Contact copy and proofing
Contact copy control
When copying the film, the halftone dot size change cannot exceed ±2% compared to the original. Before each run, it must be tested on a regular basis. It is best to copy the original exposure control screed (eg, UGRA scale) in the same way as the copy material.
Use a properly calibrated transmission densitometer to record the actual value of the original exposure scale and the copied exposure scale. The two sets of values ​​and the transmission densitometer, spectral response, and other relevant information submitted to the receiving contact copy device, such as the positive color film, UV and Type1.
Proofing process
The term proofing is used to describe the inspection of operations during the printing process. In the pre-press and printing sectors, the role of proofs is to verify content and color, process control, quality control, and confirm the changes made. The method and requirements for proofing depend on different stages of production and customer expectations. There are several proofing programs that differ in quality, complexity, and price.
Samples can be categorized according to three methods:
Sample image source
1. Acquire analog proofs from the film using a UV light source (UV).
2. With laser printing, inkjet printing and other technologies, digital proofs can be obtained directly from documents.
Sample form
Use physical materials to output hard copy proofs, including:
A: The printer proofs were printed using printing plates using paper and ink.
B: Off-line proofs, sometimes referred to as "pre-press proofs," are obtained by exposing photosensitive materials to color separation films.
C: Digitized hard-copy proofs. The proofs were used not in film but directly in image files.
D: Soft proofs are the images displayed on the screen or on the terminal.
The term "proofs" contains many features, including:
"Content proofs" or "Target proofs" are used to check image content, color bursts, and content positioning (not used to see exact matches of colors).
"Contract or final proofs" is used to check the final color and the positioning of all elements.
1. It is usually produced using final film or final digitized files. The final proofs are sometimes called "color OK proofs."
2. The final proofs represent the final style of the qualified prints, including color, reproduction of tonalities, substrates, layout, location of each ingredient, graphic content, and so on.
3. The purpose of creating the final proofs is to predict the printing effect of the supplied film and documents, and all final proofs (analog or digital) must conform to the SNAP stipulated printing press sheets.
Understand "proofing"
A: All types of proofs - analog and digital, hard or soft proofing, content or final, are useful tools for evaluating print quality and image quality. Each type of proof has its own characteristics, advantages and limitations.
B: Samples that a customer or a market segment believes to be proofs of content may be seen by other customers or the market as final proofs.
C: The sample classification described above is used to promote communication and understanding. Process requirements and customer expectations determine the selection of proofing methods.
SNAP proofs requirements
Dividing proofs into four types is very beneficial: content proofs, final proofs, press proofs, and off-line proofs.
Content proofs
In order to provide printers or newspapers with full and complete information, content proofs must include the following information:
If necessary, make the proofs tiled and fit the actual size. Stick the tiled proofs to reproduce the complete image. If the actual size cannot be used, the proof should be reduced or enlarged.
The proofs have markings for cutting, folding and register positioning.
Verify that the proofs are for For-Position-Only (FPO) or calibration images only.
Confirm the elemental composition of the color page, is the fifth color, spot color, or the mixed color of CMYK, and how the proportion of each primary color.
If the image in the print is colored, a color proof is made. Color proofs can provide helpful information on color mutations and potential trapping problems, and can also clearly indicate whether the image is black and white or color.
Samples are marked with the customer's name, sample name and time, the name and telephone number of the proof, and all the style information.
Clearly mark all FPO (for positioning only) image files, including photos and special effects. Sample submissions submitted with digital files should include high-resolution scans of these photos, or original photos.
Final proofs
Final proofs of cold-set printing should be as close as possible to the final print. The final proofs accurately simulate the final printing effect in the following aspects:
Final layout
Substrate characteristics
Ink color/color range
Tone copy
The surface appearance of the graphic area
Qualified register positioning
Ability to recognize originals and production dates
Standard color scale near graphic area
Printer proofs
The ink density of the printer proofs must meet the SNAP specifications. Control and monitor sample dot gain/TVI (tonality increase) for maximum stability. Because of the variety of uncoated wood pulp papers used in the cold-fix printing industry, these papers vary widely in color, brightness, and transparency, so it is not possible to specify standard proofing materials. If print proofs are required, the proofing person must determine the parameters of the sheet and proof on the same substrate or material with similar properties. The ink sequence of the printing proof must meet the production specifications of the printing shop. The color scale should include solid, 25%, 50%, 75% dots for each color, two colors of overprint, three colors of gray blocks (40% cyan, 30% magenta, 30% yellow) from NAA , GATF, RIT and other organizations have obtained such color control proofs.
Offline proofs
There are many prepress color proofing systems on the market, including digital or analog methods (overprint or sheet). In order to simulate the final print and meet the above mentioned rules, the production of such proofs must be based on the recommendation of the manufacturer of the proofing machine. The exposure structure of the simulation proofing system must have a suitable light source, so the manufacturer's recommended parameters for the bulb and exposure time must be strictly observed. At the same time, suitable calibration and monitoring are required. Although all analog proofing systems have similarities, each system has its own characteristics and process requirements. Have any questions direct to the manufacturer.
Most digital proofers are equipped with color management systems, so the user selects the appropriate features in combination with the SNAP parameters. The RIP file used for digital proofs should be the same as the RIP file used for the final film or plate. This type of proof is often used to view content and positioning. SNAP highly recommends testing digital proofs for accuracy and stability.
The proofing program in the digital workflow is still an unresolved challenge. At present, the digitalization and simulation processes exist side by side and are used in many cases at the same time. Due to emerging emerging technologies, this field is also rapidly changing.
Vacuum exposure points
â–² Use a non-dusting cleaner and a lint-free cloth to scrub the glass table. The clean glass table reduces light absorption, refraction, and image artifacts.
â–² To ensure the cleanliness of the vacuum pump, there is no air leakage from the vacuumed film.
â–² Use a dark gray or black pad to prevent distortion. Ensure surface consistency and flatness.
â–² Check the overall seal around the gasket.
â–² Ensure that the lighting distance is appropriate, not only can cover the printed format (even under lighting conditions), but also suitable for practical lighting operations. The difference between the gray scale of the image center and the most likely image edge (level 21, from Stouffer, RIT, GATF, UGRA) cannot be greater than 1. Know the lower exposure to the edge. Determine the uniformity of exposure.
â–² Always change bulbs because their spectral output changes as they age. A lamp's efficacy drops by about 20% after its life cycle. Strictly abide by the manufacturer's replacement arrangements.
â–² The same printing method duplicates the original exposure control bar (Stouffer, RIT, GATF, UGRA). Test every day. There may be a maximum 40% gap between lamps produced by various manufacturers and lamps from the same manufacturer.
â–² ensure a stable light intensity. The light intensity is affected by factors such as the lamp to the film, the life or use conditions of the lamp, the type and conditions of use of the reflector, and the accuracy of the reset lamp brightness. A change in the voltage of the exposure exposure lamp will cause a significant change in the actual exposure.
â–² Determine the downtime through testing to ensure that there is sufficient time for the film to contact the glass table