Image destriping: Difference between revisions

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Revision as of 11:49, 29 July 2011

Download of tiles

See ASTER topography.

ASTER GDEM destriping with FFT

In some ASTER GDEM tiles, artifacts (stripes) are visible. These can be reduced with FFT filtering.


Look at the original tile (screenshot upper right map):

# set computational region to GDEM map:
g.region rast=ASTGTM_N53E004_num -p
d.mon x0
d.rast ASTGTM_N53E004_num


Perform Fast Fourier Transform (FFT; screenshot upper left map):

i.fft in=ASTGTM_N53E004_num real=ASTGTM_N53E004_num_real imag=ASTGTM_N53E004_num_imag
d.mon x1
d.rast ASTGTM_N53E004_num_imag
d.rast ASTGTM_N53E004_num_real


Create a MASK in order to remove noise (screenshot upper left map):

# digitize filter mask to reduce noise
r.digit filter
d.rast filter
r.mask -i filter
d.rast ASTGTM_N53E004_num_real


Inverse FFT to get filtered GDEM back (screenshot lower left map):

i.ifft real=ASTGTM_N53E004_num_real imag=ASTGTM_N53E004_num_imag output=ASTGTM_N53E004_num_filtered
r.mask -r
d.mon x2
d.rast ASTGTM_N53E004_num_filtered
r.colors ASTGTM_N53E004_num_filtered color=elevation 
d.rast ASTGTM_N53E004_num_filtered


Calculate the differences (screenshot lower right diagram):

# validade with differences map:
r.mapcalc "diff = ASTGTM_N53E004_num - ASTGTM_N53E004_num_filtered"
r.colors diff color=differences
d.mon x3
d.rast.leg diff

# done
File:Grass aster GDEM destriping with FFT.png
Workflow of ASTER GDEM destriping with FFT

Note: If the MASK is made larger (more to the center), more aggressive destriping occurs.