The JPG (JPEG) format
The default format for photographs for thirty years, and still the most universally supported image format there is.
What is JPG?
JPEG is a lossy compression format published in 1992 and designed specifically for photographs. It works by converting the image to a colour space that separates brightness from colour, discarding colour detail the human eye is poor at noticing, and then compressing what remains in 8 × 8 blocks.
That block structure is the source of both its efficiency and its characteristic failure mode. On continuous-tone photographs the blocks are invisible; on sharp edges and flat colour they produce visible ringing and fringing, which is why screenshots saved as JPEG look muddy around text.
The extensions .jpg and .jpeg are identical — the three-letter form is a leftover from filesystems that only allowed three characters.
Common uses
- Photographs on websites, in email and in documents
- Camera and phone output where storage matters
- Social media uploads, which are re-encoded to JPEG anyway
- Anywhere maximum compatibility is more important than transparency
Advantages
- Supported by literally every browser, operating system, printer and application
- Excellent compression on photographic content
- A tunable quality setting that trades size against fidelity
- Fast to encode and decode, with hardware acceleration nearly everywhere
Limitations
- No transparency — there is no alpha channel in the format at all
- Lossy, and cumulatively so: every re-save discards more
- Poor on sharp edges, text and flat colour
- Larger than WebP or AVIF at equivalent visual quality
Browser support
Universal. Every browser ever shipped can display JPEG, and it needs no fallback of any kind.