Extended system:

Extended Systems is the name given to a number of additional capabilities not provided by the system baseline. Each series is designed to work with, or be constructed from the internal components of the baseline, with the aim of expanding their operation modes. These optional capabilities, which include arithmetic coding, reconstruction and progressive "progressive lossless coding, and others, can be implemented individually or in appropriate combinations.

Arithmetic coding is an optional alternative, "modern" Because the arithmetic coding method is adapted to the chosen parameter values of the image, usually provides from 5 to 10 percent better compression than Huffman method chosen by JPEG. This benefit is offset by the increase in the complexity of the system.

Rebuilding progressive alternative to the reconstruction sequence is specifically useful when using databases of images with little channels of communication bandwidth. For coding progressive: first, a "coarse" is sent, then the refinements are sent by improving the quality of the image "coarse" until the desired quality is achieved. This process is carried out by applications such as databases of images with multiple resolutions and different quality requirements, in freeze frame video, photo videotext for low speeds.

Lossless coding refers to the progressive compression method, which operates in conjunction with the progressive reconstruction. In this mode of operation, the final stage of the reconstruction results in a progressive image, which is received bit by bit identical to the original.

The standard JBIG (United Group for bi-level images).

Some years back, a group of experts was formed to establish an international standard for coding of bi-level images. The JBIG (group united for bi-level images), JBIG has developed a document entitled "Progressive compression standard for bi-level images", which defines a method for compressing bi-level images (ie, an image black and white). Because the method is adapted to a wide range of features of images, encryption is a technique very robust.

The JBIG standard operates in the sequential mode and in the progressive mode. When decoding a progressively encoded image, an image of low resolution compared to the original is available first, the image resolution increases as more data are decoded. Progressive coding provides two benefits, the first is that a database of images can serve different output devices each with different resolutions. Only with such information in the file compressed images for the reconstruction to the resolution of the output device in particular needs to be sent and decoded.

other benefit is that the progressive coding provides subjectively superior images (on a monitor) on communication links of low or medium speeds. A low-resolution image is transmitted and displayed quickly, with improved resolution to be away. Each stage of improvement of the resolution is constructed in the image already available.

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