Description of the printing parameters of the hott

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Snap -- description of paper advertisement printing parameters (VI)

contact copy and proofing

contact copy control

when copying film, the size change of halftone dots compared with the original cannot exceed ± 2%. The test must be carried out on a regular basis before each operation. It is best to copy the original exposure control ladder (e.g. UGRA ladder) in the same way as the copy material

use a properly calibrated transmission densitometer to record the actual values of the original exposure scale and the copied exposure scale. These two sets of values, transmission densitometer, spectral reaction and other relevant information are submitted to the receiving contact copy equipment at the same time, such as positive color chip, UV and type1

proofing process

the term proofing is used to describe the inspection of operations in the printing production process. In the prepress and printing department, the function of the sample is to verify the content and color, process control, quality control, and confirm the changes. The method and requirements of making its addition amount proportional to the size of normal stress depend on different production stages and customer expectations. There are many kinds of proofing schemes, which are different in quality, complexity and price

samples can be classified according to three methods:

image source of samples

1. Use ultraviolet light source (UV) to obtain simulated samples from film

2. Digital samples can be obtained directly from documents by using laser printing, inkjet printing and other technologies

sample form

use physical materials to output hard copy samples, including:

a: printer samples, which are obtained by using paper and ink through the printing machine and printing plate

b: offline sample, sometimes called "prepress sample", which is obtained by exposing photosensitive materials with color separation film

c: digital hard copy sample, which uses not film but directly from imaging documents

d: soft sample refers to the image displayed on the screen or terminal

The term "sample" includes many functions, including:

"content sample" or "positioning sample" to check image content, color mutation, and content positioning (not to check the exact matching of colors)

"contract or final sample" is used to check the final color and the positioning of all elements

1. it is usually made by final film or final digital file. The final sample is sometimes called "color ok sample"

2. A high proportion of plastic deformation samples will eventually be produced, which represents the final style of qualified prints, including color, tone reproduction, substrate, layout design, location of each component, graphic content, etc

3. The purpose of making the final sample is to predict the printing effect of the provided films and documents. All final samples (analog or digital) must comply with the printing machine print specified in snap

understand "proofing"

a: all types of proofs - analog and digital, hard proofing or soft proofing, content or finally, are useful tools for evaluating printing and image quality. Each type of sample has its own characteristics, advantages and limitations

b: a sample that a customer or a market field considers as a content sample may be regarded as the final sample by other customers or markets

c: the above sample classification is used to promote communication and understanding. Process requirements and customer expectations determine the selection of proofing methods

requirements for snap samples

it is very beneficial to divide samples into four types: content samples, final samples, printer samples and offline samples

content sample

in order to provide sufficient and complete information to printers or newspapers, the content sample must contain the following information:

if necessary, make the sample flat and conform to the actual size. Glue the tiled sample to reproduce the complete image. If the actual size cannot be used, the scale of reduction or enlargement shall be stated on the sample

the sample is marked with cutting, folding and registration positioning

confirm whether the sample is only used for checking position only (FPO) or calibrating the image

confirm the element composition of the color page, whether it is the fifth color, spot color, or the mixed color of CMYK, as well as the proportion of each primary color

if the image in the printed matter is color, make a color sample. Color proofs can provide helpful information about color mutations and potential trapping problems, and can also clearly indicate whether the image is black-and-white or color

the customer's name, the name and time of the sample, the name and number of the person who provided the sample, and all the style information are marked on the sample

clearly mark all FPO (for positioning only) image files, including photos and special effects. The content sample submitted with the digital file should include the high-resolution scanned file of these photos, or the original photos

final sample

the final sample of cold set printing should be visually as close to the final print as possible. The final sample accurately simulates the final printing effect in the following aspects:

final layout

characteristics of the substrate

ink color/color range

tone reproduction

surface appearance of the graphic area

qualified registration positioning

ability to identify the original and production date

standard color code near the graphic area

ink density of the printer sample

printer sample the parameters specified by snap are reached. Control and monitor the dot enlargement/tvi (tone value increase) of the sample to obtain the maximum stability of 3. Change the correct protection and maintenance method of the experimental machine. Because there are many kinds of uncoated wood pulp papers used in the cold set printing industry, these papers have great differences in color, brightness and transparency, so it is impossible to specify standard proofing materials. If a sample is required to be printed, the proofer must decide the parameters of the print and proofing on the same substrate or materials with similar characteristics. The ink sequence of printing samples must comply with the production specifications of the printing workshop. The color code should include the field, 25%, 50% and 75% points of each color. The overprint of two colors and the gray blocks of three colors (40% green, 30% magenta and 30% yellow) can obtain such color control samples from NAA, GATF, RIT and other organizations

offline proofs

there are many prepress color proofing systems on the market, including digital or analog methods (overprint or sheet fed). In order to simulate the final printed matter and comply with the rules mentioned above, such samples must be made according to the recommendation of the proofing machine manufacturer. The exposure structure of the analog proofing system must have a suitable light source, so the recommended parameters of the proofing machine manufacturer for the bulb and exposure time must be strictly observed. At the same time, appropriate calibration and monitoring are required. Although all simulation proofing systems have similarities, each system has its own characteristics and process requirements. If you have any questions, please consult the manufacturer directly

most digital proofing machines are equipped with color management systems, so users choose appropriate features in combination with snap parameters. The rip file used for the digital sample should be the same as that used for the final film or printing plate. Such samples are usually used to view the content and positioning. Snap strongly recommends testing digital samples to ensure accuracy and stability

the proofing scheme in the digital workflow is still an unresolved challenge. At present, digital and analog processes exist side by side, and are used at the same time in many cases. Due to emerging technologies, this field is also changing rapidly

key points of vacuum exposure

▲ use trash free detergent and lint free cloth to scrub the glass table, which can reduce light absorption, refraction and image defects

▲ ensure the cleanness of the vacuum pump, and there is no air leakage of the film after vacuum pumping

▲ use dark gray or black liner to prevent deformation. Ensure surface consistency and smoothness

▲ check the overall tightness around the gasket

▲ ensure that the lighting distance is appropriate, which can not only cover the printed format (even under lighting conditions), but also suitable for the actual lighting operation. The difference between the gray scale level of the image center and the most likely image edge (level 21, from Stouffer, RIT, GATF, UGRA) cannot be greater than 1. Recognize the low exposure that points to the edge. Determines the uniformity of exposure

▲ change bulbs often, because their spectral output is also changing as they age. The efficiency of a light bulb decreases by about 20% after its life cycle. Strictly follow the replacement arrangement of the manufacturer

▲ copy the original exposure control strip (Stouffer, RIT, GATF, UGRA ladder) in the same printing method. Test every day. There may be a maximum gap of 40% between lamps manufactured by various manufacturers and lamps from the same manufacturer

▲ ensure stable light intensity. Factors such as the lamp to film, the life or service conditions of the bulb, the type and service conditions of the reflector, and the accuracy of the reset bulb brightness will affect the light intensity. The voltage change of the contact exposure lamp will cause the actual exposure to change significantly

▲ determine the downtime through testing to ensure sufficient time for the film to contact the glass table

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