[argyllcms] Re: [argyllcms] Re: "RGB"-printer and inversion in blacks
- From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 01 May 2012 19:05:58 +0400
Hello, Graeme. Thank You for Your attention.
Is it possible to detect the "rise to a dip" behavior in profiling software
itself? May be there is an automatic work-around method possible for such
devices?
I can imagine that the profiler performs the test like mine automatically -
inverse then forward conversion of a grey gradient and the checking the
resulting gradient for monotonicity. If non-monotonicity is detected, some
work-around can be performed while profile re-computing. I think the gray scale
monotonicity is the most important and it's will be acceptable to check only
greyscale inversion.
Mon, 30 Apr 2012 15:41:04 +1000 Graeme Gill wrote:
> Nikolay Pokhilchenko wrote:
> > Can You take a look on the device (TI3 attached in archieve)?
> > Perceptual and Saturation intents in ArgyllCMS profile are OK, but relative
> > intent is quite
> > strange: there is lightness inversion at the black side of a gray gradient.
>
> Hi,
> thanks for drawing this problem to my attention.
> It appears to be due to the way that out of gamut clipping transitions from
> exact using L*a*b* within the gamut, to CIECAM02 out of gamut. The crossover
> region (4 DE) sometimes gives rise to a dip, mainly because CIECAM02
> models flare which compresses the dark region behaviour.
>
> If I reduce the size of the transition region then this effect is
> much reduced, although it does not remove other effects such
> as cLUT interpolation artefacts, or other artefacts caused by the
> devices darkest point not being neutral.
>
> [This change will be in the next release. If you're compiling from
> source you could change xicc/xlut.c line 1348 from
> bf = cdist/4.0;
> to
> bf = cdist/1.0;
> ]
>
> Note as well, that perceptual intent returns the closest point
> in the gamut, so there are no guarantees about monotonicity
> or neutrality. If a gamut surface is convex (and many printer
> gamuts are convex in places), then the closest point may "jump"
> from one point on the surface to another as you move the target
> color smoothly away from the surface. Such jumps can't be
> represented in a B2A cLUT, and the resultant device value
> interpolation may behave non-intuitively.
>
> Graeme Gill.
>
>
>
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- » [argyllcms] Re: [argyllcms] Re: "RGB"-printer and inversion in blacks - Nikolay Pokhilchenko
