e178-L4.ppt

# e178-L4.ppt - Image Enhancement: Histogram Processing...

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Histogram Processing 1 Image Enhancement: Histogram Processing Reading: Chapter 3 (Spatial domain) Histogram Processing 2 Histogram Processing Histogram Equalization Histogram Specification/Matching

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Histogram Processing 3 Histogram p(r k )= n k /n r k n k : # pixels with gray level r k n : # pixels in the image r k {0,1,2, , L 1} Histogram Processing 4
Histogram Processing 5 Figure 3.15: histograms Histogram Processing 6 Histogram Modification r : Input gray level [0, 1] s : Transformed gray level [0, 1] s = T (r) T : Transformation function

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Histogram Processing 7 Histogram Equalization ( i ) T ( r ) is single valued valued and monotonically increasing in 0 r 1 ( ii ) 0 T ( r ) 1 for 0 r 1 [0, 1] T  → [0, 1] Inverse transformation : T 1 ( s ) = r 0 s 1 T 1 ( s ) also satisfies ( i ) and ( ii ) The gray levels in the image can be viewed as random variables taking values in the range [0,1]. Let p r ( r ) : p.d.f. of input level r and let p s ( s ) : p.d.f. of s s = T ( r ) ; p s ( s ) = p r ( r ) r = T 1 ( s ) (from ECE 140) Histogram Processing 8 Equalization (contd.)
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## e178-L4.ppt - Image Enhancement: Histogram Processing...

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