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Application of Delta
Encoding In Data
compression
Nisha Menon K
Mtech Communication Engg
Roll No: 16
12/6/2013

1
Contents
•
•
•
•
•
•
•
•

Delta encoding
Delta compression
Features of Delta coding
Tools for delta compression
Applicatio...
Delta Encoding
• The term delta encoding, (from the Greek letter Δ, which
in mathematics, denotes a difference) refers to ...
Example

12/6/2013

4
Delta compression
• Delta encoding used for data compression is known as
delta compression

• It is a lossless compression...
• Delta compression is the process of encoding a target
file with respect to one or several similar source files.
• If a del...
.

The key feature is that the delta encoded signal
has a lower amplitude than the original signal. In
other words, delta ...
Features of Delta coding
• Delta compression algorithms take advantage of the
statistical correlations between different f...
Tools for delta compression
• Unix diff
Classic tool for generating deltas.
Limited to text files

• Vcdiff
Delta encoding...
Applications
• Delta compression forms the core of fast and efficient content
download

• Software Revision Control System...
Improving HTTP performance:
To improve the latency for web accesses, by exploiting the
similarity between current and outd...
• Application in wireless sensor
In a wireless sensor network, sensor readings and other streamed
values can be expressed ...
• ECG compression
The successive samples of ecg have high correlation and
small difference between them so it can be effec...
Extension of Delta coding
• The idea used in delta encoding can be expanded into a
more complicated technique called Linea...
• Linear Predictive Coding (LPC) is one of the methods of
compression that models the process of speech production.
• Line...
Disadvantages
• To know the value of the signal at any point in time one
has the read (know) all the previous values.
• Da...
Conclusion
• Delta coding is beneficial only for values which are
changing smoothly
•

For higher compression efficiency d...
THANKYOU
12/6/2013

18
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Delta encoding in data compression by Nisha Menon K studying mtech at fisat

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Delta encoding in data compression by Nisha Menon K studying mtech at fisat

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Delta encoding in data compression by Nisha Menon K studying mtech at fisat

  1. 1. Application of Delta Encoding In Data compression Nisha Menon K Mtech Communication Engg Roll No: 16 12/6/2013 1
  2. 2. Contents • • • • • • • • Delta encoding Delta compression Features of Delta coding Tools for delta compression Applications Extension of delta coding Disadvantages Conclusion 12/6/2013 2
  3. 3. Delta Encoding • The term delta encoding, (from the Greek letter Δ, which in mathematics, denotes a difference) refers to several techniques that store data as the difference between successive samples (or characters), rather than directly storing the samples themselves. • The first value in the delta encoded file is the same as the first value in the original data. • All the following values in the encoded file are equal to the difference (delta) between the corresponding value in the input file, and the previous value in the input file. 12/6/2013 3
  4. 4. Example 12/6/2013 4
  5. 5. Delta compression • Delta encoding used for data compression is known as delta compression • It is a lossless compression technique – restored data is identical to original • Delta encoding can be used for data compression when the values in the original data are smooth, that is, there is typically only a small change between adjacent values. 12/6/2013 5
  6. 6. • Delta compression is the process of encoding a target file with respect to one or several similar source files. • If a delta’s target version is newer than its reference version in the history, then it is referred to as a forward delta. A reverse delta has the opposite orientation: an older target version and a newer reference version. • Reverse delta Forward delta 12/6/2013 6
  7. 7. . The key feature is that the delta encoded signal has a lower amplitude than the original signal. In other words, delta encoding has increased the probability that each sample's value will be near zero, and decreased the probability that it will be far from zero. 12/6/2013 7
  8. 8. Features of Delta coding • Delta compression algorithms take advantage of the statistical correlations between different files or packets so that common sequences between two files can be encoded using a copy reference. • From a logical point of view the difference between two data values is the information required to obtain one value from the other i.e. relative entropy. • Delta encoding followed by Huffman and/or run-length encoding is a common strategy for compressing signals. 12/6/2013 8
  9. 9. Tools for delta compression • Unix diff Classic tool for generating deltas. Limited to text files • Vcdiff Delta encoding in HTTP and is employed in Google's Shared Dictionary Compression over HTTP technology used in Chrome browser. • Xdelta This is similar to diff, but it is targeted for binary files and does not generate human readable output. • Zdelta modification of the vcdiff 12/6/2013 9
  10. 10. Applications • Delta compression forms the core of fast and efficient content download • Software Revision Control Systems: For maintaining the revision history of software projects and other documents . In these systems, multiple, often almost identical, versions of each object have to be stored in order to allow the users to retrieve past versions. • Delta Compression at the File System Level: The Xdelta File System (XDFS) aims to provide efficient support for delta compression at the file system level using a delta compressor called xdelta. This allows the efficient implementation of revision control systems of files. • Software Distribution: To generate software patches that can be efficiently transmitted over a network in order to update installed software packages. 12/6/2013 10
  11. 11. Improving HTTP performance: To improve the latency for web accesses, by exploiting the similarity between current and outdated versions of a web page. This can significantly decrease the amount of data sent to the client, and is thus more appropriate for clients connected via low-bandwidth links such as cellular modems. It has also been observed that web pages on the same server often have a high degree of similarity (due to common layout and menu structure) that could be exploited with delta compression techniques. Client already has an old version of a page in his cache He send a tag identifying this version to server The server then sends the delta between old and current version 12/6/2013 11
  12. 12. • Application in wireless sensor In a wireless sensor network, sensor readings and other streamed values can be expressed as the change in the value from some expected value. In many data sets, with well chosen expected values, these changes tend to be small relative to the range of possible values and lead to a high frequency of values within a small range. • Efficient Web Page Storage: The similarities between different versions of the same page or different pages on the same web site could also be used for increased storage. 12/6/2013 12
  13. 13. • ECG compression The successive samples of ecg have high correlation and small difference between them so it can be effectively quantised by Delta compression • IFF 8SVX sound format applies delta compression to raw sound data before transmission. 12/6/2013 13
  14. 14. Extension of Delta coding • The idea used in delta encoding can be expanded into a more complicated technique called Linear Predictive Coding, or LPC. • The algorithms used by LPC are similar to recursive filters, making use of the z-transform and other intensively mathematical techniques. 99 samples are encoded Work on sample number 100 Most likely value for sample 100?? Predict the most probable value by looking last several samples 12/6/2013 14
  15. 15. • Linear Predictive Coding (LPC) is one of the methods of compression that models the process of speech production. • Linear prediction filters attempt to predict future values of the input signal based on past signals. • LPC models speech as an autoregressive process, and sends the parameters of the process as opposed to sending the speech itself. • A variation of delta encoding which encodes differences between the prefixes or suffixes of strings is called incremental encoding. It is particularly effective for sorted lists with small differences between strings, such as a list of words from a dictionary. 12/6/2013 15
  16. 16. Disadvantages • To know the value of the signal at any point in time one has the read (know) all the previous values. • Data appearing in the target that has no similar data in the source is still compressed. In some cases, where the source and target have nothing in common, the delta is equivalent to a compressed form of the target • If the original signal is not changing, or is changing in a straight line, delta encoding will result in runs of samples having the same value. 12/6/2013 16
  17. 17. Conclusion • Delta coding is beneficial only for values which are changing smoothly • For higher compression efficiency delta coding can be used along with other compression techniques 12/6/2013 17
  18. 18. THANKYOU 12/6/2013 18

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