This document discusses several shape features that can be extracted from images, including: 1) The axis of least second moment, which provides information about an object's orientation. 2) The Euler number, which can be used in optical character recognition and is calculated based on the number of convexities and concavities in an image. 3) Projection features, boundary contours represented by chain codes, and Fourier descriptors which describe boundaries through Fourier transforms.

1. FEATURE EXTRACTION - SHAPE

2. 2/21/2024 Department of Biomedical Engineering, SRMIST, KTR 2
Shape Features
Axis of Least Second Moment
• This assumes that the
origin is as the center of
area.
• This feature provides
information about the
object’s orientation.
• This axis corresponds to
the line about which it
takes the least amount of
energy to spin an object.

3. 2/21/2024 Department of Biomedical Engineering, SRMIST, KTR 3
Shape Features - Euler Number
• Euler number can be used in tasks such as optical
character recognition (OCR).

4. 2/21/2024
Department of Biomedical Engineering,
SRMIST, KTR
4
Shape Features – Euler Number
• Euler number can also be found using the number of
convexities and concavities
Euler number = number of convexities – number of concavities
• This can be found by scanning the image for the
following patterns:






1
0
0
0






1
1
1
0
Convexities Concavities

5. 2/21/2024 Department of Biomedical Engineering, SRMIST, KTR 5
shape Features – Projection

6. Shape Features
2/21/2024 Department of Biomedical Engineering, SRMIST, KTR 6
• Chain code for boundary contour
– Obtained using a set of orientation primitives on the boundary
segments derived from a piecewise linear approximation
• Fourier descriptor of boundary contours
– Obtained using the Fourier transform of the sequence of boundary
segments derived from a piecewise linear approximation
• Central moments based shape features for the segmented region
• Morphological shape descriptors
– Obtained through the morphological processing on the segmented
region