Dot matrix display is a rectangular grid of pixels (usually redstone torches, pistons or trapdoors), where each pixel can be controlled individually. The advantages of using these over 7 segment displays is that you can easily modify the size, shape and what is shown on the display. The downside is that decoder is much larger than for 7-segment displays.
2x 5x5 dot matrix displays
Decoders[]
Main page: Decoders
hexadecimal to 5x5 pixel decoder
The top layer of the decoder for one frame. A torch represents an on pixel, so the top middle three pixels will be on
For the most simplest design of decoder for this display, it can take one input and produce infinitely as may pixels as desired, either in their on/off state. In the Photo shown at right, a hexadecimal to 5x5 pixel display has been created. There are 16 decoders, one for each number and the span along all 5 layers of the busses carrying the signal. In the next photo, you can see how each individual pixel is controlled.