OpenRaster

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Introducing common exchange file formats has become a good tradition. We have such in CAD, audio production and video. When it comes to graphics, there is none. OpenDocument seems to be a good model to imitate.

1 Requirements
2 Drafts
3 Likely Problems
4 Links

Requirements

Following features should be present:

General

full freely available documentation
OpenDocument type of file format (archive with multiple files inside)
extensible, but private undocumented extensions should be excluded, any extension should be added to the spec and documentation of the file format
applications aren't expected to support all features of the file format, but when manipulating the file they shouldn't lose any information they can't handle

Metadata

storage of metadata using {XMP - Dublin Core - IPTC} tags
possibility to store metadata tags per layer
storage of EXIF tags
all text data in Unicode (UTF-8 or UTF-16)

Layers

storage of multiple layers
storage of each layer's coordinates
storage of blending (compositing) options for each layer
storage of adjustment layers
storage of layer effects
groups of layers
color information - profile, colorspace

Other

storage of paths, clipping paths, text on path
selections, masks
embedding documents within OpenDocument framework

Drafts

Here is the list of drafts for the OpenRaster specifications:

There is page for points which are under discussion.

Likely Problems

A major problem is that because all features aren't available in all the programs, image won't be displayed the same way in different applications, especially for adjustement/filters layers. And "viewer" apps like inkscape or scribus won't have any implementation at all of those features

A likely work-around is the optional storage of a redundant extra layer containing the fully rendered pixel data as seen after all image processing, or possibly a lower-resolution snapshot of it suitable for previewing and thumbnailing.

Different implementations levels might be defined, like, tiny, simple, small, normal, full and custom.