Area of objects in binary image
bwarea
estimates the area of all of the on
pixels in an image by summing the areas of each pixel in the image. The area of an
individual pixel is determined by looking at its 2-by-2 neighborhood. There are six
different patterns, each representing a different area:
Patterns with zero on
pixels (area = 0)
Patterns with one on
pixel (area = 1/4)
Patterns with two adjacent on
pixels (area = 1/2)
Patterns with two diagonal on
pixels (area = 3/4)
Patterns with three on
pixels (area = 7/8)
Patterns with all four on
pixels (area = 1)
Each pixel is part of four different 2-by-2 neighborhoods. This means, for example,
that a single on
pixel surrounded by off
pixels
has a total area of 1.
[1] Pratt, William K., Digital Image Processing, New York, John Wiley & Sons, Inc., 1991, p. 634.