Colour proofs (correct: contract proofs) are an ISO-certified test equipment for the graphic arts industry. Colour proofs simulate the colourfulness of offset or gravure printing in a colour and legally binding manner within the narrow tolerances of ISO 12647-7. Today, they are almost exclusively calculated using a RIP and then produced with inkjet printers on special proof papers.
The proof data is converted into separations, then reassembled into a composite image to correctly simulate overprinting and trapping. The data is then transferred as a newly created composite image to an inkjet printer, usually with more than 8 colours, which prints the data. In addition to the print data, digital proofs must also carry a UGRA/Fogra media wedge in order to be colour-consistent and legally binding. Thanks to the standardised wedge, the printer is able to check the proof for correctness. Since many printing houses do not have this measuring technique at hand, the proof is often provided directly with a test report that shows the correctness of the measured values of the media wedge directly on the proof.
Earlier methods such as Chromalin etc. are no longer available on the market today.
In addition to the term “colour proofs”, terms such as digital proofs, proofs or online proofs are still in common use.
ISO 12647 defines the highest standard of contract proofs, or “proofs” (ISO 12647-7), as well as the term “validation prints” (ISO 12647-8). Validation Prints are characterised by the fact that although they are less accurate in colour, they can also be produced on laser printers. Compared to contract proofs, however, they accept much higher colour deviations and are only legally binding after prior consultation. Real “proofs”, i.e. true contract proofs according to ISO 12647-7 are currently not only by far the best variant in terms of colour but also the only legally binding proofs.
Further information:
https://en.wikipedia.org/wiki/Prepress_proofing