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In order to obtain the best process, further control of the production process, each sample of each job, whether it is pre proofs or digital proofs, and each color version of the print should contain color code. In the actual printing production process, the entire imaging area is occupied by the cutting size and the layout size of the printing press, and there is no enough space for the placement of the color mark, which is a very undesirable situation. If this phenomenon frequently occurs, the operator can operate as follows:
• Interested in printing colour marks, for example once or twice a week, to produce test plates or directly into production plates containing this information so that operators, managers and relevant technicians can understand plates and prints. Changes in machine performance, paper, ink, and other input parameters.
· With the permission of the printing customer, some target elements, such as dot gain, density and gray balance, are selected somewhere in the printing plate. This information will not cause opposition from the printing customer. In fact, some customers already include these elements. In the layout, and remind readers that these color blocks are used for quality control.
• Negotiate with the print customer to include the test object in the edit design. USA Today is an example of this, their logo is the density of the ink in the field and the overprint control object.
• Adding 75% tonal values ​​of each color and field patches at least somewhere on the plate to measure print contrast helps estimate overall print quality and the relationship between density and dot gain.
It should be noted that color patches are not a prerequisite for printing high quality images; many printers and color separation personnel can produce high quality products without using color scales. Moreover, many printers and color separation workers do not use color labels more profitably. However, printing and color separation personnel who rarely use color scales can obtain higher profits and quality levels than those who include and use color scales. The color scale is a key factor in proofing and printing in the high productivity and high profit production methods. Through the color scale, the change of the process can be determined more quickly and more objectively, and the appearance and distortion of the image can be avoided. Because the color scale can be measured objectively, it can provide the necessary parameters and information knowledge for process improvement, which helps to continuously improve quality and reduce costs.
When is the color scale measured?
In actual production, color scales should be measured frequently. The following provides some suggestions based on the information published by Gretag, which is helpful for training production operators:
During the initial stages of print preparation and ok verification, operators often use a correct proof or pre-proof proof as a color reference and rely on visual adjustments. Even during this stage of printing preparation, color patches are useful because operators can use color patches:
• Detect density, dot gain, contrast, and other data that needs confirmation to determine if the printing process can achieve the desired effect.
• Insight into possible problems during the print preparation process and ensure that the printed sheets and proofs are matched.
At the end of the printing preparation process, the role of color patches has been further expanded. At this stage it is recommended to measure the following elements of the main page and ads under standard conditions:
· Solid color patches for each color;
25% and 50% color blocks for each color, and print contrast;
• Two-color overprint blocks (red, green, and blue blocks) for field inks.
The following elements of the main page or advertisement are measured under normal conditions during the printing operation:
· Solid color patches for each color;
25% and 50% color blocks for each color, and print contrast;
• Two-color overprint blocks (red, green, and blue blocks) for field inks.
After ink adjustment or print stop, measure:
• 25% and 50% of the objects and print contrast for each color of the main page or ad.
If these rapid initial measurements show unusual values, or show that the entire operation is unstable, the operator should measure other color-coded elements on the substrate and increase the frequency of the measurements to ensure that the tracking press changes. Process, make appropriate adjustments. In these examples, an equipment operating chart or X control bar/R chart is invaluable because it will provide us with some information. Through the measurement results, we can determine whether the operation process has undergone major changes or normal fluctuations. These recommendations are only the starting point for the development of internal operating procedures and guidelines; in particular, companies that employ statistical process control (SPC) often have their own experimental and measurement methods.
Which measurement elements are included on the color scale?
Color labels usually contain two types of elements:
Objective elements: Density elements, 25%, 50%, and 75% textures, overprint colors, and other elements that can be evaluated with densitometers or other color measurement equipment.
Subjective elements: ghosting elements, plate exposure indicators, gray balance tones, and graphical elements evaluated visually.
The measurement of these two types of elements is very important and very useful, because the visual object can provide the operator and the measurement process with immediate information about unacceptable changes that can be verified, quantified, controlled, and finally measured by objectively measuring other objects. record it.
How to Measure Color Marks For a pre proofed proof (whether produced on film or digitally) or a model, the following methods can be used to effectively measure:
Prepare a densitometer and understand how it is calibrated and operated. This is the basic requirement for measuring the color scale. Although the following materials will not be used during each color scale measurement, in order to further optimize information exchange and process control, it is recommended to prepare the following resources:
A multi-band Status T densitometer;
A GCA T-Ref can be purchased from GCA.
· To ensure consistency between sample and magazine publishing parameters, there should also be a SWOP Hi-Lo color block available from the International Prepress Association (IPA).
· A copy of the dot enlargement and density table. The reader can refer to the relevant sample and collect the data to make his own data sheet.
When linking the density measurement and visual estimation of a print job, reference can be made to ANSI PH 2.30-1989 - for Graphic Arts and Photography (for printing technology and photography) - Color Prints, Transparencies, and Photomechanical Reproductions (colour printing, Slides and photocopying) - The Viewing Conditions standard establishes a lighting system which is very helpful. Any precise visual assessment of proofs (pre- proofs, models, or digital proofs) and technical evaluation of relative color needs to be performed under this standard lighting and environment.
note:
• The process of objectively measuring and subjectively evaluating color elements does not require a standard lighting environment.
• Do not attempt to subjectively evaluate objective color-coded elements such as hue (eg, using a small magnifier to detect printed tones to determine the overall apparent dot gain).
1. Read the T-Ref value on the multiband densitometer after correcting the densimeter with reference to the production manual. If the measured value matches the T-Ref value, go to the second step. If the two do not match, recalibrate the part according to the manufacturer's instructions.
2. Place a BackstopTM (a master material developed by GCA) or similar material underneath the part of the patch that you want to measure. If you plan to visually estimate the printed copy of the image in parallel with the portion of the label to be measured, make sure that the BackstopTM does not appear under the material.
3. Measure the SWOP Hi-Lo Color Reference (note: these SWOP Hi-Lo color references are only applicable to the magazine advertising market.) Each color block in the Hi value, and dot gain and density comparison table (Dot Gain and The Density Comparison Form) records these measurements. The process of measuring the ink on a printed Hi-Lo material is an absolute density measurement, which means that this measurement method includes the density of the paper. Do not empty or zero the densitometer on the surface of the paper. To make a measurement, place a standard black backing under this color patch, or make sure the patch is printed on a black backing.
4. Measure and record each color block of the Lo value in SWOP Hi-Lo (note: these SWOP Hi-Lo color references are only applicable to the magazine advertising market). The process of measuring the ink on a printed Hi-Lo material is an absolute density measurement, which means that this measurement method includes the density of the paper. Do not empty or zero the densitometer on the surface of the paper. To make a measurement, place a standard black backing under this color patch, or make sure the patch is printed on a black backing. Also note that papers that support Hi-Lo are not standard paper.
5. Measure and record the paper density with all four densitometer filters.
6. Read and record the measurements of all channels of the color scale and the portion of the image being measured. Take the absolute density reading for each color element; do not empty or zero the densitometer on the surface of the paper. Channels are patches of color that are duplicated on the color scale; industry members recommend having two duplicate patches of color on a single page or image color patch.
It is acceptable to read the color values ​​in any order within each channel. Some automatic monitoring systems use methods that prompt the user to perform measurements in the order of yellow, blue, green, and black. This is a common printing sequence.
7. Read and record the solid ink density in the table and compare it with the SWOP Hi-Lo value. (Note: These SWOP Hi-Lo color references are only applicable to the magazine advertising market.) After measuring the density of each channel, you also need to measure and record 25%, 50%, 75% color patches in each channel. Total apparent outlet expansion value.
What data should be obtained when measuring the color scale?
Various printing markets, including publishing, cold-fixed advertising, newspaper printing, commercial printing, etc., have specific demand for density values ​​and outlet expansion values. Although the actual values ​​will vary with each production process, the survey conducted by the GCA Print Properties Committee in 1991 showed that the target values ​​listed in the following table have a The meaning of sex.
Product 1.30 30% or more 24% 20%
Yellow 0.98 25% or higher 22% 16%
Black 1.65 33% or higher 28% 24%
Note: The values ​​in the above table are all industry averages and will vary depending on factors such as paper, ink, printer, press operator, plate type, etc. Also note that these values ​​are very effective for copying high quality prints, but do not necessarily disregard the appearance of the images rather than achieving these absolute data.
Is it better to measure the color scale at the time of printing or the color scale at the time of proofing?
In fact, both sensible printing operators or color separation personnel do it. Many people in the industry should know that "no one buys numbers. They buy beautiful images." In the long run, they are right. Proofs or prints with specified density values ​​or dot gain values ​​may not achieve the desired appearance, in which case experienced color separation personnel or printing operators—with the support of a knowledgeable printing customer—will make the necessary The adjustments to obtain the desired image appearance. However, these color separation personnel, printing staff, and printing customers will use color scale measurements to record the process adjustments that need to be made to achieve the desired image reproduction. Also note that the defined dot gain values, such as those provided in SWOP (Square Offset Parameter Description), SNAP (Sensor Offset Parameter Description), and other documents, usually provide an image complex.
When to use color scales?
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