ELEC317 Digital Image Processing Lecture 5 Image Enhancement Image Enhancement-- This is sharpening of desirable features in image. -- Information inside data is actually decreased. -- Whether “enhanced” image is good usually is subjective to viewer ÎNo universal quantifying criteriaÎProcedures are normally “heuristics” based on empirical observations. Common Image Enhancement Methods:1. Point Operations-- Operate on individual pixel values * Contrast Stretching * Noise Clipping * Window Slicing * Histogram Modeling / Equalization 2. Spatial Operations-- Often Filtering * Noise Smoothing * Median Filter * Lowpass, Highpass, Bandpass Filtering * Zooming – Enlarge / Reduce size of image * Unsharp Masking 3. Pseudocoloring* False Coloring * Pseudocoloring 1
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24. Transform Operations* Linear Filtering via Fast Fourier Transform ( FFT ) * Root Filtering * Homomorphic Filtering A. Point OperationsThis is a memoryless operation. Each pixel’s gray level ],0[Lu∈is mapped into a new level ],0[Lv∈where v= f (u) A.1. Contrast StretchingAims at increasing dynamic range of image. Lubbuaauvbuvauuvba<≤<≤<≤+−+−=,,0,)()(γβα-- The region where slope > 1 is stretched. -- Stretched region is normally region where most pixel values fall in. -- Refer to fig. 7.3 p236. ava=αabvvab−−=βbLvLb−−=γL= 255 LL γβαabv ubvavThis region stretched. LbvavabHistogram L. C. image