Video Compression and its Significance/3

Working with color Color images are typically represented using several ‘color planes.’ For example, an RGB color image contains a red color plane, a green color plane, and a blue color plane. When overlaid and mixed, the three planes make up the full color image. To compress a color image, the still image compression techniques described earlier can be applied to each color plane in turn. Imaging and video applications often use a color scheme in which the color planes do not correspond to specific colors; instead, one color plane…

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Video Compression and its Significance/2

Statistically speaking The number of bits used to represent the quantized DCT coefficients is reduced by ‘coding,’ which takes advantage of some of the statistical properties of the coefficients. After quantization, many of the DCT coefficients often – the vast majority of the high-frequency coefficients – are zero. A technique called ‘run-length coding’ takes advantage of this fact by grouping consecutive zero-valued coefficients (a ‘run’) and encoding the number of coefficients (the ‘length’) instead of encoding the individual zero-valued coefficients. Run-length coding is typically followed by variable-length coding (VLC). In…

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Video Compression and its Significance/4

Secret encoders In addition to the two approaches described above, many other methods for selecting appropriate candidate motion vectors exist, including a wide variety of proprietary solutions. Most video compression standards specify only the format of the compressed video bit stream and the decoding steps and leave the encoding process undefined so that encoders can employ a variety of approaches to motion estimation. The approach to motion estimation is the largest differentiator among video encoder implementations that comply with a common standard. The choice of motion estimation technique significantly affects…

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VIDEO COMPRESSION & ITS SIGNIFICANCE

Digital video compression and decompression algorithms (codecs) are at the heart of many modern video products, from DVD players to multimedia jukeboxes to video-capable cell phones. Understanding the operation of video compression algorithms is essential for the developers of systems, processors, and tools that target video applications. In this article, we explain the operation and characteristics of video codecs, and the demands that the codecs make on processors. We also explain how codecs differ from one another and the significance of these differences. Starting with stills As video clips are…

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