Lecture # 19 Image Processing II

2 Classes of Digital Filters Global filters transform each pixel uniformly according to the function regardless of its location in the image Local filters transform a pixel depending upon its relation to surrounding ones

Global Filters: REVIEW Brightness and Contrast control Histogram thresholding Histogram stretching or equalization Color corrections Inversions

Local Filters  Blurring Sharpening Unsharp Masking Edge and line detection Noise filters

Blurring Algorithm For (every pixel in column x) {For (every pixel in row y of column x) { average image[x,y] with it ’ s neighbors; }

Blurring Average each pixel with its neighbors by : multiplying each pixel and its neighbors by 1: = - add multiplied pixels and divide by 9 - store result in a new array The new array contains a blurred image

Gaussian Blur Multiply neighbors by less than middle

Blur Demo Photoshop –Filter->Blur->Blur –Filter->Blur->Gaussian Blur

Local Filters Blurring  Sharpening  Unsharp Masking Edge and line detection Noise filters

Subtract neighboring pixels by : multiplying each pixel and its neighbors by: = - add multiplied pixels - store result in a new array The new array contains a sharpened image. Sharpening

Unsharp Masking Unsharp masking also sharpens an image The Algorithm: 1. call the original (unblurred) image A 2. blur the image (call it B) 3. subtract B from the unblurred image (let C = A-B) 4. Multiply C by some number, k (k > 1) 5. Sharpened Image = A + kC

Sharpen/Unsharp mask Photoshop –Filter->Sharpen->Sharpen –Filter->Sharpen->Unsharp mask

Local Filters Blurring Sharpening Unsharp Masking  Edge and line detection Noise filters

Edge and Line Detection Multiply each pixel and its neighbors by the following corresponding patterns (numbers) - add results - clip to result = “ Edge ” image Gets Gets Vertical Edges Horizontal Edges

Edge Detection edge detection is often used to recognized objects of interest in the image

Edge Detection Photoshop –Filter->Stylize->Find Edges

Local Filters Blurring Sharpening Unsharp Masking Edge and line detection  Noise filters

Noise Filters A median filter takes away “ salt & pepper ” noise (speckles)

Noise Filter Photoshop –Filter->Noise->Median Filter

Kernel Filtering Blur Sharpen Edges Apply same algorithm at every pixel using different kernel values

Image Editing

 Selection Tools Painting Tools Cut & Paste Cloning Layers and Blending

Selection Tools Lasso Tool - manually draw outline (free hand) - manually outline (line segments) - magnetic lasso (semi-automated) Magic Wand DEMOS Tool Bar

Image Editing Selection Tools  Painting Tools Cut & Paste Cloning Layers and Blending

Painting Tools Airbrush Tool Paint Bucket Tool Paintbrush Tool Pencil Tool DEMOS

Image Editing Selection Tools Painting Tools  Cut & Paste Cloning Layers and Blending

Cut & Paste Word Processors - cut & paste strings of characters (1D arrays) Image Editing - cut & paste pixels (2D arrays) - replace old pixels with new pixels

Image Editing Selection Tools Painting Tools Cut & Paste  Cloning Layers and Blending

Cloning Copy pixels from one part of an image - to another part of an image... Interactively DEMO

Image Editing Selection Tools Painting Tools Cut & Paste Cloning  Layers and Blending

Can create arbitrary number of layers for - animation - special effects in movies - morphing Layers and Blending Layer 1 Layer 2 Layer n

The idea: Blended image =.3 x +.7 x is a weighted combination (sum) of two or more other images. Blending

Example Blend.3 x+.7 x = Bearastronaut

The idea: Create another image where the value of pixels is the weighting term for a blend operation: Masking

Summary Digital Images and pixels Digitize a picture by –Sampling –Quantization Color Models –RGB, CMYK, and HSB Storage Formats –.gif,.jpg,.png,.bmp

Summary Global Filters –Contrast & Brightness Control –Thresholding –Histogram stretching & equalization –Color corrections –Inversion

Summary Local filters –Blurring –Sharpening –Unsharp Masking –Edge and line detection –Noise filters

Summary Image Editing –Selection Tools –Painting Tools –Cut & Paste –Cloning –Layers and Blending