Imagejpg

Imagejpg refers to the JPEG image format or a digital image file encoded with the JPEG standard. The term is commonly used to describe files with the .jpg extension, or more generally JPEG-compressed images used across devices and the web.

The format was developed by the Joint Photographic Experts Group and standardized in the early 1990s as part of the ITU-T T.81 / ISO/IEC 10918 family. It became the de facto standard for storing and transmitting photographic images due to its favorable balance between image quality and compression at reasonable bitrates.

JPEG uses lossy compression based on discrete cosine transform blocks and quantization. Most implementations operate on 8-bit color samples and convert from RGB to a color space such as YCbCr. Subsampling of chroma channels (for example 4:2:0) reduces color detail to save space, while preserving luminance detail. The baseline profile is the most widely supported and is designed for reliable decoding across a wide range of devices. Progressive JPEG and other profiles exist to improve perceived quality during gradual loading.

Files typically have .jpg or .jpeg extensions and may contain metadata such as EXIF, IPTC, or XMP, describing camera settings, timestamps, and GPS information. JPEG is ubiquitous across photography, web usage, email, and mobile devices due to compatibility and efficient compression, though it is inherently lossy and can introduce compression artifacts at high levels of compression or after repeated editing.

Alternatives include PNG for lossless images and WebP for improved compression. JPEG remains widely used because of broad compatibility and a favorable balance between image quality and file size.