Link between Processes and Image Quality (2)

Second, the importance of color proofing and proofing process calibration

1. The importance of color proofing. Color proofing is one of the most important quality control tools and it occupies a very important position in printing.

Printing a proof on a printing press takes a lot of time and money. It takes the consumption of film, printing plate, and printing to see how the printing effect of a color separation film is a costly move. If you are not satisfied with the printed product, It will have to remake the separations. In addition, when the printer is operating on the press, it is wrong for the printer not to have a template. It is like building a house without drawings. Therefore, the purpose of color proofing is to check whether the dichroic sheets are correct and to check and predict the results that can be obtained before printing.

Color proofing is the simulation of what prints a color separation sheet will print.

This simulation must accurately represent the visual effects of the final print, not necessarily the exact correspondence of the film's Web site. It should indicate that the dots that will be produced in the printing will increase. The accuracy of proofing must ensure that accurate proofs can be produced if the proofing method used is stable and controllable.

Proofing has many uses. First, after the proofing process, the color separation process was challenged. The film provided by the color separation personnel could not immediately say "qualified" without proofing.

The stage of making the mesh adjustment film is essentially completing a color approximation process, and at least the color separation film produced can be printed and proofed. At this stage, less accurate proofing can be used, such as pre-proofing methods such as sublimation proofing.

In the final stage, mechanical proofing can be used, which is an accurate simulation of the printing method. It shows that the printing method can reproduce images like proofs, which is what customers expect to achieve.

In the case of multi-image imposition, it is sometimes necessary to check whether the imposition elements are complete, and whether positioning and registration are accurate through proofing. This kind of proofing is not usually for evaluating the accuracy of color reproduction.

2. The type of color proofing. Proofing is usually divided into soft proofing and hard proofing. Hard proofing is a practical sample that is easy to carry and transfer. Hard proofing can be made with paper or ink on a proofing machine, or it can be a pre proofing but it is made using a color separation sheet. There are different types of hard proofs, some are laminated films, some are single sheets, and some are glazing to simulate the gloss of printed products. The page imposition system can use stored data to produce so-called direct digital hard proofs by photo exposure. This proofing can be dot image or dotless.

Soft proofing is video display proofing to evaluate the data associated with the manuscript. People often call it a quick inspection method and have multiple uses. For example: used to quickly evaluate the results of the separation machine adjustment; evaluation of the image modified by the color system; check the imposition of several images or check the provided film images; also used to adjust the color separation and consistency control.

Mechanical proofing. Mechanical proofing is the use of paper, ink on the proofer to print the actual proofs, if the proofing of the paper, ink and the actual printing is different, then the proofs and the printing effect is inconsistent; proofer structure and the press is also an impact The parameter, a sheet-fed proofing machine may be different from the printing effect of the web printing machine, a monochrome proofer may not match the effect of the four-color printing machine. In spite of this, mechanical proofing is still an effective proofing method, which can simulate the printing effect of the printing press in the most approximate way. One of the important advances in color proofing is the application of special proofers. This type of proofing machine can make the proofing speed faster. Currently, common platform proofers and rapid transfer rotary machines are such models. Four-color sheetfed printing presses are often used to simulate the effects of web printing presses, but their dot gains are smaller than web printing presses, and they consume a lot of time. There are also costs for making and making plates.

Pre-proofing. In the 1960s, pre-proofing became popular. 3M's invention of the Color-Key color film overlay proofing is representative, but not all people can evaluate the color separation sheet based on this sample and make judgments about the final printed sheet. This proofing is to use a color separation film to perform exposure and development of each color film, and then sequentially stack and register on a sheet of paper to obtain a color proof sample.

DuPont invented the sheet-fed Cro-Mag-Polline toner proofing method; 3M introduced their Transfer-Key and Matchptimmt single-color proofing methods. There are many proofing systems on the market, but 3M's Matchprint and DuPont's Cromalin system are effective systems that deliver high quality color information standards.

The industry continues to search for faster, economical color proofing systems. Separators make color separations within 15 minutes, but the time spent on making hard proofs must be doubled. If you add time for evaluating proofing, This will greatly slow down the production process. If the separation results are unqualified, then the time will have to be further extended.

Photo color proofing. This method of proofing was reintroduced in 1986. It exposes the photographic paper with a colored gloss halftone and then develops in an automatic processor. This system has a programmed exposure module that can complete the exposure process within 5 minutes. When the first proofing is processed in the processor, the second proof is exposed. This system has advantages in newspaper printing proofing.

Soft proofing. Since Saturn introduced the first page typesetting system, soft proofing has begun to enter the application. This kind of system can observe the simulated print image on a color display. After the separation machine scans the original, the color separation information is recorded on the magnetic disk, and The disk is connected to a color video monitor. Sai Angel system can do standard scan, observe and store image files. If you are not satisfied with the separation can be corrected. The color display device produced by the color separation machine manufacturer's video display allows the color separation personnel to check the adjustment condition with a quick low-resolution scan. If the adjustment is correct, the color separation machine is adjusted to the standard grouping force so that all images can be recorded. Details; if you are not satisfied with the adjustment, you can change the adjustment and redo the scan. Using this proofing method, the waste of the film can be avoided, but in most cases, hard proofing is also required to use a color separation sheet.
Kodak developed a pre-observed electronic image network system. This system has at least two video displays with modems. This allows the operator to transmit the pre-proofing image to the customer's video display. The customer and the operator can talk to each other to decide whether to make some changes in the image, even if There is no difficulty in a long distance. Obviously, this is meaningful for saving production time, saving proofing materials and reducing costs.
In the 1990s, the color desktop publishing system developed rapidly, and the WYSIWYG mode of operation made the soft proofing method a standard function of the color desktop system.

Observing the soft-proofing image requires skill, because from the observed image to the imprinted image can only be transmitted in the brain of a person; the phosphor of the display cannot be completely matched with the printing ink; there is a difference between the soft proofing and the hard proofing illumination; The resolution of the display is obviously lower than that of the printing method. The video display has only 512 or 1024 pixels per line, and the vertical resolution is about the same, which often makes detail evaluation difficult.

Direct digital hard proofing. It is generated directly from the pixels stored in the imposition system, and a color matrix printer produces color hard proofs. The resulting proofs have very low resolution and the color quality does not match the print, but it can explain the correctness of the image file. To see the effect of a printed halftone, simulate a photocopy of a color photograph on Hull's proofing recorder.