Prepress color management

For many printers and print customers, dissatisfaction with the color of commercial prints is the main reason for their loss. A company in the industry's leading mail order catalog estimates that 30% of returned items are due to customers' dissatisfaction with the product's color, because product colors are not consistent with what they see in the catalog. As more and more people begin to order products through the Internet, the problem quickly spreads to all areas related to visual communication. When the end result does not meet the customer's expectations, the printer always suffers complaints and complaints. The printer's job is to simulate the effect of the proofer on the press. When the color space of the two devices is different, the printer's job will be more difficult. The ideal step in the ideal case should be to commission the proofer (according to the printer) so that the proofs the customer sees and signs can be obtained from the press. Designers and image processors always use the monitor's screen as the main output device in their work to determine color. However, they may not know that the monitor can be arbitrarily debugged through internal settings and contrast/contrast controls. The scanning quality of the image changes with the scanning personnel, and the scanner will also create the parameters of the scanner according to the output device. However, if a printer goes down and the printer has to use another printer, the color of the image may be affected. The main solution is to use a set of color management solutions to help you achieve stable color. Light sources created in the workplace to create a control-condition scanner will age over time. The objective method is to set the operating parameters after calibrating all the equipment and establish routine multiple calibration steps. (The monitor may need to be recalibrated monthly, and the scanner's light source should be updated annually or processed according to manufacturer's instructions).

The first step: Everyone knows that human visual perception is affected by the surrounding environment. Light, the color of the walls, furniture, clothes, etc., all affect the colors we see on the display or printed sheets. Therefore, the first step in establishing a professional color management process should be to establish a neutral gray environment and standardize the light source. The ICC Association uses the D50 light source as a standard light source for the printing industry. Second, there should be a good understanding of the equipment in this color management process. Each device has its own parameters that change with time and temperature. For example, a laser printer needs to warm up before printing a steady color. Even changing the cartridge can affect the final output. As the display's cathode tube ages, the displayed color range will also change. Before the first step, we need to perform a color check to confirm the age and condition of each device and measure the light conditions in each studio. After summing up a report, the report should highlight the changes needed and outline the suitability of color management. Step 2: By describing the characteristics of the hardware, we can create a profile for each device during the creation process. That is, the process of creating an ICC profile for each device using a colorimeter or spectrophotometer is also color characterization. The created ICC profile must be managed to avoid operator confusion. In fact, the process of file management should be expanded to manage the new files created during the color matching process, clearly identifying each file. Successful color management also requires adequate training of operators and production personnel. This is the role of the core program. These profiles may be used at each stage of the flow to properly transmit colors.

Color management terminology

Both CIE LAB and CIE LCH are three-dimensional color spaces defined by the CIE Association (International Commission on Illumination) to describe colors that can be observed with respect to a reference white eye. The coordinates of the coordinates in the LAB color space are: L indicates the color brightness (or brightness relative to the reference white), A refers to the red-green value of the color, and B refers to the yellow-blue value of the color. LCH is another method of expressing colors using different terms in the LAB color space. The coordinates of each point are defined as: L represents the brightness of the color (or brightness relative to the reference white); C is the chromaticity of the color, The distance from the center L axis (or relative to the reference white saturation); H represents the hue of the color, and the size is the angle from the A axis. For color matching, this color space has certain advantages because the L, A, B, C, and H values ​​of each color can be independently changed. (Refer to Color Matching Method and Color Matching Type). The reference white of the CIE LAB color space refers to a standard light source condition and is usually defined as a standard light source. The International Commission on Illumination recommends the use of a D50 light source as a standard in the printing industry. The British printing industry has traditionally used a D65 light source as a standard. The ICC profile is a format defined by the International Color Council for describing the conversion of any color space (RGB, CMYK, YCC) and CIE LAB color space. Currently, different manufacturers have introduced a variety of software for generating ICC profiles for scanners, monitors, printers, proofers and printers.

Color gamut: The range of colors that a device can detect or duplicate. The color matching method (CMM) means that when a certain color does not belong to the specified color range of the output device, the CMM carries some kind of software, and the software can use the algorithm to find the closest matching color in the color gamut. Select a different color match type depending on whether the object is an image, an icon (LOGO), or a graphic.

Color management type

Color matching is a method used to protect icons or Pantone colors. When matching colors to the color gamut of the device, the color matching method (CMM) has the H (hue) value of the largest priority reserve color, and maps color points correspondingly to the device's color gamut space. Visual sensation or photorealistic matching is a matching method for photographic images. At this point, the CMM has the relationship between the maximum priority reserve colors, so the level and details of the image will not be lost. Saturation matching methods are used for matching graphics or illustrations. At this point, because the color saturation is the most important factor, the color value will have the highest priority. Absolute color matching is used to generate proofs. The CMM will use the output device's reference white to recalculate all color values. (For example, you can use the newspaper's color as a reference and simulate a newspaper offset press on the proofer).

In China, digital proofing has gained popularity in the gravure field. From the field of offset printing, the overall promotion of digital proofing is under way. Some people are still waiting to see, and many people and companies have already devoted themselves to digital proofing. At this stage, the popularity of digital proofing technology has been resisted by people's ideas. To promote digital proofing, to change people’s concepts while maintaining the quality of digital proofs, and to allow people to try is the primary task to be done; most people are only asking for it. The digital proofing is the only choice when it is particularly urgent and the cycle is particularly tight. In addition, traditional proofing is still used. Customers who are accustomed to looking at outlets can hardly accept digital proofing without branches in a short period of time; some customers still have doubts about the color of digital proofing and the actual printed matter, which is not consistent with the color proofing service providers. The standards are not unrelated.

Another point is that from proofing paper, because the digital proofing paper requires special paper, on the one hand increasing the cost of digital proofing, on the other hand affect the credibility of the proofs.