how to detect the alpha channel in an image ?

[u sankarlal]

hi all,
I'm having a problem to find whether the png image is supporting alpha channel. Though, alpha channel is supported by all png files, there may be a chance to create a png image without having Alpha channels thro' photoshop, by saving as - > and selecting exclude alphachannels option.
In this scenario, I've to find whether the png is supporting alpha channel or not ? Also, If supported, i've to detect how many number of rgb pixels in that image and also how many numbers of alpha pixels in it ?
thanks in advance
Anu-Maheswari