A short history
JPEG is named after the Joint Photographic Experts Group, the committee that published the standard in 1992. It arrived exactly when digital cameras and the early web needed a way to make large photos small enough to store and transmit — and it has never really been dethroned for that job. The familiar “.jpg” extension is just a legacy of MS-DOS’s three-letter filename limit; “.jpeg” is the same format.
How it works
JPEG achieves its small sizes with lossy compression: it converts the image into frequency information using the Discrete Cosine Transform (DCT), then discards the high-frequency detail your eye is least likely to notice. The quality slider controls how aggressively it throws that detail away. Because it operates on 8×8 pixel blocks, pushing quality too low produces the tell-tale “blocky” look, especially around sharp edges and text.
When & how to use it
Reach for JPEG when the image is a photograph and needs to open anywhere — email, older software, print shops. Keep quality around 80–85 for a file that looks identical to the original at a fraction of the size. Avoid it for logos, screenshots or line art, where its block artifacts show, and never repeatedly re-save a JPEG: each save compounds the quality loss.
- Standardised in 1992 by the Joint Photographic Experts Group.
- Lossy, DCT-based compression working on 8×8 pixel blocks.
- No transparency and no animation — it stores a single flat image.
- Re-saving accumulates “generation loss”; always edit from the original.