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									                 BTC Encoding




S.R.Subramanya                  1
     Block Truncation Coding(in:I; out;code)



  • Divide the image into non-overlapping blocks of n x ni pixels
  • For each block
       › Compute the mean,  ,and standard deviation, ,for each
       block   12 n1 P[i , j ] ;   12 n n P 2 [i , j ]   2 where P[i,j]
                     i
                  n                            j 1   j 1
                                          n
       is the value of pixel at (i,j).
       › Detemine p and q be the number of pixels in the block
       which have values greater or equal, and less than 


S.R.Subramanya                                                             2
     Block Truncation Coding(in:I; out;code)



       ›Compute reconstruction levels a and b
           a    p q , b    q p


       › Quantize the pixels in each block to get a bitmap whose
       pixel values are; 1 if P[i, j ]   and 0 otherwise

 • Encode the bitmaps and reconstruction levels




S.R.Subramanya                                              3
                    BTC Decoding



     Decode
     bitmap
                 Form      Combine
                 recons.   blocks
      Decode     block
      recons.
      values
                                     Reconstructed
                                     Image


S.R.Subramanya                                       4
                        CCC Encoding

                              reconstructed
                              values
                                  a’

                      each        b’
                      block



     Original Image            bitmap

                                              color lookup table
S.R.Subramanya                                             5
                    Color Cell Compression


  NM            Dimensions of the original image I
  n m           Dimensions of each block
  P (i , j )     Pixel value in a block at relative position (i,j)
  PR , PG , PB The (R,G,B) components of pixel P(i,j)
 Y (i , j )      Luminance (brightness) components of pixel P(i,j)
                Mean brightness of a block
  aC , bC        Reconstruction pixel values
  p(q )
S.R.Subramanya
                 Number of pixels greater than,equal to (less than)
                                                                 6
      Color Cell Compression(in: I; out; code)


 • Divide the image into non-overlapping blocks of n m
 pixels. For each block do the following
 • For each pixel P(i, j ) compute the luminance (brightness)
 component, Y(i,j):
        Y (i , j )  0.3 PR (i , j )  0.59 PG (i , j )  0.11PB (i , j )

  • Compute the mean brightness,  :
                  1
                   i 1  j 1 Y ( i , j )
                      n     m

                 nm

  • Compute reconstruction values aC and bC ,where C {R, G, B}
                  1                                                1
         aC        
                  p i , j:Y ( i , j ) 
                                         PC ( i , j )   ,   bC      
                                                                   q i , j ;Y ( i , j ) 
                                                                                           PC ( i , j )
S.R.Subramanya                                                                                            7
    Color Cell Compression(in: I; out; code)



  • Compute bitmap B:
       B( i , j )  1 ,if Y ( i , j )   ;   B( i , j )  0   ,if   Y (i , j )   ;

  • Quantize (aR , aG , aB ) and (bR , bG , bB ) using CLT

  • Let the corresponding indices into the CLT be a ' and b '

  • Encode B, a ', b ' using entropy coding




S.R.Subramanya                                                                          8
                 Lossy DPCM Encoder




S.R.Subramanya                        9
                 Lossy DPCM Decoder




                           +
                                Sm
                  rm
                           Pm




S.R.Subramanya                        10

								
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