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You can't just "draw" on the Fourier side because it actually consists of complex numbers, and only the magnitude is plotted. And the Fourier plot needs to be rotationally symmetric. The closest you could get is increasing or decreasing the magnitude of pixel regions.

Maybe a DCT would be more amenable to hand-editing because it's real and has no symmetry constraints.

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I should have a 2d line chart, and I should be able to draw magnitude at each frequency. It rotates and filters. Right now, a line chart consists of 1 between two frequencies, and 0 elsewhere.

Or I should have a 2d image, and I draw dark/light. It reflects appropriately to get the other half, and multiplies the image (without rotating). Right now, this image looks like a donut.

I'm drawing the filter, you see. It applies the filter, and shows me:

* The source image FFT(what I drewFFT(image))

The point spread function / convolution kernel FFT(what I drew)

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