Compress Images Online

What is image compression?

Compression rewrites the data inside an image file so it occupies fewer bytes. Some of that saving comes from describing repeated information more efficiently; the rest comes from throwing away detail the human eye is unlikely to notice. A 4 MB photograph straight from a phone camera commonly drops below 400 KB with no visible difference on a web page, because screens display it far smaller than its full resolution.

Lossy vs lossless compression

Lossy formats such as JPEG, WebP and AVIF permanently remove detail. The quality parameter controls how aggressive that removal is. Each re-save degrades the image further, which is why you should always compress from the original file rather than from an already-compressed copy.

Lossless formats such as PNG rebuild the exact original pixels. They are the right choice for screenshots with text, logos, line art and anything with sharp edges, but they are far heavier for photographs. WebP supports both modes, which is why converting a photographic PNG to WebP often produces the biggest saving of all.

When should I compress an image?

• Before uploading photos to a website, blog post or online store.
• When an email attachment is rejected for being too large.
• When a page audit shows images dominating total transfer size — usually the single biggest cause of slow loading.
• Before sharing a batch of photos where full print resolution is unnecessary.

Does compression reduce image quality?

At high quality settings the loss is measurable but not perceptible. Problems appear as blocky squares around sharp edges, colour banding in smooth gradients and halos around text. Those artifacts are cumulative, so keep an untouched master file and compress only the copies you publish.

Practical example

For even better results, resize the image to the largest size it will actually be displayed at using the image resizer before compressing it.