Any advice or ideas on how to synthesize a signal from an image, a la Photosounder (or any of the others)?

Not sure if there's already an existing external or object for generating a whole lot of sines...

I see Sinesum but that seems to be oriented around an origin frequency and its partials, whereas I'd need an arbitrary number of arbitrary frequencies. I feel like [rifft~] would be appropriate for this but I don't really understand it yet ^_^