Re: [Lcms-user] Question related to curve smoothing

[Pekka P. <pek...@ha...>]

On Tue, 6 May 2025 19:18:55 +0200
<mar...@li...> wrote:

> Hello,
> I answered that mail on 24/3, see the answer attached.

Hi Marti,

as you can see in
https://sourceforge.net/p/lcms/mailman/lcms-user/thread/93d1cd5d-89f9-406e-965f-3ca3349aba1a%40riseup.net/#msg59164589
that email seems to have reached no-one.

Thanks for attaching it!

I was hoping for more insight with the specific use case, because I am
sure you have extensive experience in applying the "ASIC
prelinearization" algorithm. Currently we do not know of a good test
case nor what a typical situation would even look like.

Can you recommend a test case that would pose as many problems as
possible, but still be feasible to your taste for the prelinearization?
Some specific ICC profile combination, maybe?

> shaper + 3D LUT is not supported by this function.

What do you mean? Why is cmsSmoothToneCurve() not applicable to the
estimated shaper in https://www.littlecms.com/ASICprelinerization_CGIV08.pdf ?


Thanks,
pq

> -----Original Message-----
> From: Pekka Paalanen <pek...@ha...> 
> Sent: Tuesday, May 6, 2025 9:40 AM
> To: lcm...@li...
> Subject: Re: [Lcms-user] Question related to curve smoothing
> 
> On Mon, 24 Mar 2025 11:39:03 -0300
> Leandro Ribeiro <lea...@ri...> wrote:
> 
> > Hello,
> > 
> > Based on [1], we've added the code to decompose a cmsHTRANSFORM into a 
> > shaper (3x1D LUT) + 3D LUT on Weston [2].
> > 
> > We want to smooth the shaper with cmsSmoothToneCurve(), but we don't 
> > know exactly how to choose the lambda parameter. In [1] we have: 
> > "lambda is a parameter by which we can trade smoothness of z against 
> > fit to data y". But would there be any drawback in using lambda == 0, 
> > i.e. allowing "full smoothness"?
> > 
> > Any feedback from your experience with that would be appreciated.
> > 
> > [1] https://www.littlecms.com/ASICprelinerization_CGIV08.pdf
> > [2] 
> > https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1644
> >