[ptx] Display gamma (was:Vignetting correction in nona)

[Hal V. Engel]

On Tuesday 03 January 2006 10:29 am, Andrew Mihal wrote:
> On Tue, 3 Jan 2006, douglas wilkins wrote:
> > Andrew has only implemented the "pass-through" of ICC profiles for tiff
>
> The eventual goal is to use the profiles to blend colors with CIECAM02.
> This will replace the functionality of the -c parameter. After reading
> Hunt's "Measuring Colour" and Fraser's "Real World Color Management" I
> suspect that what -c currently does is essentially garbage-in garbage-out.
>
> If anyone has some info on profiling digital cameras, I'm interested. I
> get the impression that this is far from a solved problem.
>
> Andrew
>
> -----------------------------
> Andrew Mihal
> www.eecs.berkeley.edu/~mihal
> mihal at eecs.berkeley.edu

Andrew,

I have been using UFRAW for raw conversion.  It has basic but nicely done 
facilities for handling color management of the RAW images during conversion.  
I highly recommend it.  

In addition that latest version of LPROF (1.11.0 or CVS) has a tutorial in 
it's help files on the correct work flow for creating profiles for use with 
UFRAW.  The same basic principles would apply to any camera work flow but the 
specifics in places may (will) be different if you are using a different raw 
conversion program or profile creation program.  The help files for LPROF are 
html so even if you are going to use another program for creating the 
profiles you can have at look at the ufraw html help file and get a lot of 
useful tips about how to create camera profiles.

Color management in general has a significant learning curve and creating 
custom profiles is one of the harder areas.  Cameras are more difficult to 
profile than are scanners because of the additional variables and there is a 
learning curve since the whole work flow from setting up the target to using 
the profiles is critical.  But monitors are harder to profile and printers 
are far more difficult to profile.  

Get an IT8.7/2 chart from Wolf Faust or some other source (I recommend the C4 
mat chart for camera profiling - about $40 including shipping to the US) and 
the latest versions of LPROF and UFRAW and play around with it.  You will 
likely have to make several passes at it before you start to get a feel for 
how all of this works and it may take you several more tries to get a really 
good profile.  But once you have that feel you will find that it is not that 
difficult and your new custom profiles will be a significant improvement over 
not having a profile or the profiles supplied by the camera vendor.  

If done correctly you will end up with a profile that works well for most 
lighting conditions where you have a well behaved light source.  In addition, 
I also create shoot specific camera profiles when I am shooting in lighting 
conditions where I don't know what is going on with the light.  For example 
fluorescent lights or mixed lighting.  Under these conditions the custom 
profiles result in images that are hugely improved over what I would 
otherwise get.  Trying this out is a fairly inexpensive exercise as the only 
cost will be the IT8.7/2 chart since all of the software is open source. 

Hal