Re: Is a printer's full gamut used to make a profile?
Re: Is a printer's full gamut used to make a profile?
- Subject: Re: Is a printer's full gamut used to make a profile?
- From: Randy Wright <email@hidden>
- Date: Fri, 21 Sep 2001 18:12:47 -0700 (PDT)
--- Steve Upton <email@hidden> wrote:
>
At 7:55 PM -0700 9/14/01, Randy Wright wrote:
>
>I have been comparing profiles made with
>
ColorVision
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>Profiler Pro for RGB photographic printers with the
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>spectro measurements used to create the profile, in
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>ColorThink. ColorVision uses a target made up of
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>uniformly-incremented samples of all the possible
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>color combinations. If you view the patch readings
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in
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>ColorThink's 3D Grapher, they appear as concentric
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>layers. When the profile is superimposed on the
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>measurements, its outer limits lie for the most
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part
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>between the outermost layer of readings and the
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next
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>one in. In some areas, it goes in past the second
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>layer to the third. This seemingly indicates that
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the
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>full gamut of the printer is not being used. Is
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this a
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>common condition? Is it even significant? I don't
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have
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>any other profiling packages with which I could
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make a
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>comparison.
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>
Ok - bear with me here....
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>
The first test you want to do is to see if the
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proofing side of the
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profile is doing a good job. (CMYK->Lab)
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>
So try this:
>
>
- open the original CMYK reference file into
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ColorThink as a Color
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List - this may not be available with Profiler Pro.
Sans any profile, right? ColorVision automatically
tags theirs Adobe98.
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If not, I think
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you might need to make it by hand. Copy one of the
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CMYK stunt files
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and replace it's numbers with the ones that you sent
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to the CMYK
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printer using Profiler Pro. They need to be in the
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same order as the
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ones in the measurement file.
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The color list is generated top-to-bottom, then
left-to-right, correct?
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- drag your profile onto the Color List - this will
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"proof" the CMYK
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settings into Lab using the profile. This is the
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profile saying "I
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think this is what these CMYK values will look like
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if sent to that
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device".
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- open the measurement file (Lab data) into
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ColorThink. -Now you have
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the ACTUAL readings in comparison to the previous
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step's profile
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"speculation"
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- drop each list into the 3D grapher and select
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"Vector Compare". Then graph.
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ColorThink will graph the differences between the
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measured colors and
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the predicted colors. If the color shift vectors
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aren't too big, then
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you can have some confidence in the proofing side of
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the profile. If
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they are large and all over the place then the
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proofing side of the
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profile is bad. ColorVision's profiles have not
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really been known for
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their proofing accuracy, Profiler Pro should do a
>
better job as it
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has instrumented measurement data to go by.
>
My energies have been diverted from this project until
just now. The vectors are quite small in the yellows
and greens, increasing through the reds and cyans, and
starting to look significant in the magentas and
blues. I guess my question is: Why is this so? If the
gamut is defined by measurements of the printer's
capabilities, why doesn't the profile use the entire
range of those capabilities? Is this one of the
"features" that separate on profiling package from
another?
>
These steps and tests are undergoing a fairly major
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revision in
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ColorThink 2.0 to make them easier and faster to do.
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Once you find
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that you are happy with the proofing side of a
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profile you can do
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some round-trip tests with profiles that can
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illustrate rendering
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intent behavior quite well... ya'll hafta stay tuned
>
fer that...
Actually, trying to understand how the rendering
intents played out was what led me into this in the
first place.
Thanks,
Randy Wright
Color Services