Region Detection & Description Flashcards
What is a blob?
A set of pixels that
- Share some PROPERTY
- Are connected
What does it mean for 2 pixels to be connected?
You can trace a path between them
What is a connected component?
A contiguous set of pixels that share some property
What is the process of finding connected components called?
Connected component analysis
How many ways of doing component analysis?
- iterative
- recursive
- two pass
Describe the two pass algorithm for connected component analysis
1st pass: (If pixel might be in component, label numerically)
If in adjacent pixels:
-all unlabelled-> give next component label
->= 1 same label -> give this
->=2 different labels -> give one, store equivalence
2nd pass:
- relabel inconsistent labels according to equivalence table
How to calculate area of regions?
Histogram (number of pixels/regions)
How to calculate compactness of region?
C = p^2/A
We have methods for extracting and describing the boundaries of regions from binary images, some are closely related to the data and others are more abstract,. What is the use of the abstract ones?
- Remove noise
- Better approximation of scene
How can we describe the outline of a region?
chain codes
What does a chain code include?
coordinate of a boundary point + sequence of displacements
Is it actually possible to have a pixel on the boundary?
no, it can be inside or outside the image
Will picking chain code pixels inside or outside affect anything?
Yes, measurements derived from chain code will vary
Does a chain code differ depending on where the object is in an image?
nope
How to calculate total perimeter length from chain code?
= #even numbered codes + sqrt(2)*#odd numbered codes
