1

How can I determine that which level of DWT is suitable for embedding watermark?

Like somewhere I read that if you use less than level-4 DWT, then it will decrease the capacity and similarly, if use more than level-4 DWT, it would affect the quality?

If I have to embed collusion resistant fingerprint in an image, which level would be most suitable to get both robustness and good imperceptibility?

rypel
  • 4,686
  • 2
  • 25
  • 36
Alexandera
  • 11
  • 1

1 Answers1

1

Embedding collusion secure fingerprints as watermarks depends on several factors, not only the robustness and imperceptibility.

First of all, one of the main issues of collusion secure codes is the length, so you should think about the payload in the same scale as robustness and imperceptibility. Of course, the length the depends on several factors such as size of coalition, number of users, max error, and even the algorithm (if you're using Tardos codes, or the Boneh & Shaw approach, etc...).

The more levels you use, the more robust the watermark will be but at the same time, the less data available to embed you'll have. For example, if your image has a resolution of 1024x1024 pixels, then decomposing it to a DWT to embed the WM in the LL sub-band will give you only an image of 512x512 pixels to do so (and now the payload constraints make all the difference). From my own experience, while using DWT transform to embed fingerprinting codes as watermarks in images I used only a single level DWT transform and embedded the watermark in the L-L sub-band of the image.

If your images are somewhat small, I suggest you then to use 1 level decomposition, because DWT embedding provides great imperceptibility (even on the 1st level) but if you have large images and/or the fingerprinting code is not so long then you can go for 2 or more levels.

mustakarhu
  • 63
  • 1
  • 5
  • @Haru.. Thank you for your valuable comment. I am using Tardos codes (approximate length of code is 344 bits) and want to embed it in a video.Still do you recommend to go for 2 level decomposition? – Alexandera May 30 '13 at 10:31
  • Well, taking into account that your code length isn't too long I would say that it is a good commitment to use the 2nd level decomposition. But if your video frame is like 320x240 pixels, which means that it gives you a total of 80x60 pixels if using the 2nd level decomposition, you might have payload problems to embed these 344 bits (actually in each color channel you'd have 4800 pixels which gives you around 14 pixels per bit). Furthermore, you shouldn't forget that you might need to apply redundancy to your watermark as well.:) – mustakarhu May 30 '13 at 23:47