[argyllcms] Re: RGB profile for HP Color LaserJet. Targets.

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 19 Aug 2009 15:32:54 +0400

Graeme Gill wrote:
> invprofcheck only checks the A2B table against the B2A table, and doesn't
> make any reference to the original test data, so it only gives an indication
> of the loss of precision in the way the B2A table is formed. The numbers
> it produces are rather sensitive to how it determines that colors
> are out of gamut though.

OK. Clear.

> If color quality is critical, don't use the B2A table, it is inherently
> a poor way of transforming color since it grids out the whole PCS,
> wasting lots of table entries or demanding a very high grid resolution
> which consumes lots of processing power to invert mostly out of gamut
> grid values. Instead create a device link using collink -G. A device
> links CLUT maps from in gamut to within gamut, making much
> better use of your profile size and CPU cycles. It's easy to create
> a profile aimed at being used with collink -G, with a high res. A2B
> table and low res. B2A table by using the coloprof -b option.
> [This assumes of course that a device link is usable within your workflow.]

OK. Clear. I do collink -G usually. But I've used invprofcheck to verify the 
precision of B2A. If B2A was bad, the resulting tone eveness on print was 
usualy bad too (even by collink -G). I'm advisedly increase "-r" value in 
colprof to get smoothed profile behavior for collink -G too. Generally, the 
invprofcheck may be an indicator of B2A inversion quality, so it may be the 
quality indicator for collink -G too (in some degree).

Will be the utility "invlinkcheck"  useful too?
For example:

invlinkcheck -k -x -w -h Image.gam Profile.icc Link.icc

Computation direction:
Image.gam -> ingamut_PCS_values -> Link.icc -> Device_values ->
-> Profile.icc -> print_PCS_values -> comparing ingamut_PCS_values & 

The PCS values inside of image gamut should be converted by Link.icc into 
device values, then obtained device values should be converted by Profile.icc 
into PCS values again. The original and converted PCS values should be 
compared. Such procedure can show gamut mapping vectors across the PCS volume. 
It can be an instrument for gamut mapping control.

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