## Forums Search for: DCT

## DCT

inHi, I am looking for some technical information rgarding DCT. Why DCT is used in image/video/audio instead of transform like FFT?...

Hi, I am looking for some technical information rgarding DCT. Why DCT is used in image/video/audio instead of transform like FFT? What information we get after taking a DCT? Is DCT just the real part of FFT? Please send me some info regarding this. Thanking you

## Simple DCT problem

inHi all, I am new to DCT and now testing my FDCT and IDCT program. I found some of my high frequency DCT part is higher than low frequency DCT...

Hi all, I am new to DCT and now testing my FDCT and IDCT program. I found some of my high frequency DCT part is higher than low frequency DCT part. And I don't know whether it is correct. Where can I find example of 8*8 DCT input and output to test my code,thanks! BTW, my code's DCT input: 55 60 58 55 60 58 55 60 58 55 60 58 55 60 58 55 60 58 55 60 58 55 60 58...

## how to relate 8x8 DCT to 4x4 DCT?

inDear all, Can anybody tell me how to express 8x8 DCT in the form of 4x4 DCT? 8x8 DCT = function( 4x4 DCT) ??? Is there any simple...

Dear all, Can anybody tell me how to express 8x8 DCT in the form of 4x4 DCT? 8x8 DCT = function( 4x4 DCT) ??? Is there any simple relationship? Thanks a lot, -Walala

## DCT Scalings

Hello All, I am trying to implement forward and inverse DCT based on Y. Arai, T. Agui, and M. Nakajima, "A Fast DCT-SQ Scheme for Images,"...

Hello All, I am trying to implement forward and inverse DCT based on Y. Arai, T. Agui, and M. Nakajima, "A Fast DCT-SQ Scheme for Images," Trans. of the IEICE, vol. E-71, no. 11, pp. 1095-1097, Nov. 1988 paper. Both flow graphs for the forward and inverse DCT are given in the paper. When I tried to implement the forward DCT I got a different result from the DCT given in MATLAB. I know th...

## how is the discrete cosine transform matrix transform equivalent to the standard dct definition (DCT-II)

inCan some one explain or point me to a paper with the proof of how the DCT matrix transformation Y=DCT(X) = AXA' (where A is the DCT transform...

Can some one explain or point me to a paper with the proof of how the DCT matrix transformation Y=DCT(X) = AXA' (where A is the DCT transform matrix, X is the input data matrix, Y is the transformed data coeff's) A(u,v) = (1/N)^(1/2) for u =0 A(u,v) = (2/N)^(1/2) * cos(PI*(2v+1)*u/(2*N)) for u > 0 is equivalent to the DCT def: N-1 N-1 Y(

## DCT & IDCT algorithm problems

inHowdy, I'm trying to get the DCT and IDCT algorithm correct for MPEG-4 encoding/decoding. Following the DCT equation that I've put...

Howdy, I'm trying to get the DCT and IDCT algorithm correct for MPEG-4 encoding/decoding. Following the DCT equation that I've put here: http://www.teamearth.com/wiki/Main/MPEG4 , I generated the following DCT and IDCT algorithms: void dct(int data[8][8]) { int u,v,x,y; double temp[8][8] = {{0}}; for (u=0; u

## A question on DCT

inHI all, I have a query on DCT. How does DCT gives energy compaction compared to DFT when it is applied to say an image? ~R

HI all, I have a query on DCT. How does DCT gives energy compaction compared to DFT when it is applied to say an image? ~R

## DCT in audio compression

inAfter reading, what seems like a lot of material, I'm still in doubt why DCT isnt used in audio-compression. Seeing as DCT assumes mirror...

After reading, what seems like a lot of material, I'm still in doubt why DCT isnt used in audio-compression. Seeing as DCT assumes mirror symmetry, my only idea for not validating DCT over MDCT is that with real-life signals you can rarely (if ever) expect a signal to have that property? Is that correct or is there a better explanation.

## help with 10-point DCT

inhello, i know that it is possible but i don't know how. radix-2 DCT are well covered but i can't find radix-5 references for DCT or...

hello, i know that it is possible but i don't know how. radix-2 DCT are well covered but i can't find radix-5 references for DCT or FFT.... can anybody drop me the algorithm ? thanks in advance, YG

## DCT vs. DFT

inHi! Can anyone explain me, why you use DCT instead of DFT for transformation of image-data (like it is done for JPEG). I know that the DCT...

Hi! Can anyone explain me, why you use DCT instead of DFT for transformation of image-data (like it is done for JPEG). I know that the DCT can be performed by a DFT with a post-rotation. But what are the advantages of the DCT compared to the DFT? Are there any benefits from the post-rotation? Regards, Matthias

## Regarding DCT

inHi All, I am performing Integer DCT on Lena image. I am using " C "& i am not able to reconstruct the image correctly. Before applying DCT I...

Hi All, I am performing Integer DCT on Lena image. I am using " C "& i am not able to reconstruct the image correctly. Before applying DCT I am subtracting 128 from all pixels of input image. After IDCT i am adding 128 to the result image. I want to compare my results with MATLAB . Is anybody know how to use dct i.e. dct2 function of MATLAB? if anyone has the related code in MATLAB please...

## KLT & DCT

inHi We know that DCT is almost as good as KLT for a 1st order markov process. But under what cases ( if any) will they both KLT and DCT be the...

Hi We know that DCT is almost as good as KLT for a 1st order markov process. But under what cases ( if any) will they both KLT and DCT be the same. regards Abraham This message was sent using the Comp.DSP web interface on www.DSPRelated.com

## FFT VS DCT

inI see that all are asking why DCT is better than FFT or DFT. Where FFT is prepered than DCT? Why ? Is it only for phase...

I see that all are asking why DCT is better than FFT or DFT. Where FFT is prepered than DCT? Why ? Is it only for phase information? _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

## Fixed Point DCT

inCONTEXT: I have implemented DCT's in fixed point (DCT-IV and DCT-II). Currently I allow one extra bit, each time there is an addition, to...

CONTEXT: I have implemented DCT's in fixed point (DCT-IV and DCT-II). Currently I allow one extra bit, each time there is an addition, to avoid overflow. For example for a size 64 transform there are 6 stages of decomposition in radix-2 and each stage involves addition, which means I need log2(64)= 6 extra bits to losslessly transform the worst case input. QUESTION: Is there some way of ...

## does the current DCT/IDCT hardware use the same architecture for both DCT and IDCT?

inDear all, I came across an interesting problem: for a device both encodes and decodes video, do the designers seperately design circuit for...

Dear all, I came across an interesting problem: for a device both encodes and decodes video, do the designers seperately design circuit for DCT and another circuit for IDCT? I suspect that they have one universal transform circuit, then with some modification, IDCT can be computed using the DCT circuit(the universal circuit). Is that true? If so, how does that work? How to modify a little ...

## Understanding a DCT

inHello, I am sorry for this naive question but it is something that has been nagging me. I wanted to understand the interpretation of the DCT of...

Hello, I am sorry for this naive question but it is something that has been nagging me. I wanted to understand the interpretation of the DCT of any image. These are the questions I have, hope someone can answer them for me: 1. Are DCTs always done on 8x8 pixel sets? If so, each DCT block will consist of 64 basis image coefficients( a white represents a presence and a black indicates and absence...

## challenge: how to do filtering in DCT domain?

inDear all, I guess this is a little simple... Don't largh at me if it is too simple... Basicall I have a 3x3 filter, let's say [ -0.1 0.2...

Dear all, I guess this is a little simple... Don't largh at me if it is too simple... Basicall I have a 3x3 filter, let's say [ -0.1 0.2 -0.1; 0.2 0.6 0.2; -0.1 0.2 -0.1]; I want to do this in DCT domain... I know convolution in spatial domain is multiplication in frequency domain... but here the DCT ...

## Computing DFT of a signal from its DCT coefficients?

inHello, I have the following question regarding obtaining the DFT of a signal directly from its DCT representation: Say we are given the...

Hello, I have the following question regarding obtaining the DFT of a signal directly from its DCT representation: Say we are given the N-point DCT coefficients Xdct(k) of some real-valued signal x(n), but what we really want is the N-point DFT of x(n), Xdft(k). I need to obtain the power spectrum of the signal x(n) in the DFT domain, but I only have the DCT domain information. One me...

## DCT-lms

Hi all, Is there a best way for eigenvalue estimation in speech case for DCT-lms? I test my algorithm with power normalization as proposed by...

Hi all, Is there a best way for eigenvalue estimation in speech case for DCT-lms? I test my algorithm with power normalization as proposed by Farhang, Ali H Sayed and Haykin, my convergence still under the NLMS one and when I increase the number of taps(500 taps) it become difficult to converge. Is DCT-lms useful for AEC. thank you in advance

## Coefficient DCT

Dear all, Some watermarking technique is done in DCT domain. To embed the watermark bit we can modify DCT coefficient, for example I use the...

Dear all, Some watermarking technique is done in DCT domain. To embed the watermark bit we can modify DCT coefficient, for example I use the embedding formula : C'(i,j)=C(i,j)+alpha * w(i,j) but,there is problem in decide factor alpha How we can set the alpha factor rightly? There is a fix rule for it? Thank you, Reinhart