JPEG at a Glance
- Stands for
- Joint Photographic Experts Group
- File extension
.jpg, .jpeg, .jpe, .jif, .jfif, .jfi
- Eric Hamilton, Joint Photographic Experts Group, Tom Lane,
Independent JPEG Group
- 1990 (JPEG), 1991 (JFIF)
- ISO/IEC 10918
- Colors & bit depth
- maximum 16,777,215 colors
- 8 bit grayscale, 24 bit true color , 12 bit
- Optional Goodies
- Progressive rendering
- Chroma subsampling
- Detail smoothening
- Color profiles (ICC) support
- Metadata support (ICC, EXIF, IPTC)
- Lossy – JPEG compression (lossy discrete cosine transform
followed by Huffman coding).
- How it works
- JPEG compression is designed to reduce things that don’t make a
noticeable difference in the picture. It’s based on studies of
human perception, and it throws away data you won’t notice.
In computing, JPEG (pronounced JAY-peg; IPA: /ˈdʒeɪpɛɡ/) is a commonly used method of compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10 to 1 compression with little perceivable loss in image quality.
JPEG is the most common image format used by digital cameras and other photographic image capture devices, and is the most common format for storing and transmitting photographic images on the World Wide Web.
JPEG is good for
In fact, this is the intended usage for JPEG images. Most digital cameras save by default in this format. When you’ve got an image that looks mostly like a photograph, JPEG will nearly always do the best job for you. Note that JPEG compression is lossy, and this is not the best way to keep the maximum quality of photos. Furthermore, the quality degrades at each re-compression, so watch out for multiple editing of JPEGs.
Images with many colors (more than 256 colors)
It is worth trying also PNG for these images, either paletized using quantization or true color.
JPEG Is Bad For
Text or black/white scans
Images with sharp edges
Drawings, cartoons, images with few colors
Advanced graphics programs will let you turn off chroma sub-sampling, and while you’ll pay a price in image size, these kind of images may look better with no/less chroma sub-sampling.
Images with transparency
JPEG does not support transparency. In these cases GIF or PNG are the alternatives.