Export non square or rectangle image

[Ace71425]

So im looking to export an image that is a triangle...easy enough to do with a transparent background and it looks like you have a triangle...but im my case I need the dimensions of the picture to fit the triangle perfectly not be a triangle within a square or rectangular transparent dimension...it's kind of like I'm looking for an option of setting the image to be width, height, and diagonal or something like that. Thanks!

[Blighty]

All bitmap images are rectangular/square. So you need the triangle with the transparent bits.

What are you trying to achieve? Maybe someone can help if we know that.