Does anyone know of an available (downloadable) test charts to determine the appropriate relationship between LAB values of primaries and density? The testchart I have seen uses wedges of CMYK to affect the ink desity accross the sheet and one measures the solids to find the closest desired LAB value (gracol, etc) and records the corresponding density to use as a process control. Thanks in advance.
That is definitely the most efficient method that I've heard of. GMG has a version to be used with one of their softwares, but you can easily build your own.
Would you think it would matter if the target patches lined up with the ink keys or not?
Generally test target patches are positioned to average out any inline or variation in density around and across the form area. So the same patches (e.g. solid C, M, Y, and K) will be positioned across the width of the sheet at the lead, center and tail as well as in the direction of the press sheet at left, center, and right.
Could you post a low res version of the test file you are currently using?
We've used a test form from GMG for this (see attached) and then tapered the press ink keys to lay down thin to thick ink film (see other attached press console view). But as Rich said, designing your own form is pretty simple...solid bars across the sheet is all you really need. Great way to determine optimal wet solid ink density/dry CIELab. With RGB bars you can also optimize overprints (often at the expense of ideal solid Lab values).
I am currently building the file. I opted to make my patches align with the ink keys as it only took a little longer to figure out and I had to pick something. In this case, the idea is to create varying ink density across the keys to find the closest match to the target LAB values (when dry), then use the corresponding wet density as a process control. This is all I have so far. Rich mentioned my inspiration, GMG, and their solution looks very easy to use and quite well thought out . The reason for the DIY is that I have functionality in other software product to adjust for gray balance, trend and report, etc.
Thanks for the info. It seems that even with fairly drastic wedges, you still needed to taper the keys on press to get enough difference for comparison? Do I understand that correctly?
Thanks for the info. It seems that even with fairly drastic wedges, you still needed to taper the keys on press to get enough difference for comparison? Do I understand that correctly?
You might find that, yes. In fact, we noticed little density drop off without tapering the ink keys.
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Originally Posted by kbaker
