Re: [Gimp-user] opening 2.9.3 file in 2.8.14 (NOT)

[Jehan Pagès <jehan marmottard gmail com>]

Hi,

On Sat, Dec 5, 2015 at 7:26 PM, Akkana Peck <akkana shallowsky com> wrote:
> > scott092707 (forums gimpusers com) wrote:
> > > Will this always happen, if I try to open a file saved in an earlier-vintage
> > > GIMP?
>
> Simon Budig writes:
> > No, this will not always happen, just when you use features that are not
> > available in the older gimp version - e.g. high precision pixel formats.
>
> If I load a JPEG into git master built a few days ago, make no
> changes and immediately save as XCF, then exit and try to open
> that XCF in GIMP 2.8, it fails:
>   "Opening '/tmp/can7795-scale.xcf' failed: XCF error:
>   unsupported XCF file version 8 encountered"

We have a new zlib compression, which is much more efficient than the
previous RLE compression (like 2 or 3 times smaller files). Yet we are
aware that for some people, retro-compatibility is more important than
small files. This is why you have a case "Save this XCF file with
maximum compatibility" in the save dialog. When you check it, it will
save a XCF with the older compression, which can be opened with GIMP
2.8, probably even GIMP 2.6 or older!

BUT jpeg images have metadata, and as you know, GIMP 2.9 has new
metadata support. This by itself is a new feature which was not
supported on older GIMP. So when you create a XCF from a JPEG made by
a camera, the checkbox "Save this XCF file with maximum compatibility"
will be grayed-out because anyway, this is not possible to make the
file 2.8-compatible if you want metadata support.

Same if you create high precision images.

Same if you use the new overlay mode on layers.

> It would be great if the files were incompatible only if you use
> new features that the old XCF doesn't support, as Simon says; but
> so far, it seems XCFs saved by 2.9 are never compatible with 2.8.

As explained above, no it is exactly as Simon says. If you create an
image from scratch (as a painter or designer for instance), in 8-bit
and without overlay layers, you will always have the possibility to
check the "compatibility" box if retro-compatibility is very important
to you.

But images from photos made by camera (hence with a lot of metadata), nope.

Now, it would be cool if you could get rid of the metadata, for people
who don't care about them and prefer retro-compatibility.
Unfortunately we don't have metadata editing (hence erasing) support
yet. Only reading and saving. We welcome developers interested by the
topic and who want to contribute. I believe metadata editing is a
much-needed and wanted features by many people. :-)

But for now, until some people comes up and implement this, we can't
have the cake and eat it: new features in the XCF format means higher
format version. There is no escaping it.

Maybe a good feature could be to have a small text listing exactly the
reason(s) why an image cannot be saved in compatibility mode (overlay
layer, high bit depth, metadata or a mix of 2 or 3 of these features.
The new compression is the only feature which is bypassable and does
not block compatibility mode).

Jehan

> I've wished many times for a way to save "old XCF" format. I've been
> using 2.9 for most of my GIMPing, but there are a few images I'd
> like to be able to share with other people or edit on machines that
> don't have the libraries needed for 2.9. I try to remember to edit
> those images only with 2.8, but I forget, and once they've been
> saved with 2.9 even once they're forever out of reach of 2.8.
>
>         ...Akkana
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