thumbnails

A thumbnail is a small image that represents a larger image or video, used to provide a quick visual preview and to reduce bandwidth by loading a smaller file first. Thumbnails are common in image galleries, search results, feeds, and video platforms.

Generation and sizing: Thumbnails are produced by downsampling the source image or by cropping to a target aspect ratio. Common practices include preserving the original aspect ratio, applying center or focal-point cropping, and selecting representative frames for videos. Thumbnails may be created automatically on upload, cached by a content system, or generated on the client side for dynamic pages.

Formats and performance: Typical formats include JPEG, PNG, and increasingly WebP. Sizes vary from small icons (roughly 64 to 150 pixels) to larger previews (up to 1280 pixels in some contexts). To improve loading times, thumbnails are often compressed, served via content delivery networks, and loaded with lazy loading to prioritize above-the-fold content.

Accessibility and search: Thumbnails should include descriptive alt text and, when relevant, concise captions. Descriptive file names and titles aid search engines and assistive technologies, while appropriate sizing and lazy loading reduce layout shifts and improve user experience.

Related concepts: Thumbnails are part of image processing and responsive design. They function as navigational aids and previews in media-heavy interfaces, complementing the full-size media they represent.