[Digikam-users] Re: DNG to PNG file size

[Gilles Caulier]

DNG use a JPEG loss-less compression, supporting 16 bits color depth.
It's an improvement of JPEG algorithm done by Adobe.

http://en.wikipedia.org/wiki/Digital_Negative_%28file_format%29

DNG store RAW data, not demosaiced, from your bayet filter sensor :

http://en.wikipedia.org/wiki/Bayer_filter

PNG (or TIFF), store demosaiced image data, which take more size.

http://en.wikipedia.org/wiki/Demosaicing

PNG use LZW like compression for image data. It's loss-less too, but
compression ratio is not the same than JPEG lossless, or better than
Wavelets (JPEG2000 or PGF)

Gilles Caulier

2010/10/20 Josh Jones <jrjones00 at gmail.com>:
>  Hello,
> I am using Digikam 1.5 with Kubuntu 10.10. I shoot  and import into
> Digikam with DNG and save as PNG when using the image editor.  My
> question is why do I get such a large PNG file after performing very
> small changes (levels, etc) to the images?  For example, I started out
> with a 10.7MB DNG file, adjusted the level, saved file as PNG with level
> 9 compression, and received a 45.7MB file.  Both are 16bpp, and I just
> can't figure out where all the extra comes from.  Any thoughts?
> Thanks
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