Study on Printing Quality of Different Properties of Paper by Ink Jet Printing (4)

Fourth, printing quality

Judging the standard of print quality, the judgment of print quality is controversial, because each person's acceptance of print quality is different, so when it is judged, personal color preferences or other psychological factors will influence the result, resulting in different views. Therefore, before discussing the printing quality, it is necessary to understand the characteristics of the printing quality that must be possessed in order to determine the quality of printing. (Zheng Maoti, 1998)

(I) The characteristics that should be taken into account when making print quality judgments:

1. Paper Formation
2. Evenness of Paper Thickness
3. Surface Strength
4. Surface Smoothness
5. Dimensional Stability
6. Brightness
7. Gloss
8. Opacity
9. Ink Receptivity
10. Dot Sharpe
11. Dot/Tone Rendition/Tone Gradation: Dot/Tone Reproduction/Tone Gradation
12. Print Gloss
13. Evenness of Optical Density

(B) Evaluation of Print Quality

When assessing the quality of prints, people are the most important judges of the eyes. Although the eye hates the keen observation of print influence and color difference, it cannot quantify and standardize it. Therefore, in order to evaluate print quality in a fair and objective manner, it is necessary to use quantitative instruments, microscopes, spectrographs, and other instruments to "quantify" the print quality, and then use this as a criterion for judgment. (Zheng Maoti, 1998)

Fifth, the color characteristics

In the color of a variety of media devices, the actuator can be divided into two types of regions, one representation genus color device colors (Device Dependent Color) using RGB, CMYK, etc.; the other is the use of CIE XYZ, LAB, LUV, etc. household device independent color represented by color (device independent color); so-called device dependent color space (e.g. MonitorScanner, digital Camera RGB space or a list of numbers and other machine, proofer, printer CMYK space, etc.), because each device has its Color characteristics, even if the media device of the same brand has different gamut color space, the device independent color space (such as CIEXYZ, CIE xyz, CIELAB, CIELVU, etc.) belongs to the CIE International Color Standards Institute. In the developed color coordinate system, the image color data data will not change the color coordinate data because of different devices. Because the characteristics of the device's independent color will not change due to changes in the device media, the system will change under the open system architecture. The use of device independent color technology to solve the problem of cross-media device color control. (Zhang Shizhao, 1999)

(I) Device Color Characterization (Characterization)

It is used to define the gamut range that the input device can recognize and the gamut range that the output device can copy. As a result, calibrated input or output devices can capture or copy images accordingly. The result of the device's color profile description is stored in the color profile. Therefore, the color profile is a digital data file used to describe the color characteristics of the media device; and the manufacturers of media devices and color management systems do not have uniform color profile specifications, resulting in the inability to implement color management. Therefore, the International Color Consortium (ICC) provides an industry standard format that manufacturers can follow. In the future, as long as the media device's color profile is in compliance with the ICC standard format, color management software such as Color Sync or ICM can be used to achieve color reproduction. (Gentile, 1995)

(B) Color Space Conversion

Based on the numerical data of the profile of each media device, the conversion of the image color data from the device-dependent color space to the device-independent color space color space conversion can be performed in four aspects. Evaluation: accuracy, calculation speed, memory size, and difficulty of calibration. The regression method and the internal difference method of the comparison table are empirical conversion methods. The common advantage is that it is applicable to various media devices. As long as the resolution is increased, the error can be reduced. The disadvantage is that it is not conducive to extrapolation calculations, the error in the low-resolution mode is large, and the high-resolution mode is slow. As for the advantages of the analytical model, it requires fewer data samples and inaccurate area errors. It is easy to calibrate, facilitates extrapolation calculations, and has a smoother print color. The disadvantage is that the design must be precise in design, and the application scope is more difficult than the bow. . (Viggiano, 1993)

(C) tone reproduction curve (Tone Reproduction Curve) adjustment

In the process of image data conversion, either the RGB or the device-independent LCH mode provides a design that adjusts the tone curve. The user can adjust the tone curve of a certain mode according to the characteristics of the imaging device. In the color reproduction curve, an S-shaped curve (Yule, 1967) can be used depending on the image characteristics:

If the original has the same density as the copy, the ideal tone reproduction curve has a slope equal to 1. However, in fact, the density range of the copy is mostly smaller than the original density range, so the shape of the curve must be adjusted in order to obtain a better copying effect. On average, normally normal images perform better with S-curve color reproduction (Todd, 1969).