Author: Xie Tiesheng
Generally, the size of postage stamps is 30mm × 40mm, the scanning input accuracy is 400dpi, the phototypesetting accuracy is 4000dpi, and the output is 300 lines / inch. It is required to show extremely rich gradations and infinitely varied colors in a very small range. Stamp paper (90g / m2) is far less expressive than high-end album paper (157g / m2), so the field density and dot increase rate required for proofing must be stable so that the correct proofs can be seen during the adjustment and the adjustment should be minimized The number of image data files can achieve the purpose of restoring the original.
Proofing data management
Offset proofing, gravure proofing and digital proofing must be carried out in strict accordance with the requirements of color management, so that the provided proofs have reference value and serve as the basis for scanning, adjustment, retouching, editing and final approval. Table 1 shows the contents that should be included in the digital management of offset proofing, gravure proofing and digital proofing.
Table 1 Data management contents of offset proofing, gravure proofing and digital proofing
Proofer model plate paper type ink brand proofing blanket plate temperature plate pressure test strip plate printing machine model light source vacuum extraction exposure time development time development temperature 2% 25% 50% 75% 95% YMCK 75% 2 % 50% 95% density / increasing rate Gravure printing machine model solvent paper type ink brand proofing data version roller specifications printing pressure doctor blade electric carving machine model light source electric carving C, M, Y, K data electric carving needle model electric carving needle angle 2% 25% 50% 75% 95% YMCK 75% 2% 50% 95% density / increasing rate Digital proofer resolution Zhang Zhang type ink brand nozzle diameter proofing software proofing speed digital proofer C, M, Y, K data INK ICC profile PAPER ICC profile 2% 25% 50% 75% 95% YMYK 75% 2% 50% 95% density / increasing rateBasic essentials
Faithful to the original is the basic principle that should be followed when scanning and lengthening. Foreign image files must be digitally sampled, and then the data of the image file must be adjusted. After repeated adjustment and confirmation, the image is retouched. For fine levels, transitional colors, Brush strokes and thin lines are trimmed in more detail. Picture adjustment is a comprehensive examination of personal qualities, which requires the operator not only to have a correct understanding and judgment of the input, but also to give a correct understanding of the output from the perspective of printing technology, as shown in Figure 1.
1. Ideas and techniques for adjusting pictures
The idea of ​​adjusting the image should start from the overall situation. The method of adjusting the image is shown in Figure 2, as follows.
(1) Start with gradation and gradation. The gradation should not be too strong. The richer the gradation, the better. Consider the limited size of stamps, rationally distribute the proportions of light tones, middle tones and dark tones, and the printing suitability of the paper.
(2) In order to make the color closer to the original, it can be achieved by reducing the saturation and making the color old.
(3) The performance of ink and stamp paper restricts the complete restoration of the original. Therefore, the use of spot color ink is common in the stamp printing process, and some areas can only adopt the method of selecting areas, and even need to separate multiple layers.
(4) The use of digital proofing helps reduce costs, shorten production cycles, and increase production efficiency.
Gravure printing and offset printing are two very different processes. The dot value (recommended value) of bright and dark tone is completely different. The basis weight of paper (90 ~ 250g / m2), coating, fiber (stamp paper, recycled postage card paper, The quality of postage seals, offset stamp paper), the type of ink, the state of the printing press, the printing color sequence, the use of postage products, the flexible matching of spot color inks (anti-counterfeiting colorless fluorescent ink, gold ink, silver ink, brown ink, (Beige ink and gray ink) are also different. Unusual changes of these factors (the root cause of rework) will interfere with the correctness of the adjustment. Therefore, the above procedures must be managed digitally.
Photoshop image processing software is a commonly used image adjustment tool. The various functions are endless. Menus such as "Edit", "Image", "Layer", and "Select" can be used in combination. The production process is improved and the technical level of the image adjustment personnel closely related.
2. Adjustment steps
The steps to adjust the image using Photoshop software are as follows.
(1) Analyze the acceptance criteria of the construction order and read the workshop production process plan.
(2) Determine the maximum density of the spot color version (refer to the spot color patch or experience value) and the dot value, spot color selection, and the tone between spot colors.
(3) Arrange the electronic files provided by the customer, create a folder for image adjustment and backup, select the PSD or TIFF format as needed, and use layers and selections (in order to maximize the level of expansion) need to know the image repair personnel. Analyze the electronic files, inkjet samples and manuscripts provided by customers, and start to adjust the picture in combination with the actual printing conditions.
(4) The printing of stamps requires the reproduction of the richest possible levels of graphics and text within a limited size, and the true reproduction of the three primary colors and spot colors. The lines, brushstrokes, and subtle levels also need to cooperate with the retouching personnel.
Gravure printing and offset printing are completely different due to the difference in paper, ink, plate material and printing equipment. In general, stamp printing is different from high-end and exquisite albums. The contrast and texture are emphasized when making high-end and exquisite albums. The tone curve of stamp copy is relatively smooth, the black tone is very long, and spot colors are often used.
Thoughts and methods of retouching pictures
The stamp production process can be roughly divided into two stages. The former stage includes electrical distribution, adjustment and retouching, and the latter stage includes proofing and printing. Among them, the proportion of retouching can be large or small, but it does play a finishing touch. . The steps for retouching are as follows.
(1) Analyze the acceptance criteria of the construction order and read the workshop production plan.
(2) Comprehend the thoughts and methods of adjusting pictures.
(3) Make clear the relationship between layers, selections and spot color channels.
(4) Correctly understand the structure of the picture, the relationship between light and dark, color ratio and creative ideas.
(5) Within the limited size, the richer the graphic layers, the better. The three primary colors and spot colors must be reproduced realistically. The lines, strokes, and subtle levels need to be carefully digged, dug, painted, drawn, hooked, painted, and combined with Photoshop Flexible use of various functions.
(6) Make anti-counterfeit spot color version, and make large version according to the production and construction order.
Retouching is a very flexible job. Retouchers must be able to use various software (including anti-counterfeiting software and spot color separation software) proficiently, have certain common sense of art, understand the printing process and printing suitability, and understand the adjustment. The idea of ​​the picture is to accurately grasp the creativity of the stamp.
Adjusting and retouching pictures is a "soft" work, and it must be implemented in a standardized environment, but it must be brought into play and created, and small stamps are also a great place to display talent!
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