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Lecture # 19 Image Processing II

Lecture # 19 Image Processing II. 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.

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Lecture # 19 Image Processing II

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  1. Lecture # 19 Image Processing II

  2. Image Processing II

  3. 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

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

  5. Local Filters • Blurring • Sharpening • Unsharp Masking • Edge and line detection • Noise filters

  6. 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; } }

  7. 1 1 1 1 1 1 1 1 1 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.

  8. Gaussian Blur Multiply neighbors by less than middle

  9. Blur Demo • Photoshop • Filter->Blur->Blur • Filter->Blur->Gaussian Blur

  10. Local Filters • Blurring • Sharpening • Unsharp Masking • Edge and line detection • Noise filters

  11. Sharpening • 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. 0 -1 0 -1 +5 -1 -1 0 0

  12. 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

  13. Sharpen/Unsharp mask • Photoshop • Filter->Sharpen->Sharpen • Filter->Sharpen->Unsharp mask

  14. Local Filters • Blurring • Sharpening • Unsharp Masking • Edge and line detection • Noise filters

  15. +1 -1 0 -1 +1 0 -1 +1 0 Edge and Line Detection • Multiply each pixel and its neighbors by the following corresponding patterns (numbers) - add results - clip to 255 - result = “Edge” image -1 -1 -1 0 0 0 +1 +1 +1 Gets Gets Vertical Edges Horizontal Edges

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

  17. Edge Detection • Photoshop • Filter->Stylize->Find Edges

  18. Local Filters • Blurring • Sharpening • Unsharp Masking • Edge and line detection • Noise filters

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

  20. Noise Filter • Photoshop • Filter->Noise->Median Filter

  21. 0 -1 0 -1 +5 -1 1 1 1 1 1 1 1 +1 -1 0 -1 0 0 1 -1 +1 0 1 -1 +1 0 Kernel Filtering Edges Blur Sharpen -1 -1 -1 Apply same algorithm at every pixel using different kernel values 0 0 0 +1 +1 +1

  22. ImageEditing

  23. Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

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

  25. Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

  26. Painting Tools • Airbrush Tool • Paint Bucket Tool • Paintbrush Tool • Pencil Tool DEMOS

  27. Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

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

  29. Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

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

  31. Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

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

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

  34. Example Blend .3 x +.7 x = Bearastronaut

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

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

  37. Summary • Global Filters • Contrast & Brightness Control • Thresholding • Histogram stretching & equalization • Color corrections • Inversion

  38. Summary • Local filters • Blurring • Sharpening • Unsharp Masking • Edge and line detection • Noise filters

  39. Summary • Image Editing • Selection Tools • Painting Tools • Cut & Paste • Cloning • Layers and Blending

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