BaselineJPEG

Baseline JPEG is the original, non-progressive profile of the JPEG image compression standard. It is defined in ITU-T T.81 and ISO/IEC 10918-1 and forms the most widely supported JPEG mode in software and hardware. Baseline JPEG encodes images with a single sequential scan using 8x8 pixel blocks transformed by the discrete cosine transform, followed by quantization and entropy coding. The color data are typically converted from RGB to YCbCr and may use chroma subsampling (commonly 4:2:0 or 4:4:4), though subsampling is optional.

In the data stream, each 8x8 block is processed independently; the DCT coefficients are quantized and then encoded with Huffman coding using standard or custom tables. The byte stream is framed with markers such as DQT (quantization tables), DHT (Huffman tables), SOI, SOS, and EOI; restart markers (DRI) may be inserted for error resilience. The encoding is strictly non-progressive, meaning the image is reconstructed as the scan is decoded rather than progressively refining an image over multiple scans.

Baseline JPEG typically uses 8-bit samples and implements zig-zag ordering of coefficients for efficient run-length coding. It is designed for fast decoding and broad compatibility, making it the default JPEG profile for most applications.

History: Baseline JPEG emerged with the development of the JPEG standard in the late 1980s and early 1990s, with the baseline profile formalized in the early 1990s. It remains the most widely supported JPEG mode, though optional features and extensions have expanded JPEG usage, including progressive and lossless variants.