[Digikam-users] File sizes after conversion

[Martin (KDE)]

Am 22.01.2012 21:50, schrieb Conway Upshur:
> Hello,
> I'm new to digikam and RAW processing.
> I converted a RAW (CR2) file to DNG and it went from about 8MB to 17MB.
> I edited and then saved it as PNG.  The PNG size is 40MB.
> What am I doing wrong?   Thanks, Conway

Raw data does not contain any colour information. it is a
black/white/grey picture where the so called bayer-pattern is layed
over. The bayer-pattern takes four points from the raw greyscaled photo
and sets one to red, one to blue and two to green and then you have
coloured photos (this process is called demosaicing). With raw data you
have to compress the grey values only (but with 12 up to 16 bit). See
http://en.wikipedia.org/wiki/Bayer_pattern and
http://en.wikipedia.org/wiki/Demosaicing for more information.

For DNG conversion: This depends. You can embed the original raw data
together with the converted DNG data, so the result will have at least
double size.

PNG on the other had is a RGB colour format (with alpha channel). If you
encode it with 16bit per colour you increase the data again. If this can
have 40MB depends on the size and the data. Uniform coloured areas can
be compressed better, high iso noise is worse.

Regards
Martin