ThumbHash

ThumbHash is a compact image placeholder format designed to give visually rich, low-bandwidth previews while the full image loads. It encodes an image into a tiny byte array that captures approximate colors, gradients, and aspect ratio, then decodes that array back into a blurred thumbnail at render time. Unlike simple color blocks or very low-resolution thumbnails, ThumbHash packs more detail per byte and includes alpha support, so it works well even for images with transparency. The design intentionally targets inlined storage: hashes are small enough to live directly in JSON payloads, databases, or HTML attributes without ballooning page size. Libraries in multiple languages make it easy to generate and decode hashes on the server or client. For UI developers looking for smooth image loading experiences—especially in galleries and feeds—ThumbHash is a modern alternative to placeholder techniques like BlurHash, with improvements in color accuracy and aspect preservation.