[argyllcms] Re: How can I tell if I'm using my profile? (and other questions)
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sat, 01 Nov 2008 02:30:25 +1100
Adrian Mariano wrote:
No, not at all. Not applying the adjustment is simply not
altering the response target curve from what's specified.
Well, does ambient light matter or not?
It matters if you want it to matter. If you want it to matter,
then a viewing condition rendering adjustment is made to the
target response curves. If not, no adjustment is made,
and you get exactly the response curve you've asked for,
rather than an viewing conditions altered version of them.
If it truly matters then any
model that doesn't include it explicitly necessarily includes it
implicitly. (Otherwise you violate my initial assumption that it truly
matters.) In this case, any model that does not include ambient light
is an approximation to or a reduction of the "real" model that does
include it.
It's not a matter of "real", it's a matter of reproduction refinement
and user choice. Making an adjustment for the viewing conditions
is a refinement that can be applied on top of the more fundamental
business of colorimetric type reproduction.
So the question then becomes what ambient light do you have
to assume that leads to "not altering the response target curve from
what's specified"?
You don't need this, since the correction is based on a ratio.
You remove both sides of the ratio, so nothing needs altering.
(in fact the whole business is simply not computed).
If you take the model that includes ambient light,
how do you make it reduce to the one that does not include ambient
light? What value do you put on ambient light to get it to reduce to
the model where you "simply [don't] alter the response target curve".
It doesn't work that way. The basic task of creating a certain target
curve has nothing to do with ambient light, so there is no
need to reduce it to one that doesn't include it. When ambient levels
are know, the curves are altered appropriately.
To put it in simple terms, if you ask for a gamma of 2.2,
then you get 2.2. If you ask for ambient light correction,
and on the basis of the light levels a viewing correction
of 1.1 is needed, then a gamma of 1.1 x 2.2 will be targeted
instead.
Graeme Gill.
Other related posts:
