How to compress images without visible quality loss

Start with pixels, not with quality

The biggest savings in image weight rarely come from a quality slider. They come from sending fewer pixels to a screen that cannot display more. A 4000-pixel-wide photo placed in a 720-pixel-wide article column wastes bandwidth on almost every device.

Resize to roughly twice the largest display width you expect. For most blog headers, 1440 pixels wide is generous. The visible difference on a phone is usually zero, while the file size can drop by more than 80 percent.

Choose a format for the content

JPEG remains excellent for photographs because it keeps luminance detail efficiently and discards colour information people notice less. PNG is the right choice for screenshots, flat illustrations and anything that needs transparency. WebP usually beats both at equal visual quality and is supported by every current browser.

Converting a small, already-optimised JPEG to WebP can occasionally produce a slightly larger file. Compare both numbers instead of assuming a newer format is automatically smaller.

Use a quality band, then verify

For photos, 70 to 82 percent is the practical band in a canvas-based compressor. Below 65 percent you start to see blocking in smooth gradients such as skies. Above 85 percent you pay a lot of bytes for detail that screens cannot show.

Verification matters more than the number. Open the compressed file at the size it will be displayed, not at 200 percent zoom. Check faces, fine text, straight edges and gradient backgrounds. If none of those show artefacts, the compression level is fine.

A repeatable workflow

• Export from your editor at the final display size.
• Compress at 75 percent and compare the file size with the original.
• Keep PNG for screenshots and use WebP when transparency matters.
• Check faces, text and gradients at real display size before uploading.
• Rename the file descriptively; file names are read by search engines and humans.

Do not forget metadata

Canvas-based compression rewrites the image, which normally strips EXIF data such as GPS coordinates, camera serial numbers and timestamps. That is good for privacy when publishing customer photos, but it also removes orientation and colour-profile information. Rotate photos in your editor before compressing.