Color standard application (five)
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Need to zero on the paper when measuring the color code?
No need. Paper density and paper color are important reference data during image copying and should be included in the density measurement process. The paper density measurement should be performed simultaneously using four densitometer filters, which are used in actual operations to calculate other aspects of the printing characteristics.
Is the density meter the only way to measure color code?
The role of the color scale is to allow operators and other relevant personnel to measure and communicate the various changes that occur during the printing process, so the densitometer is not the only measurement tool. This is because when the printer is proofing or printing a job, the most effective way for the operator to change the appearance of the image is to change the ink balance by controlling the ink supply system or the fountain solution system. The key measurement factors that characterize the success of this control are density values and dot gain, while the latest colorimeter and spectrophotometer can be used to calculate the density and dot gain required for press operation. . But compared to this, the density meter is probably the most effective, lowest cost, and most intuitive tool for measuring color standards.
What is the difference between the production color code, proof color code and GCA/GATF Proof Comparator?
From a technical point of view, these three color scales are very similar. They all have color patches that measure printing characteristics, such as solid ink density patches, dot gain, trapping, gray balance, and ghosting at 25%, 50%, and 75% tonal values. The main difference is that the GCA/GATF Proof Comparator has a flesh-colored and light-colored graphic patch that helps visually identify color shifts quickly. The GCA/GATF Proof Comparator and GATF proofs also contain 25%, 50%, and 75% tinted overprint patches.
From the application point of view, these three color standards are completely different. The color code for production should be as narrow as possible (approximately one-fifth of an inch) to ensure that it can be pasted into the free space of the plate, and the objects in the color code are closely arranged to form a long row. The proof color code, because of its different uses, will not have the above constraints and restrictions. It is about 1.25 inches wide and contains large objects and additional control elements. Proofing color standards are often used for proofing on a printing press. The GCA/GATF Proof Comparator was developed specifically to test the quality of pre-samples. The GCA/GATF Proof Comparator has a width of 2.25 inches and contains all the objects in the proof mark to detect the reproduction of the printed primaries, overprints, gray balance patches and graphic elements.
What is the number of screen lines and dot shapes on the color scale?
There are two basic principles that are generally followed when selecting the number of screen lines for a color patch:
• It is recommended that the number of screen lines on the color scale be the same as the number of screen lines used in the print job. This is mainly because the amount of dot gain will be affected by the number of screens. The higher the number of screens per inch, the larger the dot gain. Using the same number of screen lines as the actual production, the color code is added to the screen, which can truly reflect the operating conditions of the printing machine, consistent with the halftone color separation method.
• It is recommended that the color scale use a slightly higher number of screen lines than the print job. The basis of this principle is that, because the number of screen lines is more fine, the color code is more sensitive to changes in the printing process, and it can reflect various changes through dot gain and dot sharpening faster than actual production, so the operation can be warned. The person performs the necessary process adjustments before the image begins to change visually, reducing waste.
Whether the color code with a higher number of screen lines is more sensitive to process changes, the investigation of this problem shows that this principle is correct in theory:
• The sensitivity of the number of screen lines between 133 lines and 150 lines per inch is minimal.
• When measuring the color code, the method used and the measurement difference inherent in the device can be used to cover any difference in the number of color-coded lines.
There are currently two different views on the discussion of dot shape. Some people think that the color patch should use the dot shape that matches the color separation film to provide the best correction. It has also been suggested to use round, square and elliptical dots, each of which has its own advantages, and the difference in the reproduction caused by the dot shape is small, and the number of screen lines is the same as the number of screen lines. The change is much less than the change brought about by copying or copying the color-coded film.
The following methods are recommended:
• It is more important to consistently use the same color-coded screen line number than to associate the number of color-coded screen lines with the actual number of screen-added lines. As experience continues to accumulate, operators, managers, etc. begin to relate objective measurements to the appearance of images. The use of different color-coded color-coded lines can hinder the understanding of these changes, introduce chaotic factors, and increase the complexity of quality control.
• Whenever possible, use a color code that matches the actual number of screen lines. The number of screen lines of the color standard is consistent with the number of screen lines of the color separation sheet printed side by side. When measuring, it is easy to connect with each part through the visual appearance of the image, and the confusion caused by the difference in the number of screen lines is reduced to The smallest.
• The color scale can take any dot shape as long as the dot shape is consistent across all applied films and all objects containing those patches.