Glossary · JPEG
What is JPEG? The everyday photo format
Short answer
JPEG is a lossy image format standardised in the early 1990s by the Joint Photographic Experts Group, and it is still the default for most Android cameras. It discards fine detail people barely notice to make files small. Almost every device, browser and app opens JPEG, which is why chat apps and websites convert photos to it.
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How does JPEG make files small?
- The image is converted from RGB into brightness and two colour channels.
- Colour is usually stored at lower resolution, since human vision is less sensitive to colour detail than to brightness.
- Each 8x8 block of pixels is turned into frequencies with a discrete cosine transform.
- Fine high-frequency detail is rounded off according to a quality setting.
- The result is packed with lossless coding.
Step four is where data is lost. A higher quality setting keeps more detail and makes a bigger file.
The format is defined by ITU-T T.81 and ISO/IEC 10918-1. The familiar .jpg file is technically JFIF or Exif wrapped around that compressed data.
Why does a JPEG lose quality when re-saved?
Each save repeats the rounding step, so edits and re-shares slowly add blocky artefacts and colour banding. Chat apps make this worse because they also shrink the image. A photo forwarded through several groups can look visibly softer than the camera original, even though it opens as a normal JPEG. That is also why a re-sent copy counts as a near-duplicate photo rather than an exact one.
Quality settings in camera apps are usually fixed between 90 and 95 on a 100-point scale, which is high enough that a single save shows no visible loss.
How big is a phone JPEG?
| Photo | Typical size |
|---|---|
| 12 MP camera photo | About 2 to 5 MB |
| 50 MP full-resolution mode | About 10 to 25 MB |
| WhatsApp standard-quality copy | A few hundred KB |
| Screenshot saved as JPEG | Under 1 MB |
A detailed scene, like leaves or gravel, compresses less than a blue sky, so two photos from the same phone can differ by several megabytes.
Phone cameras also embed a small preview image and EXIF data inside each JPEG. That adds a few dozen kilobytes per file, which only matters when you multiply it by tens of thousands of pictures.
JPEG or HEIC on Android?
HEIC saves space; JPEG is the universal choice. If storage is tight, a better win than switching formats is deleting what you never look at. GalleryJury, an AI photo cleaner for Android that is not out yet, scans the JPEGs and HEICs on your phone and keeps one good shot per moment.
Compression trade-offs across formats are covered on the image compression page.
Frequently asked questions
Is JPG different from JPEG?
No. JPG is the same format with a three-letter extension, a leftover from old Windows file-name limits.
Can JPEG be lossless?
Standard JPEG is lossy. Lossless variants exist but phones and browsers rarely use them.
Why do my JPEG photos look worse after WhatsApp?
WhatsApp re-compresses photos at a smaller size unless you send them as a document or pick the HD option. The copy you receive is not the sender's original.
Sources
- Wikipedia: JPEG (checked 31 October 2026)
- Android Developers: Supported media formats (checked 31 October 2026)
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