Morphological Filters
Prerequisites
Before starting this lesson, you should be familiar with:
Learning Objectives
After completing this lesson, learners should be able to:
Design morphological filters using rank filters
Execute morphological filters on binary or grayscale images and explain the output
Motivation
Filters can be used to change size and shape of objects in an image. [*] Concept map below assumes bright objects on dark background. For dark objects on bright background effect of min and max filters is inverted.
Concept
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]
max1
min1
d[max - min]
end
max1 --> dilation
min1 --> erosion
max3 --> opening
min3 --> closing
d --> gradient
subgraph morphological filter name
dilation
erosion
opening
closing
gradient
end
Activity
Open the image, xy_8bit_binary_two_spots_different_size.tif, and explore how structures grow and shrink, using erosion and dilation
Formative assessment
Exercise 1
Fill in the blanks, using those words: “shrinks”, “increases”, “decreases”, “enlarges”.
- 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.
Exercise 2
True of false? Discuss with your neighbour!
- 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.
Follow-up material
We recommend reading these modules next:
TODO
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