What is a JPG file?
JPG (or JPEG, from the committee that designed it in 1992) is the most widely used photo format. It compresses images by discarding detail the eye is least likely to notice, which lets a camera photo shrink to a tenth of its raw size with little visible change. The quality setting controls how much is thrown away.
The trade-off is that the discarded data is gone for good, and every re-save discards a little more. JPG has no transparency and handles sharp edges, text and flat colours poorly, producing the familiar blocky halos around letters. Camera and phone JPGs also carry EXIF metadata: date, camera model and often GPS coordinates.
When JPG is the right choice
Strengths
- Small files for photographs and other continuous-tone images
- Opened by every device, browser and program made in the last thirty years
- Adjustable quality lets you trade size against fidelity
Limitations
- Lossy: detail is lost at every save and cannot be recovered
- No transparency and no animation
- Text, logos and screenshots come out blurry with artefacts
How to open a JPG file
Every operating system, browser and photo app opens JPG. Before publishing a photo, check what it reveals with the EXIF viewer and strip location data with Remove EXIF.
How to convert a JPG file
JPG to PNG gives a lossless copy for editing or for adding transparency, JPG to WebP shrinks photos for the web, and JPG to PDF turns scans or photos into a document. For smaller JPGs without changing format, Compress Image re-encodes at a lower quality.