JP2023045624A - Image processing device, image processing method and program - Google Patents

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

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

In recent years, metallic ink or lustrous ink containing metal particles and capable of imparting metallic luster to a recording medium has been used for printing using a recording apparatus or the like. Metallic ink or glossy ink is also used in combination with color ink, and various printing methods have been proposed to add metallic luster to high-quality color printing.

In Patent Document 1, the reflection characteristics of prints are divided into diffuse reflection characteristics and specular reflection characteristics, and even in an environment where the illuminance is the same, colors change depending on the brightness of the illumination in the specular direction when observing the prints. It looks like In addition to conventional color management, such as applying a color profile according to the viewing environment, it also selects the appropriate mode based on the differences in diffuse reflection characteristics and specular reflection characteristics depending on the image output mode, and generates prints suitable for the viewing environment. technology is described.

JP 2016-54356 A

There is a demand for the generation of prints that are more suitable for viewing environments.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to form a print that is more suitable for viewing environments.

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 includes target image acquisition means for acquiring target image data. an illumination luminance distribution obtaining means for obtaining an illumination luminance distribution in an observation environment in which the recording medium is observed; an observer position obtaining means for obtaining an observation position of the recording medium; and when observing the recording medium from the observation position normal line determining means for determining unevenness to be applied to the recording medium and ink amount determining means for determining the ink amount of each ink so that the illumination luminance in the specular reflection direction obtained in the normal reflection direction has a desired brightness. It is characterized by

According to the present invention, it is possible to form a print that is more suitable for viewing environments.

FIG. 4 is a schematic diagram showing deflection angle reflection characteristics of a printed matter; FIG. 4 is a schematic diagram showing changes in appearance depending on viewing conditions using metallic ink. 2 is a diagram showing the hardware configuration of an image processing apparatus; FIG. It is a figure which shows the logical structure of an image processing apparatus. 1 is a diagram showing the configuration of an image forming apparatus; FIG. FIG. 3 is a schematic diagram showing representation of an image controlled by the area coverage modulation method; 4A and 4B are diagrams for explaining the operation of the image forming apparatus; FIG. FIG. 4 is a diagram for explaining a concavo-convex layer and an image layer generated on a recording medium; 4 is a flowchart showing the flow of operations of the image processing apparatus; It is a top view which shows the positional relationship of a print display position, a camera, and an illuminating device. 4 is a flowchart showing the flow of operations of the image processing apparatus; FIG. 10 is a diagram showing luminance in combination of lighting luminance ratio and metallic ink amount;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiments do not necessarily limit the present invention. Moreover, not all combinations of features described in the present embodiment are essential for the solution means of the present invention.

<<Embodiment 1>>
FIG. 1 is a schematic diagram for explaining the deflection angle reflection characteristics of a printed matter using metallic ink. The deviation reflection characteristic is a characteristic that indicates the difference in brightness under different geometric conditions. Patterns (a) to (i) in FIG. 1 show deviation angle reflection characteristics when different amounts of colored ink and metallic ink are used. Patterns (a) to (i) indicate that the amount of colored ink increases as the arrow moves to the right. Also, the amount of metallic ink increases as the arrow goes downward. The dashed arrow indicates the incident light on the print, and the shapes on the print indicate the intensity of the light reflected at each angle from the point of incidence of the light. Pattern (a) on the upper left shows the declination reflection characteristics of white paper on which no ink is printed. This distribution has little bias such as strong reflection in a specific direction, and there is little change in brightness when viewed from any angle. Pattern (c) shows the deflection angle reflection characteristics when printing using only colored inks. Similar to the pattern (a), there is less bias for each angle, but the amount of reflection is reduced because the colored 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 direction. Due to such characteristics, when the viewing angle is changed from specular reflection light to diffusion direction by the same amount, the change in brightness is greater for metallic ink than for colored ink. Therefore, when the light source is reflected and observed, it looks bright according to the brightness of the light source. However, since there are few components that diffuse in directions other than the specular reflection direction, it looks dark unless the light source is reflected.

Both color ink and metallic ink can generate intermediate characteristics such as pattern (b) and pattern (d) by area gradation. Further, when color ink and metallic ink are mixed, it is possible to generate a characteristic obtained by multiplying the deviation angle reflection characteristic of each ink. In practice, it is common for prints with only colored inks to show slightly stronger reflection in the specular direction than in other directions. do. It should be noted that such a difference in deflection angle reflection characteristics is modeled by a bidirectional reflectance distribution function or the like, and can be measured by a commercially available BRDF measurement device.

FIG. 2 is a schematic diagram showing changes in the appearance of a print using metallic ink depending on viewing conditions. FIG. 2(a) shows the relationship between the deflection angle reflection characteristics, the light source, and the viewing position shown in FIG. 1(g). 2(b) and 2(c) show the brightness of the figure 103 printed with metallic ink viewed from different directions. As shown in FIG. 2B, when observed from a direction 102 deviating from the specular reflection direction with respect to the main light source 101, the figure 103 looks dark because not much light is reflected in that direction. On the other hand, as shown in FIG. 2(c), when observed from a direction 102', which is the direction of specular reflection with respect to the main light source 101, the figure 103 looks bright because much light is reflected in that direction. When the observer observes the figure 103 and moves from the direction 102 in which the figure 103 appears dark to the direction 102' in which the figure 103 appears bright, the brightness changes greatly.

So far, the angular reflection characteristics and their appearance have been explained using a simple light source as an example. For this reason, things other than light sources must be treated as secondary light sources. In the present embodiment, illumination is considered to be in all directions around the half-height from the printed matter, centering on the direction normal to the surface of the printed matter.

Next, a printed matter using metallic ink and a method for managing the viewing environment thereof will be described. As described above, the appearance of printed matter is affected by the viewing environment, so the recommended viewing environment for printed matter is defined by the ratio L _spec /E between the illumination luminance in the specular reflection direction and the illuminance. The relationship between the brightness of printed matter and illumination will be described below.

Assuming that the print is a perfect diffuse reflection surface, its luminance is expressed by the following formula.
Lw=E/π Expression (1)

Here, Lw is the luminance of the perfect diffuse reflection surface, E is the illuminance, and π is the circular constant. If the surface is a perfect diffuse reflection surface, the light is diffused in all directions no matter which direction the light is incident on, so the brightness of the illumination in the specular direction need not be considered.

On the other hand, the brightness of a perfect mirror surface is expressed by the following formula.
Lm= _Lspec Expression (2)

Here, Lm is the brightness of the perfect specular surface, and L _spec is the illumination brightness in the specular direction. If the printed matter is a perfect mirror surface, the brightness of the reflected illumination will be the brightness of the printed matter.

In addition, a general printed matter has intermediate properties between a perfect diffuse reflection surface and a perfect specular surface, and its brightness is expressed by the following formula.
L=E·ρ _diff /π+L _spec ·ρ _spec Expression (3)

Here, L is the brightness of the printed matter, E is the illuminance, π is the circular constant, L _spec is the illumination brightness in the direction of specular reflection, ρ _diff is the reflectance in diffuse reflection, and ρ _spec is the reflectance in specular reflection. In other words, the brightness of general prints, including those using metallic ink, can be represented by the sum of the diffuse reflection component and the specular reflection component.

In general, the color of printed matter is often managed by the luminance ratio based on the whiteness 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 to the brightness of the surroundings. Therefore, when the appearance of the printed matter is rewritten in terms of the luminance ratio normL, it is expressed by the following equation.
normL=L/Lw= _ρdiff + _Lspec · _ρspec /(E/π) Equation (4)

This equation is derived from equations (3) and (1) by regarding paper white as a perfect diffuse reflection surface. The absolute value of the luminance, which is the brightness of the white of the paper viewed by the observer, is approximately proportional to the illuminance on the printed matter. This is because the reflection characteristic of white paper is relatively close to that of a perfect diffuse reflection surface, and the specular reflection component can be almost ignored compared to the diffuse reflection component.

In equation (4), the specular reflection component is expressed by L _spec ·ρ _spec /(E/π), and the lighting luminance L _spec and illuminance E in the specular reflection direction change depending on the viewing environment. Therefore, if the ratio of the illumination luminance L _spec and the illuminance E is specified, it becomes possible to manage the influence of illumination in the direction of specular reflection, that is, the specular reflection component.

As described above, when metallic ink is used, images with different appearances can be obtained by changing the brightness of the projected illumination. However, when the lighting environment and viewing position are limited, it may not be possible to obtain the desired print appearance. Specifically, it has been difficult to control the appearance of prints under multiple viewing conditions.

Therefore, in this embodiment, the lighting environment where the print is exhibited and two observation positions are acquired, and in order to obtain the target appearance at each observation position, the print is formed by controlling the surface normal line by forming unevenness. .

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

The CPU 301 uses the RAM 303 as a work memory and executes an OS (operating system) or various programs stored in a ROM 302 or a HDD (hard disk drive) 315 or the like. Also, the CPU 301 controls each component via the system bus 308 . It should be noted that program codes stored in the ROM 302 or the HDD 315 are developed in the RAM 303 and executed by the CPU 301 in the processing according to the flowcharts described later. A display 317 is connected to the VC (video card) 304 . A general-purpose I/F (interface) 305 is connected via a serial bus 309 to an input device 310 such as a mouse or a keyboard, an illumination device 311 consisting of a plurality of light sources, a camera 312 , or an image forming device 313 .

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

<Logical Configuration of Image Processing Apparatus 1>
FIG. 4 is a diagram showing the logical configuration of the image processing apparatus 1 according to this embodiment. The image processing apparatus 1 has 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 line determination unit 405 . The image processing apparatus 1 also has a specular 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 .

The target image acquisition unit 401 acquires first image data and second image data indicating appearance target values under different geometric conditions. A color conversion unit 402 converts the color information of the first image data and the second image data into tristimulus values XYZ. The illumination brightness distribution acquisition unit 403 acquires a photographed image used for estimating the illumination brightness distribution on the print from the camera 312 installed at the print display 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 the input device 310 or the like.

The normal determining unit 405 outputs the normal vector information to the regular reflection lighting determining unit 406 and the clear ink amount determining unit 409 . The normal vector information is information for controlling the surface normal for determining unevenness to be given on the printed matter. A specular reflection illumination determination unit 406 determines the illumination brightness in the direction of specular reflection from the observer's position via the print surface normal line. A metallic ink amount determination unit 407 determines the amount of metallic ink based on the luminance difference between the first image data and the second image data. A color ink amount determination unit 408 determines the color ink amount based on the first image data and the metallic ink amount. A 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 .

<Configuration of Image Forming Apparatus 313>
FIG. 5 is a configuration diagram of the image forming apparatus 313. As shown in FIG. The image forming apparatus 313 in this embodiment is an inkjet printer that forms a three-dimensional object by recording ink on a recording medium. A three-dimensional structure is formed from a concavo-convex layer formed with clear ink and an image layer formed with color ink and metallic ink.

The head cartridge 501 has a print head having a plurality of ejection ports and an ink tank for supplying ink to the print head. A connector is also provided for receiving a signal for driving each ejection port of the print head. The ink tanks are independently provided with a total of six types of ink, namely cyan, magenta, yellow, and black color inks, metallic ink, and clear ink. Metallic ink has a stronger specular reflection component than other inks. Clear ink has a higher concentration of solid content such as resin than other inks, and can form unevenness by depositing the solid content on the recording medium.

The head cartridge 501 is positioned and mounted on a carriage 502 so as to be replaceable. 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 can reciprocate along the guide shaft 503 . Specifically, the carriage 502 is driven by a driving mechanism such as a motor pulley 505, a driven pulley 506, and a timing belt 507 using a 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 called "main scanning", and the moving direction is called "main scanning direction". A recording medium 508 such as a print sheet is placed on an auto sheet feeder (hereinafter “ASF”) 510 . During image formation, a pickup roller 512 is rotated via a gear by driving a paper feed motor 511, and the recording medium 508 is separated from the ASF 510 one by one and fed. Further, the recording medium 508 is conveyed to a recording start position facing the ejection opening surface of the head cartridge 501 on the carriage 502 by the rotation of the conveying roller 509 . The conveying roller 509 is driven via gears using a line feed (LF) motor 513 as a drive source. Determination of whether or not the recording medium 508 has been fed and determination of the feeding position are performed when the recording medium 508 passes the paper end sensor 514 . The head cartridge 501 mounted on the carriage 502 is held so that the ejection 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, storage means, or the like, receives data for forming each layer described above from the outside, and controls the operation of each part of the image forming apparatus 313 based on the data.

<Operation of Image Forming Apparatus 313>
The operation of forming the uneven layer and the image layer in the image forming apparatus 313 having the configuration shown in FIG. 5 will be described below. A generally used inkjet paper is used as the recording medium 508 in this embodiment.

First, when the print medium 508 is transported to a predetermined print start position, the carriage 502 moves along the guide shaft 503 above the print medium 508, and color ink is ejected from the ejection openings of the print head during the movement. be. When the carriage 502 moves to one end of the guide shaft 503 , the transport roller 509 transports the recording medium 508 by a predetermined amount in a direction perpendicular to the scanning direction of the carriage 502 . In this embodiment, this conveyance of the print medium 508 is called "paper feeding" or "sub-scanning", and the conveying direction is called "paper feeding direction" or "sub-scanning direction". After the recording medium 508 has been conveyed by a predetermined amount, the carriage 502 moves along the guide shaft 503 again. In this way, by repeating scanning by the carriage 502 of the print head and paper feeding, an uneven layer is formed on the print medium 508 . After the uneven layer is formed, the conveying 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.

FIG. 6 is a schematic diagram showing representation of an image controlled by the area coverage modulation method. In order to simplify the explanation, the print head in this embodiment is controlled by two values, ie, whether or not to eject ink droplets. In the present embodiment, ink on/off is controlled for each pixel defined by the output resolution of the image forming apparatus 313, and the state in which all pixels are turned on in a unit area is assumed to be 100% ink recording amount. shall be handled. "ON" indicates that ink is ejected, and "OFF" indicates that ink is not ejected. In such a binary printer, a single pixel can express only 100% or 0% ink recording amount, so halftones are expressed by a set of a plurality of pixels. In the example shown in FIG. 6, instead of expressing halftones at a density of 25% as shown in the lower left of the figure, by ejecting ink to 4 pixels out of 16 pixels (4×4) as shown in the lower right, 25% (4/16) of the area is expressed. Other gradations can be similarly expressed. The total number of pixels for expressing halftones, the pattern of pixels to be turned on, and the like are not limited to the above examples. A periodic screening process called halftone dot or error diffusion process can be used to determine the pattern of pixels that are turned on. By extending the above-described binarization processing to multi-value processing to multiple levels that can be modulated, it can be applied to a recording head in which the ink ejection amount can be modulated, and is limited to binarization. isn't it.

In the formation of the uneven layer by the image forming apparatus 313 in this embodiment, the unevenness is controlled for each position using the concept of the ink recording amount described above. When a substantially uniform layer is formed with an ink recording amount of 100% in forming the uneven layer, the layer has a certain thickness (height) according to the volume of the ejected ink. For example, when a layer formed with a recording amount of 100% has a height of 2 μm, it is sufficient to stack the layers 10 times in order to reproduce a height of 20 μm. In other words, the recording amount of ink ejected at a position requiring a height of 20 μm is 1000%.

FIG. 7 is a diagram for explaining the operation of forming the image layer and the concavo-convex layer by scanning the print head over the print medium 508 . A layer is formed by the width L of the recording head by main scanning by the carriage 502, and the recording medium 508 is conveyed by a distance L in the sub-scanning direction each time one line of recording is completed. To simplify the explanation, it is assumed that the image forming apparatus 313 in this embodiment can only eject ink up to a recording amount of 100% in one scan. Scan the same area multiple times without For example, when the maximum recording amount of ink to be shot is 500%, the same line is scanned five times. 7, after scanning the area A five times with the printhead (FIG. 7A), the printing medium 508 is conveyed in the sub-scanning direction, and the main scanning of the area B is repeated five times (FIG. 7A). (b)).

In order to suppress image quality deterioration such as periodic unevenness caused by the driving accuracy of the recording head, there are cases where multiple scans, so-called multi-pass printing, are performed even if the recording amount is 100% or less. FIGS. 7C to 7E show an example of 2-pass printing. In this example, the main scanning by the carriage 502 forms a layer by the width L of the recording head, and the recording medium 508 is conveyed by a distance of L/2 in the sub-scanning direction each time one line of recording is completed. Area A is printed by the m-th main scan (FIG. 7C) and m+1-th main scan (FIG. 7D) of the print head, and area B is printed by the m+1-th main scan of the print head (FIG. 7 ( d)) and the m+2th main scan (FIG. 7(e)). Although the operation of two-pass printing has been described here, the number of passes for printing can be changed according to the desired accuracy. When n-pass printing is performed, for example, the printing medium 508 is conveyed in the sub-scanning direction by a distance of L/n each time one line of printing is completed. In this case, even if the ink recording amount is 100% or less, the uneven layer, the gloss layer, and the image layer are formed by dividing into a plurality of print patterns and main-scanning the same line of the recording medium n times with the recording head. In this embodiment, multipass printing is not performed in order to prevent confusion between scanning by multipass printing and scanning for depositing 100% or more of ink. It is explained as a thing of Note that the recording medium 508 is not limited to paper, and various materials can be used as long as they can be used for layer formation by the recording head.

<Regarding the model formed on the recording medium>
FIG. 8 is a cross-sectional view of a model formed of a concavo-convex layer and an image layer formed on a recording medium. In this embodiment, an uneven layer having a height distribution of about several tens of μm at maximum is formed on the surface of the glossy paper for inkjet, and an image layer is formed thereon. Strictly speaking, the image layer also has a distribution of heights, but the thickness is sufficiently smaller than that of the uneven layer, and the effect on the final uneven shape is negligible. FIG. 8A is a schematic diagram showing the cross-sectional structure of image data used for printing. The print resolution of the image forming apparatus is 1200 dpi, and the normal lines formed by the uneven layer are formed in units of 4×4 pixels. The width of one unit is about 80 μm, and the height of one uneven layer is about 2 μm. FIG. 8(b) is a cross-sectional view showing the shape of the modeled object for which the image data shown in FIG. 8(a) is output. A modeled object 801′ in FIG. 8B corresponding to the unit 801 having three layers of maximum unevenness shown in FIG. be able to. Similarly, a modeled object 802' corresponding to the unit 802 having a maximum height of 6 uneven layers can form a normal line inclined by about 8 degrees with respect to the vertical direction of the recording medium. Although a two-dimensional cross-sectional view is used for explanation, a unit that can control the normal in both the x-axis direction and the y-axis direction can be formed by inclining in the depth direction as well. A normal line determination unit 405 stores in advance a plurality of unit shapes that can be created by the image forming apparatus and normal vector information thereof.

<Flowchart of Processing Executed by Image Processing Apparatus 1>
FIG. 9 is a flow chart showing the operation flow of the image processing apparatus 1 of this embodiment. As described above, in the present embodiment, a method will be described for suitably obtaining illumination light in the direction of specular reflection at an arbitrary position by forming unevenness on a printed matter in a state where the brightness of the lighting in the room does not change. do. The processing in each step in FIG. 9 is performed by the CPU 301 of the image processing apparatus 1 developing the program code stored in the ROM 302 in the RAM 303 and executing it. Also, the symbol "S" in the description of each process means a step in the flow chart.

First, in S<b>901 , the target image acquisition unit 401 obtains first image data I<b>1 representing a target appearance under the first geometric condition and a target image under the second geometric condition to be formed on a recording medium from an external device such as the HDD 315 . Second image data I2 representing appearance is obtained. The first image data and the second image data are two target image data in which the same subject is recorded, but one has a bright appearance and the other has a dark appearance. It should be noted that the two target image data are selected after determining how much brightness difference is desired between the two images. Let RGB1(x, y) be the pixel value at the pixel position (x, y) of the first image data. Also, let RGB2(x, y) be the pixel value at the pixel position (x, y) of the second image data. The first image data and the second image data are images having 16 bits for each color of R (red) value, G (green) value, and B (blue) value, for a total of 48 bits of color information for each pixel.

The pixel values of the first image data and the second image data in this embodiment are RGB values defined on the sRGB space. In addition, an RGB image defined by generally used AdobeRGB, or a Lab image corresponding to CIELAB can 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.

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. 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 on the CIE1913 XYZ color space. Specifically, pixel values XYZ1(x, y) and XYZ2(x, y) after conversion are determined based on the following equations (5) and (6).

R _L =degamma(R)
G _L =degamma(G) Equation (5)
B _L =degamma(B)

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 on the sRGB space are given gamma characteristics corresponding to the characteristics of standard displays. degamma is a function that converts these RGB values into linear RGB values R _L , G _L , and B _L that are linear with XYZ values, which will be described later. X, Y, and Z are the X, Y, and Z values that make up XYZ1(x,y) and XYZ2(x,y), respectively. M is a transformation matrix that transforms linear RGB values defined on the sRGB space into XYZ values defined on the CIE1913 XYZ color space.

In S903, the illumination brightness distribution acquisition unit 403 acquires an illumination brightness distribution image and illuminance from the camera 312 installed at the print display position. FIG. 10A is a plan view illustrating the positional relationship among the print display position, camera 312, and illumination device 311. FIG. 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 display position and photographs the printed matter centering on the vertical direction. Note that the information acquired by the illumination luminance distribution acquisition unit 403 is assumed to be information under the environment where prints are actually exhibited. Also, the print display position is a position where the printed matter is scheduled to be displayed in that environment, and the lighting is provided with an illuminance assuming actual observation. These pieces of information may be stored in advance in the ROM 303 or the like and acquired in S903.

FIG. 10B is a schematic diagram showing an example of an image captured by the camera 312. As shown in FIG. The photographed image is captured using a fish-eye lens or the like, and becomes an image in all directions around the half-dome that serves as illumination for the printed matter. The illumination luminance image is obtained by gamma-converting the pixel values of the image captured by the camera 312 so as to be linear with the luminance. When photographing, it is preferable to photograph with underexposure so that the brightest point of the illumination distribution does not deviate from the dynamic range of the camera 312, or to synthesize a high dynamic range image by photographing in multiple stages. In addition, the illuminance E can be estimated by multiplying the pixel value of each pixel of the photographed image by a weight set for distortion correction for each coordinate, and accumulating the values. In addition, a separate illuminance meter may be used.

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 are arbitrarily designated to achieve appearances corresponding to the respective target image data. In step S<b>905 , 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 to the regular reflection illumination determination unit 406 .

In S906, the regular reflection illumination determination unit 406 determines illumination luminances Ls1 and Ls2 based on the illumination luminance distribution, the observer position, and the normal vector information. A vector representing the direction of each pixel position is known from information such as the lens used in the camera 312 . Accordingly, a vector representing the specular reflection direction is determined based on the following equation from the vector corresponding to the point p, which is the observer position, and the normal vector.

In the following, vector arrows are omitted. L is a vector representing the direction of specular reflection, E is a vector corresponding to point p which is the position of the observer, n is a normal vector, and E·n represents the inner product of vector E and vector n.

Here, FIG. 10(c) shows the relationship between the points p1 and p2 and the regular reflection illumination positions s1 and s2. Normally, when the normal vector is the same as the vertical direction of the printed matter, that is, when the printed matter does not have unevenness, as shown in FIG. The position becomes the regular reflection illumination position.

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

In S907, the normal line determination unit 405 evaluates the following formula and determines a normal line that satisfies the conditions.
|Y1−Y2|<|Ls1−Ls2|·ρ _{Me_max} /(E/π) Equation (8)

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; is the illuminance and π is the circular constant. Here, it is determined whether the illumination luminances Ls1 and Ls2 determined by the normal vector are sufficient to reproduce the difference in brightness between the input first image data and second image data. If the above expression cannot be satisfied, the luminance difference |Y1-Y2| between the two images cannot be expressed even if the maximum amount of metallic ink is printed. In that case, the process returns to S906 and the process is repeated to search for the normal vector that becomes the illumination luminances Ls1 and Ls2 that satisfy the conditions. If the normal vector that satisfies the above formula can be searched, the searched normal vector information can be output to the clear ink amount determination unit 409 .

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

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.

ρ _Me is the reflectance of the specular reflection component of the metallic ink of each pixel. The conversion from the reflectance ρ _Me to the metallic ink amount Me is performed by using an LUT (lookup table) or the like prepared by measuring these relationships in advance.

In S909, the color ink amount determination unit 408 converts XYZ1 (x, y), which is the XYZ value of the first image data determined by the color conversion unit 402, to the metallic ink amount Me determined by the metallic ink amount determination unit 407. Based on this, the color ink amounts CMYK are determined. Note that XYZ2(x, y), which are the XYZ values of the second image data, may be used to determine the amount of color ink. Here, the amount of color ink is determined taking into consideration the influence of the previously determined diffusion color of the metallic ink. First, XYZ _color , which is the XYZ value of color ink, is determined by the following formula.
_XYZcolor =XYZ1/ _XYZMe Expression (10)

Here, XYZ _Me is an XYZ value representing the diffusion color of metallic ink. XYZ _Me can be determined by preliminarily holding the relationship between the amount of metallic ink and the colorimetric value as an LUT using a 0°/45° colorimeter that excludes the influence of specular reflection light, for example. In addition, if a coloring model is established in which the XYZ values of the printed matter can be obtained by multiplying the XYZ values of the metallic ink and the XYZ values of the colored ink, dividing the target value XYZ1 by XYZ _Me The required XYZ values can be determined. This step is performed to adjust the amount of colored ink, since the brightness of the diffused light decreases depending on the amount of metallic ink added. To determine the color ink amounts CMYK from XYZ _color , a general method such as using a prepared LUT can be used. If the determined XYZ _color cannot be reproduced, it can be kept within the reproduction range by clipping or the like. Also, a method of adjusting the amount of metallic ink to fit within the reproduction range is also conceivable.

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 can be created by the image forming apparatus 313 as described above, the clear ink amount Cl for creating that unit shape is output on the front surface of the print. Alternatively, the metallic ink amount Me data 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 a unit shape only in the area where the metallic ink is printed.

In S911, the output unit 410 determines the metallic ink amount Me determined by the metallic ink amount determination unit 407, the color ink amount 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. is output to the image forming apparatus 313 .

As described above, according to the present embodiment, it is possible to form a printed matter in which the surface normal is controlled. Specifically, based on the lighting environment in which the print will be displayed, two target images, and two viewing positions, it is possible to obtain a print with surface normals to reproduce the luminance difference between the two images. become. By controlling the surface normal, it is possible to obtain illumination light in a desired direction of specular reflection, so that a suitable appearance of the printed matter can be obtained at two viewing positions.

<<Embodiment 2>>
In Embodiment 1, a method for determining the surface normal of a printed matter from two target images and two observation positions for one printed matter that provides a desired luminance change has been described. In the present embodiment, a method for performing so-called high dynamic expression that reproduces a color brighter than paper white from one target image and one observation position will be described. Note that the description of the parts common to the first embodiment will be omitted or simplified, and the differences will be mainly described below.

FIG. 11 is a flow chart showing the operation flow of the image processing apparatus 1 of this embodiment. The processing in each step of FIG. 11 is performed by the CPU 301 of the image processing apparatus 1 developing the program code stored in the ROM 302 in the RAM 303 and executing it.

First, in step S<b>1101 , the target image acquisition unit 401 acquires monochrome 1-channel first image data as a 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 luminance Y. Here, luminance Y=1.0 corresponds to the reflectance of paper white at illuminance E. FIG. The image data has so-called high dynamic range information of luminance Y>1.0.

In S1103, the illumination brightness distribution acquisition unit 403 acquires an illumination brightness distribution image and illuminance from the camera 312 installed at the print display position. In S1104, the observer position obtaining unit 404 presents the illumination luminance distribution image obtained in S1103 together with the UI on the display 317, and sets the observer's eye position p1 as the observation position from an input device or the like.

In S1105, the normal determining unit 405 determines a normal vector for each unit forming 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 coordinates 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 print. In other words, no unevenness is formed on the printed matter. If a pixel with luminance Y>1.0 is included, the lookup table shown in FIG. 12 is referred to determine the normal vector.

FIG. 12 is an LUT showing luminance in combination of specular reflection lighting luminance ratio and metallic ink amount. Here, E is the illuminance, π is the circular constant, and Ls/(E/π) is the ratio of specular reflection illumination luminance to the illuminance. The brightness of metallic ink is determined according to this ratio. For example, in the table shown in FIG. 12, if the maximum value of luminance required to express the brightness of the target first image data is Y=1.75, then Ls/(E/π) is 14.0. Choose a normal vector that is equal to or greater than Also, the metallic ink amount Me at that time is found to be 1.0. Also, if the maximum required luminance value is Y=1.0, then a normal vector with Ls/(E/π) equal to or greater than 8.0 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) changes depending on the normal vector at the coordinates. Note that the relationship between the normal vector and the regular reflection direction vector can be determined by Equation (7) as in the first embodiment.

In S1106, the specular reflection illumination determination unit 406 determines the illumination luminance Ls in the specular reflection direction obtained at the determined normal vector. In S1107, the metallic ink amount determination unit 407 determines the metallic ink amount Me based on the illumination luminance Ls in the specular reflection direction using the lookup table shown in FIG. Note that a general table interpolation method may be used.

In S1108, the color ink amount determination unit 408 determines the black ink amount K based on the target luminance for the pixels where the metallic ink amount Me is 0.0. For this, a general table or the like showing the relationship between the target brightness 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 processing from S1105 to S1109 is repeated until all pixels are processed.

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. Output to the image forming apparatus 313 .

As described above, the surface normal of the printed matter can be controlled based on the lighting environment in which the printed matter is exhibited, the target image, and one observation position, and the appearance of the printed matter including the luminance Y brighter than the paper white can be obtained.

<<other embodiments>>
In the above-described embodiment, the metallic ink is used as the ink having a deviation angle reflection characteristic. In addition, the same effect can be obtained by using so-called gloss control ink such as clear ink that increases the smoothness of the print surface and strengthens specular light, or high refractive index ink that uses a material with a high refractive index to obtain strong specular light. It is possible to obtain

Further, in determining the XYZ values of the colored inks in the colored ink amount determining step in the first embodiment, the color development model based on the multiplication of the XYZ values has been described. It is possible to use other coloring models or coloring simulations suitable for the image forming apparatus used.

The present invention supplies a program capable of operating one or more functions of the above-described embodiments 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 reads the program. It can also be realized by executing processing. It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

1 image processing device 401 target image acquisition unit 404 observer position acquisition unit 405 normal line determination unit

Claims (15)

An image processing apparatus for generating data for forming an image using ink for forming unevenness on a recording medium,
target image acquisition means for acquiring target image data;
Illumination luminance distribution acquisition means for acquiring an illumination luminance distribution in an observation environment in which the recording medium is observed;
an observer position obtaining means for obtaining an observation position of the recording medium;
normal line determination means for determining unevenness applied to the recording medium so that the illumination luminance in the specular reflection direction obtained when the recording medium is observed from the observation position has a desired brightness; and an ink amount of each ink. ink amount determining means for determining
An image processing device comprising: 2. The image processing apparatus according to claim 1, wherein the specular reflection direction is determined based on the observation position and information on unevenness of the recording medium. 3. The image processing apparatus according to claim 1, wherein the illumination brightness in the specular reflection direction is determined based on the illumination brightness distribution acquired by the illumination brightness distribution acquiring means. 4. The inks according to any one of claims 1 to 3, wherein the inks include glossy ink capable of imparting gloss to the recording medium, clear ink capable of imparting unevenness to the recording medium, and color ink. 1. The image processing device according to claim 1. 5. The image processing apparatus according to claim 4, wherein the glossy ink includes at least one of metallic ink, gloss control ink, and high refractive index ink. When the target image acquisition means acquires the first target image data and the second target image data, and the observer position acquisition means acquires the first observation position and the second observation position,
The normal determining means determines that illumination luminance in a specular reflection direction obtained when observing the recording medium from the first observation position corresponds to the first target image data, and from the second observation position 5. The unevenness of the recording medium is determined so that the illumination luminance in the specular reflection direction obtained when observing the recording medium corresponds to the second target image data. The image processing device according to any one of . The first target image data is image data reflecting light in the direction of specular reflection, and the second target image data indicates the same subject as the subject of the first target image data, and reflects light in the direction of specular reflection. 7. The image processing apparatus according to claim 6, wherein the image data is not processed. The ink amount determination means
8. The image processing apparatus according to claim 6, wherein the amount of glossy ink is determined based on the target image data and the illumination luminance in the specular reflection direction. When the target image acquisition means acquires one target image data and the observer position acquisition means acquires one observation position,
The normal determining means determines the unevenness given to each coordinate of the recording medium so that the luminance of each coordinate obtained when observing the recording medium from the observation position becomes the luminance of the target image data. 5. The image processing apparatus according to any one of claims 1 to 4, characterized in that it determines. The normal determining means and the ink amount determining means
10. The image processing according to claim 9, wherein the unevenness or the ink amount of the glossy ink is determined by using a lookup table for indicating the brightness in a combination of the regular reflection illumination brightness ratio and the ink amount of the glossy ink. Device. The ink amount determination means
11. The image processing apparatus according to claim 6, wherein the amount of clear ink is determined based on the information on the unevenness. The ink amount determination means
11. The image processing apparatus according to claim 6, wherein the amount of color ink is determined based on the target image data and the amount of glossy ink. 5. The image processing apparatus according to claim 1, wherein the brightness of said target image data is determined by converting it into tristimulus values.
place. A control method for an image processing apparatus for generating data for forming an image on a recording medium using ink for forming unevenness, comprising:
a target image acquisition step for acquiring target image data;
an illumination brightness distribution acquisition step of acquiring an illumination brightness distribution in an observation environment in which the recording medium is observed;
an observer position acquisition step of acquiring an observation position of the recording medium;
a normal line determination step of determining unevenness to be applied to the recording medium so that illumination luminance in a specular reflection direction obtained when the recording medium is observed from the observation position has a desired brightness; and an ink amount of each ink. an ink amount determination step for determining
A control method for an image processing device, comprising: 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.

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