Mpeg family
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VIDEO COMPRESSION & VIDEO COMPRESSION & MPEGMPEG
0992970-0992970- 楊凱翔楊凱翔0992969-0992969- 林江瑜林江瑜0992965-0992965- 連重凱連重凱
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OutlineOutline
• VIDEO COMPRESSIONVIDEO COMPRESSION– VIDEO CODING BASICSVIDEO CODING BASICS– MOTION COMPENSATIONMOTION COMPENSATION
• MPEG FAMILYMPEG FAMILY– MPEG-1 VIDEO standardMPEG-1 VIDEO standard– MPEG-2 VIDEO standardMPEG-2 VIDEO standard– MPEG-4MPEG-4– H.264H.264– MPEG-7MPEG-7
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VIDEO COMPRESSIONVIDEO COMPRESSION
• Why do we use compression?Why do we use compression?– Temporal RedundancyTemporal Redundancy– Spatial RedundancySpatial Redundancy
time
x
y
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Two Stage Coding Two Stage Coding ProcessProcess
FRAME ( t - 1 ) FRAME ( t )
Processing for reducing temporal reduncy
Framedifference
Processing for reducing spatial reduncy
Stage 1
Stage 2
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Reducing Temporal Reducing Temporal RedundancyRedundancy
• Segment a frame into macroblocks, not Segment a frame into macroblocks, not search by pixelssearch by pixels
• Output energy( bit rate) is increased witOutput energy( bit rate) is increased with the degree of temporal redundancyh the degree of temporal redundancy
• Interframe coderInterframe coder ( only use temporal red ( only use temporal redundancy reduction)undancy reduction)
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Reducing Spatial RedundancyReducing Spatial Redundancy
• Using DCT codingUsing DCT coding• Intraframe coderIntraframe coder (use only spatial redun (use only spatial redun
dancy reduction, only for current frame)dancy reduction, only for current frame)• Hybrid( intra-/ inter - frame) coding metHybrid( intra-/ inter - frame) coding met
hodhod
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Motion CompensationMotion Compensation• Often used and dOften used and d
eveloped by MPEeveloped by MPEG familyG family
• 將相鄰的將相鄰的 frameframe 中中出現的移動物件進出現的移動物件進行互相補償的過程,行互相補償的過程,因為該物件移動範因為該物件移動範圍不大且形狀在短圍不大且形狀在短時間內不易變動時間內不易變動
• It is preceded by It is preceded by motion estimatiomotion estimationn
Motion Vector
Search Range
Current Frame
Reference Frame
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MPEG-1 IntroductionMPEG-1 Introduction• DCT for intra- and inter- framesDCT for intra- and inter- frames• Block-based motion compensationBlock-based motion compensation• Huffman CodingHuffman Coding• Source input format : YUV, why not RGBSource input format : YUV, why not RGB• Y : luminance component(Y : luminance component( 亮度亮度 ))• U(Cb), V(Cr) : color difference or chrominaU(Cb), V(Cr) : color difference or chromina
nce componentnce component (色差)(色差)
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MPEG-1 Picture TypeMPEG-1 Picture Type
• Intra-Picture( I )Intra-Picture( I )
• Predicted- Pictures( P )Predicted- Pictures( P )
• Bidirectional-Predicted-Picture( B )Bidirectional-Predicted-Picture( B )
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MPEG-2MPEG-2
• 與 與 MPEG-1 MPEG-1 通用通用• Difference from MPEG-1Difference from MPEG-1
– 好很多的畫質好很多的畫質– 更多的輸入格式更多的輸入格式 ( ex: RGB, more YUV form)( ex: RGB, more YUV form)– 在雙向傳輸時有較短的在雙向傳輸時有較短的 delay timedelay time– Higher bit rateHigher bit rate– We can adjust our pictures qualityWe can adjust our pictures quality
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MPEG-4MPEG-4
•針對整合多媒體、通訊、電腦之應用上,具體內針對整合多媒體、通訊、電腦之應用上,具體內容則是以內容為基礎容則是以內容為基礎 (Content-based)(Content-based) 的應用上。的應用上。
•將影片區分為前景及背景將影片區分為前景及背景(( Object-BasedObject-Based )),,只要記錄動態圖像的軌跡即可,因此在壓縮量及只要記錄動態圖像的軌跡即可,因此在壓縮量及品質上,能較品質上,能較 MPEG-1MPEG-1 及及 MPEG-2MPEG-2 來得更好,每來得更好,每秒動態資料處理速率彈性更大。 秒動態資料處理速率彈性更大。
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Some MPEG-4 Video FeatureSome MPEG-4 Video Feature
• SegmentationSegmentation
• SpriteSprite
• TrackingTracking
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MPEG-1 vs. MPEG-2 vs. MPEG-4MPEG-1 vs. MPEG-2 vs. MPEG-4
一般解析度
最大解析度
一般資料量
最大資料量
Mpeg-1
Mpeg-2
Mpeg-4
3Mbps80Mbps
5~10Mbps
0.88Mbps6.5Mbps
1.38Mbps
720X5761920X1152
352X288
720X576720X576
352X288
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MPEG-1 vs. MPEG-2 vs. MPEG-4MPEG-1 vs. MPEG-2 vs. MPEG-4
影像規格影像規格 Mpeg-1Mpeg-1 Mpeg-2Mpeg-2 Mpeg-4Mpeg-4
壓縮能力壓縮能力 中中 中中 強強
檔案大小檔案大小 中中 大大 小小
影像品質影像品質 可可 很好很好 可至很好可至很好
網路傳輸網路傳輸 勉強勉強 不可能不可能 最佳化 最佳化