PNG
PNG - Portable Network Graphics
PNG
PNG is a raster graphics file format that supports lossless data compression. PNG was created as an improved, non-patented replacement for Graphics Interchange Format (GIF), and is the most used lossless image compression format on the World Wide Web.

Lossless Data Compression:

Lossless data compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. By contrast, lossy data compression, permits reconstruction only of an approximation of the original data, though this usually allows for improved compression rates.
Reference
Wikipedia
Image File Formats
GIF
JPEG
PNG