COL783: Digital Image Processing

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COL783: Digital Image Processing

Prem Kalra

[email protected]

http://www.cse.iitd.ac.in/~pkalra/col783

Department of Computer Science and Engineering

Indian Institute of Technology Delhi

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Digital Image Processing http://www.cse.iitd.ac.in/~pkalra/col783

Image Segmentation

Image segmentation is the process of partitioning a digital

image into multiple segments (regions)

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Image Segmentation

Image segmentation is the process of partitioning a digital

image into multiple segments (regions)

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Image Segmentation

Segmentation: Dividing into the regions/segments of similar

properties

• Discontinuity – boundary

• Similarity – region

Discontinuity Detection: Point, Line and Edge

Mask Operation (Review)

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Image Segmentation

Mask Operation Point

Line with fixed orientation

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Image Segmentation

Edge: Sharp change in intensity (discontinuity)

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Image Segmentation

Edge: Sharp change in intensity (discontinuity)

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Image Segmentation

Edge Detection

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Image Segmentation

Edge Detection

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Image Segmentation

Edge Detection

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Image Segmentation

Edge Detection

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Image Segmentation

Edge Detection

Laplacian of

Gaussian (LoG)

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Image Segmentation

Edge Detection

Laplacian of

Gaussian (LoG)

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Image Segmentation

Edge Detection

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Image Segmentation

Edge Detection

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Image Segmentation

Canny Edge Detection

• Low error rate

All true edges should be found

• Edge points should be well localized

Edges should be located as close as possible to the true edges

• Single edge point response

One point for each true edge point

No of local maxima around true should be minimum

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Image Segmentation

1. Smooth image with a Gaussian filter Low error rate

2. Compute gradient magnitude M[x,y] and direction a [x,y]

3. Apply non-maximal suppression to the gradient magnitude

4. Use double thresholding (and subsequent connectivity analysis) to detect

link edges

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Image Segmentation

M[i,j] will have large values where the gradient is large. We need to find the local maxima in this array to locate the edges.

Must be thin so only points of the greatest local change remain.

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Image Segmentation

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Image Segmentation

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Image Segmentation

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Image Segmentation

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Image Segmentation

Edge Detection