Color and Proofing (6)

Print contrast is an objective feature related to the compensation of shadow details in the process. This value is affected by the solid density of the ink, the brightness of the substrate, the density value of the 75% shaded area, and the gloss. Absolute values ​​or tolerances cannot be defined here. Print contrast is very important for copy quality and is a very useful parameter in copying.

The print contrast can be calculated by the following formula (CGATS.4):

% Printing contrast = (Ds-DT)/Ds font-family: Song Ti; mso-bidi-font-family: "Times New Roman"; mso-font-kerning: 1.0pt;
Mso-ansi-language:EN-US;mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA">×100%

Here:

Ds = primary filter density in the field.

DT = 75% shade primary filter density.

The print contrast should be between the following parameter ranges:

Satisfying or exceeding the minimum percentage of each color is important to obtain a proper printing contrast, and the highest value can also not exceed the upper limit. Excessive printing contrast indicates that halftone dot sharpening is not normal during the process of negative-drawing, which will lead to excessive loss of high-light color tone dots.

Color proofs and seals

The number of proofs and color proofs is often defined by individual publishers.

The following materials are necessary for providing offset proofs for rotary offset printing: a. cyan; b. coloring; c. yellow; d. black; e. combination of yellow coloring; f. four color proofs. (Other printers and customers may need more sophisticated proofs, especially for more thorough evaluation of proofs, but the specified proofs are sufficient for rotary printers.)

The cover of the color separation proof should indicate the name, address, and telephone number of the prepress service provider and, if possible, the name of the contact person if there is a problem. In addition, the date of proofing and the type of press used for proofing (1/c, 2/c, 4/c, etc.) should also be shown.

It is not possible to classify color proof sheets by color patch areas because it is very difficult to measure the color scales with a densitometer. Color proofs and seals can be classified according to the opposite color standard.

change

If the colorimetric values ​​on the four-color film change, it is important to provide new proofs and separation proofs to ensure the best reproduction quality. For some minor changes, if there is no time to re-proof the sample, pay attention to the changes that have occurred on all monochrome and four-color proofs. This also applies to two-color and monochrome ads.

Positioning register

All dichroic proofs and finished proofs for four- and two-color printing must be accurately positioned. During the operation of the printing press, inaccurate positioning of the material will have a great influence on the printing quality.

Color change

All proofs and proofs should be matched to each other and consistent in density, dot gain, and balance.

Pre-proofing

Pre-proofing of traditional (from film)

Most of the publishing process uses pre-proofing instead of machine samples. The pre proofs used in this case must be visually matched to the model produced by the SWOP specification. One way to achieve this is through the use of the SWOP calibration toolkit, which is available through GATF.

SWOP has developed a calibration kit for validating pre-proofing products. The kit contains a set of separation film, calibration machine, and an instruction manual.

Users of pre-proofing materials should note that the manufacturers of these products will specify the density and dot gain points, printing sequence, and substrate that should be used. Since the imaging parameters of each individual pre-proofing system will be different, the density and dot gain may also be different from the SWOP. Users of pre- proofs should also note that because of the different optical parameters of each pre- proofing system, the tonal range of printed proofs may also be different. The quarter tones may be too dark, and the shadow area may be more open and so on. These may affect the visual matching of these areas on the pre- proofs and presses.

The preview should contain control images recommended by the manufacturer. The "Guide to Control" should include solids, overprints, and appropriate colorimetric values, as those contained in printed ink proofs.

The application data sheet for the pre-proofing system can be obtained through SWOP.

Digital Direct Proofing (DDCP)

In prepress operations, using electronic files instead of film requires the use of the DDCP system, which can generate images directly from digital data. Some of these systems will translate it into halftone dots. Other systems use different CT or error diffusion techniques to copy proofs to match the color and tone of the final print.




Source: Bison