[argyllcms] Re: Best way to proceed?
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 1 Jun 2008 13:10:30 -0700
On 2008 Jun 1, at 2:42 AM, Alastair M. Robinson wrote:
Ben Goren wrote:
Does the i1 itself average the reading of everything that makes it
through its aperture?
That I don't know. My gut feeling is that it must do to *some*
extent, to cope with halftoned patches. How much this is centre-
weighted, I don't know, though.
I tried some experiments with that this morning, using the i1 scanner
target.
I first created a 128 px x 64 px Lab file in Photoshop. Next, I
sampled adjacent patches on the chart. I set each half of the
Photoshop document to one of the sampled values, and then ran the
``average'' filter. I then very carefully placed the i1 to straddle
the two patches, and compared the reading with Photoshop's averaged
value.
The more similar the two patches, the closer the match...but the
results weren't even close when I picked near-white and near-black.
The L channel showed the most variability; a and b, not so much.
And, unfortunately, white oak (e.g.) is mostly pale yellow with
streaks of very dark reddish brown....
I imagine the averaging could be reverse-engineered. I further imagine
that such a thing could be very useful for other cases. For example,
you could shoot / scan the artwork, have software identify points for
you to sample, and then have the software auto-correct the image with
a one-off internally-generated profile created on the fly for that
purpose.
I also imagine that'd be a lot of work....
If so, I suppose I might be able to punch similar-sized holes in
some paper and sample and shoot through that...
I'm not sure that's a good idea - the presence of paper in the
scene, especially if it's bright white, is likely to have a subtle
effect on the camera's response, especially if your lens is anything
less than factory-perfect spotless.
Well, it's a Canon 180 macro on a 5D, so that shouldn't be as much of
a problem....
But I fear this is ignoring the elephant in the room -- that is,
wood's dramatically varying color with changing light angles. It's
what makes wood do beautiful...but it also would seem to make it
impossible to (accurately) photograph.
Cheers,
b&
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