Re: Photography editing spaces
Re: Photography editing spaces
- Subject: Re: Photography editing spaces
- From: "Fleisher, Ken" <email@hidden>
- Date: Mon, 06 Oct 2008 18:09:12 -0400
- Thread-topic: Photography editing spaces
On 10/2/08 2:36 PM, "Matt Beals" <email@hidden> wrote:
> Given that many images from con/pro-sumer digital cameras use sRGB as
> their native color space is there any reason for me to not make color
> adjustments in sRGB? Typically for graphic arts people prefer Adobe RGB
> 1998. For GRACoL work I have a few friends who suggest using ECI RGB.
> But if I'm working on images that are destined for a photo lab for
> printing (even a Costco/CVS/Snapfish type service) is there any
> advantage in converting to ProPhoto or any other color space than sRGB?
> I don't see the advantage, but that doesn't mean there isn't one. I'm
> open to all suggestions.
I personally have an issue with visual color editing in a large color space.
Most monitors, even high-end monitors, have roughly the color gamut of sRGB
or slightly better (sometimes worse). If you have one of the new DreamColor
monitors, or if there are other Adobe RGB (1998) monitors available, then
you do get a larger color gamut on the display so you are a bit better off.
The problem arises when making color editing decisions based on the visual
image on your monitor. The argument for using a larger color space, such as
ProPhoto RGB, is that you retain the larger gamut of your original scene and
you don¹t have to compress the color into the smaller gamut of your working
color space. This is supposed to make any future conversions more accurate
if we develop devices that can later reproduce the additional colors
contained in the wider gamut.
However, in my opinion, when you edit in ProPhoto RGB you are not getting
what you think you are getting. In fact, you are making color decisions
based on an image that is already being clipped to roughly sRGB (or A98 with
the DreamColor). The result is that you are not really using the extra gamut
that the color space makes available because you simply can¹t see what¹s
happening there. By the process of making sound decisions, the colors in
your file will generally wind up being restricted to the color gamut of your
monitor anyhow. I¹ve tested this by using ColorThink to examine a number of
images that were edited in ProPhoto RGB and plotting a sampling of colors
from the images against the color gamuts of sRGB, my monitor, and ProPhoto
RGB. It turned out that the colors were almost entirely restricted to my
monitor¹s color gamut. The few colors that fell beyond that gamut I consider
incidental and I don¹t believe they represent anything more accurate about
the original scene. For those of you with ColorThink, try this for yourself
with your own images. I¹d be interested to see what you found reported back
on this list.
Photoshop does provide a means for dealing with this problem. Under the
advanced color settings, you can desaturate your monitor so that you can see
color separation in the regions beyond the monitor¹s gamut. However, while
in this mode, the color is no longer accurate. I doubt that very many people
actually use this feature when editing, even in a space like ProPhoto RGB,
as it takes a very sophisticated user to understand what he/she is looking
at. It is also a cumbersome and somewhat ineffective way of dealing with the
problem (no, I don¹t have a better solution to offer!). So I don¹t really
see that as an argument to continue editing in a large gamut space.
The only way a large color space like ProPhoto RGB makes sense to me is if
your original input is color managed and mapped, accurately, directly to the
correct colorimetry. This is possible with scans of transparency film, so in
that case it might make sense to use a large gamut color space. However, the
question was posed regarding digital cameras and with cameras, I believe it
only makes sense if the camera is color managed and the colors are mapped
directly to the correct LAB values. But not so fast! When we calibrate our
cameras (for those of us who do), we use a target like one of the
ColorCheckers. What this means is that the color gamut of our input is now
restricted to the color gamut of the target and any colors outside of the
gamut of the target are essentially undefined. So, even if you export to
ProPhoto RGB from your camera software, all of the colors are already
restricted to the gamut of your target, which, as you may have guessed by
now, is no where near as large as ProPhoto RGB. Once again, the advantages
of a large color space will not be realized.
With HP/BetterLight¹s new ColorSage solution (and the solution that Eric
Walowit has recently discussed) we seem to now have a way to characterize
our input directly into a large color space and have the correct color
without any visual editing. This is the only way that it makes any sense, to
me, to use something like ProPhoto RGB with camera captures. Until I see how
these solutions perform, I can¹t really say if that is working yet or not.
Based on the discussions on this list, it sounds like the ColorSage solution
³might² be restricting the colors to the gamut of the required HP printer in
order to optimize the printed output (this is purely my own speculation and
I apologize if it is way off base). So, as a camera profiling solution, we
still might not be quite there, but this is certainly a step in the right
direction.
Therefore, I believe that there is no point in using a working color space
that is much larger than your monitor¹s color gamut if you are making color
editing decisions of your digital camera captures based on the visual image
on your screen--or a hardcopy print of it for that matter. ProPhoto RGB and
other large gamut color spaces are great as containers for images that need
to record the full color gamut of a wide gamut scene, but ONLY if there
doesn¹t need to be any visual color editing.
--
Ken Fleisher
Photographer
Imaging & Visual Services
National Gallery of Art
Washington, D.C.
Phone: (202) 712-7471
email@hidden
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