Digital proofing color management technology development

I. Introduction

Due to the development of digitalization around the world, the emergence of digital technologies, such as computer-to-plate (CTP) and computer-directed network (CTF) printing in the printing industry, has increased the demand for improved digital processes in the entire printing industry market to replace existing ones. Traditional production methods. The digital process involves a very wide range, among which the digital proofing is the most talked and concerned. The industry was initially skeptical of digital proofing, and it is gradually accepted and adopted today, with a transition period of several years in between. In theory, if the equipment is good, the stability of the digital proofing should not be in doubt. However, there are many factors influencing the digital proofing. So until now, what seems to be no longer unpredictable digital proofing has been repeatedly discussed and improved.

Second, is your digital type accurate?

â—† Digital proofer's sophisticated and ink system and proofing paper?

â—† proofing software calibration method and color space corresponding limit?

â—†Evaluation Key: Correct interpretation, color, dot shape, resolution, angle?

â—† measuring instruments and color management software?

â—† pre-press system manufacturers color knowledge background and color correction ability?

â—† Observing environment and conditions such as color (metamerism)?

â—† Analog printer characteristics and ink color gamut?

â—† different printing plants and different brands of ink?

â—†Printer?

â—†What is the standard color

â—† What are the international standards?

The questions listed above should be some of the problems that the general industry will have. Simply write it out. When doing digital proofing, the printer is a prerequisite. If the printer is not good, it is doing color management. A placement quality may not be ideal, relatively affect the color gamut, so of course we must choose a better printer, but the choice of some ink is not the same, for example, like we are playing special colors In the past, the ink should probably be different. Unlike the past, some of the inks we now popular, whether they are four colors or eight colors, are not the same, so the use of ink in different industries is selective, and many special Color is not printed on the printer, the only way is to change the ink. Again, the paper used, we have been talking about the paper determines the color, if the quality of the paper is not good in the performance of the color gamut or want to make the color performance more accurate can not be done, so there are three key points in this topic Must have a printer, a good ink system and a good color rendering paper.

There are color cores in the way of proofing software, whether CMM can achieve a perfect conversion, and the limit of the color gamut is very relevant to the paper used. It is better to use coated paper to produce better results. It is not good, this is the limit of the innate, what kind of paper to use to determine what color gamut, even with a good paper to simulate a relatively poor color gamut, in fact, can do it.

The correctness, color, dot shape, resolution, and angle of the RIP explanation are the same. The above points can be done with the current digital sample. The point of printing is very close to the point of printing. He can print more than the printing dot. solid. The accuracy of the instrument, the accuracy of the instrument and the calculation method of the color management, have previously been doing color management has been not good, not their own skill is not good, but the software and instruments are not good, so a good software is calculated it is more accurate, This is a problem with the instrument.

Observing environment and conditional color (metamerism). When you are doing color calibration, it is very important to observe the environment. When you watch under a non-standard light source, the colors you see are difficult to match. Conditional equal color, if the two colors have different spectral distributions (spectral reflectance curve, or spectral transmittance curve. This curve can be measured by the spectrometer), when under a certain lighting and observation conditions, two colors will It looks the same, but if the lighting and observation conditions are changed, the two colors will look different because they do not have the same tristimulus value. This phenomenon is called the conditional isochromatic phenomenon, or the same color. Different spectrum phenomenon. Different printers use different printing presses and inks, as well as the masters of printing companies, to print different effects. This is the most difficult problem to improve.

Third, the color correction criteria

Color scientist RWGHunt once said: People can feel more than 10 million different colors. We can't remember all colors completely, and that one is not surprised. If you can measure the color, you can control the color. In the early days, color analysis was used to analyze the quality of homework and math equations, and qualitative analysis of visual psychology was used to correct natural colors. The three elements of color production are the specific light source, the matching object, and the standard observer. The International Commission on Illumination CIE 1931 did a color matching experiment with a 2 degree angle of view based on the principle of color mixing. We quantified the reaction of the human eye to light. Three reaction curves were obtained for the red, green, and blue cell responses. We call this the 1931 Color Matching Function. In 1964, color matching experiments at 10 degrees were performed.

D50 is the standard illumination body of CIE, x-bar, y-bar, and z-bar are the color matching functions of the 1931 standard observer, respectively. The result of stimulating the light to the eye's quantification is to represent the tristimulus value as three data, respectively XYZ. To get X, just adding each of the wavelengths (D50 values ​​*x-bar* objects) to get X, Y and Z is the same algorithm. The tristimulus values ​​are then converted to horseshoe-shaped chromaticity coordinates x and y, while the chromaticity coordinates of the D50's standard light source are falling within the white horseshoe-shaped area. That is, the spectrum of the read color patch (380 nm to 730 nm) is converted to XYZ or Lab using the formula for convenience of calculation. According to different colors, it can be verified from here that when the observer does not change, and the reflected spectrum of the illuminated object does not change, but the light source changes, so the color data is also different. For example, when you use printed materials to look at customers, you should look at the bottom of a standard light source. If you don't use a standard light source, the color may not be the same, because the light source will not see the same color.
There are some instruments with software. It can be measured by the spectrum method. Finally, it is determined how much the standard light source is used. It may be 6500 color temperature. If you can know how many color temperatures the customer is, you can substitute this color temperature. The ICC profile made out there is more consistent. That is to say, what is the reflectivity of every ten nm, and when a spectrum is integrated, it can be converted into a color. The representations with CIE digitized colors are the tristimulus value (XYZ) and the color of CIE Lab. Spatial calculations. So the instrument will show the measured color data, which is consistent with what the eye sees. So when doing color measurement, the instrument is also calculated according to the person's way. If you use CIE Lab, because Lab is probably more difficult to understand, that is to say in the end what the color is, and then converted a color representation Lch, Lch then refers to the chroma, CHROMA, hue angle is how much, then you can use this one The color representation shows how this color is probably located.

The true meaning of the color data is the reflectance of the object, the CIE standard light source, and the human color matching function. Finally, the product of the equations yields a data XYZ. This site specializes in color correction, it can input a lot of spectrum, it can help you convert to RGB, Lab, Lch can be converted in various ways is no CMYK. For example, XYZ to convert RGB, Lab can convert RGB, color space and Lab how to use this formula, as long as the input data can be, so this pair is very easy to use in color calculations,