Re: Target Reference file
Re: Target Reference file
- Subject: Re: Target Reference file
- From: Terence Wyse <email@hidden>
- Date: Fri, 16 Jul 2010 16:25:07 -0400
I'm clipping out some of the previous quotes for brevity.
On Jul 16, 2010, at 2:42 PM, david wollmann wrote:
>>
>> I'm not really sure if Delta E values would tell you much in this context. It would tell you they were "different" but not which one is better. I would look at....1) gamut volume 2) gamut "boundary" 3) tonal distribution of the primaries/secondaries (change view to "points" in CTPro and 4) the "Curves" display and neutral analysis. The lower the chroma values along the neutral axis (using absolute colorimetric), the better neutral stability the profile should have.
>
> Okay, I like these check points. #3 is very nice, I had not used that very much. When looking at the neutral analysis and the chroma values, #4, the target in bottom right corner of the Profile Inspector-Curves window in ColorThink Pro, these are the "chroma rings" and we are looking down, on top of, the L* axis?
Yes. You're looking at the a*/b* or "chroma" plot.
>
> A Chroma value is given at the bottom of the target but what are the two numbers at the top of the Neutral Rendering Chroma Target?
The value below the a/b/chroma plot is the chroma value as you stated. The lower this value is, the better. Under 2.0 is good, under 1.0 is excellent.
The values above the a/b/chroma plot are the a*/b* values.
The chroma value below tells you how far off of neutral you are, the a*/b* above tells you which way the neutral is "casted". You can also watch the little red dot in the plot and see which direction it goes as you scroll/mouse across the neutral curves.
Unless you really screw up the separation parameters, you should see values well below 1.0 until you get closer to the shadow where things will start to go a bit "wonky". Generally speaking, if the values start creeping up >2.0, you probably need to reduce your total ink limit some. What I do for an inkjet printer is start with a profile at 400% total ink and look at both the *actual* total ink in the profile, the chroma value in the neutral rendering curves (use absolute!) and also look at the L* Out: value. The juggling act is reducing the total ink limit until you get a nice neutral rendering but without compromising the L* Out value (lower the better). You'll generally find a "sweet spot" of low chroma and good L* out values but you'll reach a point where the L* out value starts getting compromised if you reduce your total ink limit too much. The total ink value you get from the 400% profile is usually a good starting point for further ink reduction.
>
> "Curves" shows the CMYK ink curves for neutral rendering and a fifth element in the opposite direction displayed with a gradient, what is this, is it L*? Does it show the gray ramp from media white point to Dmax using all channels?
Yes, that's the L* output curve.
Regards,
Terry
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