[argyllcms] Re: Best way to proceed?

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:

JPEG image
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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