Datacolor User to User Support Group.

On Jan 21, 2008, at 4:27 AM, boborlehanneton wrote:

> David Miller said:
> - There's supposed to be a blue cast on the white patch (meaning:
> the white of the paper that you're profiling/measuring); because  
> that's
> the color of the paper. Most papers measure with a slight blue cast.
>
> C. David Tobie said:
> - Whites turning blue indicate that you are using an artificially
> whitened paper. Checking the checkbox in Ref White should solve that.
> Checking the checkbox in Ref Black should reduce your "grayveil"
> effect as well, especially on matte papers.
>
> - If the whitepatch (paperwhite) of your target measurements (after
> calibrating on the white tile!) is showing up as a bright Cyan,
> instead of white, that is hardware issue, and you will need to contact
> support at ColorVision.com to get your spectro replaced. But first,
> clean the whitetile with rubbing alcohol and a paper towel (don't use
> cloth, it may have whiteners in it). See if white then measures as
> white; if its still bright Cyan, then contact support for a  
> replacement.
>
> - Then you will need to contact colorvision support to get a
> replacement unit.
>
> What is usual and what is wrong?
> Paper is Hahnemuhle Natural Art Duo. Matte paper.
> - Grammage g/m2 256
> - Thickness mm 0,38
> - Whiteness % 88,5
> - Opacity % 98,5
> - Media Colour natural white not bleached
> - pH-Value total 8,1
> - Cobb g/m2 74,0
> - Ink limit % 250
> - Water resistance very high
> - Special features coated on both sides
> Chart is printed in Qimage (ICM off...), soft proof is realised in
> Qimage (I haven't tried in S3P), prints are printed in Qimage (profile
> with black ink compensation).
>
> Calibration of the spectrocolorimeter on the base (white disk) gives a
> light gray, 0.1 density.
>
That's fine. What you're talking about is: calibrating the spectro
on the white tile; and then taking a measurement of it; which is  
technically
possible (by using the extra commands we provide in the Tools menu;
you can use the Calibrate command there, and then the Measure command,
to take a spot measurement of anything that you like, including the
calibration tile itself).

(In the normal course of running through the software's UI, you would
not take a measurement of the white calibration tile).
>
> Measure on a not printed piece of paper (natural art duo) gives a
> light cyan. Which could be explained, as you said, by the artificial
> white of the paper.
>

It should never measure as a "light cyan" - any measurement of paper
white that looks like cyan is wrong.

The "slight cast" being referred to for a paper with optical brighteners
is very slight, for instance: a "b" component of -3, or -4. This won't
look like cyan at all, the paper white measurement will be something
like Lab = (95, -1, -3), which will look like a very light gray with
an extremely slight bluish cast.
>
> The prints are quite good (better when calibrated on the paper instead
> of the white disk of the base).
> Does the spectrocolorimeter need a replacement???
>
>
There's a world of difference with what I'm describing here and an
incorrectly measured paper white that turns into cyan. (The "b"
component in the "bad" case will be more like -127, not -3). The
patch measurement will look like a brightly colored cyan if its
wrong that way. It would poke you in the eye as being obviously
and totally wrong.
> The issue is soft proof. Automatic ref white (with calibration on the
> base), soft proof is yellow and psychedelic :D
>
Psychedelic is wrong. If you're seeing banding or weird colors in the
soft proof, you have bad measurement(s), and white measuring incorrectly
as cyan (which should, remember, being poking you in the eye if you just
look at your measurements) would count towards that quite heavily.

Checking your measurements should be a simple thing; everyone who is
using PrintFIX PRO/Spyder3Print should be doing this, so in the interest
of all of our mental health, I'm going to post a separate message here
as followup telling everyone -exactly- how to do this...! :-)
>

David Miller
Senior Software Developer, Digital Color Solutions
Colorvision