On the use of wide-gamut RGB working spaces [was: Photography editing spaces]
On the use of wide-gamut RGB working spaces [was: Photography editing spaces]
- Subject: On the use of wide-gamut RGB working spaces [was: Photography editing spaces]
- From: Marco Ugolini <email@hidden>
- Date: Tue, 07 Oct 2008 01:06:20 -0700
- Thread-topic: On the use of wide-gamut RGB working spaces [was: Photography editing spaces]
In a message dated 10/6/08 3:09 PM, Fleisher, Ken wrote:
> 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.
Ken,
I feel obligated to interject that it's not just "a bit" better -- it's *a
whole lot* better. Roughly 45% better, since the approximate volume gamut of
sRGB is 897,000 versus AdobeRGB's 1,299,000.
> 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.
Using ProPhoto RGB as the preferred working color space allows not so much
for more *precision*, as for preserving colors in the file that
bleeding-edge or future printing and/or display technologies might be able
to reproduce.
Of course, this advantage may turn out to be of little or no interest to
professionals who do not expect to use their images in an unspecified future
or with more advanced output devices, but instead need them right now, and
possibly will never use them again.
But it's easy to see how a fine artist could be interested in producing
prints that are even more vibrant and vivid than the ones that are possible
with the current means. So, it all depends on the user and the intended use.
> 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.
There are ways in Photoshop to "peek" into overly-saturated detail while
using smaller-gamut displays. But again, that's not of interest to everyone,
since some users are not interested in preserving the largest gamut possible
in their images.
Also, some images, even in ProPhoto RGB, use only a fraction of the
available gamut -- in which case a conversion to a smaller space may cause
no loss whatsoever of saturated detail.
> 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.
That need not be necessarily so. Several inkjet printers already surpass the
gamut of many middle-of-the-road monitor displays. Intentionally chopping
off saturated detail could run counter to the interests of the user. The
inability of the monitor to display printable colors that live outside its
gamut is not a compelling reason to forgo those colors in the file.
So, the user must find ways to analyze the images, realize the strengths of
the output device, and, depending on the characteristics of the individual
images, exploit those strengths to the largest extent possible, in spite of
the display's weaknesses. Running test prints in what may seem a tedious
procedure of probing the output device's capabilities may pay off handsomely
in the end.
Also, for these discriminating users, buying the largest-gamut display
affordable within their budget would be a wise choice too, instead of
shackling oneself to the strictures of a more-limited tool.
> 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.
Yes, that may be the case in several instances. As I hope you will agree,
the pure and simple fact that an image is in ProPhoto RGB does *not* in
itself mean that the actual colors in it *necessarily* exceed the gamut of a
smaller color space. Using ColorThink to analyze the colors in an image is
an excellent idea, specially for images that one views as important.
But please do not jump from such fortuitous coincidences (where the actual
colors in an image fall short of the available gamut) to the conclusion that
images in ProPhoto RGB really occupy a smaller gamut anyway, and so can be
safely chopped to a smaller color space. That would be an overly broad
generalization, and certainly not all users would be well-served by it.
> The few colors that fell beyond that gamut I consider incidental and I don¹t
> believe they represent anything more accurate about the original scene.
I think that those are personal opinions better left for the individual user
to form as the case may be.
> 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.
Each image is different. Even if a majority of the respondents should happen
to agree with your conclusion, that would still not make it *universally*
valid for *all* types of users.
> 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.
That tool is very useful, in small doses. Turn it on, see what detail is
there in the saturated areas, then turn it off and go back to "normal". You
cannot efficiently work with that feature permanently turned on: it's too
disruptive that way.
Incidentally, another available way to verify the presence of detail in
saturated areas is by looking at individual channels (R, G, B). Those are
just grayscale, and any existing detail will be visible there, even in the
areas that are most highly saturated.
> 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.
That is valid for, say, imaging oriented towards scientific applications,
where dead-accurate source colorimetry may be needed for exact results. But,
barring that, the rest of us is usually interested in plausible color (i.e.,
accurate, certainly, though not to the demanding standards of exact
science), but also *pleasing* color -- much more so than simply
*dead-accurate* color. Of course, starting from color that is "accurate
enough" does help a lot. But from that point onward one is free to exercise
artistic license and stretch the results this and that way, as circumstances
and artistic inclinations dictate.
Common sense would seem to advise that a fine art photographer whose work
contains strongly-saturated colors use a color space that is larger than
that of any output device available today (inkjet or others), in order to
preserve elements that may add esthetic value to the images if not
immediately, then in a reasonably not too distant future -- or simply to
keep that option open as a cautionary measure, if nothing else. After all,
once clipped, saturated color and detail cannot be recovered.
So, to say that the use of ProPhoto RGB makes sense only when accurate
source colorimetry (scene-referred) can be captured without gamut
restrictions, with perfect accuracy, and with no need for further editing,
seems rather limiting to me, because it does not include the needs of fine
art photography/imaging from Raw captures, which are *not* necessarily in
agreement with that description.
> 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.
I disagree, and hope that I have already stated my reasons clearly enough.
Best regards.
Marco Ugolini
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