What is progressive JPEG and how does it differ from regular JPEG?

Progressive JPEG differs from regular JPEG in that the image loads gradually, in layers, rather than from top to bottom. A low-quality version is displayed first, which is gradually refined as more data loads. Regular JPEG loads sequentially.

Main differences:

• Loading: Progressive loading versus baseline (sequential).
• Perception: The user sees the image immediately, albeit in low quality, which improves UX. Regular JPEG displays in blocks.
• File size: For very large images, progressive JPEG may be slightly larger than regular, but for medium-sized files, the difference is minimal or nonexistent.
• Support: Good, but older browsers and some programs may not fully support progressive loading.

Progressive JPEG is useful for websites as it allows users to get an idea of the image before it is fully loaded, which is especially important with slow internet connections.