Help put equation into code

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  14 years ago

  by Michael H

  Michael H

  Chicago, USA, United States

  Joined 19 years ago

  What I'm struggling with is understanding JPEG.
  
  Now that noone is reading anymore , what I don't understand is the DCT.
  Wikipedia shows it as (in Discrete cosine transform - Wikipedia, the free encyclopedia) (DCT-II):
  Assuming N = 8, in doing one row (or column, but lets just assume row):
  
  Xk = sum(0..7) { Xn * cos((PI/8)(n+.5)(k)) }
  
  Now if X is a 8 element array of ints, and k and n are indeces, then:

  Code:

  float sum = 0;
  for(int n=0;n<8;n++)
  {
  sum += X[ n] * cos((PI/8)(n+.5)k);
  }
  
  
  
  

  I have no idea what 'k' is supposed to be. I think it's either 1..8, or it could be
  1..7. It could be one of those ranges incrementing through the sum, or incrementing for each new Xk.
  
  Can anyone help me out?
  
  Many thanks in advance!
  
  
  
  
  
  
  
  
  
  
  
  
  

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• • Reply

  14 years ago

  by Michael H

  Michael H

  Chicago, USA, United States

  Joined 19 years ago

  I managed to figure some things out. Xk is a different array from xn in the wiki formula.
  Now for the 2-d version, I can take the Xk array and do the columns into another array.
  
  This is indeed going to be slow, eh?
  
  
  
  
  

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