read_image (Image, ‘surface_scratch’)

invert_image (Image, ImageInverted)

get_image_size (ImageInverted, Width, Height)

gen_sin_bandpass (ImageBandpass, 0.4, ‘none’, ‘dc_center’, Width, Height)

fft_generic (ImageInverted, ImageFFT, ‘to_freq’, -1, ‘none’, ‘dc_center’, ‘complex’)

convol_fft (ImageFFT, ImageBandpass, ImageConvol)

fft_generic (ImageConvol, Lines, ‘from_freq’, 1, ‘n’, ‘dc_center’, ‘byte’)

scale_image_max (Lines, ImageScaleMax)

*gen_rectangle1 (Rectangle, 30, 20, 100, 200)

*reduce_domain (ImageScaleMax, Region, ImageReduced)

threshold (ImageScaleMax, Region, 20 , 255)