Correcting out of gamut colors
Correcting out of gamut colors
- Subject: Correcting out of gamut colors
- From: Nick Wheeler <email@hidden>
- Date: Tue, 10 Jul 2001 09:06:30 -0400
on 7/5/01 4:00 PM, Anthony Sanna at email@hidden wrote:
>
A "how to", if you please, Nick. A lot of my work ends up at a Lambda.
Peter, Tony:
Make sure to set up [View - Proof Setup] with your appropriate profile and
Relative Colorimetric Intent. I leave paper simulation off but that is
personal preference. Then you can toggle between {View - Proof Colors] and
[View - Gamut Warning].
Since the Lambdas and Light Jets have such large gamuts on most photographic
images you will probably see little or no "Out of Gamut" warning mask. If
none then just convert to output profile with relative colorimetric intent.
Try comparing the result (just on the screen is fine) with perceptual
intent. Depending on the software (and settings) used to make the profile
there can be quite a significant difference.
If you do have significant out of gamut problems then there are three ways I
go about color correcting. In ascending order of degree of difficulty they
are use of the [Hue and Saturation] tool, use of the [Curves] tool combined
with layer masks and finally [Image - Apply Image] and [Image -
Calculations].
The calculations and apply image solutions basically involve creating
"shape" in a color channel that has none by borrowing from another channel
that does. I make duplicate images onscreen, RGB, CMY (CMYK with black
generation set to none) and LAB. If you have a weak blue in an RGB image you
may be able to borrow from the Y in the CMY or the L in the LAB etc. This is
fairly complicated but very powerful, Dan Margulis has devoted almost an
entire book to the subject.
Curves works very well in conjuction with layer masks. If you create a mask
for the out of gamut color you are working on, and leave the "gamut warning"
checked ON while tweaking the curves, you can actually watch the "gamut
warning" disappear. The trick is to get the "gamut warning" to disappear
while still holding acceptable color onscreen. You can blur your mask to
help mellow out the transitions. The amout of blur will vary depending on
the quality of your mask and the amount of correction you have applied.
Excellent masking techniques are described in "Photoshop Artistry", "Real
World Photoshop" and "Professional Photoshop". I am sure there are many
others.
My Hue/Saturation technique is the least powerful but works well some of the
time.
First set up to view out of gamut colors. Then open the hue/saturation
dialog box. Notice that with the hue/saturation dialog box open you can
toggle the gamut warning and proof colors on and off with [command y] and
[command shift y]. So toggle gamut warning on and off to check to see whats
out - say some form of red.
Toggle the gamut warning off and then choose reds in hue/saturation and
click in the out of gamut red area, notice how the slider in the dialog box
hops aroud as you click around in the reds of the image. But you really only
want to modify a specific range of reds.
Use the range tool at the bottom of the dialog box to dial in the precise
range. If you take the two sets of sliders and just squeeze them together
tight you are defining a very narrow range indeed. By shift clicking around
in the out of gamut reds you will slowly increase the range, if you set any
of the hue, saturation or lightness sliders to their maximum setting you can
actually get a good look at what range in the image you are actually
selecting. You can "smooth" the selection by spreading the triangles wider
than the thin vertical lines. Think of the thin vertical lines as "range"
and the triangles as "smooth".
So set the "range" by shift clicking around in your out of gamut color and
then smooth with the triangles all the while toggling back and forth between
view out of gamut and some form of preview of your selecton by firewalling
one of the sliders as mentioned above. Once you have the selection figured
out just return the firewalled slider to zero and then begin to tweak
saturation, lightness and hue to bring the defined color into gamut.
If you leave the gamut warning mask ON you can watch it magically dissolve
as you bring the color into gamut. Doing all the out of gamut colors in your
image with this one dialog box works pretty well. Just start with the reds
and work your way down. If you do it as an adjustment layer obviously you
can tweak to your hearts content.
Once you have all the color in the image in gamut you can then do a relative
colorimetric conversion secure in the knowledge that no colors in the image
will loose shape. And you did the gamut mapping intelligently not blindly a
la perceptual rendering.
Nick Wheeler