Assuming progressive is a different or better compression method, when it only reorders the same quantised data.
Compression
Progressive JPEG
Also called progressive jpg, interlaced jpeg or baseline vs progressive. Here is what it means, when it changes what you export, and what people get wrong.
CompressionRuns on your deviceUpdated 10 August 2026
The short answer
A progressive JPEG stores the image as a series of scans that each add detail, so a rough version of the whole picture appears first and sharpens as more data arrives. A baseline JPEG instead loads strictly top to bottom. Both use the same lossy compression and decode to the same final image.
Updated
The short version
Progressive JPEG at a glance
| Quick fact | Detail |
|---|---|
| Compression | Identical to baseline, only the ordering differs |
| Two mechanisms | Spectral selection and successive approximation |
| Best for | Large hero and banner images on slow connections |
| Poor fit | Thumbnails, icons and other small images |
| Decoding cost | More CPU and memory than baseline |
Slide the table sideways to see every column.
How do the scans work?
Nothing changes about how the picture is compressed. The image is still split into 8x8 blocks, transformed and quantised in exactly the same way. What changes is the order those numbers are written into the file.
A baseline JPEG writes every coefficient for the first strip of blocks, then the next strip, and so on down the image. A progressive JPEG writes several passes over the whole image instead. The specification allows two ways of splitting them up, and encoders usually combine both. Spectral selection sends the low-frequency coefficients first, which is enough to draw a blurry version of the entire frame, then sends the higher frequencies that add edges and texture. Successive approximation sends the most significant bits of each coefficient first and refines them with the remaining bits in later scans.
Because the same coefficients are simply grouped differently, the decoded result at the end is identical to the baseline version.
When is progressive worth choosing?
The clear case is a large image above the fold on a slow or unreliable connection: a hero banner, a full-width lifestyle shot, a big product image on a mobile network. The visitor sees the composition almost immediately and watches it sharpen, rather than staring at a half-drawn picture with a blank space underneath. Perceived load time improves even though the total bytes are the same.
On larger photographs, progressive encoding also tends to produce a slightly smaller file than baseline, because grouping similar coefficients together gives the entropy coder more predictable data to work with. The gain is small and depends on the image, so treat it as a bonus rather than a reason to switch. For small images such as thumbnails and icons, progressive often ends up the same size or a little larger, and there is nothing meaningful to reveal progressively anyway.
What are the trade-offs?
A progressive decoder cannot finish any part of the image until it has seen all the scans, so it has to hold the full image in memory and do more work per pixel than a baseline decoder. On modern hardware that is rarely noticeable, but it matters on constrained devices and when decoding very large batches.
The bigger practical issue is compatibility. Progressive is part of the JPEG standard and every mainstream browser handles it, but plenty of non-browser software does not deal with it gracefully, including some older print workflows, embedded devices, and image pipelines inside third-party systems. If you are uploading to a marketplace or a client system you cannot test, baseline is the safer default. For images you serve from your own site, progressive is the better choice for anything large.
What people get wrong about progressive jpeg
Each one is a real failure mode, not a style preference.
Turning progressive on for a whole batch including thumbnails, where it adds decode cost and can make files slightly larger.
Uploading progressive JPEGs to a third-party system that rejects or mishandles them, then blaming the image itself.
Expecting a big file size win, when the reduction is modest and depends entirely on the image.
Questions people ask
Progressive JPEG, answered
The follow-up questions people search for once they have the definition.
Is a progressive JPEG better quality than a baseline one?
No. At the same quality setting the two decode to the same image, because progressive only changes the order the compressed data is written. Any visible difference comes from the quality setting or the encoder, not from progressive encoding itself.
How do I tell if a JPEG is progressive?
Most image inspection tools and command line utilities report it directly from the file's markers. In a browser on a slow connection you can also see it: a progressive file appears blurry across the whole frame first, a baseline file fills in from the top down.
Should I use progressive JPEG for marketplace listings?
Baseline is the safer choice for uploads to systems you do not control, since some image pipelines handle progressive poorly. The marketplace will usually re-encode your image anyway, so the encoding you upload rarely reaches the shopper unchanged.
Can you convert a baseline JPEG to progressive without losing quality?
Yes. The conversion reorders and re-entropy-codes existing data without re-quantising it, so the pixels are unchanged. It is one of the few JPEG operations that is genuinely lossless, and it sometimes trims the file slightly at the same time.
Same cluster
More from the glossary
Neighbouring entries, so every term in the set is one hop from every other.
Quality setting
A quality setting is the number, usually 0 to 100, that tells a lossy encoder how aggressively to discard detail.
Profile picture
A profile picture is the small image that represents a person or a business on a platform.
Raster image
A raster image is a picture stored as a grid of coloured pixels, which is how photographs, screenshots and most web images work.
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Sources
Where the facts on this page come from. Every link opens the specification, standard or documentation the claim was read at.
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