imread (repost)

[soren at hauberg.org]

Quoting Daniel J Sebald <daniel.sebald at ieee.org>:

> soren at hauberg.org wrote:
>> Quoting Daniel J Sebald <daniel.sebald at ieee.org>:
>>
>>> 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.
>>
>>
>> But what does 'not visible' mean? Should we just show the  
>> background  color of the figure?
>
> Yes, whatever is behind the image (up to the point of plotting the  
> image) gets blended with the image.  Wherever the image is 100%  
> transparent the contents behind it is completely visible, i.e.,  
> unaltered.

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?

Søren