0082] 1 Image processing apparatus 401 Target image acquisition unit 404 Observer position acquisition unit 405 Normal determination unit

Claims

1. An image processing apparatus for generating data for forming an image using ink for forming unevenness on a recording medium, comprising: first acquisition means for acquiring target image data; second acquisition means for acquiring an illumination luminance distribution in an observation environment for observing the recording medium; third acquisition means for acquiring an observation position of the recording medium; first determination means for determining unevenness to be imparted to the recording medium based on the illumination luminance in the specular reflection direction obtained when observing the recording medium from the observation position; second determination means for determining the ink amount of each ink; An image processing apparatus characterized by comprising the above.

2. The image processing apparatus according to claim 1, wherein the specular reflection direction is determined based on the observation position and information on the unevenness of the recording medium.

3. The image processing apparatus according to claim 1 or 2, wherein the illumination luminance in the specular reflection direction is determined based on the illumination luminance distribution acquired by the second acquisition means.

4. Each of the inks includes a gloss ink capable of imparting gloss to the recording medium, a clear ink capable of imparting unevenness to the recording medium, and a color ink. The image processing apparatus according to any one of claims 1 to 3.

5. The image processing apparatus according to claim 4, wherein the gloss ink includes at least one of a metallic ink, a gloss control ink, and a high refractive index ink.

6. When the first acquisition means acquires first target image data and second target image data, and the third acquisition means acquires a first observation position and a second observation position, the first determination means determines the unevenness of the recording medium such that the illumination luminance in the specular reflection direction obtained when observing the recording medium from the first observation position becomes the brightness corresponding to the first target image data, and the illumination luminance in the specular reflection direction obtained when observing the recording medium from the second observation position becomes the brightness corresponding to the second target image data. The image processing apparatus according to any one of claims 1 to 4.

7. The first target image data is image data that reflects light in the specular reflection direction, and the second target image data shows the same subject as the subject of the first target image data and is image data that does not reflect light in the specular reflection direction. The image processing apparatus according to claim 6.

8. The second determination means The image processing apparatus according to claim 6 or 7, characterized by determining the ink amount of the gloss ink based on the target image data and the illumination luminance in the specular reflection direction.

9. When the first acquisition means acquires one piece of the target image data and the third acquisition means acquires one piece of the observation position, the first determination means determines the unevenness to be imparted to each coordinate of the recording medium such that the luminance of each coordinate obtained when observing the recording medium from the observation position becomes the luminance of the target image data. The image processing apparatus according to any one of claims 1 to 4.

10. The first determination means and the second determination means The image processing apparatus according to claim 9, characterized by determining the unevenness or the ink amount of the gloss ink by using a look-up table showing the luminance in the combination of the specular illumination luminance ratio and the ink amount of the gloss ink.

11. The second determination means The image processing apparatus according to claim 6 or 10, characterized by determining the ink amount of the clear ink based on the information of the unevenness.

12. The second determination means The image processing apparatus according to claim 6 or 10, characterized by determining the ink amount of the color ink based on the target image data and the ink amount of the gloss ink.

13. The luminance of the target image data is determined by being converted into tristimulus values. The image processing apparatus according to any one of claims 1 to 4. placement.

14. A control method for an image processing apparatus that generates data for forming an image on a recording medium using ink for forming unevenness, comprising: a step of acquiring target image data; a step of acquiring an illumination luminance distribution in an observation environment for observing the recording medium; a step of acquiring an observation position of the recording medium; a step of determining unevenness to be imparted to the recording medium based on the illumination luminance in the specular reflection direction obtained when observing the recording medium from the observation position; a step of determining the ink amount of each ink; A control method for an image processing apparatus, characterized by including.

15. A program for causing a computer to function as each means in the image processing apparatus according to any one of claims 1 to 13.

Images