Colour proof quality verification

Abstract: BACKGROUND When a customer delivers a colour proof to a printer, they expect the final print to look similar to that proof. Today it is impossible to control if a match between proof and print is technically possible to reach at all. This is mainly due to the fact that no information regarding the production circumstances of the proof is provided, for instance the printer does not know which proofer, RIP or ICC-profile that was used. Situations where similarity between proof and print cannot be reached and the press has to be stopped are both costly and time consuming and are therefore wished to be avoided. PURPOSE The purpose of this thesis was to investigate the possibility to form a method with the ability control if a proof is of such good quality that it is likely to produce a print that is similar to it. METHOD The basic assumption was that the quality of a proof could be decided by spectrally measuring known colour patches and compare those values to reference values representing the same patches printed at optimal press conditions. To decide which and how many patches that are required, literature and reports were studied, then a test printing and a comparison between proofing systems were performed. To be able to analyse the measurement data in an effective way a tool that analyses the difference between reference and measurement data was developed using MATLAB. RESULT The result was a suggestion for a colour proof quality verification method that consists two parts that are supposed to complement each other.The first one was called Colour proofing system evaluation and is supposed to evaluate entire proofing systems. It consists of a test page containing colour patches, grey balance fields, gradations and photographs. The second part is called Colour proof control and consists of a smaller set of colour patches that is supposed to be attached to each proof. CONCLUSIONS The method is not complete since more research regarding the difference between measurement results and visual impression is needed. To be able to obtain realistic tolerance levels for differences between measurement- and reference data, the method must be tested in every-day production. If this is done the method is thought to provide a good way of controlling the quality of colour proofs.