Suggest an editImprove this articleRefine the answer for “What is progressive JPEG?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**Progressive JPEG** is a way of saving JPEG images in which the picture loads in several passes, showing the whole image right away, even if blurry, while the detail gradually improves. **Key point:** unlike regular (baseline) JPEG, which is drawn top to bottom, progressive JPEG improves the perceived loading speed, though it does not change the actual network speed.Shown above the full answer for quick recall.Answer (EN)Image**Progressive JPEG** is a special way of saving JPEG images in which the picture **loads gradually**, in layers: first a **blurry version** is visible, then it becomes **sharper and sharper**, until it is fully in focus. This differs from regular (baseline) JPEG, which loads **from top to bottom**: first a gray rectangle, then the top, then the middle, then the bottom. --- ### 1. What the difference looks like #### **Regular (Baseline) JPEG:** - Loads **line by line, top to bottom**. - Until it loads completely, only a "cut-off" piece of the image is visible. - The user does not understand what the photo shows until the entire file has finished loading. #### **Progressive JPEG:** - Loads **in several passes** (usually 3-5). - A rough, "blurry" version is visible right away. - With each pass, the picture becomes more detailed. In other words: > Progressive JPEG shows *the entire image at once*, even if in low quality, > and then gradually improves it. --- ### 2. How this works technically JPEG stores data not simply as pixels, but as **frequencies (DCT blocks)**. In the progressive variant, these blocks are transmitted not in row order, but **by level of detail**: from low frequencies (general shapes) to high ones (fine details). After each "batch," the browser can already render an approximate version of the image. --- ### 3. Advantages of progressive JPEG | Advantage | Description | |---|---| | **Better perceived speed** | The picture "appears" right away, even if blurry, which creates a sense that everything is loading fast | | **Smooth loading** | No "image being drawn top to bottom" effect | | **Sometimes a smaller file size** | Compression can result in a slightly smaller size | | **Works well on slow internet** | The user immediately sees an approximate version of the photo's content | --- ### 4. Disadvantages | Disadvantage | Explanation | |---|---| | **Requires more CPU** | The browser needs to decode the image several times | | **Not all tools display it progressively** | Older programs may display it only after it fully loads | | **Does not speed up the actual load** | Network speed stays the same, only the *perception* of speed changes | --- ### 5. Where it is used - Most **modern sites** (especially news and e-commerce ones) use progressive JPEG; - Supported by **all modern browsers**; - Often enabled automatically when compressing in tools like **TinyPNG**, **Squoosh**, **ImageMagick**, **Photoshop ("Save for Web")**. Example with ImageMagick: ```bash convert input.jpg -interlace JPEG output.jpg ``` --- ### 6. How to tell if a JPEG is progressive You can check it online (via [JPEGsnoop](https://github.com/digitalpreservation/jpegsnoop)) or look at the properties in Photoshop → "Progressive: Yes". --- ### Summary: | JPEG type | How it loads | Visual effect | |---|---|---| | **Baseline** | Top to bottom | Appears "in pieces" | | **Progressive** | All at once, gradually improves | Smooth appearance | --- **In simple terms:** *Progressive JPEG* is when the image "develops," like a photo on old film: first blurry, then sharper and sharper. The user sees the content sooner, and the page feels **faster and more pleasant**.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.