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Image Analysis Training: Morphological filters

Morphological filters



This module explains how filters can be used to change size and shape of objects in the image.

Learning objectives

Concept map

graph TD
    image --> max1[max]
    image --> min1[min]
    image --> max2[max]
    image --> min2[min]
    image --> d 
subgraph rank filter sequence
    max2 --> min3[min]
    min2 --> max3[max]
    d[max - min]
    max1 --> dilation
    min1 --> erosion
    max3 --> opening
    min3 --> closing
    d --> gradient
    subgraph morphological filter name

[*] Concept map above assumes bright objects on dark background. For dark objects on bright background effect of min and max filters inverses

Activity: Explore erosion and dilation on binary images

Activity: Explore opening and closing on binary images

Formative assessment

Fill in the blanks, using those words: shrinks, increases, decreases, enlarges.

  1. An erosion _____ objects in a binary image.
  2. An erosion in a binary image _____ the number of foreground pixels.
  3. A dilation in a grayscale image _____ the average intensity in the image.
  4. A dilation _____ objects in a binary image.

True of false? Discuss with your neighbour!

  1. Morphological openings on binary images can decrease the number of foreground pixels.
  2. Morphological closings on binary images never decreases the number of foreground pixels.
  3. Performing a morphological closing a twice in a row does not make sense, because the second closing does not further change the image.

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