Hi Mike,
Quote:
Originally Posted by Mike Strickler
I recommend paying close attention to dH on the 3-color gray patches, as this is a good measure of gray balance. I would look for a dH of .5 or better on these patches.
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One of the problems with dH by itself as a metric for neutrals as it doesn't take chroma into account. This can be a problem as a slight cast in the reference neutral could mean that a significant and largely visible difference in chroma in the sample can report a dH or zero (slightly green reference, gleaming green sample along the same hue angle, zero dH). Or, here's an example (from Mike Rodriguez) that compares dH to a proposed metric dF (which is essentially deltaE minus the lightness component).
Reference Neutral: Lab = 50 0 0
Sample Neutral: Lab = 53 4 0
Delta-E = sqrt( 9 + 16 + 0) = 5
Delta-H = sqrt( 25 - 9 - 16) = 0
Delta-F = sqrt( 16 + 0 ) = 4
These are extreme examples, but I'm of the opinion that dH in and of itself can be misleading for neutrals in some cases and you'd want to couple it with another metric (dE76, or replace it with dF or dE2000).
Quote:
Originally Posted by Mike Strickler
I do not personally feel that dH on primaries is a consistently useful metric for inkjet proofs, as these "solids" are merely simulated and an error there does not tell you, as it does on a laminate proof or press, for example, that there is an ink/colorant problem...... pure primary solids are statistically rare in a print job--except in the color bars, of course.
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Great point. The solids are probably the least likely color patches to occur in live imagery, yet often the most heavily weighted.
Quote:
Originally Posted by Mike Strickler
EFI's new Dynamic Wedge is an interesting development in this regard. It samples the predominant colors in the job and puts them in the color bar, where they can be verified with the same user-adjustable standards as can the standard wedges. It also contains all the spot colors present. This is not part of any official verification regime and likely never will be, but it can be highly relevant to the usefulness of a particular proof.
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This is indeed a useful feature...downright nifty even. Unfortunately it really can't maintain verfiable relevance outside of an in-house check for accuracy as those who receive the proofs would have no practical means of evaluating the strip themselves. So you'd want to include a more standard colorbar as well. Another really cool feature is the ability to optimize the Lab values for the particular image based on the dynamic wedge measured results. This is the quickest correction toward a passable verification I've seen. Unfortunately, the correction appears to be only applied to the dynamic wedge patches and associated imagery, so it won't "optimize" for example, color representing patches of an ISO 12647-7 control strip..again, making exchanging proofs with verifiable proof of conformance to a reference a little tricky.
Quote:
Originally Posted by Mike Strickler
As for "Selective Correction" in the RIP, I'm unsure what feature you're referring to. Colorproof XF has a relinearization tool, an L*a*b* optimization for tightening the proof-reference match, and a profile white point editor, which can help you match your proof to a "nonstandard" proof substrate color, which in reality is pretty much all press substrates.
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I originally suggested the selective correction, but I'm not intimately familiar with EFI's features. GMG for instance has a feature that lets you select particular patches and "edit" them while selecting the "range" of adjacent patches that will be affected. This could be useful in correcting minor issues in solids for example while still maintaining the integrity of the original profile. This is often unecessary, and usually only relevant when trying to get particular patches to pass a particular tolerance that is being required of the proof supplier...allude back up to your point on solid patch relevance.
best,
mike
