多媒體技術(shù)第二講ppt課件(已修改)
2025-05-10 23:21 本頁面
【正文】 第二講 多媒體處理理論及共性技術(shù)基礎(chǔ) ? 信號的數(shù)字化理論 ? 主要媒體形式介紹 ? 信號的線性變換技術(shù) ? 信號的統(tǒng)計編碼技術(shù) ? 多媒體系統(tǒng)特點(diǎn) Why Digital? ? Universal storage, transmission format ? CD, inter ? Precision (Range of values, number of bits, floating point) ? Lossless transmission/storage BUT: ? sampling rate distorts information ? size requirements may be ?large? pared to analog Digitization Process ? Sampling from an analog signal ? Sampling Errors relate to signal frequencies ? Quantization Errors Sampling: Nyquist sampling theorem ? 目的 — 用最少的時間離散信號樣本來精確表示原來的連續(xù)信號。 ? Nyquist采樣標(biāo)準(zhǔn) — 采樣頻率至少為連續(xù)信號帶寬的兩倍。 ? 如果采樣頻率小于這個標(biāo)準(zhǔn)，就會產(chǎn)生 “ 混疊 ” 現(xiàn)象，即采樣后離散信號不能重構(gòu)原連續(xù)信號。 2/o r 2 TTff ss ??Nyquist System: Quantization: Linear and Nonlinear Linear quantization: 均勻量化 Nonlinear quantization: 非均勻量化 (大信號采用大間隔 , 小信號用小間隔 ) 舉例：圖象非均勻量化 Types of multimedia data ? Text ? Graphics ? Picture/image ? Audio ? Speech ? Video ? Generated media Text ? ASCII, Unicode ? Formatted Text, Rich Text ? Document Formats: – Structured: Tex, HTML – Page Descriptions: Postscript, PDF Graphics ? Objects – circles, splines, rectangles, lines ? Editable – resize, reshape, move, colorize ? Synthetic Images (Pictures) ? Fixed digitized representation – bitmap, colors per pixel ? Editable in limited ways – retouch, cut and paste, remap colors, filter [Photoshop tools] – no ?model? of the thing ? Captured – not just from real life, clip art, screen
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