 Explain the theory of image, audio and video compression.
In This Chapter, you’ll learn on:
 Describe raw multimedia data representation
 Describe data compression for image, aud...
 Raw Multimedia Data Representation
 What exactly is Raw Multimedia Data
Representation? In simple terms with reference ...
 Compression for Image, Audio and Video
 Data compression is the removal of redundant data. This,
therefore, reduces the...
 Lossy and Lossless Compression

 The above techniques are either lossless or lossy
compression techniques.
 LOSSLESS
...
 LOSSLESS
 Run-Length Encoding
 This is a very simplistic approach that counts
sequences of repeating symbols — storing...
 LOSSLESS
 Image 1 – Run-Length Encoding - Illustrates run-length
encoding for a data sequence having frequent runs of
z...
 LOSSLESS
 LZW Compression
 LZW compression is named after its developers, A. Lempel and
J. Ziv, with later modificatio...
 LOSSLESS
 LZW Compression
 Image 2 – LZW Compression - Illustrates in the table the values
between 0-255, from 256 to ...
 LOSSY
 Lossy Compression reduces a file by permanently eliminating
certain information, especially redundant informatio...
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Chap54

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Chap54

  1. 1.  Explain the theory of image, audio and video compression.
  2. 2. In This Chapter, you’ll learn on:  Describe raw multimedia data representation  Describe data compression for image, audio and video  Describe lossy and lossless compression
  3. 3.  Raw Multimedia Data Representation  What exactly is Raw Multimedia Data Representation? In simple terms with reference to Digital Imaging it literally means "raw" as in "unprocessed". A RAW file contains the original image information as it comes off the sensor before in-camera processing so you can do that processing afterwards on your PC with special software. RAW files are huge in file size and contain redundant data
  4. 4.  Compression for Image, Audio and Video  Data compression is the removal of redundant data. This, therefore, reduces the number of binary ‘bits’ necessary to represent the information contained within that data. To achieve the best possible compression requires not only an understanding of the nature of data in its binary representation but also how we as humans interpret the information that the data represents.  Data compression is the general term for the various algorithms and programs developed to address this problem. A compression program is used to convert data from an easy-to-use format to one optimized for compactness.  There are a few different techniques involved in data compression such as Run-Length, LZW & JPEG.
  5. 5.  Lossy and Lossless Compression   The above techniques are either lossless or lossy compression techniques.  LOSSLESS  Lossless Compression is used when it is important that the original and the decompressed data are exactly identical, or when no assumption can be made on whether certain deviation is uncritical.
  6. 6.  LOSSLESS  Run-Length Encoding  This is a very simplistic approach that counts sequences of repeating symbols — storing the symbol’s value and the number of repeats.   Consider the following example: 
  7. 7.  LOSSLESS  Image 1 – Run-Length Encoding - Illustrates run-length encoding for a data sequence having frequent runs of zeros. Each time a zero is encountered in the input data, two values are written to the output file. The first of these values is a zero, a flag to indicate that run-length compression is beginning. The second value is the number of zeros in the run. If the average run-length is longer than two, compression will take place. On the other hand, many single zeros in the data can make the encoded file larger than the original.  Another example of Lossless compression is LZW Compression. 
  8. 8.  LOSSLESS  LZW Compression  LZW compression is named after its developers, A. Lempel and J. Ziv, with later modifications by Terry A. Welch. It is the foremost technique for general purpose data compression due to its simplicity and versatility. Typically, you can expect LZW to compress text, executable code, and similar data files to about one-half their original size.   LZW compression is always used in GIF image files, and offered as an option in TIFF and PostScript. 
  9. 9.  LOSSLESS  LZW Compression  Image 2 – LZW Compression - Illustrates in the table the values between 0-255, from 256 to 4095 any sequence of data is translated to that number in the table.   As the image above applies the compression method to a series of numbers, in image compression the LZW method works by finding patterns of data to which it assigns codes. It works best on highly patterned images.
  10. 10.  LOSSY  Lossy Compression reduces a file by permanently eliminating certain information, especially redundant information. When the file is uncompressed, only a part of the original information is still there (although the user may not notice it). Lossy compression is generally used for video and sound, where a certain amount of information loss will not be detected by most users. The JPEG image file, commonly used for photographs and other complex still images on the Web, is an image that has lossy compression. Using JPEG compression, the creator can decide how much loss to introduce and make a trade-off between file size and image quality.

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