Run Length Encoding
Run length encoding (RLE) is a simple compression algorithm for lossless compression.
Worked example
Given example image data representing Red (r), Green (g) and Blue (b) pixels
rrrbbggggggbrrrrrr
The sequences of repeated characters can be represented by a single character and a count so that this data becomes
3r2b6g1b6r
18 pieces of information has become 10. This is a compression ratio of 9:5, or 1.8.
Compression ratio
The compression ratio of a compression algorithm is uncompressed size / compressed size
A higher compression ratio is better. values below 1 mean that the compression has made the data larger instead of smaller.