def canny(iImage, thr_type = 1):
    iImage = np.asarray(iImage)
    iImageG = rv.colorToGray(iImage)
    # glajenje slike
    iKernel = np.ones([5,5])/25
    iImageGL = ndimage.convolve(iImageG, iKernel)
    # dolocimo kriterij za povezovalne tocke
    if thr_type == 1:
        m = np.median(iImageGL)
        std = np.std(iImageGL)
    #elif thr_type == 2:
    #    m = np.median(iImageGL)
    #    std = np.std(iImageGL)
    y, x = iImageGL.shape
    grad_0 = grad_45 = grad_90 = grad_135 = np.zeros_like(iImageGL)
    for dy in range(1, y-1):
        for dx in range(1, x-1):
            grad_0[dy, dx] = abs(iImageGL[dy, dx+1]-iImageGL[dy, dx-1])
            grad_45[dy, dx] = abs(iImageGL[dy+1, dx]-iImageGL[dy-1, dx])
            grad_90[dy, dx] = abs(iImageGL[dy+1, dx]-iImageGL[dy-1, dx])
            grad_135[dy, dx] = abs(iImageGL[dy+1, dx]-iImageGL[dy-1, dx])
    return None