Study on Printing Quality of Different Properties of Paper by Ink Jet Printing (5)

(D) Color Appearance Model

It has been mentioned in the previous section that the cross-media color reproduction accuracy factor lies in the way that the color appearance mode is adapted to visual color adaptation, so the color appearance mode is important for the technical importance of cross-media device color control.

1.Von Kries' visual color adaptation model

According to von Kries (1902)'s Theory of Visual Color Adaptation, “Compo- nents” are based on their respective function modes and are independent of the light source. Later generations applied this "visual color adaptation theory" to the conversion of the XYZ color space.

2.Cielab, CIELUV

In these modes, the developer changes the reference-white setting and converts the XYZ color space to the "independent observation environment" color space. However, this simple method deals with the problem of visual adaptation and considers factors such as background color and ambient light in the model. Therefore, although this model provides the LCH color appearance scale, multi-disciplinary researchers still disagree with CIELAB and CIELUV as a color appearance mode.

3. The visual color adaptation model of Bartleson and Breneman

The illumination of the observation environment (Surround) is also one of the factors affecting the color adaptability. According to Bartleson's theory of replicating curves (1967), Breneman proposed the "brightson copying model with Breneman" in 1978 through experimental statistics. This model is based on CIELAB (LUV) and retains the AB (LUV) chroma formula in LAB (LUV), replacing the lightness L with its lightness formula.

The characteristics of Bartleson's and Breneman's lightness models take into account the factors of the ambient light (Surrond Light Soures), and different ambient light will use different formulae [Viggiano, 1992]

4.Nayatani color appearance pattern

Since 1981, Nayatani et al. have published a nonlinear visual color adaptation model. The Nayatani color appearance pattern is constantly being modified. This model is based on the cone-cell response model of Hunt-Pointer-Estevez and takes into account the effects of Hunt, Stevens, and Helson-Judd. (Luo Meijun, 1995)

5.Color appearance mode of Hunt

Hunt has introduced modified Hunt mode since 1987. This mode is similar to the old Nayatani mode but considers more factors and the calculation is more complicated. Compared with the Nayatani model, the biggest difference in the Hunt model is that "the calculation of the model not only considers the visual psychological response." (Luo Meijun, 1995)

6.Rlab

Fairchild (1991) and others tried to modify the Von Kries and CIELAB models to improve the accuracy of cross-media color reproduction. The color mode, like the Hunt mode, considers physiological responses and psychological visual responses, as well as the effects of various visual effects, as a mode design consideration. The RLAB color appearance model establishes a "standard reference environment" with the reference environment setting CIE D65, illumination 348ce/m2, and reference white-triple stimulus (X=95, Y=100, Z=109). The chromaticity values ​​in different environments will be converted to corresponding calculations in this environment.

7. Comparison of color appearance patterns

Kim et al. (1993) studied the color reproduction performance of the eight color appearance modes under different lighting conditions, and the manuscript and the reproduction were visually evaluated under the light sources of A and D65 (three lighting levels), respectively. The experimental results show that the average performance of the eight models is from CIELAB, Hunt, RLAB, von Kries, Reilly-Tanb, Nayatani, Labhun, CIELUV.

Wei Yuchang, Xu Mingjing et al. (1995) studied the color reproduction of the three color appearance modes under different ambient light and reference white settings. Originals and duplicates are output by a sublimation printer (D50 light source) and a CRT screen (D65 light source), respectively. As a result of the experiment, the performance of the three-mode average from good to bad is von Kries, CIELAB, and RLAB.

Luo Meijun (1995) studied the color reproduction of various color appearance patterns under different color temperatures. The original copy is displayed on the screen under the light box. The visual assessment results show that when the color temperature of the two observation environments is the same, XYZ, Hunt, and RLAB have the best direct conversion with XYZ three-excursion: when the two observation environments have different color temperatures, CIELAB, CIELUV, Hunt, Nayatani, and von Kries Of the eight modes of BRD, RLAB, BFD mode was the best on average, and CIELUV was the worst.

Hung (1995) believes that the general color appearance pattern experiment only studies the color reproduction accuracy of the corresponding color, and it cannot be seen whether the color appearance of the color appearance pattern really conforms to the human visual specification. If color/field gamut compression is used in image copying, the gamut-matched color may be visually color cast. Hung measured the hue accuracy of the four modes of CIELAB, CIELUV, Hunt, and Nayatani with 132 patches. The results of the study show that the first three have large errors in the blue hue. In the error performance of each hue, the four modes have advantages and disadvantages. On average, Hunt performs best, and CLELAB and CIELUV perform similarly. It must be emphasized here that as new models (Hunt, Nayatani, RLAB) continue to publish revised versions, it is necessary to pay attention to the “version” of the model used in the experiment when reading the “pattern comparison” literature. (Zhang Shizhao, 1999)

(E) Gamut Mapping Technology

Since different media devices (such as CRT screens, ink jet printers) each have different color representation ranges (color gamuts), it is difficult for users to duplicate the same image colors by these different color gamut media devices. In order to obtain the "visual" approximation of the same image on different media devices, it is necessary to use the "gamut mapping" technique to reduce the visual difference before and after image copying in the process of color reproduction. Hunt (1994) mentioned that there are seven basic forms of color space compression:

1. Preserve Chroma mode

Under the premise of keeping the hue constant, the difference in chroma before and after is as small as possible.

2. Constant Lightness mode

Under the premise of maintaining brightness and hue, the difference between before and after the chroma is minimized.

3. Equal Chromatography (Clipping)

The color within the color gamut is output as the original color, and the portion beyond the color gamut is replaced with the closest color.

Proportional compression mode

Under the premise of keeping the hue constant, based on the self-setting reference point (line), the color gamut is corresponding to a certain compression ratio.

5. Preserve Primary mode

Under the premise of keeping the hue constant, adjust the brightness and saturation so that the color difference before and after the six main colors (RGBCMYK) is as small as possible.

6. Differentiation mode adjustment

Taking the chroma compression as an example, the low chroma region does not compress, and the high chroma region does proportional compression.

7. Compression mode depending on image characteristics (Imahe Dependent)

Modes 1 to 6 are the "gamma-neutral" mode of "Image Independent" color mode, that is, regardless of the content of the image, a corresponding mode is used for color space compression. The compression mode “depending on the characteristics of the image” is based on the color gamut range of the image, and the color space compression is performed only on the portion where the image exceeds the copy color gamut. In fact, the modes corresponding to the color gamut are not only the above models. The seven basic modes can be mixed and used to create more complex and better color gamut counterparts. (Zhang Shizhao, 1999)