Total Memory Footprint max is 512k, dimension limits are 4000x4000 but there is no way you can get a Fractal of any considerable size down to 512k without Shrinking and Compressing the hell out of it, this ain't POSER were dealing with here.
That still sucks! At 50% jpeg compression, that leads for crappy views. At 1800 pixels on the big side, 70 to 90% compression may be better if you don't use color reduction on it like 256 colors! That really can suck!! I don't know!