pixon_variable_metric

If set, use the fast algorithm. It is 2 to 4 times faster, but requires a lot of memory. For a 64x64 image, you need 300MB or more of memory. For a 128x128 image, you will probably need 3 to 5 GB. The memory required scales as the fourth power of the linear image dimension.

Setting bit 3 of pixon_snr (pixon_snr OR 8) has the same effect as setting this keyword.