Re: use of sRGB as a default
Re: use of sRGB as a default
- Subject: Re: use of sRGB as a default
- From: Chris Murphy <email@hidden>
- Date: Mon, 21 Jun 2004 16:52:51 -0600
On Jun 21, 2004, at 2:05 PM, Steve Upton wrote:
I think that using profiles other than sRGB to tag user images coming
from cameras or scanners is not necessarily a bad idea. The standard
suggestion, that sRGB is where most cameras aim their color and so is
best used as the source profile is not too tough to prove wrong. If
Apple comes up with a better generic profile that, when applied to
these images, meets user expectations better (on average) then it is
probably a good idea. Purple blues and tomato reds are common with
sRGB applied to camera images. (at least in my experience)
When demonstrated for particular models of camera that claim sRGB for
their behavior, but in fact do not have such behavior, I have no
problem with Apple providing a default source profile that does a
better job. But the file should be immediately tagged with this profile
upon capture, and is embedded when saved, and can be overridden with
something else. Image Capture actually has the ability to work like
this, but at least with my S50 it does something rather odd by default.
It embeds "Camera RGB Profile" which has Generic RGB primaries but a
per channel TRC of 2.199. Gamma 2.2 does not describe the TRC of this
camera so I'm not sure why Image Capture is embedding such a profile in
the image.
My complaint is not on the capture end of things, but the notion of a
hardwired system-level assumption across the board that the source
profile for untagged images regardless of their origin is something
other than sRGB, cannot be overridden, and may be Monitor RGB or may be
Generic RGB, gee let's flip a coin and find out what it's going to be.
The very small possible improvements gained by using gamma 1.8 in
either image encoding OR display calibration are just not worth the
confusion and incompatibility it causes.
Legacy display gamma 1.8 is a no-win situation because it means there
are two potential options for handling untagged images depending on
what platform they originated on. It adds to ambiguity. It contributes
nothing of value.
From one perspective, if any Macintosh application were to open an
image and assume Generic RGB (or anything other than sRGB for that
matter), it should immediate embed the assumed profile. That way it's
color appearance is being immediately defined on the spot from the
moment it is viewed, and can be preserved. From another perspective,
such a policy mean alteration of the file data without express consent
of the user, and we can't build consumer-level applications that prompt
users for such permission every time they open untagged images.
We are left with a dilemma, and no real solution for handling it except
manually on a case by case basis. And all because of legacy support for
a 1.8 display gamma.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
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