How to reduce image file size without ruining quality

A phone photo is often several megabytes, far more than a web page, an email or an upload form needs. Four things decide a file size. Working through them in this order gets the biggest saving for the least damage.

1. Dimensions: fewer pixels

File size grows with the number of pixels, which is width times height. Halving both sides leaves a quarter of the pixels. A photo taken at 4000 x 3000 pixels is 12 million pixels, far more than a screen needs; scaled to 1600 pixels wide it is about 1.9 million. Resizing is the biggest lever and costs the least visible quality. Use the image resizer.

2. Format: pick the right one

• JPEG suits photos. It discards detail the eye barely notices, so files are small, and it is accepted everywhere. It has no transparency.
• PNG is lossless and keeps transparency, which makes it ideal for logos, screenshots and text, and large for photos.
• WebP makes smaller files than JPEG or PNG at similar quality and supports transparency, but some older programs and upload forms reject it.

A photo saved as PNG is usually many times larger than the same photo as JPEG. Convert with the PNG to JPG converter.

3. Quality: lower it, but not too far

JPEG and WebP have a quality setting. The first reductions save a lot of space with little visible change; past a point the savings shrink and blocky artefacts appear. A setting in the range of 75% to 85% is a sensible place to start, then look at the result. The image compressor shows the before and after sizes so you can decide.

4. Metadata: strip what you do not need

Photos carry extra data such as the camera model and, often, GPS location. It is usually small, but removing it is good for privacy. Saving an image through a canvas, as these tools do, drops it.

Compress to an exact size

When a form or site has a limit, such as 100 KB, 50 KB or 20 KB, the tool searches for the highest quality that fits, and reduces dimensions in steps if quality alone is not enough. Always keep the original, because lossy compression cannot be undone.