JPEG
Also known as: JPG, jpeg file, jpg vs png
JPEG (.jpg) is the most widely supported photo format. It uses lossy compression to shrink photographs dramatically, trading a small amount of detail for much smaller files. It has no transparency and is larger than newer formats like HEIC or WebP at the same quality.
- Lossy compression; no transparency
- Universally supported, but larger than HEIC or WebP
- Re-saving repeatedly degrades quality
Why JPEG files are smaller than the original
JPEG is lossy: it permanently discards detail the eye is unlikely to notice, especially fine color variation, to reach file sizes a fraction of an uncompressed image. That is why it became the default for cameras and the web for decades.
Quality is adjustable. A high-quality JPEG looks nearly perfect but stays larger; a heavily compressed one is tiny but shows blocky artifacts. Re-saving a JPEG repeatedly degrades it further each time, since the loss compounds.
What it costs in storage
A typical phone photo saved as JPEG is roughly twice the size of the same shot in HEIC, which is why switching an iPhone to "Most Compatible" makes the camera roll grow. JPEG also cannot store transparency, so screenshots and graphics with clear areas are better off as PNG or WebP.