What is JPG?
JPEG (Joint Photographic Experts Group), created by Joint Photographic Experts Group (ISO/IEC and ITU-T) in 1992.
The JPEG committee formed in 1986 with a specific brief: make photographs small enough to be practical on the hardware of the day. Their answer, standardised in 1992, was built on the discrete cosine transform — split the image into 8×8 blocks, express each block as a sum of frequency patterns, then throw away the high-frequency components the human eye barely registers.
That last step is the whole trick, and it is why JPEG is described as perceptually lossy rather than merely lossy. It does not discard data at random; it discards the data you are least likely to miss. The quality slider in any JPEG encoder is really a control over how aggressively that discarding happens.
Two design choices explain most of JPEG's behaviour. It works in blocks, which is why over-compressed images show 8×8 squares. And it stores colour at lower resolution than brightness — chroma subsampling — because human vision is far more sensitive to luminance detail than to colour detail. This is also why red text on a blue background looks terrible in JPEG.
Its longevity is not technical. Every camera, every browser, every operating system, every printer and every piece of software written since 1993 reads JPEG. That is a moat no newer format has crossed.
Technical specification
| Property | JPG |
|---|---|
| Compression | Lossy (discrete cosine transform); a lossless mode exists in the standard but is effectively unused |
| Bit depth | 8 bits per channel |
| Transparency | No — there is no alpha channel at all |
| Animation | No |
| HDR | No |
| Maximum dimensions | 65,535 × 65,535 px |
| Colour spaces | YCbCr from sRGB; embedded ICC profiles including CMYK |
| Metadata | Full EXIF, IPTC, XMP, GPS, thumbnails |
JPG support in browsers and operating systems
Checked on 2026-08-10. We re-verify this table every quarter.
| Platform | Support |
|---|---|
| Chrome | all versions |
| Safari | all versions |
| Firefox | all versions |
| Edge | all versions |
| iOS | all versions |
| Android | all versions |
| Windows | all versions |
| macOS | all versions |
JPG compared with nearby formats
Against WebP. WebP is about 25–30% smaller at matching quality, supports transparency and animation, and works in every current browser. For anything on a web page it is the better format. JPEG's remaining edge is outside the browser — email clients, older photo software, print shops.
Against AVIF. AVIF is dramatically better, often half the size of JPEG at comparable quality, with 10-bit colour and HDR. Its costs are encoding time measured in seconds rather than milliseconds, and support that stops at the browser — most desktop applications still cannot open one.
Against PNG. Different jobs. JPEG is for photographs and PNG is for graphics with flat colour and sharp edges. Using JPEG for a screenshot produces visible artefacts around every letter; using PNG for a photograph produces a file five to ten times larger for no benefit.
When to use JPG, and when not to
Use JPG when the image is photographic and the recipient is unknown. It is the format with no compatibility questions attached, which is exactly why it remains the right answer for email attachments, form uploads, printing services and anything a person will open on hardware you cannot see.
Use quality 80–85 for photographs headed to a screen. Above 90 the file grows quickly for differences nobody can see; below 70 the block structure starts showing in skies and skin.
Do not use JPG for screenshots, logos, line art or anything needing transparency — there is no alpha channel, so transparent pixels are filled with a solid colour. Do not use it as a working format either: every save re-compresses, and the damage accumulates across edits.
Frequently asked questions
What is the difference between .jpg and .jpeg?
Nothing. The files are identical — the shorter extension exists because MS-DOS allowed only three characters. Some Windows tools also produce .jfif, which is again the same JPEG data under a different name. Our converter treats all three as one format.
Does resaving a JPEG make it worse each time?
Yes. Every save re-runs lossy compression on data that has already been compressed, and the artefacts compound. Editing the same JPEG repeatedly will visibly degrade it. Keep an original in a lossless format and export JPEG at the end.
What quality setting should I use?
For screen use, 80–85 is the sweet spot: no visible artefacts at normal viewing distance and a file roughly a third the size of quality 95. For print or archiving, use 95 or a lossless format. Below 70, block artefacts appear in gradients and around edges.
Why does my JPEG show coloured smears around text?
Chroma subsampling. JPEG stores colour information at half the resolution of brightness because the eye tolerates it in photographs — but text has hard colour edges, and halving the colour resolution smears them. This is the clearest sign that an image should have been a PNG.