238_1_lecture2 - 1 EE 238: Multimedia communications and...

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1 EE 238: Multimedia communications and Multimedia communications and networking networking Prof. Mihaela van der Schaar Prof. Mihaela van der Schaar email: mihaela@ee.ucla.edu email: mihaela@ee.ucla.edu www www - - page: page: medianetlab.ee.ucla.edu medianetlab.ee.ucla.edu
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2 Lecture 2: Lecture 2: Multimedia compression and Multimedia compression and streaming concepts streaming concepts
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3 Outline Source coding concepts Packetization principles Hinting concepts Traffic models Questions/comments/observations are always encouraged, at any point during the lecture!!
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4 Aim of this class Understand Basic multimedia source coding concepts Media stream layout – important for packetization Why not all bits are created equal -> priority assignment Rate-distortion performance – useful to decide how to match a specific multimedia source to a specific channel constraint, useful for joint source-channel coding How delay deadlines can be computed -> important for real- time media communication! Hinting of media bitstreams for transmission purposes (how to create packets) Traffic characteristics (often not following Poisson distributions)
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5 Source Coding Basic components and models in a multimedia signal compression scheme Signal- zerlegung, Dekorrelation Quantisierung Codierung Signal-, Inhalts- und Erzeugungs- modelle Perzeptions- Statistische Modelle Eingangs- signal Codierter Bitstrom Signal decompos., Decorrelation Quantization Entropy Coding Signal models, content models Perception models Statistical models Input Signal SOURCE CHARACTERISTICS Coded bit stream TRAFFIC
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6 Multimedia Signals (Input) – Digital Representation Resolution: -Spatial -Temporal -Pixel-depth -Color
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7 Digital Representation of Multimedia Signals f(x, y): (x, y) denote the spatial coordinates. In a “digital image”, (x,y) is a discrete picture element ( pixel, pel). For a gray-scale image, f() at any point (x,y) is the brightness (or gray-level) of the image. For color images, each pixel contains 3 numbers representing 3 color components. f(x,y)
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8 Digital Representation of Multimedia Signals Color image: 24 bits per pixel 512 x 512 198 , 202 , 195 75 , 82 , 60 80 , 65 , 63 25:1
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9 Digital Representation of Multimedia Signals Images and Videos are represented digitally by B-bit/component sample => 2 B different levels can be represented B=8 (256 levels) is generally regarded as sufficient for representation of images/videos acquired by video cameras, scanners, acquisition chips in digital cameras The 3 primary components of active light - R , G , B –aremost commonly used to capture color images/videos For the representation of color images/videos: 1 luminance component Y 2 chrominance (color difference) components Cr, Cb (or U, V) Y U V 0.299 0.587 0.114 -0.147 -0.289 0.436 0.615 -0.515 -0.100 R G B =
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10 Example of a 4:2:0 raw (uncompressed) file format Y U V Frame 1 Y U V Frame N Video sequence Luma (Y) sample Two Chroma (UV) samples Y UV 4:2:0
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11 Image format Resolution 720 x 480 720 x 576 352 x 240 352 x 288 352 x 288 176 x 144 CCIR-601 (NTSC) CCIR-601 (PAL) SIF (NTSC) SIF (PAL) CIF
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238_1_lecture2 - 1 EE 238: Multimedia communications and...

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