st: graph export does not seem to save very large images?

["Victor C. Van Hee" <vvanhee@gmail.com>]

I'm having trouble saving very large images of multiple combined
graphs in Stata.  If I go beyond a width of about 3500, I get the
following error:

. graph export histograms.png,width(5000) replace
could not create PNG file: histograms.png
r(693);

[r(693) looks like an IO error]

Is this a memory problem (I might have too little memory in this
computer)?  The size of the images I'm able to save seems to vary
quite a bit depending upon what else is running.  Does anyone know a
solution to this problem?
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