Dot gain calibration method and apparatus

Abstract

A method for providing in use estimation of dot gain in digital printing using digital printing plates, the method comprising: applying to a digital printing plate a calibration strip, the strip comprising at least one set of patches, each patch comprising a plurality of dots at a predetermined gray level within said dynamic range, gray levels of said set of patches being distributed over said dynamic range, printing from said calibration strip under a current set of printing conditions, measuring intensities of said printing, and interpolating from said measurements to generate a curve of dot gain over said dynamic range. The curve can then be used to compensate. When moving to a different set of printing conditions, a single test print is then carried out and a new dot gain estimation is available.

Description

RELATIONSHIP TO EXISTING APPLICATIONS [0001] This application is a divisional of copending U.S. patent application Ser. No. 10 / 442,302 filed May 21, 2003, which claims the benefit of priority from U.S. Provisional Patent Application No. 60 / 382,525, filed May 22, 2002.FIELD AND BACKGROUND OF THE INVENTION [0002] The present invention relates to a dot gain calibration method and apparatus and, more particularly, but not exclusively to dot gain calibration for use with a pre-press system, press or proofing printer. [0003] Dot gain on a printed sheet is an increase in halftone dot size in comparison with dot size on the printing plate. The magnitude of the dot gain depends on factors such as the ink absorption characteristics of the paper, the ink, the screening parameters and the press variables. [0004] The total measured dot gain on the paper is a combination of two separate and unrelated gain factors; plate-related dot gain and press-related dot gain factors. The two gains may be dea...

AI Technical Summary

Benefits of technology

[0068] printing one or more test sheets using a currently mounted printing plate comprising a calibration strip, said printing according to said scheduled printing paramete

Problems solved by technology

The above cycle is very expensive and time consuming and the curve is only valid as long as conditions remain exactly the same.

Another common technique used in press sites due to the high cost of the current calibration cycle is on-press compensation.

This is a difficult and time consuming task, that becomes even more difficult and almost impossible as use of high screen ruling and FM screening gains popularity.

Even when a dot gain measurement cycle has been performed for a given paper and screen set, the validity of the tone reproduction curve is limited to a time frame, as paper and press characteristics often change over time.

Furthermore, conventional calibration methods are manual, and therefore prone to operator mistakes.

There is no closed-loop process of feed

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