# Compute region area in an image

```
import numpy as np
M = np.zeros((400, 300)) # pretend it's an image
def area(matrix):
return len(matrix.ravel())
Ax, Ay = 20, 30 # left, top
Cx, Cy = 200, 160 # right, bottom
area1 = (Cx - Ax) * (Cy - Ay)
area2 = area(M[Ax:Cx, Ay:Cy])
# From four points (clockwise ordered)
# Measuring areas from (0,0) to each (x,y) coordinate of each point
Bx, By = Cx, Ay
Dx, Dy = Ax, Cy
area3 = area(M[:Cx, :Cy]) - (area(M[:Bx, :By]) + area(M[:Dx, :Dy]) - area(M[:Ax, :Ay]))
print(area1, area2, area3) # 23400 23400 23400
```