PNG at small filesizes

[vitch2002]

Hi,
Is it possible to create PNG's with small filesizes using the GD functions? I am resampling uploaded images using GD functions and then saving the resampled versions to disc. But the resampled version is MASSIVE (i.e. original image exported from fireworks: 14KB, generated image - physically smaller: 170K😎.
With ImageJPEG you can specify a quality - is there something similar to this for PNG's?
TIA,
Kelvin.