[argyllcms] Re: xicclu -g predictability issue
- From: Elena [service address] <1007140@xxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 25 Jan 2011 14:18:14 +0100
Hello Graeme
On 25-Jan-2011, Graeme Gill wrote:
> Sure. I agreed that adjusting K in the whole gamut to meet smoothly
> with the K at the gamut surface would be a next step, in an email
> some time back. That would help many cases, but doesn't address
> the issue of K on the gamut surface being "bumpy" itself.
What to tell... maybe "search for all matching candidates. If the first chosen
one generates a severe discontinuity, then chose the second one. And so on"...
> I don't think that the standard imposes any such limit, it's a matter of
> practicality. I doubt that you could invert that many grid points using
> the current code, in a reasonable amount of time. If "ultra" with
> a res. of 45 takes up to several hours, then a full resolution table
> would take about two weeks...
mmm... then something strange is happening here ?!
Yesterday I computed a device link profile with -G -qh (maybe redundant) -r100
(the
maximum allowed, -r101 start being refused) in a time that I didn't measure but
which
is infinitely faster than just generating the original -qh (33) profile !
Miracles ? Or just I going mad ? :-D
Btw, it's interesing to notice how the results match the intended behavior.
See these softproofs (made with BPC as usual in order to keep the dark area
with artifacts well visible). I chosen as subject one RGB gradient which I
judge the most "bastard" in showing possible profile unevenesses:
http://www.elenadomain.it/pub/argyll/Softproof_profile.png
[this converted using the original test5.icm profile, LUT res=33]
http://www.elenadomain.it/pub/argyll/Softproof_link33.png
[this one using a device link profile created from srgb to test5.icm,
with -n -qh -G -ip -cmt -dpp -k 0 0 1 .2 .5 which are the same parameters
used for creating test5.icm, converted with cctiff. The only difference
is substantially due to lack of conversion and interpolation in the
intermediate Lab space]
http://www.elenadomain.it/pub/argyll/Softproof_link51.png
[same as above but using devicelink created with -r51]
http://www.elenadomain.it/pub/argyll/Softproof_link100.png
[same as above but -r100]
As you can notice, incrementing the grid resolution has the predicted effect
of reducing the bumps to thinner and thinner outlines - just because the
number of interpolated points around the offending knots progressively
diminishes. All right. So with a -r256 [currently refused by collink] I should
definitely see no artifacts at all!
So far... I don't like having discontinuities in my profiles, of course,
even because I could be wanting perhaps to convert 48 bit images at some point,
but as trade off I would be happy enough. Since you told you don't think the
standard imposes limits for the LUT resolution, and since [to be understood yet]
I could generate in few minutes a device link with 100^3 points, why don't
allow -r upto 256 ? Nice, huh ? :-)
/&
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