If this is a repeat posting I
apologize, I never saw the earlier version appear on the digest.
I am puzzling over a glitch
which is beyond my understanding. There are two different paths that have lead
me to the same question concerning absolute rendering and
luminosity.
The first path concerns gamut
warning using absolute. The fact that Gamut warning only seems to reveal out of
range tones while soft proofing is configured to absolute, puzzles me for three
reasons. Firstly, as it was
explained to me here recently, the displaying of out of gamut colours is
independent of conversion settings, secondly if they are not independent then
why doesnt relative rendering without black point compensation reveal the same
out of range tones, and thirdly this seems to suggest a difference
between absolute and relative rendering with respect to dynamic range,
(especially since BPC is unavailable with absolute rendering.)
The second path involves the
glitch I am puzzling over. I have two scans of the same 4x5 chrome before me in
their input profiles, one made with an Epson 4900 the other with an Eversmart.
Both profiles are homemade using Monaco Proof. A blocked highlight area of the
image scanned by the Eversmart appears muddy white on the Epson scan.
With relative rendering
configured in my colour settings the bright white highlight of the Eversmart
reads as L*100 and the muddy white highlight of the Epson reads as L*87. With
absolute configured in my colour settings the bright white highlight of the
Eversmart scan remains bright white but now reads L*87. If I convert to a
RGB workspace using relative the highlight remains at L*100, yet if I convert
the file using absolute the highlight (now visually changing) becomes
L*87. On the other hand, a
conversion of the Epson scan using either relative or absolute produces exactly
the same luminosity. This could
simply be the case of a bad profile, yet again there seems to be a behavioural
difference between absolute and relative regarding luminosity.
The good book ( Fraser,
Murphy, Bunting), probably because it is written for
practitioners and not scientists,
leads us to believe that the only difference between absolute and
relative rendering is in the remapping of white.
Are there other differences
between relative and absolute that account for this behavioural difference with
respect to luminosity?
Thanks for any help
understanding this.
Eugene
Appert