How to Compress Images Without Losing Quality

The trick is knowing where the limit is. Compress too gently and you save almost nothing; compress too hard and the photo turns blocky, with smudged details and banded skies. This guide shows how to find the sweet spot, with a worked example you can repeat on your own photos.

What compression actually does

Most photos are JPG files, and JPG is a lossy format: when it saves, it throws away detail the eye is least likely to notice. A quality setting of around 80 out of 100 typically removes a large amount of data while keeping the image looking identical at normal viewing sizes. PNG files work differently — they are lossless, so they compress by finding patterns in the pixels instead of throwing detail away, which is why screenshots and graphics with flat colours shrink well as PNG, while photos do not. WebP, a newer format, usually beats both for photos, often producing files 25–35% smaller than an equivalent JPG.

One important point: compression is a one-way street. Once detail is thrown away, saving the file again at a higher quality will not bring it back. Always compress a copy, and keep the original somewhere safe.

Worked example: a 4.2 MB holiday photo

Take a typical phone photo: 4032 × 3024 pixels, 4.2 MB as a JPG. First, resize it to the size it will actually be shown at — a photo displayed at 1200 pixels wide does not need 4032 pixels, and resizing alone often cuts the file to around 1 MB. Then compress the resized image at quality 80. The result is usually 250–400 KB, roughly a tenth of the original, and on a phone or laptop screen it looks the same. If the photo will be printed, skip the resize and compress the full-size original at quality 85–90 instead; print shows flaws that screens hide.

Check your result by zooming to 100% and looking at areas with fine detail — hair, leaves, fabric — and smooth gradients like skies. If you see blocky squares or banding, raise the quality by 5–10 points and try again.

Step by step

1. Open the Compress Image tool and add your photo.
2. Choose the size it will actually be used at, and resize first if it is much larger.
3. Set the quality to around 80 for JPG photos, or convert to WebP for the smallest file.
4. Compress, download the result, and compare it with the original at full zoom.
5. If you see artefacts, raise the quality slightly and compress again — from the original, not from the compressed copy.

Common mistakes

• Compressing a compressed copy. Every round of lossy compression throws away more detail. Always start from the original file.
• Using PNG for photographs. PNG is lossless, so a photo saved as PNG can be several times larger than the same photo as JPG. Use PNG for screenshots, logos and graphics — not photos.
• Keeping full resolution for a thumbnail. A 4000-pixel image shown at 400 pixels is wasted weight. Resize to the display size first.
• Judging quality from a tiny preview. Artefacts hide in thumbnails. Always check at 100% zoom before you publish.
• Deleting the original. Keep the original until you are sure the compressed version is good enough — you cannot undo compression.

Tips for the smallest files

For the web, WebP is usually the best choice: same visible quality, noticeably smaller files than JPG. For photos with transparency, PNG is still the format to use, since JPG cannot do transparency at all. If you need to send many photos at once, compress each one before attaching them — ten 300 KB photos send far more reliably than ten 4 MB ones. And remember that the biggest saving usually comes from resizing, not from the quality slider: cutting the pixel dimensions in half cuts the file size by roughly three quarters.

Frequently asked questions

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