Rotating without changing Image Pixel Value

I am doing a project on Image Watermarking using Discrete Wavelet Transform. I have done with watermarked image,Now I am attacking image with attack like rotation. My question is that when I apply function imrotate to the watermarked image, all the pixels that are not included in the rotated image becomes zero as it is property of imrotate. Due to this I got very low PSNR between Original Image and rotated Watermarked image.

My question is-I want to rotate the image but also need to have high value of PSNR after rotation. Is there any method that after rotation all or most pixels of rotated image resembles with pixels of original image.

Shortcoming of imrotate ie zero value of pixels outside rotated area can be removed by which method???????????????

Answer 1

[Image Analyst]

Since psnr and mse operate on a pixel by pixel basis, they're terrible for comparing any rotation beyond the slightest angle. You cannot rotate your watermarked image by any noticeable angle, and have it have anywhere close to the same PSNR as with an unrotated original or watermarked image.

It doesn't even matter what they do. The thief does whatever they do - rotate, crop, add noise, change intensities or colors - you have to deal with whatever the thief did to it . I'm not an expert in watermarking but I've heard that Fibonacci methods are pretty discreet (unnoticeable) and robust to attack by a variety of methods such as rotation. See http://www.comlab.uniroma3.it/Marco/Articoli%20Battisti/Watermarking%20and%20encryption%20of%20color%20images%20in%20the%20Fibonacci%20domain.pdf

Answer 2

[Matt J]

You could use the 'crop' flag that imrotate offers. However, my impression is that you should not be computing PSNR based on all pixels anyway. You should be computing it based on an ROI that is present in both images.

[Manpreet]

I have used crop(bbox) but have not effect. Sir, by the way How I could use ROI of the both the images...........

[Manpreet]

I am attaching the preview of my work.IF you look at the Image, 4th subplot is my watermarked image and I rotated it at an angle 45degree. Now I am unable to extract the watermark and decrypt it.

Edit by Matt J -- moved Manpreet's "Answer" here:

Below is a version where I have done no rotation and watermark is easily extracted and decrypted. I think this occurs because in the 4th subplot the value of pixels are 0 outside the rotated area.

[Matt J]

I was talking about using imrotate with the syntax

     imrotate(...,'crop')

Answer 3

[Manpreet]

Thanks a lot Sir!!!!!!! Your Efforts are highly appreciable, now i will work with more spirit and passion. I will try to handle attacks in better way.

Thanks again!!!!!!!!!

[Matt J]

You're welcome.