[Digikam-users] File sizes after conversion

[Remco Viëtor]

On Sunday 22 January 2012 12:50:40 Conway Upshur wrote:
> 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

I can't give the exact details, but here are some indications:
- CR2 -> DNG: DNG has the possibility to embed the original file (thus adding 
a few MB), further, teh compression of the RAW data might be different, and 
certain metadat could be stored in a different format (text, instead of binary 
codes, esp. for makerdata fields).
- PNG: forgetting compression for now, RAW (CR2) files store 12 or 14 bits per 
pixel.  But those pixels have no inherent colour information (look up 'Bayer 
matrix'). The PNG stores an image that has as many pixels as the RAW file, but 
with colour information, at either 8 or 16 bits/colour, and possibly 
transparency (also 8 or 16 bits). That gives you at least 24 bits/pixel (8 
bits/colour, no alpha channel) and at most 64 bits/pixel. And you might have 
added tags, caption, title, etc.

Given that you go from 8 MB for the raw to 40 MB for the png, I suspect you 
use 16-bit colour depth

Remco