Re: help with camera profiling
Re: help with camera profiling
- Subject: Re: help with camera profiling
- From: Jon Meyer <email@hidden>
- Date: Sat, 02 Nov 2002 07:50:07 -0500
QUESTION
- Why does a black to white gradient made in photoshop 'Lab' and
'Grayscale' mode have a gradation that looks very different to black to
white gradation made in RGB mode?
I just ran a quick test. PS7 over OS 10.2
The appearance matches on all three files. I would suggest that the
monitor and calibration/profiling should be evaluated in your system.
- Which gradient, if any, are the gradations in my 21 step
transmission step wedge equivalent to, the RGB, k or Lab gradation?
Calibration of a scanner depends on film density correlated to RGB
system values. As films vary in Dmax potential, based on
characteristic curve/developer formulation/temp/time, everyone who
does zone (or attempts to get close) will find what is realistic for
each film type. A value of 2.2 is an index average.
Please note that we are not at the profile stage. We are simply
handling b/w neg processed out to Dmax and calling the scanner
calibration for that density to equal 5's RGB.
By contrast, Dmin should be 250's
.74 density above base+fog = 18% gray = 128's
No ICC profile is required if the b/w gradation is set accurately.
(In fact, an accurate gradation is a key to achieving a solid
platform for building good scanner profiles - when progressing to
characterizing Ektachrome or Fujichrome.)
----
A little homework on the Zone system. Page 37 of Ansel Adams' "The
Negative" indicates, "We need not concern ourselves if we find that
the metered values of pure whites of the subject fall higher than
Zone IX on the scale; in this case we may want them to show as a pure
white value in the print, and any opacity above Zone IX will print as
pure white.
This is based on 10 physical stops, as measured with a light meter,
between zone 0 (Paper Dmax) and zone 9 (Paper Dmin), with zone 5
being 18% gray.
- Jon
--
*******************************************************
Jon Meyer
GrafixGear
email@hidden
http://www.GrafixGear.com
8 West Glen Avenue
Ridgewood, NJ 07450
USA
(201) 447-1510 voice
(201) 447-3326 fax
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