JPEGStandard

JPEGStandard refers to the ISO/IEC standard for digital image compression commonly known as JPEG. It was developed by the Joint Photographic Experts Group and published by ISO/IEC and ITU-T in 1992 as ISO/IEC 10918. The standard defines a family of methods for lossy and, to a limited extent, lossless image compression based on discrete cosine transform (DCT) coding and entropy-coding, together with a flexible file format for storing compressed data.

The core process of JPEG involves converting the image from RGB to a luminance–chrominance color space such as YCbCr, applying chroma subsampling, dividing the image into 8×8 blocks, performing a discrete cosine transform on each block, quantizing the coefficients, ordering them in zigzag order, and entropy-encoding the results using Huffman coding (with some variants permitting arithmetic coding). The standard supports multiple modes, including baseline (sequential), progressive, and hierarchical, as well as different chroma-subsampling patterns (for example 4:4:4, 4:2:2, and 4:2:0). A compressed stream is typically wrapped by metadata containers such as JFIF or Exif and uses a marker-based syntax with markers like SOI, EOI and SOS.

In practice, JPEG is the most widely used format for photographic images on the web and in digital cameras, prized for its balance of image quality and file size. It remains a foundational technology in image processing and has influenced later formats, although newer standards such as JPEG 2000 and JPEG XR address some of JPEG’s limitations.