Progressive JPEG
Also known as: progressive jpg, baseline vs progressive jpeg, interlaced jpeg
A progressive JPEG loads as a full-size but blurry image that sharpens in successive passes, instead of drawing top-to-bottom like a baseline JPEG. Both store the same photo; progressive encoding mainly changes how the image appears while it downloads, and can be slightly smaller for large images.
- Loads as a full blurry preview, then sharpens
- Baseline JPEG instead draws top-to-bottom
- Same format; often slightly smaller for large images
Progressive vs baseline loading
A baseline JPEG renders line by line from the top, so on a slow connection you see a sharp top half while the bottom is still blank. A progressive JPEG stores the image in layers of increasing detail, so the whole frame appears immediately as a low-quality preview and then refines.
The visible content is identical once fully loaded. The difference is the experience on slower networks, where progressive gives an early sense of the whole image.
When to use it
Progressive encoding suits larger images on the web, where the early full-frame preview feels faster and the file is often a bit smaller than baseline. For tiny images the benefit is negligible and baseline can decode faster.
Both are still ordinary JPEG files that any viewer can open; converting between baseline and progressive re-saves the same image and does not change its format or resolution.