基于子帶離散余弦變換DCT應(yīng)用于圖像水印的技術(shù)已經(jīng)被提出并應(yīng)用。水印是波在所有選定的含有若干系數(shù)的四個(gè)頻帶段的1級(jí)分解。應(yīng)用大量的系數(shù)使每個(gè)波段給出了不同的檢測(cè)輸出結(jié)果。其結(jié)果是采取平均檢測(cè)結(jié)果的所有頻段的值。結(jié)果表明，最終的結(jié)果是優(yōu)于所檢測(cè)輸出的每個(gè)波段所得的結(jié)果的，從而實(shí)現(xiàn)了非常強(qiáng)大的水印方案。
1、導(dǎo)言
數(shù)字媒體技術(shù)在當(dāng)今社會(huì)已被大范圍的使用，從而促使其創(chuàng)立知識(shí)產(chǎn)權(quán)來(lái)保護(hù)。就其性質(zhì)而言，數(shù)字媒體是能夠100％被完整復(fù)制的，因此，必須采取有效的標(biāo)識(shí)系統(tǒng)（是顯而易見(jiàn)的）。這就是水印的由來(lái)。水印技術(shù)是指將無(wú)法被看見(jiàn)的數(shù)據(jù)埋入圖像中，從而確定合法的創(chuàng)建者/擁有者。水印應(yīng)當(dāng)具有健全的可以適用于（抵擋）各種各樣的圖像攻擊的技術(shù)。任何嘗試從原始圖像刪除所有權(quán)信息的方法（被稱為）攻擊。一些常見(jiàn)的攻擊包括過(guò)濾，壓縮，直方圖修改，剪裁，旋轉(zhuǎn)和縮小。（水印）主要有兩個(gè)嵌入方向，即空間域和變換域。變換域的技術(shù)對(duì)普通的圖像攻擊技術(shù)更敏感，如過(guò)濾或JPEG壓縮。
A subband-DCT approach for image watermarking is proposed in this communication. The watermark is casted in a selected number of coefficients of all four bands of a one-level decomposition. A great number of coefficients is being used. Each band gives a different detection output. The result is taken as the average detection result of all bands. It is shown that the final result is better than the detection output of each individual band, thus leading to a very robust watermarking scheme.
1. INTRODUCTION
The great spread of digital media in nowadays, has urged for the protection of the intellectual property rights of the creators. By their nature, digital media are 100% reliably copied, so the need for an effective marking system is obvious. This is where watermarking comes in. Watermarking