Industry Articles
Data compression tutorial: Part 3-June 28, 2007 |
By Steven W. Smith, Ph.D.
JPEG
Many methods of lossy compression have been developed; however, a family of techniques called transform compression has proven the most valuable. The best example of transform compression is embodied in the popular JPEG standard of image encoding. JPEG is named after its origin, the Joint Photographers Experts Group. We will describe the operation of JPEG to illustrate how lossy compression works.
We have already discussed a simple method of lossy data compression, coarser sampling and/or quantization (CS&Q in Table 27-1). This involves reducing the number of bits per sample or entirely discard some of the samples. Both these procedures have the desired effect: the data file becomes smaller at the expense of signal quality. As you might expect, these simple methods do not work very well.
JPEG
Many methods of lossy compression have been developed; however, a family of techniques called transform compression has proven the most valuable. The best example of transform compression is embodied in the popular JPEG standard of image encoding. JPEG is named after its origin, the Joint Photographers Experts Group. We will describe the operation of JPEG to illustrate how lossy compression works.
We have already discussed a simple method of lossy data compression, coarser sampling and/or quantization (CS&Q in Table 27-1). This involves reducing the number of bits per sample or entirely discard some of the samples. Both these procedures have the desired effect: the data file becomes smaller at the expense of signal quality. As you might expect, these simple methods do not work very well.