Tips on color management and how to 'get it right' for your customer.
By Jared Smith
Taking vital steps
You now need to output, compare, revise, and repeat. This process involves outputting a file or test file that is known to produce predictable results. These color-test files can contain raster images, color bars, varying gray levels, and many other attributes that all serve their own purpose. The file we use most often at our shop is the IDEAlliance ISO 12647-7 Color Control Wedge 2009 (idealliance.org). Once we have this color-strip output on the printer we’re seeking to characterize, we use a spectrophotometer to scan this media in to obtain readings.
These readings come in as variances in Lab (sometimes referred to as L*a*b) values – in other words, how far from the desired reading was our actual reading? This difference is referred to as the Delta. A Delta E of 3 or under is great, 5 or under is “industry acceptable,” and proofing devices should be at 1 or under. Lab values are the best way to identify color value. L+ to L- refers to how bright a color is, with the higher the L value the “more white” a color is. a+ to a- refers how red to green a color is. b+ to b- refers how yellow to blue a color is. So a Lab value of L22, a38, b-74 describes a color that is relatively dark, has a little red, and a lot of blue – so I would imagine a bit of a purple color here. This color would conversely not appear yellow, green, or white at all. The good news is that we don’t have to remember this – we just have to understand it.
After you have scanned in these strips, it’s time to make the revisions. There are many ways to do this, and they vary greatly depending on the RIP that’s being used. The concept, however, is the same with all methods: Let the software know what color values your printer output so the software can make the adjustments to remove the cast and get to neutral. This might require multiple rounds of outputs and scanning to get the desired result of neutral printing.