JPEG Format.

Summary

JPEG stands for Joint Photographic Experts Group, who invented this format to display full-color photographic images in a portable format with a small file size. It can display true-color images (up to 16 million colors), which makes them much better for images such as photographs and illustrations with large numbers of colors. The main disadvantage of the JPEG format is that it is lossy. This means that you lose some of the detail of your image when you convert it to JPEG format.

History

       "JPEG" stands for Joint Photographic Experts Group, the name of the committee that created the standard. The group was organized in 1986, issuing a standard in 1992.The JPEG standard specifies both how an image is compressed into a stream of bytes and decompressed back into an image, and the file format used to contain that stream.

Properties

  • JPEGs support 24-bits of color depth or 16.7 million colors.

  • JEPG does not discard pixels. Instead it changes the color detail of some pixels in an abstract mathematical way.

  • The first 24 bit format with lossy compression.

  • JPEG is designed to exploit certain properties of our eyes, namely, that we are more sensitive to slow changes of brightness and color than we are to rapid changes over a short distance. 

  • Compression:
  • JPEG is a lossy compression algorithm.  When you create a JPEG or convert an image from another format to a JPEG, you are asked to specify the quality of image you want.  Since the highest quality results in the largest file, you can make a trade-off between image quality and file size.  The lower the quality, the greater the compression, and the greater the degree of information loss.

  • Compressed data capacity depends on image contents. Compression degree may come up to 25:1 without visible loss in quality.

 

Disadvantages:

  • Compression effects are cumulative. This means that every time you re-save a JPEG file, you are compressing it further, and thereby tossing away data (photographic detail) that you can't get back.

  • Animations cannot be created, nor can a transparent color be defined.

  • Not suitable for images containing typography or geometrical patterns.

 

 

Advantages

  • Ability to control the compression level in image editors

  • JPEG is great for sending photographs via email, and for photographic images on the web.

  • JPEG format is primarily used to hold photorealistic graphic images with a large number of color (can display up to 16.7 million colors).

  • Compressed data capacity depends on image contents. Compression degree may come up to 25:1 without visible loss in quality.

  • JPEG supports Progressive Jpeg standard, which is conceptually similar to interlacing. That means that Jpeg Progressive format images are loaded by parts, which are displayed, as they are loaded. Such format is good for large files. Unfortunately, it is a new standard, so some programs may not support it.

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