I want to transmit images that are captured by camera to wireless device
(using MIDP of J2ME) via intenet. Because MIDP-enabled device can only
display png image, I must convert captured image to png format. I have
compressed the png image and file size is still big enough to transmit via
internet in short interval. I have reduced image's bit depth from 24 to
16, but still have big file size (about 20 Kb). If I use jpeg format, I'm
sure I can get 2 to 4 Kb of file size.

Any idea how to reduce png file size ?