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The JPG (JPEG) format

The default format for photographs for thirty years, and still the most universally supported image format there is.

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O que é 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.

Usos comuns

  • 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

Vantagens

  • 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

Limitações

  • 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

Suporte dos navegadores

Universal. Every browser ever shipped can display JPEG, and it needs no fallback of any kind.

Conversões

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