[Digikam-users] raw (CR2) thumbnail generation

[Gilles Caulier]

2007/11/7, Enrico <enrico at hotmail.com>:
>
>  Hallo Everybody!
>
> I'm a "digital photographer", and I would like to ask you a question, that
> still haven't found answers after my researches. I'm not so expert, but
> before asking to you, I checked on the documentation and in Internet, no
> results.
>
> When I download raw (.CR2) photos from my digital SLR, I used to convert
> them in this way:
>
> dcraw -T -w *.CR2
>
> ...and I got "standard" tiff pictures. Then, I installed Digikam, and I
> got similar results using the raw batch converter, leaving the recommended
> settings (use camera white balance, automatic color balance), only changing
> the savefiles to TIFF.
>
> But what really shocks me is this: as soon as I download the CR2, Digikam
> shows the thumbnail...and the thumbnail of CR2 has better colors than the
> thumbnail of the converted TIFF!!!
> My question is: which parameters are used to generate the thumbnail from
> the CR2? I suppose that dcraw is used.
>

The thumbnail are generated to extract the jpeg image embeded in RAW file.
(dcraw -e option)

RAW files are container : raw image data + reduced JPEG image + metadata.

The reduced JPEG image is used to render picture on TV screen very quickly.

Same behaviours when you display the Preview of RAW picture (F3 in Album
GUI). Of course it completly different when you edit image (F4 in Album
GUI). In this case the real RAW image data are used.

Gilles Caulier
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