Png cropping

[Renato Fiorenza]

I read in the documentation that it is possible to create a cropped png by 
using "-dbackend=eps -dresolution=600 —png" and inserting this \paper block:

\paper{
    indent=0\mm
    line-width=120\mm
    oddHeaderMarkup = ##f
    evenHeaderMarkup = ##f
    oddFooterMarkup = ##f
    evenFooterMarkup = ##f
}

However, I think the cropping is too heavy. How can I produce a png with some 
nonzero margins? I've tried to add top-margin, bottom-margin, 
top-system-spacing, last-bottom-spacing, left-margin, right-margin, 
paper-width, but none of them seem to work.

Thanks a lot in advance,
  Renato