REVERSIBLE AND HIGH- CAPACITY DATA HIDING IN MEDICAL IMAGES 報告學生：翁偉傑 1 Published in IET Image Processing Received on 25th June 2008 Revised on 15th June 2010 doi: /iet-ipr
OUTLINE Abstract Introduction Proposed method Experimental results and evaluations Conclusion 2
ABSTRACT 3 introduce a highly efficient reversible data hiding system. It is based on dividing the image into tiles and shifting the histograms of each image tile between its minimum and maximum frequency. The authors show how histograms of image tiles of medical images can be exploited to achieve these requirements. Additional advantages of the proposed method include hiding data in the regions of non-interest and better exploitation of spatial masking.
INTRODUCTION (1/2) Data hiding is the insertion of a message, watermark or embedded message, into a host document or cover media. In applications where additional information is required to describe another information media, such a process can be very useful. ex: in medical images, patients’ details and the doctors’ views can be inserted into the medical images to form a comprehensive data bank. 4
INTRODUCTION (2/2) 各種醫療影像資料隱藏可能遇到一些問題： one may embed information in the region of non-interest (RONI) ， The main drawback of this method is the ease of introducing copy attack on the non-watermarked regions. the embedded data may replace some image details such as the least significant bit of the image or details are lost after lossy image compression. * Peak Signalto Noise Ratio (PSNR) ： 通常在經過影像壓縮之後，輸出的影像通常都會有某種程度與原始影像不一樣。 為了衡量經過處理後的影像品質，我們通常會參考的 PSNR 值來認定某個處理程 序夠不夠令人滿意。 5
PROPOSED METHOD (1/3) 6 the shifted-histogram data hiding method is to find a pair of maxima and minima in the image pixel intensity histogram and then shift the intensity of those pixels within the maximum and minimum frequency range by one level. medical images it has two drawbacks: 1. then their values are also modified. 2.This restricts the data hiding capacity of the system.
PROPOSED METHOD (2/3) 7 the image is partitioned into sub-images ： 1.RONI:the histograms of image tiles that contain region of interest are not modified. 2. High payload:shifted-histograms of the image tiles can hide more watermark data. 3. Higher objective/subjective quality:hence image quality will be at its best;the subjective quality of the watermarked image will be at its best.
PROPOSED METHOD (3/3) Embedding 8 因此可以看出，每幅圖像中嵌入瓷磚分別提高了數據隱藏的能力。
E XPERIMENTAL RESULTS AND EVALUATIONS (1/5) 9 We have implemented and compared the performance of algorithms in [11–13] with our proposed method (for 4 and 16 image tiles) on a variety of medical images. The original image sizes were 512 × 512 pixels with 8 bit resolution. In the following, results of the experiments to verify the advantages and properties of image tiles against the whole image are presented.
EXPERIMENTAL RESULTS AND EVALUATIONS (2/5) 10 以十張圖進行實驗： 在這以四張圖進行說明。 Shifted histograms of whole, 4- and 16-tile versions. WSH, TSH-4 and TSH-16.
EXPERIMENTAL RESULTS AND EVALUATIONS (3/5) 11
EXPERIMENTAL RESULTS AND EVALUATIONS (4/5) 12
EXPERIMENTAL RESULTS AND EVALUATIONS (5/5) 13
CONCLUSIONS 14 We have shown that data hiding based on the shifted histogram is better to be applied to image tiles rather than the whole image itself. This not only improves the data hiding capacity, but also improves the marked image quality. Sum of the peaks of the individual pixel intensity histograms is greater than the single peak of the image histogram itself. The individual histograms are much narrower and sharper than the histogram of the image itself.