Re: Colormatch vs Adobe 98 - Don to Bruce part 1 of 2
Re: Colormatch vs Adobe 98 - Don to Bruce part 1 of 2
- Subject: Re: Colormatch vs Adobe 98 - Don to Bruce part 1 of 2
- From: Don Hutcheson <email@hidden>
- Date: Thu, 31 Jan 2002 19:40:10 -0500
Bruce,
A thoughtful and valid response. No less than I'd expect from you. Clearly
both of our methods achieve something 'usable', proving there's more than
one way to skin a cat.
I'll keep my comments sparse so this doesn't drag out. We agree on many
points but draw different conclusions. Admittedly I'm a little harsh on D65
but in my workflow it offers zero advantages. Call me conservative but in a
D50 landscape, the use of D65 for anything seems like a time-bomb.
First I need to clarify a point I made rather poorly.
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> 1. Three-and four-band colorimeters are normally 'hardwired' to D50 and
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> CANNOT measure D65 correctly.
What I MEANT to say is "Three-and four-band colorimeters are normally
'hardwired' to produce CIELab(D50) values and CANNOT produce true
CIELab(D65) values correctly."
My error above explains why I actually agree with your response.
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>
While it's relatively rare for Don and I to have major disagreements,
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this is one of them. Some three years ago, I had teh opportunity to
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compare various monitor calibrators using a 0.5nm spectroradiometer
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as a reference. The X-Rite DTP 92, the Gretagmacbeth Spectrolino
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(which is admittedly not a colorimeter), and the Sequel instrument of
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the day all came within 100K or so of producing 6500K tristimulus
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values on the subject (CRT) monitors.
My experience is the same as yours; i.e. that any colorimeter can of course
measure the ratio of CIEXYZ(D50) and convert that into an equivalent 'color
temperature', pretty much as well as a spectrophotometer. But that's not the
point I was trying to make.
The point I'm trying to make here is that a typical colorimeter's Lab
measurements are based on X-sh, Y-ish, Z-ish filters that simulate the D50
spectral weighting functions. The only way to get CIELab(D65) values is
either to transform through something like Bradford or to send a signal to
the device itself to change it's internal filter mixture factors. I don't of
any colorimeters allow that kind of software control, or even support the
D50/D65 switching function internally.
I'll concede that the error is usually unnoticeable, but it can sometimes be
large. That's what I call a time-bomb.
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>
> 2. Any D65 color space will give you a blue cast if you convert from it
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> with Absolute intent, or a yellow-red cast if you convert to it with
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> Absolute intent.
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This is true, but not terribly relevant.
Yeah, OK.
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> 3. All graphic arts viewing booths and viewing standards specify D50 for
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> color comparisons.
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>
Around the same time I did the monitor calibrator comparison, I also
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went through the rather depressing exercise of measuring some dozens
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of viewing booths in everyday use in the SF Bay Area. All were
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nominally D50, but the measured range went as far south as 3600K, and
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as far north as 7500K. The dimmable viewing booths tend to be less
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accurate in color temperature than the non-dimmable ones.
Again we share similar experiences. In fact over the years I've probably
seen worse than you. Ironically the real problem is not color temperature,
because the eye adapts wonderfully to simple color temperature differences.
The far worse horror is when the transparency viewer is reddish and the
overheads are greenish (e.g.)! All booth manufacturers were guilty for years
on this point but hid behind barn-door standards and mass-production woes.
The latest standards are no better (I can't complain if I won't sit on the
committee) but I've finally convinced GTI to attack the problem and in the
last couple of years they've made great strides in improving the match
between T and R.
In spite of this, I would contend that twenty thousand old or incorrect
booths don't invalidate the standard. Accurate or not, the assumption has to
be that the AVERAGE Fred will be looking at my proof in a D50 booth.
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> 4. Virtually every printer, separator, agency, photolab, photographer or
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> publisher has access to some form of D50 viewing condition and uses that to
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> make color judgements. Changing to D65 puts you out of sync with your
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> clients, vendors and industry standards.
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See above.
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> 5. The ICC PCS (Profile Connection Space) defaults to D50.
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>
Again true but not terribly relevant unless you insist on using
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Absolute renderings inappropriately.
Yep. However errors resulting from a Bradford transformation can affect
other intents and soft proofing, as well.
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(continued)