Image lena256.      1,128 ; 1,129:
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**********  RED  **********

Huffman coding:

proj Diff:  ~= 5.46 bpb (bits per bin)
proj orig interp (1,129) : ~= 8.04 bpb

1 proj + Diff:
33151 * 8.04 + 33151 * 5.46 = 447 539 bits

Orig:
256*256 * 8 = 524 288 bits

Difference: 76 749 bits
Percentage: 76 749 * 100 / 524 288 = 14.63 %

**********  GREEN  **********

Huffman coding:

proj Diff:  ~= 5.81 bpb (bits per bin)
proj orig interp (1,129) : ~= 8.23 bpb

1 proj + Diff:
33151 * 8.23 + 33151 * 5.81 = 465 440 bits

Orig:
256*256 * 8 = 524 288 bits

Difference: 58 848 bits
Percentage: 58 848 * 100 / 524 288 = 11.22 %

**********  BLUE  **********

Huffman coding:

proj Diff:  ~= 5.84 bpb (bits per bin)
proj orig interp (1,129) : ~= 7.66 bpb

1 proj + Diff:
33151 * 7.66 + 33151 * 5.84 = 447 539 bits

Orig:
256*256 * 8 = 524 288 bits

Difference: 76 749 bits
Percentage: 76 749 * 100 / 524 288 = 14.63 %
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Total RGB:

Orig RGB:
256 * 256 * 3 * 8 = 1 572 864 bits.

Compressed Projections:
447 539 + 465 440 + 447 539 = 1 360 518 bits

Difference = 212 346 bits
Percentage : 212 346 * 100 / 1 572 864 = 13.50 %

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NOTE that it is possible to significantly reduce the compression rate by taking into account the intra-projection compression...