[Digikam-users] questions about the raw importer

[Gilles Caulier]

2008/9/3 Gandalf Lechner <gandalf.lechner at univie.ac.at>

> Hi Gilles and thanks for the fast answers.
>
> Regarding png vs jpg:
>
> > I don't recommend to use JPG in your workflow. Use PNG instead.
>
> Yes I would like to use a lossless file format, but with png I have the
> problem
> that it can produce really big files. For example, I have a raw (cr2) file
> 9.7
> MB big, but the png version I got from the digikam converter is 42MB! In
> comparison to 1.1 MB for the jpg that's just way too big; in particular
> since
> it's much larger than the raw itself.
>

PNG (or TIFF) file size against RAW file size are relevant of 2 points:

- 1/ image data are in RGB color space and take more place.
- 2/ image data are lossless compressed (deflate compression for PNG and
TIFF)

Both file format don't know wavelet compression yet.

Alternative to PNG or TIFF :

- JPEG2000 : wavelet/lossless compression and support all metadata (need
future Exiv2 0.18 for that). File size are reduced (x1/2 - 1/4 against PNG).
Big problem : it very slow to compress/uncompress

- DNG : use lossless JPEG compression with 16 bits color depth (not wavelet
based). file size reduced (x1/2) but DNG SDK is patented, do not support
Linux as well, and documentation is dumy for developpers. Licence is not
opensource but you can use as well with many restriction.

- HDPhoto : wavelet based. file size reduced (as JPEG 2000). But it's M$
stuff patented and do not support Linux as well, and licence is anti open
source.

I recommend to read my blog entry for details :

http://www.digikam.org/drupal/node/368

Best

Gilles


>
> Best,
> Gandalf
>
>
> > your problem to overwrite an existing image is new for me. Somebody can
> > reproduce it ?
> >
> > best
> >
> > Gilles  Caulier
>
>
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