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DCT watermark

DCT watermark. 作法. 將 watermark 的每一個 bit 藏在 lena 的中頻～高頻中 將頻域的 lsb 用 watermark 的資料取代 3bit Ex dct[102][54]=00001010 藏入 1  00001 111. 結果. 1bit 會爆炸 2bit 勉強有外型 3bit 正常解出有些許雜點. 加入雜訊. ＰＳ的 5% 解出來就不能看了. 遭遇的問題.

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DCT watermark

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  1. DCT watermark

  2. 作法 • 將watermark的每一個bit藏在lena的中頻～高頻中 • 將頻域的lsb用watermark的資料取代3bit Ex dct[102][54]=00001010 藏入1  00001111

  3. 結果 • 1bit會爆炸 • 2bit勉強有外型 • 3bit正常解出有些許雜點.

  4. 加入雜訊 • ＰＳ的5%解出來就不能看了

  5. 遭遇的問題 • 將原空間域數位影像經DCT轉換後，以IDCT還原的空間域數位影像內的所有像素值不應該有誤差的存在。但在做DCT及IDCT運算時，我們是使用浮點運算但卻將其尾數四捨五入取成interger，以便我們在dct的結果中藏水印這就造成了尾數的誤差。 　並且，我實際測試了啥都沒作只做dct idct使用助教的code發現，idct之後的圖與原圖作比較，一個pixel數值最多可以差到6左右，但是照著講義上的dct+idct公式去對照 Code又沒看出啥錯誤，所以就不知道發生啥事了～～

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