I don't want to draw an image. I want to draw a filter of an image. Right now, I have a rock-hard cutoff at two frequencies. I'd like to draw a curve, and have

I don't want to draw an image. I want to draw a filter of an image. Right now, I have a rock-hard cutoff at two frequencies. I'd like to draw a curve, and have it Fourier filter based on that curve.