Imagemagick is a life saver when you need to convert the format of figures.
- install :
https://www.imagemagick.org/script/index.php
- example of converting
convert -units PixelsPerInch -density 600 SimPlot.wmf image.png
- white background to transparent (be cautious)
convert -density 600 -transparent white SimPlot.wmf trans_bg.png
- transparent background to white
convert -background white -alpha remove trans_bg.png white_bg.png