A Digital Proof (Contract Proof) is an ISO certified test equipment for the graphics industry. A digital proof simulates the colour of offset printing or gravure printing colour accurate binding within the tight tolerances of ISO 12647-7. Today, a digital proof is processed via a RIP and then produced with pigment inkjet printers on special proofing papers.
The proof data is converted to colour separations, then reassembled into a composite image to simulate overprinting and trapping correctly. The data is then passed as a composite image to a usually more than 8-colour inkjet printer, which prints the data. In addition to the proof data, a digital proof must carry a Mediawedge by UGRA / FOGRA or IDEAlliance to be legally binding. Thanks to the standardized mediawedge, the print shop is able to check the proof for correctness. Since many printers don’t have the neccessary metrology at hand, digital proofs are often directly provided with a test report, which documents the accuracy of the measured values of the media wedge directly on the proof.
Older proofing methods as chromalin or Kodak Approval etc. are today hardly any more found in the market.
In the ISO 12647 “Contact Proofs” (ISO 12647-7) are the highest standard of proofs, but the term “Validation Prints” (ISO 12647-8) is also defined. A “Validation Print” is distinguished in that it is less accurate in colour, but therefore can also be produced on laser printers. Compared to the contract proof, a Validation Print has higher colour variations and is NOT automatically legally binding – only after prior consultation. A real “proof”, ie a real contract proof according to ISO 12647-7 is currently not only the most colour accurate and best option, but also the only legally binding proof.
In the case of a dot proof, the halftone screening of the final print is simulated in the proof. This screening shows possible moiré or other disturbing effects, that by dot proofing can be seen in advance on the proof.
Two different variants are possible. Firstly, for the production of printing plates in the RIP screening, imposed 1Bit data files are combined in the proofing software and then proofed. Secondly, some proofing systems can simulate the printed screen without using real 1-Bit Data. Screen angle, dot form and LPI are then specified within the proofing system, and the system then simulates the printing screen.
Perfectly suited for halftone proofing proofing systems are like the Kodak Approval system. Due to their high resolution, printing and proofing details are superior to common inkjet systems. Due to the high price in acquisition and in consumables, the long processing and laminating time and the small color gamut of these systems, they have never really got a large markt share outside of the US.
In particular, in recent years the halftone proof is much less common in the Proof practice and can be found today mostly only in the range of proofs within a printing house. Proofing Service providers today mainly focus on inkjet proofs without screening, because they have much larger color spaces and lower the cost of a proof compared to systems such as the Kodak Approval lower by up to 90%. The higher modern printing screen and other screening methods such as hybrid screening and frequency-modulated screens also decreased noticeably the risk of unwanted Moiré-patterns in print during the last couple of years. The focus is now more on the color accuracy of the proof and the reproduction of spot colors, as in the simulation of dots and screening.
Due to the high cost of consumables (market prices for Kodak Approval proofs are up to 100 Euro / A3 sheet) and the long processing time in the proofer and the elaborate laminating of the the proofs, Kodak Approval system are now only rarely found in the market. They were replaced by the faster, cheaper and in the color rendering significantly better and more accurate inkjet proofing systems.