DSPP Lab Experiences

Patent Review: Wavelet Domain Watermarks Publication number: US6385329 B1 Date of Patent: May 7, 2002 Inventors: Sharma et al. Summary: The invention relates to encoding and decoding auxiliary signals in a media signal, such as an audio, video or image, using wavelet decomposition of the signal. This method performs the wavelet decomposition of the signal and embeds a watermark into the wavelet decomposition. Another aspect of the invention is a method of detecting an auxiliary signal embedded in a media signal, where the auxiliary information is substantially imperceptible in an output form of the media signal. Another aspect of the invention is the alternative method of encoding of the auxiliary signal in a media signal. This method performs a wavelet decomposition of the media into two or more levels of resolution. . Link:  http://www.freepatentsonline.com/6385329.pdf IEEE Paper Review: A robust wavelet-based digital watermarking using level-adaptive thresholding

This was a relatively easy assignment as the MATLAB function fir1() directly generates the required filter based on the given specifications. The only task was to decide the appropriate window function based on the given stop band attenuation, as taught in the lecture.

This experiment refreshed the concepts learnt during the Embedded systems course that I had attended during my first year. I had to demonstrate the practical to my batchmates and we executed assembly instructions on the DSP Processor kit available at the laboratory.

Lots of time was spent in designing a High Pass IIR Filter using IIM, but in the end we realized that it was not possible. This was because of the many-to-one mapping of frequencies when using IIM method of filter design.

Programming the codes of this experiment was confusing and time-consuming as it involved manipulations in the various signal lengths of inputs, decomposed inputs, decomposed outputs and the final result. This had me referring the class notes and online resources, again and again, to make changes in the code and finally, the result was satisfactory. Also, many of my concepts were strengthened and overall it was a great programming assignment!

Using structures for performing operations on complex numbers made programming this experiment relatively simpler. I have used recursion in the FFT function which makes it functional for any radix-2 value of N, unlike the example codes provided, which had separate functions for different values of N. Because of this, the input signal of any length has to be first converted into a radix-2 form by appending the necessary amount of 0's and then calculating FFT. IFFT simply uses FFT for its calculation.