BasICColor and "vcgt" tag
BasICColor and "vcgt" tag
- Subject: BasICColor and "vcgt" tag
- From: Marco Ugolini <email@hidden>
- Date: Thu, 19 May 2005 17:53:55 -0700
In a message dated Thu, 19 May 2005 20:00:00, Carlo Lavatori wrote:
> I don't know if what I am saying makes any sense, but from what I understood
> so far about calibrating/profiling LCD monitors such as Eizo CG 21, the best
> thing a calibrating/profiling soft can do is to make all the necessary
> adjustment in the monitor video card through DDC/CI since it's got more bit
> depth than the apple video card does
>
> Correct?
Yes, if you use DDC/CI-aware software (like your BasICColor 3.0.4), the
software itself will take care of sending the proper instructions
(regarding luminance, contrast, color balance, etc., via USB, in your case)
to the LUT internal to the monitor, which works in a higher-bit mode.
Ideally, this leaves a minimum of work to be done on the graphic card's LUT,
which operates in 8 bits and therefore is more prone to creating visual
artifacts when its curves are modified. The adjustments made on the
higher-bit LUT (inside the display) do a far smoother, cleaner job of
avoiding the banding, color seepage and crossover pitfalls so common in
lower-bit modifications in the graphic card. (That is, until the fateful day
when higher-bit graphic cards are introduced on the mass market...)
> My question is:
>
> I created two profiles for my Eizo through an Eye-One spectrophotometer
>
> First Profile with Color Navigator 3.0.1 - D50 Gamma 2.2 -
> 90 Cd/m2
>
> Second Profile with BasICColor 3.0.4 - D50 Gamma 2.2 - 90 Cd/m2
How bright is the environment surrounding the display? It seems to me that
90 cd/m2 is a bit low. Personally I would advise something upward of 120
cd/m2 (even as high as 140), unless you work in very dim surroundings.
> The profile created with ColorNavigator has a "vcgt" tag (apple display card
> table) with the RGB channels set at gamma 1.0, minimum 0 maximum 1 - a
> straight line - therefore I assume the values of the LUT in the computer video
> card have not been touched
>
> The profile created with BasICColor 3.0 has a "vcgt" tag which is not
> straight for the 3 RGB channels,
> each channel has it's individual curve/correction,
> for example, blu has a minimum value of 0,001 and maximum of 0,984
>
> Am I wrong to assume that therefore BasICColor has changed somehow the
> values in the computer video card's LUT?
>From what I have read on this discussion board from owners of the Eizo CG21
(which, unfortunately I do not own), I understand that BasICColor does a
better job overall with this display than the Color Navigator software. If
it appears to modify the LUT curves on the graphic card, it's not ipso facto
a cause for alarm.
I wouldn't worry too much about whether BasICColor alters your vcgt curves
(specially since the values that you mention appear rather minimal anyway,
almost negligible). I would suggest that the ultimate test is to evaluate
the results of your calibration/profiling by viewing a visual target (in
100% view). A good one for this purpose was developed by Mark H.
McCormick-Goodhart. Please contact me offline, if you want a copy of it.
Another way to quickly evaluate the neutrality and linearity of your
calibration/profile is to create a grayscale gradient in Photoshop (in L*a*b
or RGB), viewing it at 100%. Any banding, tonal compression, color casts and
crossovers will become readily apparent.
Buona fortuna!
--------------
Marco Ugolini
Mill Valley, CA
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