Prepress process knowledge 2

(3) Manual revision. Photographic plates are often used to manually modify the method to enhance or reduce the density of negative and positive images, respectively, with black ink coating and corrosion method to complete. This is a remedial process in photolithography. Taking the revision of the color separation negative image as an example, the effect of coating the black ink is to increase the density of the opposite color portion on the color separation negative image, that is, the color amount of this portion is reduced in accordance with the original document in various degrees, and the converse is increased. The proportion of the basic color, in order to obtain the balance with the basic color system tone.
The erosion of the negative image is just the opposite of applying the black ink, that is, increasing the density of the basic color portion on the negative image, and objectively playing a role of relatively reducing the proportion of the opposite color. The main components of the etching solution used for correction of the film are red blood and soda, and the corrosion principle is:
Second, direct screening color separation method (hanging process). Direct Screening is a platemaking process in which screens are screened at the same time as color separation through contact screens or glass screens. as the picture shows. The direct screen color separation method reduces the number of photographs, shortens the plate making time, and improves the sharpness of the image. However, the level reproduction step is indirect and indirect, especially the dark tone adjustment.
(1) Mask production. The masks used in direct color separation and screening are mostly colored masks, which can both correct the color and correct the level. After it is mounted on the camera, the color separation does not need to be replaced, and it is easy to register. The production of the mask is shown in the figure, and the color is used as an example. The main production process is shown in the figure.
(2) The original and the color cover are placed on the transmissive original holder of the camera, a color filter is installed in front of the light source, and the photosensitive film and the touch screen are arranged on the image forming surface. As shown in the figure, the image is developed and fixed by the exposure, that is, Score color plus net negative film.
(3) Direct-screen color separation requires the use of a high-magnification, short-focus zoom lens such as EL-NIKKON. The number of screen lines depends on the printing conditions and the paper used, typically 150 lines/inch or 175/inch. For cable angles, the most prominent color version is generally set to 45°, and the other two color versions are different from each other by 30°. The inconspicuous yellow plate angle can be inserted between these angles by 15°. For example: Black Edition: 15 °, Magenta version: 45°, Cyan version: 75°, Yellow version: 30° or 90°, Black version: 15°, Magenta version: 75°, Cyan version: 45°. Yellow Edition: 30° or 90°;
Kodak's color filters are often used for color filters. In addition, the laminated film and mask should be punched so as to register with the positioning pin.
(4) Auxiliary exposure. In order to obtain all shaded halftone dot negatives, in addition to performing exposure through the screen to establish the basic reproduction of the original layer, auxiliary exposure is also required.
1, flash exposure. Through the screen, but not through the lens, give a slight and even full-scale exposure. You can make up the minimum point in the dark tone to extend the dark tone of the halftone tone to the midtone tone.
2, high light exposure. After the main exposure and flash exposure are completed, the screen is removed, and as with the main exposure, the light is exposed through the lens to expose the original, and the exposure amount is only 2-6% of the main exposure to improve the highlight contrast of the original.
(5) Back color removal in the direct color separation screening process. For a high-contrast natural color original, a special hard full-color film can be used to produce a base color removal mask using a contact exposure method. The density of the solid portion corresponding to the original on the under color removal mask is higher.
After the main exposure is completed by direct color separation screening, the natural color mask and the color correction mask are removed from the document holder, the mask is removed by the background color removal, and the trace exposure is performed through the mask to remove the mask pair with the background color. The dark part of the flash exposure, to control the dark part of the network.
Section 2 Electronic Separation Process Electronic Separation is the process of decomposing colored originals into monochrome versions using electronic scanning.
Electronic color separation machine referred to as electric extension. It is a device that decomposes color originals into monochrome versions using electronic scanning separation. Is a combination of optical, mechanical, electronic technology and computer precision plate making equipment. The color separation of the manuscript is performed by using the original scanning drum and the film cylinder to make a circle rotation, and the scanning head and the recording head make a horizontal movement, and the principle of mechanical point by point scanning and exposure is realized.
The color separation of the electronic color separation machine is different from that of the photoengraving process, but it is performed on a point-by-point basis. Therefore, to understand the principle of the electronic color separation machine, it is important to transfer the image information at a certain point on the original document to the photosensitive sheet. The process to understand the principle of electronic color separation machine. The image information of a certain point on the basic manuscript of the electronic color separation machine is transmitted to the photosensitive sheet to understand the principle of the electronic color separation machine. (to be continued)