JPEG Files (.JPG)

The Joint Photographic Expert Group (JPEG) defined this standard for the representation of photographic images. Its aim was to allow varying levels of compression, based on the requirements of the user, but the format should be 24bit true colour allowing for high quality colour balanced images where required.

JPEG compression is the forerunner of MPEG for motion video. MPEG, and derivatives, is used throughout the computer industry. For example, MPEG version 2 is used in DVDs to squeeze 2 hours of high resolution video onto a single layer DVD (4.7GB).

JPEG offers compression level settings ranging from 1 (high quality - larger size) through to 99 (low quality - very small size). The examples below show these settings:

Original Windows Bitmap - 176KB JPEG compression - level 1 - 65KB JPEG compression - level 15 - 24KB
JPEG compression - level 40 - 10KB JPEG compression - level 75 - 5KB JPEG compression - level 99 - 3KB

Detailed view of each level

The images below are sections of each of the above images blown up to 1200 percent:

Detail of original Detail of JPEG - level 1 Detail of JPEG - level 15
Detail of JPEG - level 40Detail of JPEG - level 75 Detail of JPEG - level 99

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