The Discrete Cosine Transform expresses a sequence of finitely many data points in terms of a sum of cosine functions oscillating at different frequencies.
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Conversion between DCT to DFT frequency domains
It is well known that the DFT can be interpreted as a filter bank. The same can be done for the DCT, for instance Fig. 3.29, pag. 129 in [1] shows a plot of the frequency response of a DCT filter ...
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4answers
106 views
Why are there only a few high frequency components in the Discrete Cosine Transform?
I am learning about the Discrete Cosine Transform (DCT) and I read somewhere that, in general, images have very few high frequency components. Can someone give me an intuitive explanation for why this ...
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45 views
DCT of 4x4 checkerboard matrix - what's the correct result?
I'm trying to work out what the correct solution is for a DCT of a 4x4 checkerboard matrix (let's call it A) and for a matrix of ones (let's call it B). So A is:
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0answers
32 views
Why is Cepstral Coefficients decorrelated?
Why is the Mel Frequency Cepstral Coefficient (MFCC) decorrelated in each frame; as far as I understand, this is because of the step where we take the Discrete cosine transform (DCT) of the log ...
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1answer
130 views
Can the Walsh Hadamard transform be computed for non power of 2 sizes?
Can the walsh hadamard transform be calculated for odd image block sizes such as 5x5 or 7x7? Most of the examples I've seen are for 4x4 and 8x8?
I fear it probably can't from the description I read ...
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1answer
199 views
Relationship between DCT and PCA
I have a basic implementation knowledge of the 2D 8x8 DCT used in image & video compression. Whilst reading about Principle Component Analysis, I can see a lot of similarity, albeit PCA is clearly ...
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1answer
153 views
DCT and hard thresholding
If I have an Image and i find the DCT and then apply hard thresholding on the coefficients and then IDCT then I have attenuated the noise. Can someone please explain in detail or point me to the ...
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votes
1answer
558 views
Fast Cosine Transform via FFT
I want to implement the Fast Cosine Transform. I read on wikipedia, that there is a fast version of the DCT which is similarly computed to the FFT. I tried to read the cited Makhoul* paper, for the ...
3
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1answer
104 views
Why motion cannot be estimated in DCT domain using block match?
In all video coding standards, motion estimation is always done in pixel domain using block matching. I wonder why it cannot be estimated in DCT(Discrete cosine transform) domain using block matching ...
3
votes
1answer
165 views
DCT Steganograhy
I'm trying to implement a simple steganography algorithm (similar to JSteg algorithm) for hiding data in LSB of DCT coefficients in Matlab, and I ran into a problem.
a. I apply DCT.
b. modify LSB ...
3
votes
1answer
186 views
Determining the resulting pixel value before creating a compressed JPEG image
Is it possible to determine the resulting pixel values and modify them before the compressed jpeg image is actually created?
For example, I'm at the stage where I already have the quantized DCT ...
6
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1answer
218 views
Non-orthogonal basis which offers better energy compaction in image compression
I am aware of image-independent basis, i.e. DCT, and image-dependent basis, i.e. Karhunen–Loève, which are used in compacting energies for image compression. These bases are orthorgonal.
Are there ...
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2answers
195 views
JPEG steganography
Aside from Jsteg of Derek Upham, Outguess of Neils Provos, and F5 (improvement of F3 and F4) of Pfitzmann and Westfeld, What other methods can you use in information hiding in JPEG images?
The ...
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4answers
730 views
Do the DCT coefficients correspond to particular pixels?
Getting the DCT coefficient based on what I've read, is usually done through a matrix, usually 8x8 or 16x16 using these formulas:
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votes
1answer
250 views
1-D discrete cosine transform(DCT)
This was a past year paper question. Not sure how to answer it.
Question: The 1-D discrete cosine transform(DCT) of a sequence f(x), x =0,1,...,N-1 is
F(u) = c(u)* Summation of f(x) cos ( ...
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1answer
346 views
Could a DCT be used for an audio magnitude spectrum rather than DFT?
From what I understand, the DCT has half the bin size as a DFT of the same size N. The DFT also includes phase information, but often this is not needed when only the magnitude spectrum is desired. ...
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4answers
4k views
What is the difference between a Fourier transform and a cosine transform?
In speech recognition, the front end generally does signal processing to allow feature extraction from the audio stream. A discrete Fourier transform (DFT) is applied twice in this process. The first ...
