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I've been working with Discrete Wavelet Transform, I'm new to this theory. I want to access and modify the wavelet coefficients of the decomposed image, Are those wavelet coefficients simply the pixel values of the decomposed image in 2D DWT?

This is for example the result of DWT Decomposition: enter image description here

So, when I want to access and modify the Wavelet Coefficients, can I just iterate through the pixel values of above image? Thank you for your help.

mfathirirhas
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1 Answers1

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No. The image is merely illustrative.

The image you are looking on does not exactly correspond to original coefficients. The original wavelet coefficients are real numbers. Unlike them, you are looking on their absolute values quantized into a range from 0 to 255.

It is not true that the coefficients were calculated as pairwise sums and differences of the input samples. The coefficients were calculated using two complementary filters. See the description here. However, it is essential that these coefficients were adjusted and it is no longer possible to synthesize the original image. If you need to synthesize the image, you cannot access the pixels of the referenced image.

DaBler
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  • I know that the ways you search the coefficients was to sum up pair pixel of image and divide them by 2, that's what you get for your approximation coefficients, and for your detail coefficients was from different between original pixel and approximation values. So, if i want to access and modify the wavelet coefficients, how to access them? – mfathirirhas Apr 26 '16 at 03:47
  • @William: I have update the answer. If you ask about the particular implementation, please provide more details. – DaBler Apr 26 '16 at 11:42
  • I'm implementing watermarking using DWT. In order to embed watermark, it's been add to the wavelet coefficients value. So, I just want to add some values to each wavelet coefficients in the decomposed image. – mfathirirhas Apr 26 '16 at 11:57
  • @William: Which tools do you use? MATLAB, C++, ...? Can you provide a fragment of your code? – DaBler Apr 26 '16 at 21:05
  • I'm using C#, which Code?, decomposing code?, I learned from this source about decomposing the image into DWT domain, it looks similar to this source of decomposing image: http://www.codeproject.com/Articles/683663/Discrete-Haar-Wavelet-Transformation – mfathirirhas Apr 27 '16 at 14:13