I'm running this program to generate a plot: using Images, Colors, FixedPointNumbers, Gadfly
function cond(color) mean = (color.r + color.g + color.b) / 3. var = (color.r - mean)^2 + (color.g - mean)^2 + (color.b - mean)^2 if sqrt(var) < 0.25 return 1 else return 0 end end function x_array(dim) buf = zeros(Int, dim) for i = 1:dim[1] for j = 1:dim[2] buf[i,j] = i end end return buf end function y_array(dim) buf = zeros(Int, dim) for i = 1:dim[1] for j = 1:dim[2] buf[i,j] = j end end return buf end function on(img) buf = zeros(UInt8, size(img)) for i = 1:size(img)[1] for j = 1:size(img)[2] buf[i,j] = cond(img[i,j]) end end return buf end img = imread("test.png") pap = on(img) lX = x_array(size(img)) lY = y_array(size(img)) draw(PNG("output.png", 18cm, 11cm), plot(x=lX, y=lY, color=pap, Geom.rectbin , Theme(background_color=color("white")))) This results in the following plot: <https://lh3.googleusercontent.com/-8C3SfWCfS0k/Vg8Qt_JiMJI/AAAAAAAAHp4/vJfiJJ48UPw/s1600/output.png> Since the cond-function returns only 1 or 0, the plot should have only 2 colors, but there seems to be a grid pattern across the whole picture. Where does this come from and how do I remove it?