Java ME games or applications should be designed to be as compact as possible to make it compatible with more number of devices in the market. In graphics intensive applications, the PNG images used must be optimized to the maximum extend so that it takes up less amount of space. There are two nifty tools that allows you to minimize the size of your PNG images without loosing noticeable quality. PNGCrush & OptiPNG

You may be surprised to see your 100 KB PNG image crushed into an 8 KB one without noticeable quality loss!