JPEG

Definition:JPEG is an image compression standard (ISO IS 10918-1) published by The Joint Photographic Experts Group in 1994.

JPEG has become the most widely used format for storing digital photographs ever since. The original JPEG specification defines four compression modes [1, 2]:

• • Sequential (baseline): based on the DCT and adequate for most applications;

• • Hierarchical: used to encode the image in a hierarchy of several different resolutions;

• • Progressive: delivers lower-quality versions of the image quickly, followed by higher-quality passes; enjoyed popularity in the early days of the World Wide Web;

• • Lossless: a variant that employs a simple differential coding method instead of DCT followed by quantization.

In this discussion we will limit ourselves to the sequential (default) mode.

The JPEG encoder (Figure 1) consists of the following main stages:

• 1. The original RGB color image is converted to an alternative color model (YCbCr) and the color information is subsampled.

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