تقنيات ضغط البيانات - محاضرة (10)

Multimedia Technologies - Lecture (10)

• Data Compression is a process of modifying, encoding or converting data bits to use less space on a disk. The resulting data is compressed data.
• The inverse operation of producing the original data from the compressed data is called decompression.
• Compression Ratio: The ratio of the uncompressed data size to the compressed size.
• Higher compression ratio indicates greater space saving.
• Data compression is used to improve storage usage by reducing file size, speed up file transfer and save time.

Data Compression Techniques - Classifications

• Lossless Compression: Decompressed data is identical to the original. Used for text and programs.
• Lossy Compression: Some data is lost during decompression. Used for images, audio, and video.
• Symmetrical Compression: Encoding and decoding take equal time.
• Asymmetrical Compression: Encoding time is longer than decoding time.

Data Compression Techniques - Methods

• Run-length encoding (RLE): Replaces repeating symbols with the symbol and its repetition count (e.g., "aaabbcccccaaaaaabaaaa" becomes "a4b2c5a6ba4").
• Huffman Coding: Variable-length codes are assigned to symbols based on their frequency (e.g., the most frequent symbol gets the shortest code).
• Lempel-Ziv: Compresses data by finding and replacing repeated sequences with pointers.

Binary Code

• Binary code represents each character as a binary sequence (codeword).
• Fixed-Length Encoding: Each character has a codeword of a set length.
• Variable-Length Encoding: Codewords have variable lengths based on frequency.

تتناول هذه المحاضرة عملية ضغط البيانات وأساليبها المختلفة. سنتعرف على الفرق بين ضغط البيانات بدون فقدان وبتقنية فقدان البيانات، بالإضافة إلى التعرف على نسب الضغط وتطبيقات الضغط في تحسين استخدام التخزين ونقل الملفات. هذه المعلومات ضرورية لفهم كيفية تحسين الأداء في أنظمة المعلومات.