Data Compression In The Technology

Data Compression In The Technology
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Compression : Data Compression In The Technology

 Data Compression In The Technology : File compression is the practice of packaging a file. Files to use less disk space.

 The File Compression category includes software programs that will archive your files. Extract archived files such as ZIP and RAR files.

 Many products in this category let you manage files and protect them with encryption.

Data Compression : Data Compression In The Technology

 In signal processing, data compression, source coding, or bit-rate reduction involves encoding. Information using fewer bits than the original representation.

 Compression can be either lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy.

Lossy DCT-Based Compression : Data Compression In The Technology

 A discrete cosine transform (DCT) expresses a finite sequence of data points. In terms of a sum of cosine functions oscillating at different frequencies.

 DCTs are important to numerous applications in science and engineering, from lossy compression of audio (e.g. MP3) and images (e.g. JPEG) (where small high-frequency components can discarded), to spectral methods for the numerical solution of partial differential equations.

 The use of cosine rather than sine functions critical for compression, since it turns out (as described below) that fewer cosine functions needed to approximate a typical signal, whereas for differential equations the cosines express a particular choice of boundary conditions.

Compression Efficiency : Data Compression In The Technology

 Compression ratio – (size of the original data) / (size of compressed data)

a.Positive compression if radio > 1; negative compression otherwise

 Figure of Merit = (size of compression data) / (size of original data)

a.Reciprocal of compression ratio


 “Joint Photographic Expert Group”. An international standard in 1992.

 JPEG is a lossy compression. Technique for color images.

 Although it can reduce files sizes to about 5% of their normal size. Some detail lost in the compression.


 The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU); it coordinates standards for telecommunications.

 The Video Coding Experts Group or Visual Coding Experts Group (VCEG) is the informal name of Question 6 (Visual coding) of Working Party 3 (Media coding) of Study Group 16 (Multimedia coding, systems and applications) of the ITU-T. Its abbreviated title is ITU-T Q.6/SG 16. It is responsible for standardization of the “H.26x” line of video coding standards, the “T.8xx” line of image coding standards, and related technologies.

H.261 (px64)

 The basic approach to H.261 Compression summarized as follows:

 H.261 Compression has specifically designed for video telecommunication applications:
a. Developed by CCITT in 1988-1990
b. Meant for videoconferencing, videotelephone applications over ISDN telephone lines.
c. Baseline ISDN is 64 kbits/sec, and integral multiples (px64)

 We typically have a group of pictures – one I-frame followed by several P-frames – a group of pictures

 Number of P-frames followed by each I-frame determines the size of GOP – can fixed or dynamic.


 H.264 or MPEG-4 Part 10, Advanced Video Coding (MPEG-4 AVC) a video coding format that currently one of the most commonly used formats for the recording, compression, and distribution of video content.


 The Moving Picture Experts Group (MPEG) a working group of authorities that formed by ISO and IEC to set standards for audio and video compression and transmission.

 MPEG compression is essentially an attempt to overcome some shortcomings of H.261 and JPEG: H.261 dependencies

Motion Compensation : Data Compression In The Technology

 Uses the motion vectors. To compensate the picture.

 Parts of a previous (or future) picture. Can reused in a subsequent picture.

 Individual parts spatially compressed. JPEG type compression

Huffman Code : Data Compression In The Technology

In computer science and information theory, a Huffman code a particular type of optimal prefix code that commonly used for lossless data compression.

Hybrid Encoding : Data Compression In The Technology

 A hybrid encoding method used to assemble the double-random phase-encoding. Technique and the binary encoding method.

 Because the double-random phase-encoding technique is robust for noises. The binary encoding method is free of using external keys, the proposed hybrid encoding method has their advantages.

 The hybrid encoding method first encodes a covert image to form a complex-number matrix by using the double-random phase-encoding technique. Where two random real-number matrices used to increase the security of the encoding work.

 Then the elements of the two random real-number matrices and the elements of the complex-number. Matrix encoded to form a binary-bit string by using the binary encoding method.

 Finally, the binary data in the binary-bit string encoded into a host image to form an overt image. With hidden information by using a gray-value modulation method. The decoding work is easy for authorized people, but it is very difficult for unauthorized people. Therefore, the proposed hybrid encoding method is a very useful encoding method.

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