Re: questions about the raw importer

Posted by Gilles Caulier-4 on Sep 03, 2008; 8:06am
URL: http://digikam.185.s1.nabble.com/questions-about-the-raw-importer-tp1741494p1741498.html

2008/9/3 Gilles Caulier <[hidden email]>

2008/9/3 Gandalf Lechner <[hidden email]>

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

I forget to said that a possible opensource alternative will be OpenEXR which use a loosless compression based on wavelet. The problem is metadata support. I currently investiguate this point to support this foramt in digiKam as new photo container.

Gilles

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