[Vis5d-users] image quality with vis5d

I made a surface temperature raster image with vis5d but the result is not
very nice: As you can see from the attached image (example.gif) the limit
betwwen two different colours is not clear (is shaded). Besides, the limit
is not smoothed (it follows the resolution). Does anyone know how to make a
better image?
Thanks, Matteo.