Digital proof color reproduction

For the evaluation of digital proof color reproducibility, apart from relying on human visual and experience for subjective evaluation, it is more important to use a spectrophotometer for objective evaluation.

1. Subjective evaluation of color reproducibility. The subjective evaluation of color reproducibility mainly refers to the subjective evaluation method based on color perception. Color perception is an electromagnetic wave emitted by a visual object (or reflected, transmitted) at a wavelength of 300-700 nm, which produces a physical psychological stimulus in the human brain's central nervous system. The factors that affect color perception are the observation light source, the observation environment, the observer, and the color observation mode.

1 Influence of illumination source on color perception. Due to the different spectral distribution of different illumination sources, the same color perception effect cannot be obtained even with the same observation object. In addition, when a certain light source illuminates two objects with the same color perception, the color perception will also change when the irradiation light source is changed, which is due to the phenomenon that the object has different spectroscopic reflectance of light.

2 Observe the influence of the environment on color perception. Color perception is also affected by the surrounding environment in which the visual object is located. When several colors are placed in the same space to observe, the feeling of color vision is different from that observed by placing them alone, and the color senses the complementary colors of adjacent objects.

3 Observers' influence on color perception. If the observer's visual system characteristics are different. Color perception also produces differences.

4 The effect of color observation mode on color perception. When observing colors, some experience color expressions are called color observation modes. Such as surface color and light source color observation mode. The surface color refers to the perceived color obtained by observing the surface of an object. The color represented by printed matter is the surface color; the light source color refers to the perceived color obtained by observing the luminous object itself. The color that CRT shows is light source color. The same visual object, in different color observation modes, the same color perception will produce differences.

If the control of all factors affecting the perception of color is consistent, the consistency of the color vision value and the color measurement value can be obtained. But in fact. This is impossible to achieve because the observed values ​​are also related to the local environment around them. Therefore, the contrast effects obtained are also different. At this time, it is difficult to achieve the consistency of the color vision values ​​and the color measurement values. It can be said that this subjective evaluation method is not reliable.

2. Objective evaluation of color reproducibility. In general, the objective evaluation of color reproducibility uses an objective evaluation method based on the chromaticity value, that is, the use of spectrophotometer to objectively evaluate the color reproducibility, mainly the color of digital proofs and printing proofs after matching the printing color scale. The measured values ​​are compared to compare the color difference between the two, and the number of colors allowed for the color difference is controlled within the specified range. If the user product type is complex, multiple different types of control parameters can be established to solve. The specific method is: using a spectrophotometer to measure the surface color of the sample, and obtain the tristimulus values ​​X, Y, and 2 in the ClEXYZ color system, or the chromaticity coordinates in the CIEL*a*b* color system. *, b* and lightness value L*. The color difference between the reproduced color and the standard draft is calculated using the formula: CIEl976L*a*b* color difference: 厶E:[(厶L)2 厶a)2 十(Ab)2]1/2 , although the color measurement value cannot replace the color sensation value. However, it can still be used as an industry standard. In a certain sense, there is a certain relationship between the color vision value and the color measurement value.

The relationship between color difference and visual perception is: When AE ≤ 1, almost no color difference is perceived; when AE is greater than 6. Strong sense of color difference. Based on the above objective evaluation methods of colorimetric values, we can establish an absolute comparison standard for color reproduction, and measure the degree of difference between the two colors in terms of absolute values, providing a reference for comprehensive evaluation of color reproduction. This method can better evaluate digital proof reproducibility to meet the color matching between proofing and printing.