Image destriping - Revision history

Neteler: +ref

2015-10-10T14:34:26Z

+ref

← Older revision		Revision as of 14:34, 10 October 2015
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	== See also ==		== See also ==

			* https://www.mapbox.com/blog/debanding-the-world/ (about Landsat7 SLC off debanding)
	* [http://paulbourke.net/miscellaneous/imagefilter/ Image Filtering in the Frequency Domain]		* [http://paulbourke.net/miscellaneous/imagefilter/ Image Filtering in the Frequency Domain]
	* [https://www.mapbox.com/blog/debanding-the-world/ Landsat 7 destriping]		* [https://www.mapbox.com/blog/debanding-the-world/ Landsat 7 destriping]

	[[Category: Image processing]]		[[Category: Image processing]]

Neteler: +maxbox destriping url

2014-08-11T15:18:09Z

+maxbox destriping url

← Older revision		Revision as of 15:18, 11 August 2014
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	* [http://paulbourke.net/miscellaneous/imagefilter/ Image Filtering in the Frequency Domain]		* [http://paulbourke.net/miscellaneous/imagefilter/ Image Filtering in the Frequency Domain]
			* [https://www.mapbox.com/blog/debanding-the-world/ Landsat 7 destriping]

	[[Category: Image processing]]		[[Category: Image processing]]

⚠️Ychemin at 02:26, 18 June 2014

2014-06-18T02:26:11Z

← Older revision		Revision as of 02:26, 18 June 2014
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	<source lang="bash">		<source lang="bash">
	# digitize filter mask to reduce noise		# digitize filter mask to reduce noise
	r.digit filter		r.digit filter #not working in Grass v7
	d.rast filter		d.rast filter
	r.mask -i filter		r.mask -i filter

Neteler: +see also

2012-02-17T11:41:27Z

+see also

← Older revision		Revision as of 11:41, 17 February 2012
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	== Image destriping with FFT ==		== Image destriping with Fast Fourier Transform (FFT) ==

	In some image maps, artifacts (stripes) are visible. These can be reduced with FFT filtering.		In some image maps, artifacts (stripes) are visible. These can be reduced with FFT filtering ({{cmd\|i.fft}}).

			First we take a look at the original tile (screenshot upper right map):
	~~Look~~ at the original tile (screenshot upper right map):
	<source lang="bash">		<source lang="bash">
	# set computational region to GDEM map:		# set computational region to GDEM map:
Line 13:		Line 12:


	~~Perform~~ '''Fast Fourier Transform''' (FFT; screenshot upper left map):		Then we perform '''Fast Fourier Transform''' (FFT; screenshot upper left map):
	<source lang="bash">		<source lang="bash">
	i.fft in=imagemap real=imagemap_real imag=imagemap_imag		i.fft in=imagemap real=imagemap_real imag=imagemap_imag
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	Note: If the MASK is made larger (more to the center), more aggressive destriping occurs.		Note: If the MASK is made larger (more to the center), more aggressive destriping occurs.

			== See also ==

			* [http://paulbourke.net/miscellaneous/imagefilter/ Image Filtering in the Frequency Domain]

	[[Category: Image processing]]		[[Category: Image processing]]

Neteler: /* Image destriping with FFT */

2011-10-23T20:48:15Z

Image destriping with FFT

← Older revision		Revision as of 20:48, 23 October 2011
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	Note: If the MASK is made larger (more to the center), more aggressive destriping occurs.		Note: If the MASK is made larger (more to the center), more aggressive destriping occurs.

			[[Category: Image processing]]

Neteler: generalize it

2011-07-29T11:59:55Z

generalize it

← Older revision		Revision as of 11:59, 29 July 2011
Line 1:		Line 1:
	== ~~Download of tiles~~ ==		== Image destriping with FFT ==

	~~See [[ASTER topography]].~~		In some image maps, artifacts (stripes) are visible. These can be reduced with FFT filtering.

	~~== ASTER GDEM destriping with FFT ==~~

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


Line 11:		Line 7:
	<source lang="bash">		<source lang="bash">
	# set computational region to GDEM map:		# set computational region to GDEM map:
	g.region rast=~~ASTGTM_N53E004_num~~ -p		g.region rast=imagemap -p
	d.mon x0		d.mon x0
	d.rast ~~ASTGTM_N53E004_num~~		d.rast imagemap
	</source>		</source>

Line 19:		Line 15:
	Perform '''Fast Fourier Transform''' (FFT; screenshot upper left map):		Perform '''Fast Fourier Transform''' (FFT; screenshot upper left map):
	<source lang="bash">		<source lang="bash">
	i.fft in=~~ASTGTM_N53E004_num~~ real=~~ASTGTM_N53E004_num_real~~ imag=~~ASTGTM_N53E004_num_imag~~		i.fft in=imagemap real=imagemap_real imag=imagemap_imag
	d.mon x1		d.mon x1
	d.rast ~~ASTGTM_N53E004_num_imag~~		d.rast imagemap_imag
	d.rast ~~ASTGTM_N53E004_num_real~~		d.rast imagemap_real
	</source>		</source>

Line 32:		Line 28:
	d.rast filter		d.rast filter
	r.mask -i filter		r.mask -i filter
	d.rast ~~ASTGTM_N53E004_num_real~~		d.rast imagemap_real
	</source>		</source>

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	'''Inverse FFT''' to get filtered GDEM back (screenshot lower left map):		'''Inverse FFT''' to get filtered GDEM back (screenshot lower left map):
	<source lang="bash">		<source lang="bash">
	i.ifft real=~~ASTGTM_N53E004_num_real~~ imag=~~ASTGTM_N53E004_num_imag~~ output=~~ASTGTM_N53E004_num_filtered~~		i.ifft real=imagemap_real imag=imagemap_imag output=imagemap_filtered
	r.mask -r		r.mask -r
	d.mon x2		d.mon x2
	d.rast ~~ASTGTM_N53E004_num_filtered~~		d.rast imagemap_filtered
	r.colors ~~ASTGTM_N53E004_num_filtered~~ color=elevation		r.colors imagemap_filtered color=elevation
	d.rast ~~ASTGTM_N53E004_num_filtered~~		d.rast imagemap_filtered
	</source>		</source>

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	Calculate the '''differences''' (screenshot lower right diagram):		Calculate the '''differences''' (screenshot lower right diagram):
	<source lang="bash">		<source lang="bash">
	# ~~validade~~ with differences map:		# validate with differences map:
	r.mapcalc "diff = ~~ASTGTM_N53E004_num~~ - ~~ASTGTM_N53E004_num_filtered~~"		r.mapcalc "diff = imagemap - imagemap_filtered"
	r.colors diff color=differences		r.colors diff color=differences
	d.mon x3		d.mon x3
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	</source>		</source>

	[[Image:Grass ~~aster GDEM~~ destriping with FFT.png‎\|450px\|center\|thumb\|Workflow of ~~ASTER GDEM~~ destriping with FFT]]		[[Image:Grass image destriping with FFT.png‎\|450px\|center\|thumb\|Workflow of image destriping with FFT]]

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

Neteler: moved ASTER GDEM destriping to Image destriping

2011-07-29T11:49:30Z

moved ASTER GDEM destriping to Image destriping

← Older revision	Revision as of 11:49, 29 July 2011
(No difference)

Neteler: new

2011-07-29T11:28:28Z

new

New page

== 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):
<source lang="bash">
# set computational region to GDEM map:
g.region rast=ASTGTM_N53E004_num -p
d.mon x0
d.rast ASTGTM_N53E004_num
</source>

Perform '''Fast Fourier Transform''' (FFT; screenshot upper left map):
<source lang="bash">
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
</source>

Create a '''MASK''' in order to remove noise (screenshot upper left map):
<source lang="bash">
# digitize filter mask to reduce noise
r.digit filter
d.rast filter
r.mask -i filter
d.rast ASTGTM_N53E004_num_real
</source>

'''Inverse FFT''' to get filtered GDEM back (screenshot lower left map):
<source lang="bash">
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
</source>

Calculate the '''differences''' (screenshot lower right diagram):
<source lang="bash">
# 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
</source>

[[Image:Grass aster GDEM destriping with FFT.png‎|450px|center|thumb|Workflow of ASTER GDEM destriping with FFT]]

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