Since DRUPA95, CTP has become the hottest topic in the printing industry. In the 21st century, computer-to-platemaking technology tends to mature. The process of computer-to-plate making omits the “filmâ€, and the traditional print process quality control system needs to be redefined.
After the computer-to-plate process was adopted, direct inspection of the printing plate became inevitable. Since the printing plate has surface characteristics different from those of the film and the paper, the question of which detection method to use in the detection, what kind of instrument, the detection conditions, the accuracy of the instrument detection, and the data stability are still to be studied. This article mainly categorizes the detection method of the printing plate, and introduces the new printing plate detection instrument.
Plate detection technology is based on different detection methods, and the suitability analysis of various printing plates is mainly divided into subjective evaluation and objective evaluation. (1) Subjective evaluation is visual evaluation, using digital test or digital control bar, through visual inspection. Or use the auxiliary amplification equipment to make intuitive judgments on the plate resolution, resolution, and other media performance parameters; (2) objective evaluation is to quantify the control process through testing equipment. It abandons the influence of human factors in the subjective evaluation and realizes the data standardization of the quality control process. This article will mainly introduce densitometers, spectrophotometers, and digital image analyzers for plate detection.
Density meter has become an effective measuring instrument for the detection and control of product quality because of its simplicity and high efficiency in the traditional printing process. It has played a decisive role in the development of printing technology and has achieved the detection and control of printed products. Human subjective to objective leap.
In most studies, the densitometry function of a reflection densitometer or spectrophotometer has been used to measure the density of solids and dots on the printing plates and proofs, and a mathematical method has been used to compare and evaluate the measurement results.
The reflection densitometer adopts the optical principle and converts the intensity of the reflected light by mathematical methods into an equal difference that is close to human vision, and is represented by a numerical value, which is the measured density value. The measurement of the dot area ratio using a reflection densitometer is based on the measured dot density and field density values, and is obtained according to the Marelli-Davis formula:
In the practice of the study of the performance of the printing plate, people have also found that the densitometer/spectrophotometer has certain limitations on the detection of the printing plate's display network, mainly as follows:
The performance of the printing plate is different from the surface of the paper. It has a certain density and is a small contrast surface. For a small contrast surface with a dot area coverage of less than 10%, dot coverage is obtained by the density measurement method, and the result has an error; dot area The determination of the N value in the rate calculation has always been a problem that cannot be solved with density measurement; the “noise†generated by the surface characteristics of the printing plate also affects the accuracy of the densitometer detection.
Densitometer Measurement Limitations As the development of computer-to-plate technology continues to be sharpened, the introduction of new precision instrumentation has become a need for development.
Digital image analysis and measurement instrument has always been a difficult problem to solve for dot area detection. The accuracy of using dot densitometry to obtain dot area values ​​in traditional printing techniques has been questioned by people. Many years ago, printing plate production companies and laboratories researched. Has begun to use the area detector and computer technology and video technology for plate detection and research. The introduction and continuous promotion of CTP technology has promoted the development of digital image analysis and measurement instrument. After solving a series of problems such as the economics, portability, and data processing accuracy of detection instruments, this technology has also gradually matured.
The integrated digital image analysis detector works as shown in Figure 1.
The digital image analysis measuring instrument adopts the CCD technology to collect the digital image of the halftone dot area. The image analysis method is the principle of the true dot area instrument. There is no problem of correction, and it is more versatile. It uses image histograms and thresholds. The binarized image can be obtained directly from the dot area, network line width, perimeter, and image features.
The digital image analysis meter has the same advantages as the density meter: portable and easy to operate.
The digital image analysis meter has advantages over the densitometer: according to the detection principle, the measurement result is more accurate; an instrument is used to detect various objects such as films, plates, and printed sheets. The storability of the test results; artificial selection of the measurement area through a random display. Avoid measurement errors. With the steady development of computer-to-plate technology, manufacturers of measuring instruments have introduced digital image analysis and measurement devices in recent years. The following describes several commonly used digital image analysis and measurement instrument:
1 . Vipcam114/116
Vipcam first introduced a hand-held offset printing plate measurement using video analysis. The three-button control of the Vipcam 114/116 makes the operation simpler. The video capture image is processed by the algorithm to obtain the required parameters, achieving a short time Accurately measure the dot area of ​​offset printing plates. The detection parameters are as follows:
Test objects: printing plates, films, printed sheets, FM and AM outlets. Positive and negative graphic plates.
Detection parameters: dot area rate, screen number, screen angle, dot diameter;
Technical data: Measurement repeatability is 0.2% soil, measurement time 1.5 seconds.
2. iCPlate
GrctagMacbcth introduced the handheld video technology plate measuring instrument, which uses three standard light sources. Almost all types of plates can be measured, enabling fast and accurate CTP and traditional plate, positive and negative plate, amplitude modulation and FM network measurements. The measurement result is directly displayed on the measuring instrument. Measurement data can be output and stored.
Measurement parameters: dot percentage, dot diameter, number of screens, screen angle, image display in the measurement area, and plate characteristic curve display.
3. TECHKON Digital MicroScope DMS910
Digital micrometer developed by Techkon. Measurable dot area rate, number of screen lines, screening angle, measuring object can be film, printing plate, printed sheet, can measure the traditional amplitude modulation network, FM network. The instrument consists of a dot-microscope collector, a USB adapter cable connected to a PC, and Windows-supported processing software. Measurement accuracy 1%, repeat accuracy ± 0.2%, measuring light hole diameter 18mm, measurement range 1. 2x1.6 mm, magnification up to 70 times.
4. X-RiteDot t
X-Rite launched a series of network inspection equipment; PlateDot, `ComboDot, PrintDot, using X-RiteDot can detect the traditional printing and CTP process film, plates, proofs.
The X-RiteDot can be connected to a MAC/PC for easy storage of data images, easy operation, real display in the measurement area, automatic calibration, support for upgrades, and precise detection.
The use of densitometers, spectrophotometers, digital image analysis measurements for the detection of plates should note:
1. Inspection of the plate should pay attention to the detection environment (excluding thermal plates). Detection should be done as soon as possible after exposure and development, if the printing plate gluing. The sizing layer should be removed;
2. Use distilled water to clean the measuring area of ​​the plate. If there is a different problem with gloss, clean the gluing site again.
3. If the printed plate is still to be used for printing after the test, the protective paper must be used in the test;
4. The long axis direction of the instrument in the measurement should be at a fixed angle with the plate edge.
5. The polarizing filter is not used in the test. The detection area should be as large as possible (diameter) 4mm) and the complementary color of the coating color should be chosen for the measurement light source. If using density meter measurements. The value of N is set to 1.
(Jiang Lei Zhou Shisheng Author: School of Printing and Packaging Engineering, Xi'an University of Technology)
After the computer-to-plate process was adopted, direct inspection of the printing plate became inevitable. Since the printing plate has surface characteristics different from those of the film and the paper, the question of which detection method to use in the detection, what kind of instrument, the detection conditions, the accuracy of the instrument detection, and the data stability are still to be studied. This article mainly categorizes the detection method of the printing plate, and introduces the new printing plate detection instrument.
Plate detection technology is based on different detection methods, and the suitability analysis of various printing plates is mainly divided into subjective evaluation and objective evaluation. (1) Subjective evaluation is visual evaluation, using digital test or digital control bar, through visual inspection. Or use the auxiliary amplification equipment to make intuitive judgments on the plate resolution, resolution, and other media performance parameters; (2) objective evaluation is to quantify the control process through testing equipment. It abandons the influence of human factors in the subjective evaluation and realizes the data standardization of the quality control process. This article will mainly introduce densitometers, spectrophotometers, and digital image analyzers for plate detection.
Density meter has become an effective measuring instrument for the detection and control of product quality because of its simplicity and high efficiency in the traditional printing process. It has played a decisive role in the development of printing technology and has achieved the detection and control of printed products. Human subjective to objective leap.
In most studies, the densitometry function of a reflection densitometer or spectrophotometer has been used to measure the density of solids and dots on the printing plates and proofs, and a mathematical method has been used to compare and evaluate the measurement results.
The reflection densitometer adopts the optical principle and converts the intensity of the reflected light by mathematical methods into an equal difference that is close to human vision, and is represented by a numerical value, which is the measured density value. The measurement of the dot area ratio using a reflection densitometer is based on the measured dot density and field density values, and is obtained according to the Marelli-Davis formula:
In the practice of the study of the performance of the printing plate, people have also found that the densitometer/spectrophotometer has certain limitations on the detection of the printing plate's display network, mainly as follows:
The performance of the printing plate is different from the surface of the paper. It has a certain density and is a small contrast surface. For a small contrast surface with a dot area coverage of less than 10%, dot coverage is obtained by the density measurement method, and the result has an error; dot area The determination of the N value in the rate calculation has always been a problem that cannot be solved with density measurement; the “noise†generated by the surface characteristics of the printing plate also affects the accuracy of the densitometer detection.
Densitometer Measurement Limitations As the development of computer-to-plate technology continues to be sharpened, the introduction of new precision instrumentation has become a need for development.
Digital image analysis and measurement instrument has always been a difficult problem to solve for dot area detection. The accuracy of using dot densitometry to obtain dot area values ​​in traditional printing techniques has been questioned by people. Many years ago, printing plate production companies and laboratories researched. Has begun to use the area detector and computer technology and video technology for plate detection and research. The introduction and continuous promotion of CTP technology has promoted the development of digital image analysis and measurement instrument. After solving a series of problems such as the economics, portability, and data processing accuracy of detection instruments, this technology has also gradually matured.
The integrated digital image analysis detector works as shown in Figure 1.
The digital image analysis measuring instrument adopts the CCD technology to collect the digital image of the halftone dot area. The image analysis method is the principle of the true dot area instrument. There is no problem of correction, and it is more versatile. It uses image histograms and thresholds. The binarized image can be obtained directly from the dot area, network line width, perimeter, and image features.
The digital image analysis meter has the same advantages as the density meter: portable and easy to operate.
The digital image analysis meter has advantages over the densitometer: according to the detection principle, the measurement result is more accurate; an instrument is used to detect various objects such as films, plates, and printed sheets. The storability of the test results; artificial selection of the measurement area through a random display. Avoid measurement errors. With the steady development of computer-to-plate technology, manufacturers of measuring instruments have introduced digital image analysis and measurement devices in recent years. The following describes several commonly used digital image analysis and measurement instrument:
1 . Vipcam114/116
Vipcam first introduced a hand-held offset printing plate measurement using video analysis. The three-button control of the Vipcam 114/116 makes the operation simpler. The video capture image is processed by the algorithm to obtain the required parameters, achieving a short time Accurately measure the dot area of ​​offset printing plates. The detection parameters are as follows:
Test objects: printing plates, films, printed sheets, FM and AM outlets. Positive and negative graphic plates.
Detection parameters: dot area rate, screen number, screen angle, dot diameter;
Technical data: Measurement repeatability is 0.2% soil, measurement time 1.5 seconds.
2. iCPlate
GrctagMacbcth introduced the handheld video technology plate measuring instrument, which uses three standard light sources. Almost all types of plates can be measured, enabling fast and accurate CTP and traditional plate, positive and negative plate, amplitude modulation and FM network measurements. The measurement result is directly displayed on the measuring instrument. Measurement data can be output and stored.
Measurement parameters: dot percentage, dot diameter, number of screens, screen angle, image display in the measurement area, and plate characteristic curve display.
3. TECHKON Digital MicroScope DMS910
Digital micrometer developed by Techkon. Measurable dot area rate, number of screen lines, screening angle, measuring object can be film, printing plate, printed sheet, can measure the traditional amplitude modulation network, FM network. The instrument consists of a dot-microscope collector, a USB adapter cable connected to a PC, and Windows-supported processing software. Measurement accuracy 1%, repeat accuracy ± 0.2%, measuring light hole diameter 18mm, measurement range 1. 2x1.6 mm, magnification up to 70 times.
4. X-RiteDot t
X-Rite launched a series of network inspection equipment; PlateDot, `ComboDot, PrintDot, using X-RiteDot can detect the traditional printing and CTP process film, plates, proofs.
The X-RiteDot can be connected to a MAC/PC for easy storage of data images, easy operation, real display in the measurement area, automatic calibration, support for upgrades, and precise detection.
The use of densitometers, spectrophotometers, digital image analysis measurements for the detection of plates should note:
1. Inspection of the plate should pay attention to the detection environment (excluding thermal plates). Detection should be done as soon as possible after exposure and development, if the printing plate gluing. The sizing layer should be removed;
2. Use distilled water to clean the measuring area of ​​the plate. If there is a different problem with gloss, clean the gluing site again.
3. If the printed plate is still to be used for printing after the test, the protective paper must be used in the test;
4. The long axis direction of the instrument in the measurement should be at a fixed angle with the plate edge.
5. The polarizing filter is not used in the test. The detection area should be as large as possible (diameter) 4mm) and the complementary color of the coating color should be chosen for the measurement light source. If using density meter measurements. The value of N is set to 1.
(Jiang Lei Zhou Shisheng Author: School of Printing and Packaging Engineering, Xi'an University of Technology)
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