2D IIR filter design (x-axis width proportional to y-axis) I want to design a 2D IIR filter (that is, created line-by-line progressively, in this case from left-to-right).  What is the best way to go about this?

I would like the response to look something vaguely like this:



The actual shape in the x-axis (time) isn't important - what's important is that the response's width for the x-axis is proportional to the y-axis position.

Any ideas?
First, you might be looking for a FIR filter (2d convolution)? If that's the case, you gave the answer yourself.

If you're actually looking for an IIR filter, then I'd like to ask for the desired order.