Silk screen printing platemaking process (10)

The following describes the relationship between the color separation film and the color filter used as follows:

Huangyin Tablet - Blue-violet filter. The blue-purple filter passes blue-violet light, absorbing red and green light (adding yellow light). The yellow part of the original document is not sensitive on the photosensitive sheet. After developing and fixing, it is transparent on the negative film. This is the yellow separation shade film. After turning into the positive image, the opaque part of the plate is the yellow part of the original.

Magenta shade - with a green filter. The green filter passes through the green light, absorbing red light and blue-violet light (adding magenta light). The magenta part of the original document is not sensitive on the photosensitive sheet. After developing and fixing, it is transparent on the negative film. This is the magenta color separation negative film. After turning into the positive image, the opaque part of the film is the magenta part of the original.

Qingyin Tablets - with red filters. The red filter transmits red light and absorbs green light and blue-violet light (added to blue light). The cyan part of the original is not sensitive on the photosensitive sheet. After developing and fixing, it is transparent on the negative film. This is the green separation shade. The opaque portion on the base after turning into a positive image is the cyan portion of the original.

Black negative film - filter fixed. Available red, green two or red, green, blue filter, yellow filter or green filter, depending on the original situation. Its main purpose is to make various colors on the manuscript slept through a variety of filter colors and obtain sufficient density on the photosensitive sheet. The black part of the manuscript is transparent on the film, which is the black separation shade. The opaque portion of the original after turning it into a positive one, that is, the black portion on the original.

The role of the black version is mainly to enhance the screen pull difference and dark tone levels. Theoretically speaking, the three primary colors of yellow, magenta and cyan materials are mixed in different proportions to reflect various colors (including black). However, due to the limitations of various technical conditions, printing with the three primary colors is difficult to achieve the desired results and waste. Color ink, so the separation also need to add a black version of the separation of negative pictures.

When copying traditional Chinese paintings, it is particularly important that Chinese paintings are mainly ink-based and supplemented by color.

In addition, the use of black text printed on the black version of the screen is much more convenient than the tricolor overlay, and the quality is good.

3 screen color separation process. Separation is the decomposition of each primary color in the color of the original. Therefore, it is necessary to use complementary color separation of the primary colors. The yellow complementary color is a blue-violet color, the magenta complementary color is green, and the cyan complementary color is red. If the green filter is mounted on the lens and the original is produced, only the green light can pass through the light reflected from the original, and the other light is blocked by the filter. Therefore, the density of the captured negative film indicates the amount of green light distributed. The positive film density indicates the density as a complementary magenta color. Similarly, negatives filmed with a blue-violet-green mirror turned into a positive film exhibiting a cyan density.

When these colors are recombined to restore the original color, the chromaticity tends to be weak, and in particular, the black portion is incompletely displayed. Therefore, an auxiliary black plate is added. A yellow filter can be used to make a black plate, but this does not separate out a certain color, but rather reduces the overall tone. In addition to using the yellow filter for the black version, it is more difficult to make the black version with the aforementioned exposure method in which three kinds of color filters are overlapped together or with a filter of a specific color (see Figure 2-81). ).

The screening color separation process has the difference between indirect screening color separation and direct screening color separation.

There are many opportunities for revision of indirect screening and color separation. The effect is easy to control, but the operation is complicated and the level loss is serious. Therefore, it is rarely used. The process is roughly as follows:

Consecutive tone color manuscript → color separation (negative film) → revision → screen shot (mesh version)

The process of direct screen color separation is shown in Figure 2-82. It is a photoengraving method that completes screening while color separation. This process has a simple process, a short plate making time, and a high definition of reproduced images. However, it only obtains a half-tone negative film, and still requires a positive film to be used for screen printing.

4 electronic color separation plate introduction. Electronic color separation is performed on an electronic scanning color separation machine. The electronic scanning color separation machine adopts a scanning method to scan the original attached to the analysis roller point by point with a scanning spot of a few microns in diameter, and decomposes the original into a plurality of tiny pixels according to each pixel. The reflected light information, such as brightness, is converted into corresponding electrical information by means of a photomultiplier tube, and then input into the computer. The color and the gradation of the scanning pixels are corrected in turn using an analog computer, and the black plate calculation, background color removal, and subtlety are performed. Levels of emphasis, such as the calculation of tablet density calibration, etc., to achieve all the necessary processing in the plate making process, and then through the proportion of computers to complete the requirements of the original size scaling, and finally the electronic signal through the electro-optical conversion, and the original scanning point phase Correspondingly, the corrected optical signal is exposed on the recording film to obtain a corresponding color separation film.

The electronic color separation machine is an optical, mechanical, and electrical precision platemaking equipment. There are many models and differences in structure and function, but their basic composition is roughly the same. Can be divided into mechanical transmission systems (including drums, motors, etc.), optical systems (including light sources, color filters, reflective mirrors, glow tubes, light guides, etc.) and electronic circuit control systems (including computer circuits and operational controls Taiwan, etc.) The three main parts.