[Openexr-devel] previews...

[wcoles]

Hiya,
        I was wondering if we could have a defined set of attributes for
.exr files describing a preview image of the contained file? Obviously, due
to the way the image header is structured, an application can define its own
preview attributes. But a defined 'standard preview' means that we won't see
many different preview formats that are incompatible across applications.

I was thinking of something along the lines of

Attribute name                  Description
previewWidth                    Width of preview image in pixels
previewHeight                   Height of preview image in pixels
previewImage                    RGB triples, a scanline at a time.

Or similar, the preview is optional and may not be present. But should
provide a reasonable representation of the full image (the gamma\exposure of
the image is pre-baked).

I'm writing an application which will be using .exr as its main format, and
I was going to add a Windows shell extension that showed the image preview
whilst the user was browsing folders. With all the compression\decompression
and format conversions required (HDRI to flat RGB, some arbitrary
gamma\exposure that doesn't necessarily make full use of the image) having
an optional pre-computed image preview would be very useful for reducing
processing time required.

Just a standard, defined preview would be great as all applications can then
remain compatible. And of course the above is a quick 'off the top of my
head' list of attributes and could probably be improved with some thought.

Thanks,
Wayney

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