Hi,
This is not exactly a color management question but it does seem to be in
the same universe anyway...
I am doing a black and white negative scanning project in which the raw
scans are 16 bit RGB (scanned as positives). They are then converted to
grayscale in Photoshop, and inverted. I've looked at various ways of doing
this. Most recently I've been converting to Lab, selecting the L* channel,
and then converting to grayscale. My armchair color management knowledge
suggests to me that this is a good idea because it separates any color
information from luminosity, so that the resulting grayscale image is truer
to the luminosity inherent in the original scan. It seems as if this is a
more "accurate" way to do it. However, I do notice that in many cases when I
select the L* channel, the entire image appears much brighter. I've been
including a Stouffer step-wedge in the scans, and the lower densities of the
step-wedge (and the similar densities in the image itself, especially in the
range d.15-.60) really seem to change alot when the a and b channels are
off.
If there is a question in there I suppose it would be:
In principle, is using the L*channel a good way to approach the grayscale
conversion? Are there better ways I should consider? Is there a reason why I
would be seeing such a shift in apparent luminosity when discarding the a
and b channels?
Thanks for any input you might have.
William Real
Carnegie Museum of Art
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