JPH07264428A - Method and device for image forming - Google Patents

Abstract

PURPOSE:To attain the processing based on a color reproduction region with high accuracy by using plural sets of luminance values and color reproduction ranges expressed in 2-dimension so as to decide a color reproduction region expressed in 3-dimension. CONSTITUTION:When colors P, Q are reproduced by using a W as a white color point by 2-dimension chromaticity, the colors W, P, Q are in existence on one straight line segment. That is, the colors P, Q are in existence in the same color layer. In this case, let a cross point between the line segment WP and a limit line RTV representing a TV color reproduction range be T and a cross point between the line segment WP and a limit line RIJ representing a color reproduction range of an ink jet printer be S, then since the color Q is reproduced without any modification but the color P cannot be reproduced without that, the color Q is converted into a color Q' satisfying the relation of the inverse of WQ'= the inverse of WQ X the inverse of WS/the inverse of WT and the color P is converted into a color P' satisfying the relation of the inverse of WP'= the inverse of WP X the inverse of WS/the inverse of WT respectively and then the converted colors are reproduced. Furthermore, in the case of 3-dimension, the processing is implemented similarly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for a color reproduction area that can be expressed.

[0002]

2. Description of the Related Art An inkjet video printer will be described below as an example.

Generally, in this type of apparatus, the color reproduction range of the input system and the color reproduction range of the output system are different. For example, in FIG.
As shown in the x, y chromaticity diagram (CIE chromaticity diagram), the color reproduction range of the television and R _TV are wider than the color reproduction range R _IJ of the inkjet printer.
still,

[0004]

[Outer 1] Is the full color range.

[0005]

Conventionally, since there has been no solution to such a problem in the related art, for example, FIG.
When trying to reproduce a color that cannot be reproduced by an inkjet printer such as A or B, the colors are equivalently reproduced as A'and B ', so the saturation difference and gradation difference originally between A and B are lost. It gets worse.

Such a phenomenon appears in a color having a high degree of purity, for example, a red rose color or a deep blue sea color, and remarkably deteriorates the reproduced image quality.

In view of the above problems, it is an object of the present invention to simply and accurately indicate a color reproduction area that can be expressed so that processing based on the color reproduction area can be performed accurately.

Further, it is an object of the present invention to enable an input image to be reproduced as a high quality image by performing color processing on the basis of an accurately indicated color reproduction area.

[0009]

In order to achieve the above-mentioned object, the present invention provides a luminance value and a luminance value of 2
Multiple settings are made in correspondence with the color reproduction range that is shown dimensionally,
In the color processing means, a three-dimensionally represented color reproduction area is determined by using a plurality of sets of the brightness value and the two-dimensionally represented color reproduction range, and the three-dimensionally represented color reproduction area is determined for the input image data. It is characterized in that processing based on the determined color reproduction area can be performed.

[0010]

1 shows the concept of the present invention. Although the color space is originally three-dimensional, in order to simplify the description, it will be described by using two-dimensional chromaticity frequencies.

Now, let's consider that W is a white point and colors P and Q are reproduced. The colors W, P, Q are on a straight line. That is, the color layers of P and Q are the same. The point where the straight line WP intersects with the limit line R _TV indicating the color reproduction range of the television is T,
Limit line showing the color gamut of inkjet printers R _IJ
Let S be the point that intersects with.

At this time, Q can be reproduced as it is, but P cannot be reproduced as it is. Therefore, Q is a bar WQ '= bar WQ on the same straight line.
× Q that satisfies bar WS / bar WT and P is bar WP ′
= Bar WP × bar WS / bar When converted into P ′ that satisfies the above to perform color reproduction, the hues of P and Q do not change, and the difference in saturation between P and Q is natural. It will be possible to reproduce with feeling.

If the color reproduction range of the ink jet printer is partially projected as shown in FIG. 3, the same idea can be applied.

When P is to be reproduced, the color reproduction may be performed after the conversion into P'which satisfies bar P'W = bar WS.times.bar WP / bar WT as before.

Actually, the same can be done in the case of three dimensions. The vector of white point coordinates is W = (X _W , Y
_W , Z _W ). In the case of television, a certain color vector P = (P _X , P _Y , P, where V _TV is a solid representing the color reproduction range and V _IJ is a solid representing the inkjet color reproduction range
Consider the case of reproducing _Z ).

Letting the point where the vector WP and V _TV and V _IJ intersect be vector T and vector S, vector T,
The vector S is uniquely determined.

At this time, the color vector P to be reproduced is

[0018]

[Outside 2] Given in.

By doing so, even if the color reproduction range between input and output is different, the hue is constant and the lightness and saturation are compressed in a natural form, and a high-quality image is obtained.

FIG. 5 shows an embodiment of a signal processing circuit for realizing the present invention.

The color compression section 51 receives the 6-bit digital input of the video signals R, G, 8 and converts them into data R ', G', B 'which have been subjected to color compression as will be described later. Here, the table conversion method using a 2 ^18- byte ROM is used, and this is a 256 Kbit ROM.
It can consist of 3 pieces.

In the density converter 52, the R ', G',
B'is converted into cyan, magenta, and yellow densities C, M, and Y by the table conversion method. For example, R'is C '
= -LogR '.

In the masking section 53, masking is performed in order to correct the asymmetrical color components of the respective color inks and realize the C, M and Y densities on the paper surface.

For example, C ′ = a ₁₁ c + a ₁₂ m + a ₁₃ y, C ′, M ′, Y ′ may be corrected by a linear equation of C, M, Y, which is implemented by using a table conversion. It

Next, the density values C ', M', Y'to be output.
Is converted into a drive voltage for each head by the head drive unit 54, and the inkjet head is driven in accordance with the converted drive voltage.

Next, a ROM stored in advance in the color compression section 51
The data will be described. The coordinate of the color solid is the tristimulus value X,
It is a direct system of Y and Z.

First, a color stereoscopic V _{TV that} can be expressed on a television
Is given by

According to the standard of NTSC

[0029]

[Outside 3] Is. Where 0≤R≤1, 0≤G≤1, 0≤B≤1
Including the condition of, this represents a rectangular parallelepiped in the XYZ system. In this case, the equation of six planes f ₁ (X, Y,
Z) = 0, ... F ₆ (X, Y, Z) = 0 determines the territory S _TV .

Further, Ryo field S _IJ ink jet of the color reproduction area V _IJ generally f (X, Y, Z) = 0 and either applied,
For example, it can be approximated as follows.

It can be assumed that aX ² + bZ ² = f (Y) ² ... (2), assuming that the radius changes according to the brightness Y direction as shown in FIG.

Now, for the inputs R, G, B, according to the standard of NTSC

[0033]

[Outside 4] And convert.

The white point is the vector W = (W _X , W _Y , W
The equation of the straight line vector PW as _Z ) is

[0035]

[Outside 5] Call

Substituting equation (4) into equation (1) and solving, 2
Two solution vectors T ₁ and T ₂ are obtained. Of these, the one in the direction of the vector WP is taken as the vector T.

Further, by substituting the equation (4) into the equation (2) and solving it, two solution vectors S ₁ and S ₂ are obtained.
Of these, the vector S is in the direction of the vector WP. These are uniquely determined. here

[0038]

[Outside 6] X ', Y', and Z'that satisfy This is the color-compressed point P '. R ', G', B'is obtained again by the formula (6) of the NTSC standard, and this data is obtained.

[0039]

[Outside 7] The values of R ', G', and B'determined from R, G, and B in this manner may be stored in the ROM 51 whose input is an address.

Here, the tristimulus value X is used as the coordinate of the color solid.
Although YZ is considered, Lab ^* system, Luv ^* system, etc. may be adopted.

In this way, since the color gamut of the input system can be compressed to the color gamut of the output system without changing the hue,
Good color images can be obtained even when forming color images having different color reproduction ranges of the input / output systems.

That is, even if the color reproduction ranges of the input system and the output system are different, the saturation or lightness can be compression-mapped in a natural form without changing the hue, and a high-quality color image can be obtained. You can

Although a television signal is used as the input system signal in this embodiment, a signal directly input from another solid-state image pickup device or the like can also be used. Further, although an inkjet printer is selected as an output system for explanation, other color printers such as an electrophotographic printer and a thermal printer can be used.

In the figure, R _TV and V _TV represent the color reproduction range of a color television, and R _IJ and V _{IJ respectively} represent the color reproduction range of an ink jet printer.

[0045]

As described above, according to the present invention, it is possible to easily and accurately indicate the color reproduction area that can be expressed, so that the processing based on the color reproduction area can be performed with high accuracy.

Furthermore, by performing color processing based on the color reproduction area that is accurately indicated, it is possible to reproduce the input image as a high quality image.

[Brief description of drawings]

FIG. 1 is a chromaticity diagram showing the concept of the present invention.

FIG. 2 is a chromaticity diagram illustrating a conventional example.

FIG. 3 is a chromaticity diagram illustrating another example of the present invention.

FIG. 4 is a diagram illustrating an example of a three-dimensional color space.

FIG. 5 is a circuit diagram showing an example of a signal processing circuit that realizes the present invention.

FIG. 6 is a diagram showing a color reproduction range by an inkjet printer in a three-dimensional color space.

[Explanation of symbols]

R _TV color television color reproduction range R _IJ inkjet printer color reproduction range

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Claims (3)

[Claims] 1. A plurality of brightness values and a color reproduction range shown two-dimensionally on the brightness plane are set in correspondence with each other, and the brightness value and the color reproduction range shown two-dimensionally are set in a color processing means. Is used to determine a representable three-dimensionally represented color reproduction area, and the input image data can be processed based on the determined color reproduction area. Image processing method. 2. A color based on an expressible color reproduction area set by using an input means for inputting image data, and a plurality of sets of a brightness value and a color reproduction range two-dimensionally shown on the brightness surface. An image processing apparatus comprising: a color processing unit that performs processing; and an output unit that outputs the color-processed image data. 3. The image processing apparatus according to claim 2, wherein the color processing is color space compression processing.