中原大學電機工程學系
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107學年度 >訊號與系統組
DCT的壓縮應用
指導老師:吳燦明   組長:方峻梃   組員:劉晉廷
DCT是與傅立葉相關的一種變換,類似離散傅立葉變換,但是只使用實數。採用圖像邊界摺翻將圖像變換為偶函數形式,再對圖像進行二為傅立葉變換,變換後僅包含餘弦項,因此稱之為離散餘弦變換。
DCT的第二種類型,經常用於信號除理及圖像處理(包括靜止圖像和運動圖像)這是由於DCT具有很強的「能量集中」特性。
DCT編碼屬於正交變換編碼方式,用於去除圖像數據的空間冗餘。變換編碼是將圖像光強矩陣(時域訊號)變換到係數空間(頻域訊號)上進行處理的方法。
利用「能量集中」特性或係數矩陣的分布規律,我們可以藉由這些規律,再頻域上減少量化比數,以達到壓縮的目的。
現今網際網路和電信網路的迅速發展為數位影像的傳輸提供了必要條件,但是不同接取方式其傳輸頻寬有很大的差別,因此,具有可擴充性的影像編碼方法有重要的意義。可擴充性編碼是指同一編碼源可以隨著接取方式的不同,提供不同品質的數位影像。針對這種需求,我們依據不同的網路條件在壓縮效率與圖像質量間做取捨。
以下是壓縮效率和圖像質量之間的大致關係:
DCT is a transformation associated with Fourier, similar to the discrete Fourier transform,but using only real numbers. The image is transformed into an even function form by image boundary folding, and then the image is subjected to Fourier transform. After the transformation, only the cosine term is included, so it is called discrete cosine transform.
The second type of DCT is often used for signal conditioning and image processing (including still images and moving images). This is due to the strong "energy concentration" characteristics of DCT.
DCT coding belongs to the orthogonal transform coding mode and is used to remove spatial redundancy of image data. Transform coding is a method of transforming an image light intensity matrix (time domain signal) onto a coefficient space (frequency domain signal) for processing.
By using the "energy concentration" characteristic or the distribution law of the coefficient matrix, we can reduce the quantization ratio in the frequency domain by these laws to achieve the purpose of compression.
The rapid development of Internet and telecommunication networks today provides the necessary conditions for the transmission of digital images. However, the transmission bandwidth of different access methods varies greatly. Therefore, the scalable image coding method has important significance. . Scalability coding means that the same coding source can provide digital images of different qualities depending on the access method. In response to this demand, we make trade-offs between compression efficiency and image quality based on different network conditions.
The following is the approximate relationship between compression efficiency and image quality.
我們決定將壓電陶瓷晶片和鞋子做結合。
   
 
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