What compressing actually does
Compressing an image means re-encoding it so the file takes up fewer bytes. The width and height in pixels stay the same, so the picture still displays at the same size on screen. What changes is how much detail the encoder keeps. Less detail means a smaller file and, past a certain point, visible softness, blocky patches, or fuzzy edges.
This page runs entirely in your browser. Images are never uploaded, nothing is stored, and the tool keeps working if you go offline after the page has loaded. There is no sign-up and no watermark.
Quality, not dimensions
Two numbers control the result:
- Pixel dimensions — the grid of dots. Changing these resizes the image. This tool does not do that.
- Quality — how aggressively the encoder discards detail. This is what changes the file size here.
A 4000 x 3000 phone photo is often 2-5 MB as a JPEG straight from the camera. Dropping quality from 100 to around 80 usually cuts that by more than half, and most people cannot see the difference on a phone screen or a normal monitor. Below roughly 60, flat areas start to look mottled and sharp edges get a halo.
Choosing a target size
If a form or upload limit gives you a number, work backwards from it:
- Start with quality 80.
- Check the resulting size.
- If it is still too big, lower quality in steps of 5-10 rather than jumping straight to 30.
- If it is well under the limit, raise quality until you are close to the cap.
For a profile photo, 100-300 KB is usually plenty. For a full-width web banner, 150-400 KB. For a print file, do not compress at all — keep the original.
Why PNG barely shrinks
PNG stores images without throwing away detail, which is why it is the right choice for logos, icons, screenshots of text, and anything with transparency. The trade-off is size: a photograph saved as PNG is often several times larger than the same photo saved as JPEG, and lowering a quality slider does almost nothing to it because there is no quality slider to lower. If a PNG photo needs to be smaller, convert it to JPEG or WebP first. Keep PNG only when you need a hard-edged graphic or a transparent background.
| Format | Best for | How it compresses |
|---|---|---|
| JPEG | Photographs, camera images, complex scenes | Quality setting discards detail; large savings, some softening at low settings |
| WebP | Photos and graphics for the web | Similar approach to JPEG with generally smaller files at the same visual quality |
| PNG | Logos, icons, screenshots, transparency | Keeps all detail; savings come mainly from reducing colours or dimensions |
| AVIF | Modern browsers, small web images | Strong compression, but slower to encode and less widely supported |
Checking the result
Look at three things before you download:
- File size — compare it with the original and with any limit you have.
- Edges and text — zoom in on a sign, a face, or thin lines. That is where compression shows first.
- Flat areas — skies, walls, and backgrounds are where blocky artefacts appear.
If the image looks worse than you expected, raise the quality by 10 and try again. If it is still too large, the next real step is reducing the pixel dimensions, which is a different operation from compressing.
When not to compress
Skip it for images you will edit again later, for print, and for anything you may need to re-crop. Compression is a one-way step: once detail is discarded, it does not come back. Keep the original file and compress a copy.
Questions
Does compressing an image change its dimensions?
No. Compressing here changes the quality setting and the file size, not the width and height in pixels. The image still displays at the same size. If you need smaller dimensions, that is a resize, which is a separate step.
What quality setting should I use?
Around 80 is a good starting point for photos and is usually hard to tell apart from the original. Go lower only if you need a specific file size, and raise it if you can see softening or blocky patches.
Why did my PNG hardly get smaller?
PNG keeps all the image detail, so there is no quality setting to reduce. Photographs saved as PNG stay large. Convert to JPEG or WebP if the file needs to be much smaller and you do not need transparency.
Are my images uploaded to a server?
No. The compression runs in your browser, so the file stays on your device. Nothing is uploaded or stored, and the page keeps working offline once it has loaded.