[argyllcms] Re: xicclu -g predictability issue

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 29 Jan 2011 12:56:05 +0100

Am 28.01.2011 23:21, schrieb Elena [service address]:
> No,the problem is more severe and it has been understood, it's due to 
> discontinue CMYK combinations (well, actually clusters of them) in the 3d x 
> 4d b2a grid which are colorimetrically correct but nonetheless discontinue, 
> so interpolating points at their boundaries causes colorimetrical errors.

Hi Elena,
why "no"? I don't think that we disagree about the root cause.

> Reducing the problem to the bones, i.e using a perceptual devicelink profile 
> (thus avoiding additional PCS conversions and relative interpolation 
> artifacts) and analyzing this way the RGBxCMYK grid (which is easier, and 
> contains no clipped
> colors) is the best way to understand and detect such problems.

I did use a device link as well.

> [...]
> Then, have a look at the attached plots of slices from the relative rgb x 
> cmyk table. Those are just a couple of troublesome areas (slices intersecting 
> the bumps). Note the disaster in RtoK. Note the mess in GtoK. Those ink 
> swappings aren't good at all.
> [...]

As Graeme suggested, I did not investigate just arbitrary slices through
the whole color space, but a very small region around an actually
visible discontinuity in the soft-proof of an image (source image
created with "timage"), in order to get even more evidence that that
these artifacts actually happen in those regions where the CMYK
colorants make steep transitions (or are crossing steeply). And
obviously, yes, this seems to be the case - so absolutely no
contradiction to your findings, IMO.

Regards,
Gerhard


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