Graphics.Image.Processing.Hough

Hough Transform is used as a part of feature extraction in images. It is a tool that makes it far easier to identify straight lines in the source image, whatever their orientation.

Documentation

sub :: Num x => (x, x) -> (x, x) -> (x, x)

Some helper functions : | Trivial function for subtracting co-ordinate pairs

dotProduct :: Num x => (x, x) -> (x, x) -> x

Compute the sum of squares or dot product of a given pair of co-ordinates

fromIntegralP :: (Integral x, Num y) => (x, x) -> (y, y)

Conversion of pair fromIntegral

mag :: Floating x => (x, x) -> x

Compute magnitude

hough :: forall arr. (MArray arr Y Double, Array arr Y Double, Array arr Y Word8) => Image arr Y Double -> Int -> Int -> Image arr Y Word8

hough computes the Linear Hough Transform and maps each point in the target image, ​ (ρ, θ) ​ to the average color of the pixels on the corresponding line of the source image ​(x,y) ​- space, where the line corresponds to points of the form ​(xcosθ + ysinθ = ρ(rho)).

The idea is that where there is a straight line in the original image, it corresponds to a bright (or dark, depending on the color of the background field) spot; by applying a suitable filter to the results of the transform, it is possible to extract the locations of the lines in the original image.

Usage :

>>> frog <- readImageRGB VU "yield.jpg"
>>> input1 <- getLine
>>> input2 <- getLine
>>> let thetaSz = (P.read input1 :: Int)
>>> let distSz = (P.read input2 :: Int)
>>> let houghImage :: Image VU RGB Double
>>> houghImage = hough frog thetaSz distSz
>>> writeImage "test.png" houghImage