Evaluation of the Press Calibration Methods by Simulation.

摘要

Press calibration is an approach to adjust the behavior of ink, paper, and press with the use of a CTP platemaking system to achieve a specified reference printing condition.;Reference printing condition defines a common color space for color image data exchange between various output devices. The advantage of a reference printing condition is to improve color image quality and reduce cost and time. Corner points of the color gamut, TVI curves, and grey reproduction are the three significant elements in a reference printing condition, which make them essential in press calibration.;There are usually two press runs in press calibration. The first press run (Run 1) is to adjust ink system of a press to achieve the color gamut conformance to the reference aims with linear plates. The second press run (Run 2) is to either adjust tonality or neutrality of the press with curved plates based on the Run 1 printing condition.;Thus, the question is "whether the two press calibration runs can meet the three requirements achieving full conformance according to the reference aims?";This research assessed two cases starting with two real Run 1 printing conditions. In the both cases, ISO Type 1 paper was used and the color gamut was in conformance to the reference CGATS TR006 printing condition.;Run 2 was a simulated calibration press run with the adjustment of either tonality or neutrality of the press. The use of A-to-B tag and B-to-A tag of the Run 1 ICC profile with absolute colorimetric rendering intent was the essential idea to simulate a calibrated Run 2 printing condition. The advantage is that no printing drafts would occur in the simulation approach, which guarantees repeatability from Run 1 to Run 2.;The calibration results were verified to be in conformance first before other assessments. In other words, TVI curves of the TVI-based calibrated results were verified to be in conformance first before grey reproduction conformance was assessed; and grey reproduction of G7-based calibration results was verified to be in conformance first before TVI curves' conformance was assessed.;The research results show that (1) if deviations of TVI curves and grey reproduction in Run 1 printing conditions are close to the reference aims, either of the two calibration methods can achieve full conformance; and (2) if discrepancies of TVI curves and grey reproduction conformance in Run 1 printing conditions are far from the reference aims, a third requirement may not be in conformance unless adjustments will be iterated within specified tolerances.