- 學位論文
一個快速與高畫質轉換JPEG影像格式成為雙模(JPEG與H.264)與雙解析視訊串流的方法
A Fast and High Quality Transcoding Method from Motion JPEG to Video Streaming with Dual Mode (JPEG and H.264) and Dual Resolution
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摘要
提供多模（multi-mode）與多解析（multi-resolution）的視訊输出是網路攝影機的發展趨勢。設計多模的目的是為讓使用者在內部網路儲存錄影資料時，可選擇影像品質較佳的格式，例如JPEG；而在外部網路傳輸時，可採用瀏覽較順暢的影像壓縮格式，例如H.264。而設計多解析的目的則是為克服網路頻寬不足的環境，藉由調降視訊解析度的方式，使影像內容依然可以順暢傳送。另一方面，由於JPEG影像品質極佳，對後續發展智慧視訊辨識系統較具優勢，且JPEG晶片製作成本低及體積相對較小，在某些產業上仍具有競爭優勢，例如PC Camera （or Web Camera）皆以包含JPEG格式之多模輸出為主。雖然JPEG也可以達到動態視訊的效果，此種格式稱為Motion JPEG（簡稱MJPEG），但由於並非通用的標準格式，因此在未來發展上受到很大的限制，並逐漸被新一代的視訊串流格式(H.264)所取代。綜合上述，在本論文中我們提出轉換單模（JPEG）與單解析影像格式，成為雙模（JPEG與H.264）與雙解析視訊串流的方法。 在過去的研究已提出將連續JPEG影像轉換成H.264串流格式的方法。其所提方法具有快速轉換與保留JPEG高影像品質的優點，但轉換後的壓縮影像大小（size）並沒有表現出H.264在壓縮上的優異性能。為此，在我們格式轉換的部分，我們提出保留JPEG高影像品質並有效降低轉換後的壓縮影像大小之方法。
並列摘要
The main objective of our research is proposing a method to convert IP cameras with single JEPG output into dual-mode (JPEG and H.264) and dual-resolution video streaming output devices. Because the DCT block of JPEG is not equal to the DCT block of H.264, the simplest solution is to decode JPEG images, obtain image pixels, and then re-encoded to H.264 format. However, repetitive decoding and encoding processes not only decrease the image quality but also increase processing time. Because all of the transform methods we proposed are processed in DCT domain, it both retains the characteristic of high image quality as JPEG, and further downsize of video streams after transcoding by building up the mechanism of frame prediction (including inter-frame prediction and intra-frame prediction) and proposing a method of downsizing resolution of video streams.
參考文獻
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