Compute gradient magnitude and orientation at each image location.
If input image has k>1 channels and channel=0, keeps gradient with
maximum magnitude (over all channels) at each location. Otherwise if
channel is between 1 and k computes gradient for the given channel.
Orientation is given modulo PI degrees. Highly optimized using mex.
If normRad>0, normalization is performed by first computing S, a smoothed
version of the gradient magnitude, then setting: M = M./(S + normConst).
S is computed by S = convTri( M, normRad ).
This code requires SSE2 to compile and run (most modern Intel and AMD
processors support SSE2). Please see: http://en.wikipedia.org/wiki/SSE2.
USAGE
[M,O] = gradientMag( I, [channel], [normRad], [normConst] )
INPUTS
I - [hxwxk] input k channel single image
channel - [0] if>0 color channel to use for gradient computation
normRad - [0] normalization radius (no normalization if 0)
normConst - [.005] normalization constant
OUTPUTS
M - [hxw] gradient magnitude at each location
O - [hxw] approximate gradient orientation modulo PI
EXAMPLE
I=rgb2gray(single(imread('peppers.png'))/255);
tic, [M1,O1]=gradientMag(I); toc
tic, [Gx,Gy]=gradient2(I); M2=sqrt(Gx.^2+Gy.^2);
O2=mod(atan2(Gy,Gx),pi); toc, mean2(abs(M1-M2))
d=abs(O1-O2); d(d>pi/2)=pi-d(d>pi/2); mean2(d)
See also gradient, gradient2, gradientHist, convTri
Piotr's Image&Video Toolbox Version 3.02
Copyright 2012 Piotr Dollar & Ron Appel. [pdollar-at-caltech.edu]
Please email me if you find bugs, or have suggestions or questions!
Licensed under the Simplified BSD License [see external/bsd.txt]