[argyllcms] Re: help with camera profile

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 18 Jul 2012 18:50:58 -0400

First, how even was the light at shooting the target, what was the light 
source, how much flare you are getting, how linear is the greyscale step wedge 
on the shot, for each of 4 channels?
Second, what colour target are you using for creating the profile - how does it 
warrant -qu for a LUT-based profile?
Third, how do you obtain the source rgb image for profiling? Is it through 
ufraw in profiling mode?
Forth, why -al instead of -ax; if not a -G which is a much more stable solution?
Fifth, does ufraw allow for a linearization tone curves over all 4 channels? If 
not - ask them to implement this option. If they are unwilling, linearize 
yourself. Linearity must be calibrated before profiling.

On Jul 18, 2012, at 5:24 PM, Alberto Ferrante wrote:

> Hi all,
> I am trying to build a camera profile for a Canon 5D MKIII and it is
> proving to be much harder than with the other cameras that I profiled in
> the past. I am working on a profile to be used with Ufraw.
> For the other cameras I was using a non-linear profile (gamma 0.45,
> linearity 0.10) built with the following colprof parameters:
> -qu -bn -y -al -nc -u
> With these profiles on the 5D I obtain a profile that works well with
> highlights, but has problems with the black point: the images look foggy
> and they require manual black point compensation. Furthermore, the
> "black" is not black but it has some color cast (if I measure it I get
> something like red 15, blue and green 4). Even more, when using a
> profile obtained with the -u option (which I used with success with
> other profiles) I cannot get any value above around 250 even burning the
> whole image.
> The profile that seems to work best is a linear profile obtained with
> the following colprof parameters:
> -qu -y -am -bn -nc
> Even if it is a bit flat and it brings out a yellish cast in some
> lightning conditions (that can, anyway, be corrected by changing the
> white balance).
> I have tried all the possible profile kinds, both by using the -u flag
> and not using it. I even tried with -U with no success. The black point
> problem is especially annoying and I cannot get rid of it with most of
> the modes (S and m seem to work better than other modes, especially
> without -u).
> Any comment or suggestion related to the problems above (especially the
> one with black point) will be highly appreciated.
> Tanks!
> Regards,
>       Alberto
> -- 
> Home page: http://www.alari.ch/people/alberto
> Photo galleries : http://albertoferrante.name
> Public key: http://www.alari.ch/people/alberto/keys/yahoo.asc

Iliah Borg

Other related posts: