imread (repost)

[Daniel J Sebald]

> The matlab version of imread supports an extra output argument that
> contains the alpha channel of an image. I don't think it is trivial (nor
> a good idea) to change imshow to make it possible to show images with an
> alpha channel. I mean, what should be to visual result when showing an
> image that s 100% transparent? I'd stick with showing RGB only.

Combining images with alpha support into one image and sending that off to the 
graphics engine is an approach that would work except for combining with other 
plot elements like lines, points, etc.

Gnuplot has experimental support for alpha images right now.  It works for 
several terminal drivers, including x11.  The fly in the oinment with alpha 
images (and it really isn't a gnuplot limitation) is that PostScript/PDF 
doesn't handle a fourth channel.  One of the more useful formats, up to this 
point, and no image blending.  Bit of a disappointment.  Perhaps PostScript 
level 3 has better support, but I'm not sure if it does so in a generic fashion.

100% transparent would be not visible, I guess.  The applications would be 
special effects or masking off a rectangular image to make it appear of a 
different shape.

Dan