Re: [GM-help] Cineon displaying - patch second try

[Bob F. <bfr...@si...>]

On Fri, 2 Nov 2007, Kai-Uwe Behrmann wrote:
>
> Then I see two ICC paths to generate a colour managable version of a
> CineonLog image:
> gm convert dlad_2048X1556.cin -profile sRGB_linear.icc dlad_2048X1556_gm_linear.tif
> and
> gm convert -colorspace RGB dlad_2048X1556.cin -profile CineonLog\ M.icc dlad_2048X1556_gm_log.tif
>
> dlad_2048X1556.cin is just a popular example.

Perhaps not as popular since it seems to be gone from Kodak's web 
site.  Other vital Cineon information has recently disappeared from 
Kodak's web site.

> So far they display nicely in CinePaint. I'd prefere the later version, as
> the log encoded image provides a wider dynamic range than the linear
> image. The later can only represent inside the traditional ICC 0...1.0
> range.

A while back I found a Cineon profile from a site called "The 
Orphanage" which worked quite well with converting to sRGB for 
viewing.  Attaching the profile delays any damage until later.

If you convert to linear TIFF, it should be at least 16 bits/sample.

> Make these 3 conversion paths, one without any profile and two with,
> sense?

It seems like it.

> Then I'd like to revise my patch as to hardcode the conversion to gamma
> 2.2 seems not appropriate to me.
> For a nice behaviour, GM would embedd the according profiles by itself.

Attaching the profiles would be nice.

> I would as well consider two output defaults. A log encoded output for
> 16-bit ICC embeddable formats, PNG and integer Tiff, and a 8-bit sRGB
> default for Jpeg and PPM.

The trick here is how the desired transformation can be requested by 
the user.  The approach currently used (call CineonLog a special 
colorspace) is not adequate.  The reason why I used this approach is 
that it worked automatically with the many image writers which already 
exist for formats which are expected to contain something similar to 
sRGB.  But some people likely want to use CineonLog in these existing 
formats.

Bob
======================================
Bob Friesenhahn
bfr...@si..., http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/