[Digikam-devel] White Balance and gamma for 16 bits RAW image without to use Color Management.

[Arnd Baecker]

Hi Thorsten,

On Tue, 11 Mar 2008, Thorsten Schnebeck wrote:

> Am Montag 10 März 2008 schrieb Gilles Caulier:
>> There is a patch here against RAW image loader from digiKam core for KDE3
>> to fix this problem :
>>
>> http://digikam3rdparty.free.fr/misc.tarballs/raw16bitsautogamma.patch
>>
>> In this patch, the following operations are processed :
>>
>> - An auto-exposure correction using white-balance algorithm from digiKam
>> core.
>> - A gamma correction to 2.0 (BT.709 adjustment) using gamma algorithm from
>> digiKam core.
>> - sRGB ICC color-space profile assignment.
>>
> [...]
>> Feedback are welcome. Thanks in advance

(Remark ahead: this is really good news!!!)

> Hi Gilles,
>
> what about comparing auto-corrected 16bit raw with the embedded jpeg version
> of the image? Would be interesting if the cam uses exif parameter to do its
> internal raw2jpeg conversion or if a fixed parameter set is enough.

Presumably this is a very hard task, because in the camera
one can specify various aspects, like color enhancements
(more vivid etc.) or even adjust sharpening.
Because of this, the converted raw will most likely not fully
match the jpg. ((Actually, for example for sharpening, it
should not IMO ;-))
However, getting white-balance and gamma
right will make at least the raw converted picture look "similar".
(I am not 100% sure about the auto-exposure though)

Of course, if the algorithms used by the different manufacturers
to convert their raw date to jpg inside the camera, were
publically available, together with the corresponding
exif (etc.) information stored in the jpg (or raw) file, then
it would be possible to get very close to the stored jpg.
However, I would be extremely surprised if we could get
the corresponding information.

Maybe something like this only works with the Windows/Mac
RAW decoders provided by the camera companies
(not sure about photoshop&Co),  or the recent RAW image codecs
for Windows Vista?

Best, Arnd