PNG

PNG (Portable Network Graphics) is a raster image format that stores image data with lossless compression and supports transparency through an alpha channel.

DEFLATE: A lossless data-compression algorithm that combines LZ77 matching with Huffman coding. PNG uses DEFLATE to compress its filtered image data.
JPEG: A family of image-compression standards commonly used for photographs, usually with lossy compression. JPEG often produces smaller photographic images but does not preserve exact pixel values.
Portable Network Graphics animation: An animation format that extends PNG with frame-control and frame-data chunks. APNG adds animation while retaining PNG’s lossless compression and transparency.
Unisys: An American information-technology company formed in 1986 through the merger of Burroughs and Sperry. Unisys’s enforcement of its LZW patent helped prompt developers to seek an alternative to GIF.
Raster graphics: Images represented as grids of discrete pixels, each storing color or other sample values. PNG is a file format for encoding raster images.
PNG filtering: A preprocessing step that transforms each PNG scanline to make its data more compressible. These predictors expose repeated patterns before DEFLATE compresses the image.
GIF: A raster image format that supports indexed color, transparency, and animation using LZW compression. GIF shares PNG’s transparency support but limits each frame to a 256-color palette.
Pixel art: A digital art style in which images are created from deliberately visible individual pixels. PNG preserves crisp pixel boundaries without compression artifacts.
LZW patent controversy: The dispute over patent claims covering LZW compression used in GIF files. The controversy was a direct catalyst for creating a freely usable replacement format.
Lossless compression: Data compression that allows the original information to be reconstructed exactly. PNG’s compression reduces storage without discarding image samples.

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