Lecture 3 (2.5.07) Image Enhancement in Spatial Domain Shahram Ebadollahi 11/29/2018 DIP ELEN E4830

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Processing Images in Spatial Domain: Introduction : Spatial operator defined on a neighborhood N of a given pixel point processing mask processing 11/29/2018

Mask (filter, kernel, window, template) processing (0,0) y (0,0) y x x 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Image Histogram normalized histogram histogram H bi-level image 255 0.5 bi-level image 255 256x256 H Pixel values linearly increasing from 0 to 255 with increasing column index histogram 1/256 255 256x256 11/29/2018

Image Histogram: example 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Point Processing: Thresholding Input gray-level value Output gray-level value 11/29/2018

Point Processing: Gamma Correction 11/29/2018

Point Processing: Contrast Stretching L-1 11/29/2018

Point Processing: Clipping & Thresholding L-1 clipping L-1 thresholding 11/29/2018

Point Processing: Gray-level Slicing L-1 L-1 11/29/2018

Point Processing: Bit-plane Slicing lsb msb where, e.g. 11/29/2018

Point Processing: Bit-plane Slicing (example) Point operation for obtaining n-th bit-plane: Bi-level image n=7 n=6 n=5 n=4 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Histogram Modification Apply a transform to an image such that the resulting image has desired histogram. Histogram Equalization (linearization) Histogram Specification (matching) Non-adaptive vs. Adaptive Histogram Modification Global histogram Local histogram 11/29/2018

Histogram Equalization Source image Equalized Image Corresponding Histograms 11/29/2018

Histogram Equalization Often images poorly use the full range of the gray scale Solution: Transform image such that its histogram is spread out more evenly in gray scale Rather than guessing the parameters and the form of the transformation use original gray-scale distribution as the cue 11/29/2018

Histogram Equalization # pixels with the j-th gray-level Point operation for equalizing histogram for the example image image size 11/29/2018

Histogram Matching Transform image such that resulting image has specified histogram Histogram Matching 11/29/2018

Histogram Matching 11/29/2018

Adaptive Histogram Equalization (0,0) y Histogram Equalization Note: local structure revealed x 11/29/2018

Today’s Lecture - Outline Review of Lecture 2 Processing Images in Spatial Domain: Intro Image Histogram Point Operations Using Histogram for Image Enhancement Kernel Operations 11/29/2018

Kernel Operator: Intro Note: need to handle borders of the image 11/29/2018

Kernel Operator: Intro Spatial Filtering kernel 11/29/2018

Smoothing: Image Averaging FT Low-pass filter * Image edges are softened 11/29/2018

Smoothing: Averaging (example) original 3x3 5x5 9x9 Noise effect is gone, but image edges are heavily blurred also 15x15 35x35 11/29/2018

Order Statistics Filter original 11/29/2018

Image Derivative 11/29/2018

Image Sharpening: 1-st derivative Image gradient: Robert’s operator Sobel filter in frequency domain Sobel’s operator 11/29/2018

Image Sharpening: 2-nd derivative Image Laplacian: 11/29/2018

Image Sharpening: 2-nd derivative + * Laplacian filter in frequency domain 11/29/2018

High-boost Filtering - + + Avg. Unsharp mask: high-boost with A=1 11/29/2018

Recap Point operations vs. Kernel Operations Image Histogram Image Enhancement using Point Operators Contrast Stretching Gamma Correction Using Image Histogram for Enhancement Histogram Equalization Histogram Matching Image Enhancement using Kernel Operators Low-pass filtering (averaging) High-pass filtering (sharpening) 11/29/2018