Mark Gritter (markgritter) wrote,
Mark Gritter
markgritter

Principal Component Analysis

A similar technique to NNMF from my last entry is Principal Component Analysis. It still factors the input matrix, but now negative values are allowed. A big challenge for using PCA is what to do with those negative numbers, which have no standard interpretation. (This is one of the advantages of NNMF, that it can be applied in scenarios in which only positive values make sense.)

PCA is better at identifying features in my sample of pixel art, and degrades more gracefully as the number of components is lowered. The graphs here show original, reconstructed, and the PCA components separated by palette color. (Blue is negative, red is positive--- sorry.)



Reduced dimension (10 components.) Using nearest-neighbor of the blended colors works pretty well at reconstructing the original images:



However, the blends between flowers are, if anything, worse. Nearest-neighbor doesn't work very well at all. The best results I got were from capping the negative contributions at 0 and blending:



Tags: geek, programming
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