GaborLayer.lua

-- Clement's old gabor function


require 'image'
require 'xlua'

-- For the similar Gabor code go to 
-- http://www.mathworks.com/matlabcentral/fileexchange/23253-gabor-filter/content/Gabor%20Filter/gabor_fn.m


-- Size should be odd number 
-- angle (in rad)
-- elipse_ratio = aspect ratio(0.5)

-- In order to get some understanding you can run the following test
--[[
win = nil
sz = 13
s  = .125
f = 2
r = .5
for a = 0,180,30 do
   alpha = a/180*math.pi
   win=image.display{image=gabor(sz,s,alpha,1/f,r),zoom=20,win=win,legend='alpha = ' .. a .. 'deg'}
   io.read()
end
]]

function eex.gabor(size, sigma, angle, period, ellipse_ratio)
      -- init matrix
      local data = torch.zeros(size,size)

      -- image -> pixel
      period = period * size
      sigma = sigma * size

      -- set params
      local halfsize = math.floor(size/2)
      local sigma_x = sigma
      local sigma_y = sigma/ellipse_ratio

      for y=-halfsize,halfsize do
         for x=-halfsize,halfsize do

            x_angle = x*math.cos(angle) + y*math.sin(angle)
            y_angle = -x*math.sin(angle) + y*math.cos(angle)
            data[x+halfsize+1][y+halfsize+1] 
               = math.exp(-0.5*(x_angle^2/sigma_x^2 + y_angle^2/sigma_y^2))
                 * math.cos(2*math.pi*x_angle/period)
         end
      end

      -- return new tensor
      return data
   end