Some suggestions for using the color scale Professor Miles Southworth of the Rochester Institute of Technology pointed out in his article “Quality Control Scanner†that the choice of color control strip is quality control. One of the most critical elements. It should at least contain solid patches, overprint patches, and gray balance patches; it doesn't matter if the color labels are micro- or half-tone screens. â€
Some printing fields have special requirements for color labels, such as the Recommended Specifications Web Offset Publications (SWOP for short) pointed out that the proofs should contain the following objects:
l Monochrome inks, two-color overprints, and three-color overprinted solid blocks.
• 25%, 50%, and 75% color value for each printing ink with 133 lines per inch screened color patches.
l Some color patches that are visually sensitive to ghosting and dot enlargement are helpful for operator personnel to observe.
l Gray balance strips placed side-by-side by three inks and different black color values, and the color values ​​of these three color patches when viewed under illumination at a temperature of 5000 degrees Kelvin must be matched with the black blocks. .
l A control element used to estimate the correct exposure of the plate.
There are different requirements in other printing fields.
It is recommended that at least five parameters of the output of the imaging system should be measured and controlled by the understanding and control of copying (or preprinting system, color printer, or copying machine) of the printing job.
l Density of printing materials
l Apparent dot gain or density at 25% color patches
l Extend apparent dots at 50% color patches
l Print contrast in 75% dot area
l Solid ink density (SID)
In addition, additional objective objects and visual objects need to be selected to help operators and management personnel quickly determine the balance of dot gain, and determine whether the problem of replication occurs in the process of copying or the problems in plate making operations.
In order to facilitate the use of color labels for communication among industry professionals, it is recommended that at least the following elements be included in the selected color standard:
1. 25% Chroma blocks for yellow, pink, black, and black inks that help measure and understand the reproduction of quarter-tone areas in the image. The use of 25% color blocks as a reference has not been agreed in the industry. Some people support the use of 25% color blocks, while others believe that the use of this color ink has a total dot gain value. If the dot gain value is used as a characteristic parameter for the measurement, 25% of the color patches should be placed close to or in close proximity to the solid color patches of the same color ink because the calculated dot gain requires a solid density value.
2. 50% color blocks for yellow, pink, blue, and black inks. These color blocks help to measure and understand the reproduction of the midtone region in the tone curve. The reproduction of important colors and details of any printed image is done through intermediate dots, so the reproduction of midtones is very important. Since the dot gain calculation requires a solid density value, the 50% chroma block should also be placed close to or next to the same color solid ink patch.
3. 75% color blocks for yellow, pink, blue, and black inks. These color blocks help to measure and understand the reproduction of the dark tone region of the tone curve. The three-quarter tone is measured simultaneously with a solid color patch to determine the print contrast of the image. The high printing contrast means that the density of the ink in the field is higher, and the level of the 75% tone zone is clear and has not been affected by the ink supply system or other factors. As with the 25% and 50% color patch objects, the calculation of the print contrast also requires a field density value, so the 75% color block should also be placed in close proximity to or in close proximity to the solid color patch of the same color ink.
4. Solid color patches for yellow, pink, blue, and black inks that help measure and understand the ink supply for these four colors. The function of changing the ink volume is one of the on-machine operations that the press operator needs to perform. Therefore, it is very important for the operator to measure and determine how high the ink density is through some control objects. At the same time, it is also possible to use the density meter to objectively measure the chromaticity values ​​of the cyan, magenta, and yellow inks to correct the gradation and chromaticity values.
5. Two-color overprint color block used to determine the overprint of the second color ink imprinted on the surface of the first color ink. Nested printing affects the effect of overprints, such as green grass (which is mainly reproduced by overprinting yellow ink on cyan ink) and red tomatoes (which are mainly created by the overprinting of yellow ink on the color ink). With the use of two-color overprint blocks, color separation data can be color corrected to know in advance the specific effects after overprinting. If overprinting does not occur as expected, the color of the overprint will change. For example, grass and tomatoes in the above example will be more blue than expected. If the printing sequence of the above ink is changed, the situation may be different because the ink supply sequence also affects overprinting.
Two-color overprinting data can use the density meter to objectively measure the chromaticity values ​​of green, red, and blue inks, and perform grayscale measurement and colorimetric correction. Two-color overprint objects should be aligned with the two color solid patches used.
6. Gray balance color blocks contain at least midtones, preferably with quarter and quarter quarter color patches. The human eye is sensitive to the color transitions appearing in the neutral grey area. A halftone block printed out of black ink is placed side by side with a halftone block consisting of three colors of cyan, magenta and yellow, and can be visually detected quickly. Out of the three colors in the slightest change in dot gain and gray balance. When a significant change occurs, the operator can take a more accurate measurement method to measure the monochromatic color blocks and solid color blocks to find the cause of dot gain imbalance.
7. The visual patches of cyan, magenta, yellow, and black allow visual evaluation of the printed paper to detect whether the exposure of the plate is appropriate. Exposure of the plate will shrink the dots or enlarge the dots, which will affect the reproduction of the film on the printing press. Since 25%, 50%, and 75% of printed color patches are affected by plate exposure and printing conditions, it is difficult to determine what caused the deleterious changes in the printing process. Visual plate elements help to analyze the source of this uncertainty.
8. Position the mark to ensure that all elements of copying and printing are fully registered.
Although the size of the element will have a slight effect on the measurement, the size of the element is not particularly specified, as long as the size of the patch can be measured with existing equipment. The object form contained in the color scale is more important than the size of these objects.
Place the color patch as far as possible, placing the patch across the entire top, center, or bottom of the roll or sheet. The color scale should have a certain width in order to understand the print reproduction characteristics of the entire paper. This is very important because the color patch object to be measured should be placed side by side with the full-color image to be monitored.
Screen Lines Although the number of screen lines will have a slight effect on the measurement, it does not explicitly specify a specific value. The user should follow the specific parameters of the print market (for example, 133 lines per inch for SWOP-specific color patches used in publishing films and printing), or the user's need to select the most appropriate color code screen line.
The dot shape is the same as the number of screen lines. Although dot shape will have a slight effect on the measurement, it does not specify a specific dot shape. Users should also choose according to their own special needs and habits.
All color film on the original film should be original film. After copying or copying the film, even if there is only one time, it will not contain the desired color value when the operator or manager analyzes the printed object. As a result, the information exchange is not good.
With today's imaging technology, it is possible for any company and company to produce their own color standard film. However, it is recommended that the following conditions must be met: 1) The film contains at least the elements listed above; 2) Strict quality control tests are performed to ensure the accuracy of the chroma and other elements in the film; 3) In the document The content and purpose of each color element are clearly marked, allowing training of the operator and communication with other staff in the printing process.
Application of color standard (six)
July 18 18:01:17, 2024
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