1 Part A Multimedia Production Chapter 2 Multimedia Basics Digitization, Coding-decoding and Compression Information and Communication Technology “Multimedia Production and Web Site Development”

Ch 2.4 Digitization, Coding-decoding and Compression 2 Digitization, coding-decoding and compression

Ch 2.4 Digitization, Coding-decoding and Compression 3 Understand the meaning of digitization, coding-decoding and compression

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5 Table of Contents 1.Overview of Digitization 2.Coding-decoding 3.Types of Compression 4.Current Standards of Multimedia Compression

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7 1. Overview of digitization What is digitization? A process of converting analog information into a digital format Information is organized into discrete binary units of data (0 or 1) Information is stored into computer Text and Graphic digitization Use scanner, digital camera or other capturing device to capture an image into computer Graphic becomes bitmap image file An optical character recognition (OCR) program can analyze text image and identify each alphabetic letter and numeric digit. Lastly, it converts each character into an ASCII code

Ch 2.4 Digitization, Coding-decoding and Compression 8 1. Overview of digitization Sound and video digitization Use some analog-to-digital conversion processes that change the continuously variable (analog) signal into multi-level (digital) signal For example: sound digitization Sampling the amplitude (signal strength) of an analog waveform at evenly spaced time markers and representing the samples as numerical values for input as digital data

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10 2. Coding and decoding Human can only sense analog signals rather than digital signals Computer stores digital data Coding is one of digitization process to convert analog signals to digital signals. (A->D) Decoding is a process to convert digital signals to analog signals. (D->A)

Ch 2.4 Digitization, Coding-decoding and Compression Coding and decoding process Coding Convert analog audio signal to digital signal. Decoding Convert digital audio signal to analog signal Computer Guitar Sound Music

Ch 2.4 Digitization, Coding-decoding and Compression Transform Coding What is transform coding? A type of data compression for “natural” data Lossy compression A lower quality copy of the original input Introduction of transform coding Transforms coordinate axes rotations Transforms basis functions decomposition Image Transform KLT DFT DCT

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Ch 2.4 Digitization, Coding-decoding and Compression Types of compression Lossy compression For diffused data This compression throws away bits which are not needed for reproducing sound, audio, image and video Fast transmission and good for streaming media and internet telephonystreaming media internet telephony Lossless compression For symbolic data An exact, bit-identical reproduction of the original data

Ch 2.4 Digitization, Coding-decoding and Compression Types of compression Lossless Vs. Lossy Compression Original data Compressed Restored data Lossless Compression Lossy Compression

Ch 2.4 Digitization, Coding-decoding and Compression Example of Lossy Compression Original Image (lossless PNG, 101 KB size) Low Compression (10% less information, 84 KB) Medium Compression (20% less information, 71 KB) High Compression (80% less information, 6.5KB) The above images show the use of lossy compression to reduce the file size of the image.file size

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Ch 2.4 Digitization, Coding-decoding and Compression Categories of Compression Techniques Lossless CompressionLossy CompressionMixed Compression Run-length Coding Huffman Coding Arithmetic Coding DPCM (Differential Pulse Code Modulation) FFT (Fast Fourier Transform) DCT (Discrete Cosine Transform) JPEG MPEG H.261

Ch 2.4 Digitization, Coding-decoding and Compression Current standards of multimedia compression Image JPEG Using four coding modes  Lossless Mode (mode 1)  Lossy sequential DCT-based mode (baseline mode)  Lossy progressive DCT-based mode (mode 3)  Hierarchical Mode

Ch 2.4 Digitization, Coding-decoding and Compression 20 Video MPEG-1 Video Used by Video CD Quality and performance similar VHS tape MPEG-2 Video The core of most digital television and DVD format Compression rate is higher than MPEG-1 MPEG-4 Video Develop for the following fields:  Digital television  Interactive graphics applications (synthetic content)  Interactive multimedia (World Wide Web, distribution of and access to content) Compression rate is higher than MPEG-1 and MPEG-2 4. Current standards of multimedia compression

Ch 2.4 Digitization, Coding-decoding and Compression Compression of video Two reasons: Reduce file size Enable live broadcast on the web Standard Compression technique is called MPEG MPEG stands for Moving Picture Expert Groups A compressed video must be decompressed before playing Compression and decompression are called CODEC

Ch 2.4 Digitization, Coding-decoding and Compression Different formats of MPEG FormatYearVideo Characteristics PurposeApplication Examples MPEG x 240 pixels 24-bit color depth CD-quality High compression ratio but in sacrifice of quality VCD (Video CD) 40 minutes of video MPEG x 480 pixels 24-bit color depth Multi-audio channels Improvement in image quality DVD 90 minutes of video MPEG x 480 pixels 24-bit color depth MP3 audio Designed for viewing online video through the Internet with broadband access Used in Internet video broadcasting. Video file with extension ASF, WMV, RM

Ch 2.4 Digitization, Coding-decoding and Compression Current standards of multimedia compression Audio MP3 Stands for MPEG-1 Audio Layer 3 Popular digital audio coding Lossy compression

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Ch 2.4 Digitization, Coding-decoding and Compression 25 References Digitization What is digitization? ci896692,00.html ci896692,00.html Transform coding What is transform coding? Introduction it09-Transform%20Coding.PPT it09-Transform%20Coding.PPT

Ch 2.4 Digitization, Coding-decoding and Compression 26 References Types of compression Lossy Compression ess_Compression ess_Compression Loseless Compression Categories of Compression Techniques Lossless Compression Run-length Coding  Huffman Coding  Arithmetic Coding 

Ch 2.4 Digitization, Coding-decoding and Compression 27 References Categories of Compression Techniques Lossy Compression DPCM  FFT  DCT   Mixed Compression H.261 

Ch 2.4 Digitization, Coding-decoding and Compression 28 References JPEG Compression MPEG-1 Compression MPEG-2 Compression MPEG-4 Compression MP3 Compression