Image Glossary

WebP is a modern image format developed by Google that provides superior lossless and lossy compression for images on the web, typically 25–35% smaller than JPEG at equivalent visual quality.

AVIF (AV1 Image File Format) is a next-generation image format based on the AV1 video codec that delivers superior compression — typically 50% smaller than JPEG — with support for HDR, wide color gamut, and transparency.

JPEG (Joint Photographic Experts Group) is the most widely used lossy image compression format, optimized for photographs and natural images. Quality is controlled by a 0–100 scale; quality 80–85 is the standard for web distribution.

PNG (Portable Network Graphics) is a lossless image format that supports transparency and produces exact, pixel-perfect copies of source images. It is the standard format for logos, icons, screenshots, and images requiring transparent backgrounds.

GIF (Graphics Interchange Format) is a lossless image format that supports animation and transparency using a palette of up to 256 colors. It is widely used for short looping animations on the web.

HEIC (High Efficiency Image Container) is Apple's default photo format for iPhone (iOS 11+) and Mac cameras, based on the HEIF standard. It produces images roughly half the size of JPEG at equivalent quality, but has limited compatibility outside Apple platforms.

Chroma subsampling is a lossy compression technique that reduces color (chroma) resolution while preserving full luminance (luma) resolution, exploiting the human eye's lower sensitivity to color detail than brightness. The notation 4:2:0 is the most common setting in JPEG and video.

Lossy compression permanently removes data from an image file to achieve smaller file sizes. The removed data cannot be recovered. JPEG and WebP lossy are the most common lossy image formats; quality settings control how aggressively data is discarded.

Lossless compression reduces file size without removing any image data — the original pixel values can be perfectly reconstructed from the compressed file. PNG, GIF, and WebP lossless are the main lossless image formats.

DPI (Dots Per Inch) measures print resolution — how many ink dots a printer places per inch of physical output. For screens, the equivalent measure is PPI (Pixels Per Inch). 300 DPI is the standard for professional print; 72 or 96 DPI is the historical screen standard.

SSIM (Structural Similarity Index Measure) is a perceptual image quality metric that compares two images for luminance, contrast, and structural similarity. Values range from 0 to 1; SSIM 0.95+ is considered visually lossless.

EXIF (Exchangeable Image File Format) is metadata embedded in JPEG, TIFF, and HEIC image files by digital cameras and smartphones. It records technical capture data including camera model, shutter speed, aperture, ISO, GPS coordinates, and timestamp.