Prepress process knowledge 1

Section I: Photographic platemaking process I. Photographic platemaking process photolithography process.
(1) Device original. The original to be produced is set to the center of the large document holder.
(2) Magnification settings. According to the copying requirement, the original zoom ratio is calculated and set on the camera.
(3) The light. Install frosted glass on the photographic plate, turn on the power, focus on the frosted glass with the maximum aperture, find the clearest image of the original, and make the original size correct and centered.
The adjustment of the focal length and the object distance in the light is performed according to the lens formula, that is, after the light is finished, the light is turned off, the aperture is adjusted, and the lens cap is closed. Thin line drawings and texts often use a 1:9 aperture.
(4) Exposure. Select high-contrast photosensitive film, the photosensitive film surface facing the lens into the photosensitive plate, open the light source, open the lens cover, exposure.
(5) The exposure time is proportional to the distance between the magnification of the original and the light distance, and inversely proportional to the size of the aperture and the angle of the light. In addition, it is necessary to master the characteristics of the original document.
(6) Development.
(7) Fixing.
Second, the production of monochrome line draft Yang. Photo negatives (negative images) must be remade or copied. Make it the same positive image as the original image (positive image) to meet the plate-making requirements.
(1) Photocopying method. The photographed negative is used as a transmissive original, and the device is placed on the original holder of the camera. If the positive figure is used for printing, the photosensitive emulsion should be placed facing away from the lens. After exposure, development, and fixing, positive images for printing plates can be obtained.
(2) Copying method: The original negative image emulsion made by photography is placed on a copy glass plate face up, and when the copy is made, the emulsion of the photosensitive film is faced downwards relative to the negative emulsion surface, followed by suction close-up, exposure, and development. Fixing, you can get a positive picture for printing.
Third, monotone continual transfer of the original photo-making process. For the continuous adjustment of the original to be screen processing, the continuous transfer image into a network of images, for monochrome manuscripts, can be screen plus screen (see figure), but also for copy screening. The photographic screening is to place the screen before the photosensitive film; the copy screening is to place the contact screen between the photosensitive material and the continuous tone chart for copying.
Section II: Photo separation process for color continuous-tone originals Photo-engraving for color continuous-tone originals has two processes, indirect color screening and direct screen color separation.
First, indirect screening color separation process. Indirect screening refers to separation and screening for platemaking processes, as shown in the figure.
(1) Photographic plate making process of color separation plus positive image. First of all, add a color filter in front of the camera's lens, use a full-color photo film to separate color, make a color separation Yin picture. To make a color separation picture, use the following color filter:
Yellow Edition: Blue filter.
Magenta version: with a green filter.
Cyan version: Use red filters.
Black version: Yellow filter or segmented exposure with red, green and blue filters. Which method is used depends on the hue of the original.
The color separation shading film was modified and installed on the original document holder of the camera, and on the screen frame of the camera, the glass screen was installed, and the positive photosensitive film was used to make the positive image of the screen. FIG. Copy screening can also be performed.
The screen angles of the positive screens for various colors are generally:
Yellow Edition: 90°=0°
Magenta version (small blue version): 15°=105°
Qing plate (red version): 75°=165°
Black Edition (gray): 45°=135°
(2) Separation and photogravure. Photographic plate making process. The production of color separation and screen negatives adopts the same color filter and network line angle as the color separation plus network positive image. Only after the continuous tone chart is made of the original, it is first converted into a continuous positive adjustment chart. After the correction, the screen is screened again to obtain the color separation screen (see the figure). There are many opportunities for correcting the indirect screening color separation method, and the plate making effect is easy to control, but the operation is more complicated. Due to the large number of photographs or the number of copies, the definition of the image may be affected to varying degrees. (to be continued)