imread (repost)

[soren at hauberg.org]

Quoting Bill Denney <bill at denney.ws>:
>> Currently (and also in matlab I believe) you can only view one  
>> image at a time. So my question is basically, what is behind image?  
>> Say I run the following
>>
>>  im = rand (100, 100, 4);
>>  im (:, :, 4) = 1; # full transparancy
>>  figure
>>  imshow (im)
>>
>> What should I expect to see?
>
> I would expect to see the axis background color.  If the axis  
> background color is set to none, then I would expect to see the  
> figure background color.  I believe that if you set the figure  
> background color to none in matlab, you see a cross-hatched pattern.  
>  When exporting, I would anticipate that the graphics backend would  
> take alpha into account relative to the output device, so if the  
> output was to ps or pdf, it would convert the background color to  
> the color as visible on the screen.

Okay, that makes sense to me, and such a version of 'imshow' I think  
could be useful.

> I'm not saying that this is easy, just that-- to me-- the above is  
> the right way to do it.

I'm not even going to pretend I know much about graphics, but I'd say  
that this isn't a trivial change. In fact I'm going to guess that such  
a feature would take quite some time to get right, which is why I'm  
advocating that 'imshow' simply doesn't handle transparancy (at least  
for now).

Søren