Image optimisation is not simply a matter of moving one quality slider as low as possible. The best result comes from choosing sensible dimensions, the correct file format and a compression level that suits the picture.
Resize before compressing
A 4000-pixel photograph is unnecessary when it is displayed at 900 pixels wide. Resize the image close to its largest real display size before compressing it. This removes pixels the visitor would never see and often saves more data than aggressive compression.
Choose a format that matches the content
- JPEG: useful for photographs and complex colour gradients.
- PNG: useful for transparency, interface graphics and images that need lossless detail.
- WebP: supports lossy and lossless compression and commonly produces smaller web assets.
- AVIF: can provide strong compression for modern browsers, although encoding may take longer.
Find the quality threshold
Compress one copy, compare it with the original at 100% zoom and pay special attention to faces, text, gradients and sharp edges. Lower quality gradually until damage becomes noticeable, then move slightly back toward quality. There is no single correct percentage for every image.
Remove unnecessary metadata
Camera files can contain location, device and editing metadata. Removing that information may reduce file size and is useful when privacy matters. Keep an untouched original if you may need the metadata later.
Practical workflow
- Keep a full-quality master copy.
- Crop unused edges.
- Resize to the required output dimensions.
- Choose JPEG, PNG, WebP or AVIF based on the content.
- Compress and compare the result visually.
- Test the final file on a real mobile screen.
Use the Image Resizer first when the dimensions are excessive, then use the Image Compressor or a format-specific compressor. For web delivery, the Image to WebP converter can create a modern alternative.
Further reading
web.dev explains how correctly sized images and modern formats reduce transferred bytes: image performance.
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