ARDUINO // IMAGE COMPRESSION

Image Compression Algorithm for the 4" TFT SPI ST7796S on an Arduino

Or… How to get the most out of the limited memory on Arduino devices for image display

The Arduino UNO interfaced to the 4" TFT SPI (with touch) ST7796S driver showing the compressed images

The c565 Image Format

Or the compressed rgb565 image format is a lossless format that reduces the memory footprint of an image, yet displays quickly and correctly.

None of the thinking behind this is new or revolutionary, and now there are two compression algorithms.

1. Compressed — a simple format that has markers to indicate whether the following uint16_t's should be repeated, or just written raw.
   Notes: If the MSB of the word is high, then it is a repeated pixel and the MSB &’ed with the word (i.e word & 0x8000) is the number, if it is low, then it is just raw colours that follow.
2. Indexed — another simple format that utilises the same compression as the format above, except that they are all uint8_t 8-bit markers and colours. The colours are then looked up in the header colour mapping for the 16-bit colour.
   Notes: This is similar to a GIF/PNG format and is only available if there are less than 256 colours (as this is an 8-bit format).