[Digikam-users] Re: Color Management Jeopardy

[Elle Stone]

On 3/15/11, Graham Dicker <graham.dicker at antecor.com> wrote:
> First question that I have is how do I deal with the
> raw images out of my Pentax K200D? There is no embedded profile in the raw
> files and I cannot find one for this camera anywhere on the internet. On the
> CD that came with the camera there are icc files for sRGB and AdobeRGB but I
> don't know if these have any bearing on the processing of PEF/DNG files.
>

Hi Graham,

I haven't finished exploring the digiKam raw converter. But there are
three choices for the camera profile: "None", "Embedded", and
"Custom".

"None":
I assume that "None" means use the default camera matrix in the dcraw
code. That's the only logical conclusion, and the output using "None"
is identical with UFRaw output, after adjusting for exposure. The only
thing is, if you use any "Workspace" color space other than sRGB,
digiKam doesn't seem to handle the Tone Response Curve ("gamma")
correctly. (TRCs aren't always a true gamma curve; sRGB doesn't have a
true gamma TRC; digiKam seems hard-coded to use the default dcraw TRC,
which may or may not be exactly the same as sRGB - I'm too lazy to
track down the answer - but the default dcraw TRC is most definitely
not a true gamma curve.)

The digiKam raw converter uses libraw, which gets its camera matrices
from the dcraw c-code. dcraw c-code does have a camera matrix for the
K200D:

 { "PENTAX K200D", 0, 0,
	{ 9186,-2678,-907,-8693,16517,2260,-1129,1094,8524 } }

The matrix above is what is used to convert your interpolated raw file
from the "raw" color to a working space.

"Embedded":
"Embedded" is an option from the dcraw code that only applies to a few
cameras. Quoting from the dcraw documentation
(http://www.cybercom.net/~dcoffin/dcraw/dcraw.1.html):

"+M or -M Use (or don't use) any color matrix from the camera
metadata. The default is +M if -w is set, -M otherwise. This option
only affects Olympus, Leaf, and Phase One cameras."


"Custom":
"Custom" requires that you have your own custom camera profile, for
which you'd need a target, the least expensive of which is made by
Wolf Faust (http://www.colorreference.de/targets/index.html - you'd
need to purchase the C1 target).

So I'm not sure how to respond to your question regarding the K200D -
is the problem that you aren't happy with the colors you are getting?
Or you are not sure about the digiKam settings to use? Or something
else altogether? (Feel free to send a private email if the problem
isn't really digiKam-related.)

Martin is correct when he says that the manufacturer's camera profile,
if you could even find one, isn't likely to work very well when using
any software other than the manufacturer's own proprietary raw
rendering software.

Many people (including myself) do choose to create their own custom
camera profile because they are not happy with the colors coming from
the default dcraw camera matrix. My own custom camera profiles are
simple, general purpose matrix profiles, just like the ones that dcraw
uses, only the colors are nicer. A lot of people who own Nikon and
Canon cameras feel that the default dng matrices produce anemic colors
for these cameras.

Elle