[argyllcms] Re: Best way to proceed?
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 2 Jun 2008 12:07:44 -0700
On 2008 Jun 1, at 9:37 PM, Mike Russell wrote:
Another problem is your choice of color space in which to curve.
You are
presumably using curves in RGB space, so each curve will change the
brightness as well as the hue, and the effect of evan a small change
near
the end of a curve can have large effects on the midpoint of the
curve. If
you are seeing wild bends in any of the curves, then adjust only hue
and
saturation, and ignore the luminance information.
That was certainly a big part of the problem, which is why I later
abandoned regular Photoshop for Camera Raw. I was able, for example,
to boost the saturation and lightness of just the yellows to match the
oak when I set the piece next to the computer. Too bad the angle of
light made the oak ``pop'' a lot more there than when it was on the
stage....
You mentioned the irridescence of the wood in a later post. Fabrics
have a
similar problem, being sensitive to both direction of view and
lighting.
The solution used in this case is to create a packed bundle of
strands, and
cut them off square at the end, and measure the end. This provides a
consistent diffuse measurement.
The fabric procedure suggests that measuring the end grain might
provide a
similar stable hue measurement, that would reflect the correct
overall color
of the wood. Including a shot of the end grain, shot under the same
lighting conditions as the main product shot, and matching that hue
and
saturation in Lab space to your colorimeter mesaurement, by
adjusting the a
and b curves. Then use the Lightness curve to add contrast and
bring out
the artwork, perhaps by matching the Lightness (ignoring the a and b
values)
of several representative points.
I won't be able to get end grain samples of the particular woods,
unless they already happen to be in the piece. Your suggestion to
concentrate on only a/b values, though, is the same as Klaus's, and
that's what I'll focus on if I have to.
I noticed also that your background has a magenta cast - this is
undesirable
because it will give the wood a more neutral appearance in your
image, and
undercut your attempts to match the colors. the brighter background
is best
adjusted in RGB space.
Oh, that won't be a problem at all -- the background will get masked,
completely desaturated, and faded so that only the bottom shadows keep
the piece grounded. Here's a sample:
Those colors are really very close, with the caveat that you might
have to tilt the work at various angles to get any particular spot to
match.
That was done with the i1 scan target and a bit of an S-curve in the L
channel. It's at least in the ballpark, which means I can deal with it
from here -- as long as I keep in mind that light angle is everything.
Oh -- and it looks like I oversharpened the Web-sized version....
Cheers,
b&
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