Re: Question about Lab and monitors....
Re: Question about Lab and monitors....
- Subject: Re: Question about Lab and monitors....
- From: "Xabier Urien" <email@hidden>
- Date: Tue, 24 Feb 2004 15:12:11 +0100
Hi....
I have made some tests with 2 monitors... Apple Studio Display 21' and
Barco 21'..
I have calibrated both to D50
Taking the advice of Roger, I calibrated to D50 and here the result...
ColorPicker and Photoshop now shows me the same RGB, starting from same Lab
value and applying the same Monitor Icc (a very insignificant differences).
Therefore, I understand that PS works better with profiles made with D50
(hopefully also D65) than other customised configurations....
Anyway, the differences between the lab image values and measured (with
GretagMacbeth Measure tool) are bigger than expected, and I have made the
measures after profile the monitors. The DE are between 3 and 9 (de94) in
both monitors.
If I measure the Lab 100,0,0 I've got L=87... tat means the significance of
the white point....
Unlike I expected, the Barco's behavior is not faraway to Apple....
the next tray that I will make is... compare the proof (cmyk epson for
sample) and the simulation in PS. To do that I will measure the printed
colors with Measure Tool and the same color in the screen with PS,
simulating the Output device... I will let you know whatever happen.....
For a moment I'm seeing that even the High level monitors has a significant
difference between what they tray and what they do....
Thanks to all ....
Kind regards....
*********************************
Xabier Urien
C.G.Otzarreta
email@hidden
*********************************
----- Original Message -----
From: "Roger Breton" <email@hidden>
To: "Xabier Urien" <email@hidden>
Sent: Monday, February 16, 2004 1:54 PM
Subject: Re: Question about Lab and monitors....
>
Thanks Roger for your answer...
>
>
>
I4ll tray like you say with D50, and I4ll let you know what's happen...
>
Anyway, I agree that could be a little bit complex, but also interesting
as
>
it seems...
>
I4ll tray to do the same test with a Barco Monitor. (I have done with the
>
Barco's measure tool with very good resoult)
>
>
Thanks to all...
>
>
>
*********************************
>
Xabier Urien
>
C.G.Otzarreta
>
email@hidden
>
>
*********************************
>
----- Original Message -----
>
From: "Roger Breton" <email@hidden>
>
To: "Xabier Urien" <email@hidden>; "Color List"
>
<email@hidden>
>
Sent: Friday, February 13, 2004 3:01 PM
>
Subject: Re: Question about Lab and monitors....
>
>
>
> With my Spectrolino and the Measure tool of Gretag (spot option) I
>
measured
>
> the color of a flat image on Photoshop. The image was create in Lab (for
>
> example 54/81/70).
>
>
That color is barely within the bounds of my monitor according to
>
ColorPicker? It's likely clipped.
>
>
> The readout of spectrolino was 48.5/65.6/57.8.
>
> Ok, de DE94
>
> is 6.46. After that, with the ColorPicker I did the next test. I
>
configured
>
> with the Icc of the Monitor in point... and insert the same Lab values
>
like
>
> "lab input". The result was another different color (52/69/60 DE94 3.4)
>
>
Yes, how come there is a difference you say?
>
>
> What means that????
>
>
> a) The monitor is not properly calibrated.
>
>
No, it is not a function of calibration or profiling since Photoshop and
>
ColorPicker are both using the Destination profile to convert from Lab to
>
RGB and back to Lab to calculate DeltaE. Are they getting there
differently?
>
That's a question for gretagmacbeth, for sure.
>
>
> b) ColorPicker tool is not a god tool to predict.
>
>
No, try some other tool like ColorShop X and it should give you the same
>
result.
>
>
> d)the Icc is not god, because if not, the ColorPicker should give the
>
measured
>
> lab (more or less)
>
>
Yes, the ICC is not god, and yes ColorPicker should give you the measured
>
Lab (more or less).
>
>
> e) The limitation of the CRTs allows these type of confusion...
>
>
True. There could be a variation between the time you calibrate and
profile
>
and the time you re-meaasure in Photoshop. But that should not be a large
>
difference.
>
>
> f) Photosop fail with the lab colors...
>
>
What are you calibrating your display to: D50, D65 or what? Try
calibrating
>
to D50 and repeat the same experiment and tell me if you see a difference.
>
As far as I know, if you calibrate to other than D50, Photoshop does not
>
manage the color 'absolutely' to the display, meaning it can't give you
>
what's called 'corresponding colors'. I'm interested to hear what others
>
have to say about this, especially the folks from Adobe (I could be
utterly
>
confused about it myself even after years of reading and experimenting and
>
thinking about this problem) but this is getting to be a complex
discussion
>
because, as far as I know, we're going to have to introduce the business
of
>
chromatic adaptation into the equation. And if you really want to
understand
>
the difference between the color you measure with your instrument, after
>
profiling, and the one predicted by your profile in ColorPicker, you are
>
going to have to take chromatic adaptation into account.
>
>
> Xabier Urien
Keep me posted!
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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