Image codec on Arduino

This post describes an implementation of a Run Length Encoding (RLE) based codec for binary images, implemented on Arduino

Run Length Encoding

RLE is a form of lossless data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. For example an image of a fax document with text in black printed on white paper contains long runs of white pixels interspersed with short runs of black pixels.

Below we consider a hypothetical scan line and its RLE compression.

WWWWWWWWWWBBWWWWWWWBBBBBWWWBWWWWWWWWWWWBB

10W2B7W5B3W1B11W2B

Block diagram

The PC is connected to the Arduino via the serial port. Arduino IDE which runs on the PC is used to program the board through the serial port. A Python code runs on the PC sends bitstreams over the serial port to the Arduino. Depending on whether an image or an RLE encoding is sent, the Atmega displays the RLE encoding or the decoded image on the LCD screen.

Codec description

The PC and the Arduino communicate using the following codec. The blue cells indicate header bytes, while the green cells indicate data bytes.

• Mode 0 for encoding: Python reads the image, binarizes it, creates the bitstream and sends it through serial port. Arduino encodes the image and displays the RLE code on the LCD.
• Mode 1 for decoding: Python encodes the image in RLE format, creates the bitstream and sends it over to arduino using the serial port. Arduino decodes the image and displays it on the LCD screen.

Code

Code for this post can be accessed here.