[NTG-context] PNG output

I want to convert my standalone formulas to PNG to display these formulas on my website. What I am doing is the following \starttext \startTEXpage \startformula e^{i x} = \cos x + i \sin x \stopformula \stopTEXpage \stoptext and process this via texexec --pdf to get a PDF file. I tried to convert the resulting PDF file via gswin32c to png but the resulting PNG output is not so good. Then I read dvipng could do the job, which means I have to produce dvi output via texexec --dvi but than I get complaints from dvips that it cannot find the file tex.pro for the specials. However a png file is produced. Help appreciated TIA Wim