[Digikam-users] png huge

[Gilles Caulier]

2010/1/18 jdd <jdd at dodin.org>:
> Le 18/01/2010 16:43, Martin Senftleben a écrit :
>
>> Do I see that right, or am I completely on the wrong track?
>
> you are completely on a wrong track.
>
> 10 Mega pixel image have a 10 mega bits size (and may be a little more
> due to info management) when saved raw.
>
> This size have nothing to do with the image *content* a it's
> uncompressed. so saving as uncompressed PNG or TIFF gives nearly the
> same size.
>
> As an other answer said, the png compress algorithm is not really
> efficient for most images, when jpeg can be very efficient.
>
> That's also why nobody can know for sure what is the size of a jpeg
> image: the size depends of the content
>

Yes. PNG compression is not efficient for photo. But it's lossless,
like TIFF provide.

Alternative :

-  JPEG 2000 : wavelets, slow (due floating point algorithms), support
metadata, partially patented, implementation not fully complete in
opensource.
- PGF : wavelets, fast (integer algorithms), support metadata with
Exiv2 >= 0.19, not patetted, open source. I recommend it for
archiving.
- JPEG-XR : know as WMP, and HD-Photo, Wavelets based, metadata
support, fully patented, not opensource : Microsoft. Warning : this
format is already set as a new standard to replace JPEG in camera
device. Do you know  ??? M$ SDK compile and run under linux, but who
want to use it really ?

All theses format provide lossless compression which give a file size
approximately PNG size /2 (following my test). Of course this is
relevant of image contents...

JPEG2000 and PGF are supported in digiKam 1.0.0. Try it.

I have no plan to add JPEG-XR for the moment, until M$ SDK still as
closed source like implementation.

Gilles Caulier