Hough space

image space
y = m0x + b0

Hough (parameter) space
b = -x0m + y0
b = -x1m + y1

polar representation for lines
d: perpendicular distance from line to origin
Θ: angle the perpendicular makes with the x-axis

Hough transform algorithm
xcosΘ- ysinΘ = d

Hough transform for circles
Circle: center(a,b) and radius r (xi-a)^2 + (yi-b)^2 = r^2

For every edge pixel (x,y):
	For each possible radius value r:
		For each possible gradient direction Θ:
		 %% or use estimated gradient
		 	a = x - r cos(Θ)
		 	b = y + r sin(Θ)
		 	H[a,b,r] += 1
		 end
	end
end