G7, as a revolutionary control method, has great advantages in the CTP era. Although it was originally designed for commercial offset printing, it can be used in any CMYK imaging process in the current actual operation, and after testing, it has been successfully extended to more printing processes, including coated paper and non-coated paper offset printing , Newsprint printing, gravure printing, flexographic printing, dye sublimation printing, inkjet printing, and electrostatic printing, etc.
When it comes to G7, we must say that the GRACoL standard is a set of operating guidelines and detailed specifications for the high-quality commercial offset printing developed by the American Offset Commercial Printing Standards Organization (GRACoL) combined with years of practical exploration of CTP. The standard is named GRACoL standard, GRACoL7 is the latest version of GRACoL. And G7 is a method for correcting printing drafts and printing machines formulated according to the GRACoL7 standard-G represents the gray value to be corrected, and 7 represents 7 basic colors defined in the ISO 12647-2 printing standard , Which is CMYKRGB. G7 achieves accurate color reproduction by controlling the chromaticity and neutral gray of CMYKRGB. Based on the visual characteristics of the human eye, it defines a series of neutral gray density curves (NPDC) for printing and copying, which can realize the difference between different materials "Similar printing".
Quality control parameters G7 proposes a number of novel quality control parameters, and in quality control, the most critical are the following two.
1. HR bright tone range: HR bright tone range is mainly used to evaluate the performance of the bright and dark parts of the printed matter. It has replaced the dots and expanded into the main parameter reflecting the overall tone and gray balance of the printed matter. There are two main HR evaluation methods, namely CMY gray (50C, 40M, 40Y) and black ink monochrome black (50K). In order to facilitate calculation and analysis, HR is mainly expressed by the value of neutral gray density (ND), and the value of ND can be calculated from the Y value in the CIE XYZ value.
ND calculation formula: ND = log10 (100 / Y) (0 <Y≤100)
HR_CMY can be obtained by subtracting the neutral gray density of the paper from the measured neutral gray density of the three-color gray block. The calculation formula is: HR_CMY = ND (50C, 40M, 40Y) -ND (paper). The HR_CMY of general printed matter is 0.54.
HR_K can be obtained by subtracting the neutral gray density of the paper from the measured neutral gray density of the monochrome gray block. Calculation formula: HR_K = ND (50K) -ND (paper). The HR_K of general printed matter is 0.50.
2. Neutral gray density curve: The neutral gray density curve (NPDC) is another new concept proposed by G7. The curve shows the percentage relationship between the measured density of the neutral gray scale and the original. Because NPDC is an absolute value, and the printed dot expansion curve (TVI) is a relative value, so NPDC can better ensure the density matching and contrast matching between different devices.
G7 defines a total of two kinds of NPDC, namely gray scales with CMY three-color superposition and gray scales with black ink. NPDC correction compares the printed gray scale with the reference scale, and then calculates the correction value of RIP in the form of percentage to change the printing state to make the NPDC reach the desired shape. The curve correction can be drawn on the drawing after manual calculation, or it can be calculated and drawn automatically by IDEA link curve software.
The calibration process of calibration method G7 mainly includes three steps, namely equipment calibration, linearization printing and gray balance calibration.
Equipment calibration: Equipment calibration mainly includes CTP calibration and printing press calibration.
1. CTP correction: CTP correction is divided into stability test of CTP printing conditions and linearization correction of CTP printing plate output. To carry out the stability test of CTP printing conditions, we must first monitor the HP value, conductivity, temperature and dot percentage of the CTP developer in a certain period, and secondly determine the CTP impact by statistically analyzing the impact of these parameters on the dot output Whether the version conditions are stable. When the CTP printing conditions are in a stable state, the linearization correction of the CTP printing plate output can be performed. The linearization correction process of the CTP printing plate output is as follows: First, the test plate without any correction is output and data measurement is performed, and secondly, the measurement data is used to generate a plate linearization compensation curve, and then the compensation plate is used to output the test plate again and perform data measurement. After the CTP linearization is completed, the error of the dot output is required to be within ± 0.5%.
2. Printing machine calibration: The stability and repeatability of the printing machine is an important premise and application basis for the realization of G7. Therefore, before the G7 test, it is necessary to calibrate the printing press to ensure that it reaches the optimal results. Both the printing press and its consumables should be properly adjusted, including blankets, linings, fountain solution, etc. The correction factors of the printing press include water-ink balance, printing pressure, registration control and ink drying, and the working state of the printing press can be quantified by the relevant attributes of the printed sample, such as solid density, printing contrast, overprint rate, dot expansion, registration accuracy Wait. The easiest way to judge whether the performance of the printing press meets the test requirements is to print a flat screen.
Linearization printing The implementation of linearization printing is to obtain the printing status of the printing machine after reaching the corresponding technical parameters, and to achieve the CIE LAB values ​​of the monochrome solid ink CMYK and the two-color overprinting ink RGB specified by ISO 2846-1. Since each ink contains three target values ​​L *, a * and b *, and there is only one solid density value, it is easier to control the solid density by measuring the CMY solid density value with a densitometer as the target density in printing control . When CIE LAB and density values ​​conflict, the former takes precedence. After reaching the calibrated solid ink volume, check the TVI of each CMYK swatch. The main purpose is to ensure that the printing status is normal, that is, all ink TVI must be smooth and smooth.
In the linear printing stage, gray balance and NPDC are not important, but the uniformity of the entire sample should be as far as possible. The color difference of CMYKRGB should be within the tolerance range (<5), the density of the bite area should be uniform (error ± 0.05 Within), the registration error is within 0.01mm.
The gray balance correction G7 mainly controls the print quality by controlling the gray balance, so the gray balance correction is crucial. There are two methods for gray balance correction, one is to adjust the device itself, such as adjusting the amount of ink, and the other is to create a CMY RIP color separation curve. It is best not to use the RIP color separation curve when performing offset press calibration, because the gray balance error of most offset printing equipment is unstable or not uniform. Conversely, for more stable devices, such as proofing systems or inkjet printers, RIP color separation curves can be used during calibration because the gray balance of these devices is relatively stable.
Control the gray balance in the production process, that is, by measuring the HR color patch (50C, 40M, 40Y) to ensure that the corrected device is still in the gray balance. Measurement of gray balance also requires the use of SC color patches (75c, 66m, 66y) and HC color patches (25c, 19m, 19y) to discover small errors in image table reproduction in the running process, but because of the inherent instability of the device, these Errors are difficult or impossible to correct. Therefore, in actual production, the standard Lab value of HR, SC and HC color patches should not be too harsh.
Today, G7 certification has become a symbol of high-quality printing. Obtaining G7 certification qualifications seems to indicate that the company has a certain quality control ability and is in line with international standards. However, it is standardizing printing production operations, improving printing quality, and enhancing operators And the professional qualities of technical management personnel also have an important role in promoting. Perhaps, we should make G7 more violent on the basis of understanding G7.
This coffee table is very popular and widely used in home, coffee shop and restaurant, you could match our home chair together.
We use environmental material and provide the perfect replica items.
The comfortable table is available in a selection of colours.
We also have many Home Accessories to decorate your home.
If you need more information, just feel free to contact me, I will send you more details pictures and information
Modern Coffee Table,Round Side Table,Side Coffee Table,Triangle Coffee Table
Ningbo Realever Enterprise Limited , https://www.realeverfurnishing.com