[Digikam-users] Color depth in lossless formats

Niels Ott niels at delta-b.net
Mon Aug 25 09:51:52 BST 2014

Hi there,

I recently got a new used camera with 14MPix and now I feel like
re-thinking my archiving options for edited images. So far, I had a
6MPix Pentax from whose PEF files I created PNG files. But with the
14MPix of the K-7, the PNGs range from approx. 69 to 76MB per image.
Outch! So I checked out the other formats that DigiKam supports.

Example (compression rates depend on particular image, of course):

PEF/RAW:  14,7MB, "16 bpp", "not calibrated"

TIFF:     72.6MB, "16 bpp", "RGB"
PNG:      70.9MB, "16 bpp", "RGB"
PGF:      62.6MB, "48 bpp", "RGB"
JPEG2000: 31.5MB, "0 bpp",  "unknown"

Now I'm wondering: What's up with the bpp values? Shouldn't they all be
the same: 48bpp (3x16 bit per pixel in RGB mode)

Also, I'm stunned by JPEG2000's apparently superior lossless performance
(and flabbergasted by the tremendously slow implementation) - or is
there simply something going wrong here?

My DigiKam Version is the one of Ubuntu 12.04.5, namely 2.5.0

I know that disk space is cheap nowadays, but I'm also doing audio
recording and video stuff, so I fill up disks quickly and the JPEG2000
compression level seems awesome to me. But how to check that it doesn't
fool me and how safe is this to still work in the future? JPEG2000 is
considered dead by many people.

Thanks in advance for your ideas.



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