A proof is only as good as the light under which it is viewed. Just going to the window or switching on the light at dusk is useless: between December and July, between 8 am and 8 pm, between cloudy and sunny days there is a huge difference in the lighting, which makes any colour evaluation impossible. And if you switch on the light, you normally switch on a bulb with 2700 Kelvin – or even worse: an energy-saving neon bulb that somehow shines in any spectra… a disaster!
The reasons for metamerism effects (in short: that two colors look identical under one light, but completely different under another) lie in the different printing technologies. Colors that look the same under a light bulb can suddenly look very different under a neon tube.
In recent years, ink-based digital proofs have established themselves in the proofing sector. Because it is printed in ink, specially coated paper must be used, which is not in any way similar to the subsequent production run. Anyone who has ever tried to print on glossy coated paper with an inkjet printer knows: the ink never lasts! Metamerism is therefore always involved when a proof is to be compared with offset printing.
The light under which proof and production run are viewed is particularly important.
ISO 3664 regulates standardized light, which is important for viewing proofs and prints. D50 is no longer D50: The International Lighting Commission CIE has revised ISO 3664 in recent years and adapted it to today’s circumstances. If UV components used to be strictly prohibited, they are now part of the standard. In the past, the focus was on consistency between slide and print, while today monitor, digital proof and offset printing are important. Therefore, proofs must always be viewed under D50 Standardized Light, so that they are really “colour-binding” in their perception.
Every print shop in Germany adheres to a predefined standard, the process standard offset printing. This standard defines target and tolerance values for printed products. In order to prove that your proof delivered to the print shop meets these standards or is within the tolerances, the media wedge is measured and the values analysed in case of doubt – i.e. in case of a streak. If these measured values are correct, the print shop is obliged to adhere to and achieve these values.
Practice generally shows the following: If you want to have a 4-page image brochure proofed and printed, it is usually sufficient to have a single media wedge printed under the 4 pages. If the media wedge is also provided with a test report, the colour accuracy for the print shop is directly confirmed as a guideline.
However, if you want to be on the safe side, have a separate media wedge (including test report) printed under each of the 4 pages of your brochure.
How does this check work?
What is the advantage of automated creation and checking of the media wedge directly in the proofing device?
Further information on the test report, the media wedge and on the work and responsibility of UGRA/Fogra can be found at www.ugra.ch and www.fogra.org.