This section introduces the new variables involved in G7, including "NPDC", "HR", "S" and "HC", and some new definitions, as well as the application of old variables such as gray balance and TVI.
Neutral gray printing density curve (NPDC)
A brand new concept in G7 is the "Neutral Gray Printing Density Curve" (NPDC), which requires measuring the neutral gray density and halftone dot values ​​on the printed grayscale bar. Because the neutral gray density is an absolute value, and TVI is a relative value, NPDC can get better contrast and density matching between devices.
NPDC has two standard curves, one for the CMY three-color combination curve, and the other is the single black version of the NPDC curve. NPDC correction compares the gray scale on the printed sample with the reference gray scale, calculates the RIP correction value in the form of halftone dot area, and then uses the new RIP value to make the printer reach the required NPDC curve shape. The curve correction value can be achieved by manually drawing the chart with G7 special chart paper, or it can be automatically generated by the IDEAlink curve drawing software, which can be downloaded from.
Find the "real" CTP curve
In order to find the actual printing curve of commercial CTP printing, GRACOL Industry Association analyzed multiple standard printing processes according to the standards of various suppliers, especially for the printing plates produced by uncalibrated CTP systems.
Each printing process is unique. On high-quality printed materials, we believe that the G7 NPDC curve can be in accordance with the ISO12647-2 standard, and can accurately reproduce each traditional CTP version (uncalibrated) printing process.
Note: The G7 NPDC curve is not an informal ISO standard. Other interpretations of ISO12647-2 may produce slightly different NPDC curves.
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