I'm drawing UML diagrams on paint. The two main colors are white and black. White is mostly in the background and the black is used to draw the boxes. There is text in the boxes. The font is a in TTF format, so it has pixel sub-sampling. When I save my diagram with pain, it's a few KBs big. When I try to optimize it with RIOT, the PNG gets three times bigger! The PNG is in 24-bit format. RIOT only seems to be able to produce a smaller file using the GIF format.
Why does Paint produces smaller PNG than RIOT?