JP2567216B2 - Color image signal processing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image signal processing method for processing a color image signal, and more particularly, to a color image signal of an input system having a wide reproduction range of brightness and saturation of a television image signal or the like for a color printer or the like. The present invention relates to a color image signal processing method for converting into a color image signal of an output system having a narrow reproduction range.

[0002]

2. Description of the Related Art For example, as shown in FIG.
* Takes saturation on the horizontal axis

[0003]

[Outside 1] Taking the red hue on television

[0004]

[Outside 2] Comparing the color reproduction range R _TV and the color reproduction range R _IJ of the inkjet printer, the former is much wider. Therefore, when reproducing the image of the television and the ink jet printer, the portion excluding the range R _IJ of the range R _TV is condensed on the boundary line and becomes an extremely unnatural image.

Therefore, in the past, Japanese Patent Laid-Open No. 60-105376 has been used.
As described in Japanese Patent Publication No. JP-A-2003-187, the input image data outside the color reproduction range is compressed on the boundary line in the same hue on the equal luminance plane.

[0006]

However, in the above-mentioned conventional example, the lightness component of the input image data is not compressed based on the color reproduction range of the output device.
The saturation component of the image data of the high brightness portion and the low brightness portion existing outside the color reproduction range of the output device has been compressed into achromatic color data.

That is, there is a problem that the saturation components of the high brightness portion and the low brightness portion cannot be reproduced.

The present invention has been made in view of the above points, and the saturation component in high brightness and low brightness is reflected by compressing the saturation component after compressing the brightness component of the input color image data. The purpose is to be able to generate the image data.

[0009]

In order to achieve the above object, the image signal processing apparatus of the present invention has the following configuration.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A block diagram of signal processing when the present invention is applied to an inkjet video printer for printing a color television signal by an inkjet printer is shown in FIG.

In the figure, 5R, 5G and 5B are respectively R and
G and B color television signal input terminals 10 are compression ROMs (Read Only Mem) that perform compression mapping.
ory), the functions are RGB → Luv * conversion unit 11, gradation (brightness) compression unit 13, saturation compression unit 15, Luv * ′ →
It is divided into R'G'B 'converters 17. 20 is additive method 3
A logarithmic conversion ROM 30 for logarithmically converting the signals R ', G', B'of the primary colors into the signals of cyan C, magenta M, and yellow Y of the three subtractive colors for printing is a masking ROM 40C for removing asymmetric colors. , 40M, 40Y are digital-analog (D / A) converters for converting digital signals into analog signals for driving an inkjet head, 50C, 50M,
50Y indicates an inkjet head, respectively.

The operation will be described below.

The RGB signal for each pixel of the television is
It is converted to Luv * by the RGB → Luv * conversion unit 11 according to the following equation.

[0014]

[Outside 3] This L *, u *, v * is converted into a predetermined constant mapping function f
_A gradation compression unit 13 and a saturation compression unit 15 according to _L , fu, and fγ.
Is converted into L * 'u *' v * ', and lightness and saturation are compressed. f _L , fu, and fγ will be described later.

[0015]

[Outside 4]

Then, the Luv * '→ RGB conversion unit 17 outputs L
R ', G', B'is calculated by reversing the above equation (1) from * 'u *' v * 'to obtain R'G'B'.

Looking back on the above, it can be seen that it is possible to uniquely determine the output R'G'B 'from the input RGB using the predetermined functions f _L , fu, f γ. Therefore, the above part can be configured by a table conversion memory (ROM 10) for inputting input RGB signals.

Since this R'G'B 'is a signal which has already been compressed within the ink jet reproduction range, it is converted into logarithmic conversion ROM 20 density signals C, M and Y, which are further converted by the masking section 30. Are converted into digital values Vc, Vm, and Vy of the head drive voltage corresponding to.

The logarithmic conversion and masking are composed of a table conversion ROM having an input as an address.

Further, D / A converters 40C, 40M, 40Y
Is converted into an analog voltage for driving the head, and the inkjet heads 50C, 50M, and 50Y are driven.

Next, the mappings f _L , fu, f for realizing the compression
A method of determining γ will be described.

First, the lightness is compressed. As shown in FIG. 2, if the maximum value and the minimum value of the brightness of the input system are L ₄ and L ₁ for a certain hue and those of the output system are L ₃ and L ₂ , the input L *, u *, v * Are L *,
Converted to u * and v *.

[0023]

[Outside 5] And convert. That is, only the brightness is compressed according to the ratio of the reproduced brightness of the input / output system (corresponding to the compression ratio of the brightness in this embodiment). This for all hues

[0024]

[Outside 6] As shown in Fig. 3, the reproduction range R _TV of the input system
Is compressed while retaining the saturation C * in the range R'as indicated by the arrow.

Next, compression is performed in the saturation direction.

First, consider a hue θ.

[0027]

[Outside 7] At this time, a certain brightness

[0028]

[Outside 8] Let l ₁ and l ₂ be the lengths in the saturation direction of the area corresponding to.
At this time, L * ″ u * ″ v * ″ is L * ′, u as follows.
* ', V *' are converted.

[0029]

[Outside 9]

As described above, the saturation is compressed according to the ratio of the reproduced saturation of the input / output system (corresponding to the compression ratio of the saturation in this embodiment).

According to the above-described method, the conversion from R'as shown in FIG. 4 to the reproduction range R _{IJ of the} ink jet printer is carried out after the saturation conversion and before the conversion while keeping the lightness.

After all, looking at a certain hue, the color range R _TV of the color television signal as shown in FIG. 5 is compression-mapped to the reproduction range R _IJ of the ink jet printer.

Although the lightness and the saturation are compressed in this order, if the saturation is compressed _first , the lightness is L ₁ -L.
_In the area of ₂ , L _{3 to} L _4, the saturation of R _IJ does not exist, so the saturation is compressed to zero, and further compression of the brightness does not change the saturation zero. That is, even if the saturation is compressed first, the saturation zero does not change. In other words, if you compress the saturation first, you get a distorted compression map,
Image quality is reduced.

On the other hand, if the lightness is first compressed as in this embodiment, it is possible to uniformly compress each point on the chromaticity diagram, and the deterioration of the image quality is small.

The above is one compression method,
An appropriate number N of representative colors (L * i, u
* I, v * i) (i = 1, 2, ... N) defines the colors (L * i ′, u * i ′, v * i ′) to be converted, and fits them by the least squares method f _L , Fu, fγ may be determined.

Further, as the color system, not only Luv * but also the other color system of the luminance one color difference system is used.

Further, in the above-described embodiment, the compression ROM
Although the 10 and the logarithmic conversion ROM 20 and the masking ROM 30 are separated from each other and configured as ROMs respectively, the output is uniquely determined from RGB of the input, so these may be combined and configured as one ROM, or in order. The compression process may be performed after reversing the logarithmic transformation.

As described above, since the input television signal is once compressed within the reproduction range of the ink jet printer and then recorded, the color range which cannot be reproduced by the ink jet printer is compressed into the reproduction range of the printer in a natural form. As a result, the resulting color image is extremely natural and of high quality. That is, based on the compression ratio, the input color image signal is compression-mapped within the color reproduction range of the output device so as to preserve the gradation for both lightness and saturation.

The color image signal of the input system is not limited to the television signal, but an output signal from the solid-state image pickup device or the like can be used if the color reproduction range is wider than that of the output system.

Further, the output system is not limited to the ink jet printer, but can be applied to various printers such as an electrophotographic printer and a thermal printer, or a display device having a relatively narrow color reproduction range.

[0041]

As described above, according to the present invention, since the compression is performed based on the color reproduction range of the input image and the color reproduction range of the output device, the input color image data is within the color reproduction range that can be reproduced by the output device. It can be converted into color image data.

Further, since the brightness component of the input color image data is first compressed and then the saturation component is compressed, the saturation component of the input image data outside the color reproduction range of the output device at high brightness and low brightness is reflected. It is possible to compress the image data.

[Brief description of drawings]

FIG. 1 is a block diagram of a color image signal processing according to this embodiment.

FIG. 2 is a diagram showing a color reproduction range of a color television signal and an ink color jet printer.

FIG. 3 is an explanatory diagram for explaining compression mapping.

FIG. 4 is an explanatory diagram for explaining compression mapping.

FIG. 5 is an explanatory diagram for explaining compression mapping.

[Explanation of symbols]

 10 compression ROM 11 RGB → Luv * conversion unit 13 gradation compression unit 15 saturation compression unit 17 Luv * ′ → R′G′B ′ conversion unit 20 logarithmic conversion ROM 30 masking ROM

Claims (1)

(57) [Claims] 1. Color image data representing an input image is input, and based on the color reproduction range of the input image and the color reproduction range of the output device, the lightness component of the color image data is first compressed, and An image signal processing method, characterized in that by compressing a degree component, the color image data compressed for the lightness and the saturation is brought into a color reproduction range of the output device.