How to remove a white marker around some Mathematica graphs

Question

I am trying to create a matrix graph with math. Using ArrayPlot [] I get a very beautiful figure, except that it is surrounded by a white edge. I have the root of the problem, in the sense of the following example.

http://img689.imageshack.us/img689/8427/badmargin.png

If I try to export the resulting graphics, it also exports the margin. I want the contents of the array to fill a rectangle of a certain size so that it can be superimposed on another image, but the ArrayPlot function creates fields that interfere.

What to do?

QuickEdit: ImageCrop will not work in my case, because: a) I want the resulting image to be a certain size, and b) without specifying how wide the fields that I want to delete automatically can go bad with my graph (first line may also be white, for example).

Answer 1

Try PlotRangePadding-> 0

Apparently my answer was too short, so I type more.

Answer 2

If you set the Background-> None option, the edges should be transparent. This will work if you attach it to another image file.