It would be technically possible to use Resample To Image to resample your polydata to a 2D image (make the 3rd dimension size 1). From there you could theoretically save as a PNG.
But the PNG file format is pretty limited. It can only accept certain types of data, so there is a good chance the save will fail anyway. It may take some custom processing to get the field data to a form that is acceptable to PNG.
@Kenneth_Moreland : I’ve never been able to use RessampleToImage with a slice. I’m planning to open an issue at some point but more investigation is needed.
Oh, yeah. There is that floating point issue of the sample points lying exactly in the plane of the polygons. I think it works out OK if you have a slice exactly in the x-y plane (z=0), but fails if you move the slice up or down.