[argyllcms] Re: Black turning down problem - help!
- From: Elena [service address] <1007140@xxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 06 Jan 2011 13:57:05 +0100
Hello Graeme
On 6-Jan-2011, Graeme Gill wrote:
> Elena [service address] wrote:
>> Any way I proceed, I'm more or less getting bluish bumps in the deep blacks.
>> And xicclu seems to confirm some serious problem in that area, when looking
>> with
>> it at the kplot. I included details, using a ofps 1300 target as reference.
>
> This is not unusual, given the way the code currently works. It
> prioritises accuracy over smoothness at the grid points, which can lead to
> sudden jumps in the black separation near the dark gamut boundary, resulting
> in
> less accurate color in the device space interpolated (ie. between grid point)
> areas. Increasing the quality level (ie. grid resolution) can help a bit,
> but the best way of minimizing the problem is to set a suitable black
> generation curve. See <http://www.argyllcms.com/doc/Scenarios.html#PP6>.
> (You can demonstrate that this is going to have an effect by seeing
> what -kz and -kr do.)
Unfortunately, yesterday later, I tried -qh also, but the problem persists.
I also tried an "abundant" approach: profiling with the original 1300 patches
PLUS new ofps patches generated with -c (merged by hand). In any case, I see
VISUAL improvement in the Rel. intent (the bluish bump is no more visible),
while
there's nothing to do for the Perc. intent, where the bump is always strong.
I don't feel to play with too many K curves since I noticed that colprof
doesn't actually fully obeys my rules. If I state for example -kp 0 0 1 1 .5
and also -l300 -L100, colprof shouldn't for any reason limit the K max level
(it does instead) or, worst, change its monotonic increasing.
However, please explain me why this strange behavior of xicclu:
plotting -g with -fb -ir does show the K turning down, while plotting the
perc. intent gray (-g -fb -ip) DOESN'T (see previous pictures) - BUT, if you
measure the C,M,Y,K values in the rgb->CMYK picture converted with Perc. intent,
you actually SEE the black ramping down! Is it a bug ??
I'm turning a bit mad...
/&
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