Viewers for PDF, PS, and DVI ⇒ dvipng generated image is very big, to make the picture smaller

[xiaohuihuiorg]

When use latex to compile .tex file and dvipng to convert .dvi file to get png image, for simple formula, the generated image is very big, is there any way to make the picture beautiful and smaller?
The command I used is :latex Template.tex and dvipng -D 600 -T tight Template.dvi -o x1.png
The resulting image is so big:
latex:\[ \sum {{{ \mathord{ \buildrel{ \lower3pt \hbox{$ \scriptscriptstyle \rightharpoonup$}} \over F} }_i}} = \frac{{d \mathord{ \buildrel{ \lower3pt \hbox{$ \scriptscriptstyle \rightharpoonup$}} \over v} }}{{dt}} = 0 \]
png:

[xiaohuihuiorg]

I have solved this question with dvipng -D 2000 -T tight -x 150 Template.dvi -o x1.png
-x parameter