Compress Images Without Losing Quality

Why image files are large

An image is a grid of pixels, and each pixel carries colour information. Two things drive file size: how many pixels there are, and how well the format can compress them. A phone photo can contain millions of pixels, and a lot of that detail is more than a screen or email needs.

Detail also matters. A flat-colour graphic compresses easily, while a photo with leaves, hair or textured fabric holds far more information and gives the compressor less to work with.

Lossless and lossy compression

Lossless compression reduces size without changing a single pixel. The saving is real but limited, especially for photographs.

Lossy compression decides some detail is unlikely to be noticed and discards it. This is how JPG and lossy WebP get much smaller. The cost is that the removed detail is gone for good, and pushing the setting too far shows up as blocky patches, blurred edges or colour banding.

The practical aim is the lowest quality setting that still looks right at the size people will view it.

Resize first

Resizing is often the biggest single saving. If a photo is 4000 pixels wide but will appear 1200 pixels wide on a page, the extra pixels are wasted. As an illustration only, halving both width and height leaves a quarter of the pixels to store.

Use the image resizer to set exact pixel dimensions, a percentage or a preset. Keep the aspect ratio locked unless you intend to crop or stretch.

Choose a quality setting

The image compressor has a quality slider and an optional scale control, and it outputs JPG or WebP. Work through it like this:

1. Choose a file and look at the preview next to the original size.
2. Start with a middle-to-high quality value.
3. Lower it gradually while checking details such as faces, text and sharp edges.
4. Stop when you can just see a difference, then go one step back.
5. Download the result. Your original file is untouched.

Different images tolerate different settings. A photo with soft backgrounds can go lower than one with fine text.

Pick a format

Format changes what compression can do. Photos suit JPG or WebP. Screenshots with text may look better kept as PNG, though they will be larger. If your images are for a website, the JPG to WebP converter can produce a smaller file in many cases, but check it opens where you need it. The JPG vs PNG vs WebP guide explains the differences in detail.

A practical routine

1. Keep your original file somewhere safe.
2. Resize a copy to the largest dimensions it will be displayed at.
3. Compress that copy at a moderate quality.
4. Compare at full size against the original.
5. If the file is still too big, lower the quality a little or try WebP.

Common mistakes

• Compressing repeatedly. Each lossy save discards more detail. Always go back to the original rather than recompressing an already compressed copy.
• Upscaling. Enlarging an image adds pixels but no new detail, so it looks soft and the file grows. Resize down, not up.
• Judging at a tiny preview. Artefacts appear when you view at full size, so check there.
• Overwriting the original. Save the compressed version under a new name.
• Using PNG for photos. It keeps every pixel exactly, which makes photographic files large.
• Chasing the smallest number. A file that looks poor defeats the purpose. Stop at the point where it still looks good.