JPG file format
Joint Photographic Experts Group (JPEG)
JPG is the world's most common photo format. It uses lossy compression to keep photos small, but it has no transparency and loses a little detail every time it's re-saved.
| Property | JPG |
|---|---|
| File extensions | .jpg, .jpeg, .jfif |
| MIME type | image/jpeg |
| Introduced | 1992 by Joint Photographic Experts Group |
| Compression | Lossy (DCT) |
| Transparency | No |
| Animation | No |
| Colour depth | 24-bit (16.7 million colours) |
| Support | Universal — every browser, OS, camera and app |
| Best for | Photos, social media, email, printing |
What is a JPG file?
JPG (or JPEG) is a lossy image format standardised in 1992 by the Joint Photographic Experts Group. It splits an image into 8 × 8 pixel blocks, converts them into frequency data with the discrete cosine transform (DCT), and throws away fine detail the human eye is least likely to notice. The result is a photo file roughly ten times smaller than the raw pixels.
Because it works so well on photographs, JPG became the default output of digital cameras, phones (before HEIC), scanners and almost every website. The .jpg and .jpeg extensions are identical; .jfif is the same format with a different file-interchange header.
Strengths and weaknesses of JPG
JPG's biggest strength is compatibility: every browser, operating system, printer, editor and upload form accepts it. Its quality setting lets you trade size for detail, and at 85–90% most people can't see any loss.
Its weaknesses are just as clear. JPG has no transparency, so cut-out logos need PNG or WebP. Sharp edges such as text, line art and screenshots pick up faint 'ringing' artefacts. And every edit-and-save cycle compresses the image again, slowly degrading it — so keep a lossless master if you edit often.
When should you use JPG?
Use JPG for photographs you want to share, email, print or upload to forms — especially when compatibility matters more than squeezing out the last kilobyte. For websites, WebP or AVIF usually deliver the same quality at 25–50% smaller sizes; for graphics with text or transparency, PNG is the better choice.