Cacti graph image format

[pnavratil]

I left default configuration in the graph template - Image format - PNG, but all images are BMP and every has aprox. 0,5 MB so it generate quite a lot of traffic. When I change it to GIF format, no image is shown.
On the same machine I have smokeping - it uses RRD as well as Cacti and it draws images in PNG format without any problem. Can someone point me, what I did wrong?

Thank you