Re: [Gimp-user] Large XCF filesize

[Simon Budig <simon budig de>]

Owen (owen cook gmx com) wrote:
> > On 13.06.19 22:25, Johannes Bauer wrote:
> >
> > > I've recently created an XCF template file that almost only contains
> > > large slabs of solid colors (i.e., no "picture"), couple of layers and
> > > layer masks. I was surprised to find that the XCF compressed this rather
> > > poorly, even though this should be an ideal case for lossless compression.
> Well, I opened that and then saved it as a .xcf.bz2 file and it was
> 10% of the original.
>
> Pretty reasonable to me?

Well, yeah. But this is not what Johannes is talking about, he is
questioning the performance of the builtin compression of XCF.

One would probably have to dissect the XCF to figure out where all the
file size is used for.

One key difference I vaguely recall is, that XCF compresses the image
on the tile-by-tile level (i.e. small square chunks of image data). Each
Tile is compressed individually, making it basically impossible to
benefit from global similiarities.

On the other hand this makes it possible to access specific parts of
image data and adress certain regions of interest without having to
decompress all of the image. But it certainly hurts the compression
ratio.

If that is enough to explain the difference I don't know.

Bye,
        Simon

-- 
              simon budig de              http://simon.budig.de/