The CTP system is part of the digital workflow, so digital control methods are essential to quality assurance. The digital plate control bar allows reasonable and effective control of the image quality of the CTP plate.
(1) Standard digital plate measurement and control bar
The digital control strips used for CTP plate control include GATF digital plate control strips, Ugra/Fogra digital stripe control strips, Kodak digital plate control strips, and Heidelberg digital plate control strips. Among them, the most widely used and most important are the Ugra/Fogra digital plate control bar and the GATF digital plate control bar.
1Ugra/Fogra digital plate control bar
The control bar contains six function blocks and control areas:
Information area: including the output device name, PS language version, screen line number, dot shape and so on.
Resolution block: Contains two semicircular areas. Lines are emitted from a point, arranged in a ray, and the intensity of the radiation is consistent with the theoretical resolution of the output device. A more or less open or closed quarter circle is formed in the center of the line. The smaller and rounder the two quarter circles, the better the focusing and imaging quality. The Yang line is on the left and the Yin line is on the right.
Linear block: Consisting of horizontal and vertical micro-lines to control the resolution of the plate.
Chessboard: A checkerboard box consisting of 1 x 1, 2 x 2, 3 x 3, and 4 x 4 (pixels x pixels). Control the resolution of the plate, showing the differences in exposure and development techniques.
Visual Reference Scale (VRS): Controls the image transfer of the plate.
Mesh grading ruler: It is mainly used to determine the gradation transfer characteristics of the printing plate. The 1%, 2%, 3%, and 97%, 98%, and 99% color patches provided at the same time can also be used to visually judge the tones that can be reproduced in the high-profile and dark-tone regions.
Among them, the visual reference scale (VRS) is a special feature of the Ugra/Fogra digital plate control bar. It is the basic element for image transfer control, controls the stability of the printing plate, and standardizes the production process of digital printing plates. The paired coarse wire reference blocks are contained in the VRS, and fine-grained areas surround it. There are 11 VRSs in the control bar, and they are increasing in 5% increments from 35% to 85% of the dot area. In the case of ideal state and linear replication, the two areas in VRS4 should have the same gradation value visually. In practice, however, VRSs with the same tone in both regions are higher or lower than VRS4, depending on the plate type and the selected calibration conditions. VRS is a very ideal process control block. It does not require measurement. It visually indicates the difference from the selected conditions and performs a visual inspection.
2GATF digital plate control bar
Information area: including the output device name, PS language version, screen line number, dot shape and so on.
The horizontal vertical thin line of the positive graph: the resolution of the test system, controlling the exposure intensity.
Chessboard: A checkerboard box consisting of 1 x 1, 2 x 2, 3 x 3, and 4 x 4 (pixels x pixels).
Micro-Arc Zones: Positive and Negative Graph-type micro-arc. Using the smallest set of dimensions to detect the system with arc segments, the micro-arc pattern is the most severe challenge to the system. If a system maintains good detail on the positive and negative arcs at the same time, this indicates a good exposure condition for the system.
Star objects: Exposure intensity, resolution, and tone transfer characteristics of the test system.
The remaining part is two sets of matching tone ladders. The difference between the two steps is that the upper one bypasses the RIP compensation procedure applied to other files, while the next one does not bypass the compensation settings. The comparison of the two ladder feet clearly shows the effect of the compensation procedure. To use a step scale, first use a magnifying glass to observe the highlights and darkness of the image system, and then use a density meter to measure the step scale from 10% to 90% to construct a dot gain curve.
(2) Self-designed digital plate control bar
In actual use, in addition to the above-mentioned standard measurement and control bar, the user can also design some patterns as measurement and control tools according to the characteristics of his own system, such as designing commonly used test exposure and resolution micro-line and star. Users can create microline and star logos in CorelDraw or Illustrator, or edit them in postscript language.
A. Microwire
The micro-wire consists of different thickness lines or curves of yin-yang lines. The size of the line is determined from the point, from 1 o'clock to 0.01 o'clock, where 1 inch = 72 points = 25.4 mm and 1 point = 0.35 mm. The line style includes four directions: horizontal, vertical, 45 degrees, -45 degrees, and semicircular, with semicircular lines and horizontal lines meeting at the junction of negative and positive figures.
Microwires can react to the plateetter's performance and imaging in all directions. If the finer curves can be accurately restored, the exposure imaging system of the platesetter will perform well. In addition, this micro-line can be a good reflection of whether the exposure is appropriate. If positive line and positive line can be clearly seen on the positive plate, the exposure is appropriate. If the line is thicker than the line, or if the line at the dock disappears, the exposure is excessive and the exposure should be reduced. If the Yinxian is significantly smaller than the Yangxian, or if the Yinxian at the butt joint disappears, the exposure is insufficient and the exposure should be increased.
B. Star
The star is composed of wedge strips 5 degrees wide and 5 degrees apart, and a total of 36 wedges are evenly distributed over a circle. The tip of the wedge toward the center of the circle is the smallest dot; the wedge is toward the edge and is the largest dot. The wedge is the thinnest at the center and eventually disappears as a blank center. The size of the blank center is determined by the amount of image detail lost during the platemaking process. Due to the geometric nature of this arrangement, stars can reflect the resolution of the system. The higher the resolution of the system, the clearer the center of the star, but when the system's resolution is too high, it will cause the dot to expand; on the contrary, the expansion of the star's center indicates the system's low resolution or inappropriate media exposure. Caused the loss of outlets.
In addition, the use of the geometric characteristics of the star can also show ghosting or overprint and other printing failures. The centre of a non-circular star indicates the difference in directionality of the system. If ghosting occurs, the center of the star is oval, and the minor axis indicates the direction of the ghost. If overprint occurs, the center is an “8†shape, and the minor axis indicates the direction of the double image.
(1) Standard digital plate measurement and control bar
The digital control strips used for CTP plate control include GATF digital plate control strips, Ugra/Fogra digital stripe control strips, Kodak digital plate control strips, and Heidelberg digital plate control strips. Among them, the most widely used and most important are the Ugra/Fogra digital plate control bar and the GATF digital plate control bar.
1Ugra/Fogra digital plate control bar
The control bar contains six function blocks and control areas:
Information area: including the output device name, PS language version, screen line number, dot shape and so on.
Resolution block: Contains two semicircular areas. Lines are emitted from a point, arranged in a ray, and the intensity of the radiation is consistent with the theoretical resolution of the output device. A more or less open or closed quarter circle is formed in the center of the line. The smaller and rounder the two quarter circles, the better the focusing and imaging quality. The Yang line is on the left and the Yin line is on the right.
Linear block: Consisting of horizontal and vertical micro-lines to control the resolution of the plate.
Chessboard: A checkerboard box consisting of 1 x 1, 2 x 2, 3 x 3, and 4 x 4 (pixels x pixels). Control the resolution of the plate, showing the differences in exposure and development techniques.
Visual Reference Scale (VRS): Controls the image transfer of the plate.
Mesh grading ruler: It is mainly used to determine the gradation transfer characteristics of the printing plate. The 1%, 2%, 3%, and 97%, 98%, and 99% color patches provided at the same time can also be used to visually judge the tones that can be reproduced in the high-profile and dark-tone regions.
Among them, the visual reference scale (VRS) is a special feature of the Ugra/Fogra digital plate control bar. It is the basic element for image transfer control, controls the stability of the printing plate, and standardizes the production process of digital printing plates. The paired coarse wire reference blocks are contained in the VRS, and fine-grained areas surround it. There are 11 VRSs in the control bar, and they are increasing in 5% increments from 35% to 85% of the dot area. In the case of ideal state and linear replication, the two areas in VRS4 should have the same gradation value visually. In practice, however, VRSs with the same tone in both regions are higher or lower than VRS4, depending on the plate type and the selected calibration conditions. VRS is a very ideal process control block. It does not require measurement. It visually indicates the difference from the selected conditions and performs a visual inspection.
2GATF digital plate control bar
Information area: including the output device name, PS language version, screen line number, dot shape and so on.
The horizontal vertical thin line of the positive graph: the resolution of the test system, controlling the exposure intensity.
Chessboard: A checkerboard box consisting of 1 x 1, 2 x 2, 3 x 3, and 4 x 4 (pixels x pixels).
Micro-Arc Zones: Positive and Negative Graph-type micro-arc. Using the smallest set of dimensions to detect the system with arc segments, the micro-arc pattern is the most severe challenge to the system. If a system maintains good detail on the positive and negative arcs at the same time, this indicates a good exposure condition for the system.
Star objects: Exposure intensity, resolution, and tone transfer characteristics of the test system.
The remaining part is two sets of matching tone ladders. The difference between the two steps is that the upper one bypasses the RIP compensation procedure applied to other files, while the next one does not bypass the compensation settings. The comparison of the two ladder feet clearly shows the effect of the compensation procedure. To use a step scale, first use a magnifying glass to observe the highlights and darkness of the image system, and then use a density meter to measure the step scale from 10% to 90% to construct a dot gain curve.
(2) Self-designed digital plate control bar
In actual use, in addition to the above-mentioned standard measurement and control bar, the user can also design some patterns as measurement and control tools according to the characteristics of his own system, such as designing commonly used test exposure and resolution micro-line and star. Users can create microline and star logos in CorelDraw or Illustrator, or edit them in postscript language.
A. Microwire
The micro-wire consists of different thickness lines or curves of yin-yang lines. The size of the line is determined from the point, from 1 o'clock to 0.01 o'clock, where 1 inch = 72 points = 25.4 mm and 1 point = 0.35 mm. The line style includes four directions: horizontal, vertical, 45 degrees, -45 degrees, and semicircular, with semicircular lines and horizontal lines meeting at the junction of negative and positive figures.
Microwires can react to the plateetter's performance and imaging in all directions. If the finer curves can be accurately restored, the exposure imaging system of the platesetter will perform well. In addition, this micro-line can be a good reflection of whether the exposure is appropriate. If positive line and positive line can be clearly seen on the positive plate, the exposure is appropriate. If the line is thicker than the line, or if the line at the dock disappears, the exposure is excessive and the exposure should be reduced. If the Yinxian is significantly smaller than the Yangxian, or if the Yinxian at the butt joint disappears, the exposure is insufficient and the exposure should be increased.
B. Star
The star is composed of wedge strips 5 degrees wide and 5 degrees apart, and a total of 36 wedges are evenly distributed over a circle. The tip of the wedge toward the center of the circle is the smallest dot; the wedge is toward the edge and is the largest dot. The wedge is the thinnest at the center and eventually disappears as a blank center. The size of the blank center is determined by the amount of image detail lost during the platemaking process. Due to the geometric nature of this arrangement, stars can reflect the resolution of the system. The higher the resolution of the system, the clearer the center of the star, but when the system's resolution is too high, it will cause the dot to expand; on the contrary, the expansion of the star's center indicates the system's low resolution or inappropriate media exposure. Caused the loss of outlets.
In addition, the use of the geometric characteristics of the star can also show ghosting or overprint and other printing failures. The centre of a non-circular star indicates the difference in directionality of the system. If ghosting occurs, the center of the star is oval, and the minor axis indicates the direction of the ghost. If overprint occurs, the center is an “8†shape, and the minor axis indicates the direction of the double image.
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