JPEG

JPEG is a family of image-compression standards best known for lossy compression of continuous-tone photographs. It reduces file size by transforming image data and quantizing visual information.

Discrete cosine transform: A mathematical transform that represents a signal as a weighted sum of cosine waves. JPEG uses it to express image blocks as spatial-frequency coefficients.
Raster graphics: Images represented as rectangular grids of discrete picture elements. JPEG encodes raster image samples rather than geometric drawing instructions.
PNG: A lossless raster image format supporting indexed color, grayscale, and full-color transparency. PNG preserves exact pixel values, unlike JPEG’s lossy quantization.
Digital photography: The capture and processing of photographs using electronic image sensors. JPEG is a common camera output when compact, ready-to-share photographs are desired.
Quantization: The mapping of values from a large or continuous set to a smaller set of discrete levels. JPEG discards precision by coarsening transform coefficients, especially at higher frequencies.
Color space: A mathematical coordinate system for representing colors as numerical values. JPEG commonly converts RGB samples into a luminance-and-chrominance representation before compression.
WebP: An image format supporting lossy and lossless compression, animation, and transparency. WebP offers photographic compression and features JPEG does not provide natively.
Image quality: The perceived fidelity and usefulness of an image for a particular purpose. JPEG quality depends on quantization settings, image content, and viewing conditions.
Chroma subsampling: A technique that stores color-difference information at lower spatial resolution than brightness information. JPEG can exploit human sensitivity to brightness detail by reducing color resolution.
Luminance: A measure of light intensity weighted to reflect human visual sensitivity. JPEG preserves brightness detail more strongly than color detail in common workflows.

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