Re: gamma 1.0 and loss of detail
Re: gamma 1.0 and loss of detail
- Subject: Re: gamma 1.0 and loss of detail
- From: Nick Wheeler <email@hidden>
- Date: Sun, 24 Feb 2002 09:26:12 -0500
on 2/24/02 1:53 AM, email@hidden wrote:
>
My interest in the topic stems from the suggestion that dark images can be
>
improved by assigning a lower gamma working space to them, and that doing so
>
is less destructive to the image than lightening to a similar extent with a
>
curve. If that is true it gives compelling reason in favor of entering that
>
space. Thus, I'm wondering if the very act of bringing an image into a gamma
>
1.0 space is destructive to the image, or just that editing an image in that
>
space is destructive?
I think the answer is that - it is the editing in that space is destructive.
"Assigning" a profile to an RGB image and "converting" to a workingspace
profile are two entirely different things.
When you assign a profile to an image you are not actually changing the
image data but rather the definition of that data. How this effects data
allocation on conversion is unclear to me.
However when you change workingspace gamma you are actually changing how you
allocate data. An neutral gray L* of 50 will translate to roughly 120, 120,
120 RGB values in a Gamma 2.2 working space, whereas it will translate to
lower RGB numbers as the gamma value is reduced. Since you are allocating
fewer levels of gray to that region darker than L* 50 with a lower
workingspace gamma, it seems more likely that you will experience
posterization with subsequent large edits in that region.
So I'm not sure it is a good idea to conclude that because a lower assigned
profile gamma works well in some situations that a lower workingspace gamma
is also a good idea.
It would be nice for me if someone on this list who really knows the answer
to this question would try to explain this situation (or who even can
decipher what it is that I am actually trying to talk about here, I
certainly don't). It may be that the way assigning a lower gamma seems to
work is a chimera as when you convert the curve then gets applied at that
time. Maybe it works better because it is a pure L* correction. Maybe
correcting with a curve layer in "lightness" or converting to LAB and
editing in L* is essentially the same thing, I don't know. It would be nice
if someone could help us out there.
Nick Wheeler
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