A 4 MB phone photo slows down a web page, clogs a mailbox and runs into the upload caps of many forms. Compressing it is easy, but not in the same way for a photo, a logo or a screenshot: applying the wrong remedy gives a file barely smaller or a damaged image.
Why an image is heavy
A 12-megapixel photo (4,000 × 3,000 pixels) holds 12 million pixels of 3 bytes each: 36 MB raw. JPEG commonly brings it down to 3 to 5 MB, roughly ten times less, by discarding detail the eye barely notices. Weight therefore depends on two things: the number of pixels and the chosen quality level.
The pixel count is the most powerful lever. Bringing the photo from 4,000 × 3,000 down to 2,048 pixels on its long side (2,048 × 1,536) divides the pixel count by nearly four (3.1 million instead of 12) and the weight in a similar proportion. And a standard computer screen shows 1,920 pixels across: beyond that, surplus pixels are invisible on screen.
Which method for which format
| Format | The tool's method | Typical saving | Note |
|---|---|---|---|
| JPG | Quality setting (75% by default), optional dimension limit. | Often 50 to 80% on a phone photo, especially with a dimension limit. | Re-saving an already compressed JPG adds loss: start from the original. |
| PNG, lossy mode | Palette brought down to 256, 128, 64 or 32 colours. | Often 60 to 80% for logos, screenshots and illustrations. | Bad for a photo or a gradient: colour bands appear. |
| PNG, lossless mode | Optimised re-encoding, pixels strictly identical. | More modest. | Pick it when pixel exactness matters. |
| WebP | Quality setting. | See JPG, PNG, WebP, SVG: which image format to choose and how to convert. | Well supported by recent browsers. |
Compressing step by step
- Drop your files (100 MB maximum each). A live estimate on the first one shows the sizes before and after and a comparison slider.
- Adjust until the difference is invisible at 100% zoom on fine areas (faces, text, gradient sky).
- If a form imposes a ceiling, use “Aim for a maximum size”: the tool finds the best quality that fits under your limit in KB, then reduces the dimensions if needed.
- Download the result. An already well-optimised file is returned as is: the tool never makes it heavier.
Practical tips
- Aim for the display size. For a blog, 1,200 to 1,600 pixels wide is almost always enough; for a thumbnail, 400 to 800.
- Quality 75 to 85% is the right compromise for a photo. Dropping to 60% shows blocks on gradients; going to 95% adds weight with no visible gain.
- The right format for the right content. A logo or text as JPG has halos; a photo as PNG is three to eight times heavier than as JPG.
- Metadata leaves with compression: GPS position and camera model are removed from recompressed images, which protects your privacy (see Hidden metadata: what your files reveal and how to erase it).
- Keep the original. Lossy compression is irreversible.
Common mistakes
- Compressing the same image several times: each pass adds loss for a diminishing gain.
- Lowering quality when reducing the dimensions would have been enough.
- Enlarging a compressed image afterwards: the flaws become visible.
- Putting a photo PNG through a 32-colour palette: the image bands. Use a format made for photos.
Honest limits
- An already heavily compressed image (downloaded from a social network, say) will hardly shrink any more.
- Images above 100 megapixels are refused to protect the tab's memory.
- The “typical” results above are orders of magnitude: the real saving depends on each image, and the tool shows the measured size.
Frequently asked questions
Which JPG quality should I choose?
Between 75 and 85% for a photo meant for screens. Below 60% flaws become visible; above 90% the weight climbs fast for a barely perceptible gain.
How do I get under exactly 200 KB?
Use the “Aim for a maximum size” option: the tool adjusts the quality, then the dimensions if needed, to fit under the limit you type.
Does compression remove location data?
Yes: metadata (GPS position, camera model) is not kept in recompressed images.
Why does my PNG barely shrink?
If it is a photo or a gradient, PNG is a poor format for that content. Convert it to JPG or WebP.
Are my images sent to a server?
No. Compression is done by your browser; nothing is transmitted or kept.