Provided by: grass-doc_7.8.2-1build3_all 
NAME
i.pansharpen - Image fusion algorithms to sharpen multispectral with high-res
panchromatic channels
KEYWORDS
imagery, fusion, sharpen, Brovey, IHS, HIS, PCA
SYNOPSIS
i.pansharpen
i.pansharpen --help
i.pansharpen [-slr] red=name green=name blue=name pan=name output=basename method=string
bitdepth=integer [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-s
Serial processing rather than parallel processing
-l
Rebalance blue channel for LANDSAT
-r
Rescale (stretch) the range of pixel values in each channel to the entire 0-255 8-bit
range for processing (see notes)
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
red=name [required]
Name of raster map to be used for <red>
green=name [required]
Name of raster map to be used for <green>
blue=name [required]
Name of raster map to be used for <blue>
pan=name [required]
Name of raster map to be used for high resolution panchromatic channel
output=basename [required]
Name for output basename raster map(s)
method=string [required]
Method for pan sharpening
Options: brovey, ihs, pca
Default: ihs
bitdepth=integer [required]
Bit depth of image (must be in range of 2-30)
Options: 2-32
Default: 8
DESCRIPTION
i.pansharpen uses a high resolution panchromatic band from a multispectral image to
sharpen 3 lower resolution bands. The 3 lower resolution bands can then be combined into
an RGB color image at a higher (more detailed) resolution than is possible using the
original 3 bands. For example, Landsat ETM has low resolution spectral bands 1 (blue), 2
(green), 3 (red), 4 (near IR), 5 (mid-IR), and 7 (mid-IR) at 30m resolution, and a high
resolution panchromatic band 8 at 15m resolution. Pan sharpening allows bands 3-2-1 (or
other combinations of 30m resolution bands like 4-3-2 or 5-4-2) to be combined into a 15m
resolution color image.
i.pansharpen offers a choice of three different ’pan sharpening’ algorithms: IHS, Brovey,
and PCA.
For IHS pan sharpening, the original 3 lower resolution bands, selected as red, green and
blue channels for creating an RGB composite image, are transformed into IHS (intensity,
hue, and saturation) color space. The panchromatic band is then substituted for the
intensity channel (I), combined with the original hue (H) and saturation (S) channels, and
transformed back to RGB color space at the higher resolution of the panchromatic band. The
algorithm for this can be represented as: RGB -> IHS -> [pan]HS -> RGB.
With a Brovey pan sharpening, each of the 3 lower resolution bands and panchromatic band
are combined using the following algorithm to calculate 3 new bands at the higher
resolution (example for band 1):
band1
new band1 = ----------------------- * panband
band1 + band2 + band3
In PCA pan sharpening, a principal component analysis is performed on the original 3 lower
resolution bands to create 3 principal component images (PC1, PC2, and PC3) and their
associated eigenvectors (EV), such that:
band1 band2 band3
PC1: EV1-1 EV1-2 EV1-3
PC2: EV2-1 EV2-2 EV2-3
PC3: EV3-1 EV3-2 EV3-3
and
PC1 = EV1-1 * band1 + EV1-2 * band2 + EV1-3 * band3 - mean(bands 1,2,3)
An inverse PCA is then performed, substituting the panchromatic band for PC1. To do this,
the eigenvectors matrix is inverted (in this case transposed), the PC images are
multiplied by the eigenvectors with the panchromatic band substituted for PC1, and mean of
each band is added to each transformed image band using the following algorithm (example
for band 1):
band1 = pan * EV1-1 + PC2 * EV1-2 + PC3 * EV1-3 + mean(band1)
The assignment of the channels depends on the satellite. Examples of satellite imagery
with high resolution panchromatic bands, and lower resolution spectral bands include
Landsat 7 ETM, QuickBird, and SPOT.
NOTES
The module works for 2-bit to 30-bit images. All images are rescaled to 8-bit for
processing. By default, the entire possible range for the selected bit depth is rescaled
to 8-bit. For example, the range of 0-65535 for a 16-bit image is rescaled to 0-255). The
’r’ flag allows the range of pixel values actually present in an image rescaled to a full
8-bit range. For example, a 16 bit image might only have pixels that range from 70 to
35000; this range of 70-35000 would be rescaled to 0-255. This can give better visual
distinction to features, especially when the range of actual values in an image only
occupies a relatively limited portion of the possible range.
i.pansharpen temporarily changes the computational region to the high resolution of the
panchromatic band during sharpening calculations, then restores the previous region
settings. The current region coordinates (and null values) are respected. The high
resolution panchromatic image is histogram matched to the band it is replaces prior to
substitution (i.e., the intensity channel for IHS sharpening, the low res band selected
for each color channel with Brovey sharpening, and the PC1 image for PCA sharpening).
By default, the command will attempt to employ parallel processing, using up to 3 cores
simultaneously. The -s flag will disable parallel processing, but does use an optimized
r.mapcalc expression to reduce disk I/O.
The three pan-sharpened output channels may be combined with d.rgb or r.composite. Colors
may be optionally optimized with i.colors.enhance. While the resulting color image will
be at the higher resolution in all cases, the 3 pan sharpening algorithms differ in terms
of spectral response.
EXAMPLES
Pan sharpening comparison example
Pan sharpening of a Landsat image from Boulder, Colorado, USA (LANDSAT ETM+ [Landsat 7]
spectral bands 5,4,2, and pan band 8):
# R, G, B composite at 30m
g.region raster=p034r032_7dt20010924_z13_20 -p
d.rgb b=p034r032_7dt20010924_z13_20 g=lp034r032_7dt20010924_z13_40
r=p034r032_7dt20010924_z13_50
# i.pansharpen with IHS algorithm
i.pansharpen red=p034r032_7dt20010924_z13_50 green=p034r032_7dt20010924_z13_40
blue=p034r032_7dt20010924_z13_20 pan=p034r032_7dp20010924_z13_80
output=ihs321 method=ihs
# ... likewise with method=brovey and method=pca
# display at 15m
g.region raster=ihs542_blue -p
d.rgb b=ihs542_blue g=ihs542_green r=ihs542_red
Results:
R, G, B composite of Landsat at 30m R, G, B composite of Brovey sharpened image at 15m
R, G, B composite of IHS sharpened image at 15m R, G, B composite of PCA sharpened image at 15m"
Pan sharpening of LANDSAT ETM+ (Landsat 7)
LANDSAT ETM+ (Landsat 7), North Carolina sample dataset:
# original at 28m
g.region raster=lsat7_2002_10 -p
d.mon wx0
d.rgb b=lsat7_2002_10 g=lsat7_2002_20 r=lsat7_2002_30
# i.pansharpen with IHS algorithm
i.pansharpen red=lsat7_2002_30@PERMANENT \
green=lsat7_2002_20 blue=lsat7_2002_10 \
pan=lsat7_2002_80 method=ihs \
output=lsat7_2002_ihs
# display at 14.25m
g.region raster=lsat7_2002_ihs_red -p
d.erase
d.rgb r=lsat7_2002_ihs_red g=lsat7_2002_ihs_green b=lsat7_2002_ihs_blue
# compare before/after (RGB support in "Advanced"):
g.gui.mapswipe
# optionally color balancing:
i.colors.enhance r=lsat7_2002_ihs_red g=lsat7_2002_ihs_green b=lsat7_2002_ihs_blue
SEE ALSO
i.his.rgb, i.rgb.his, i.pca, d.rgb, r.composite
REFERENCES
• Original Brovey formula reference unknown, probably...
Roller, N.E.G. and Cox, S., (1980). Comparison of Landsat MSS and merged MSS/RBV
data for analysis of natural vegetation. Proc. of the 14th International
Symposium on Remote Sensing of Environment, San Jose, Costa Rica, 23-30 April, pp.
1001-1007
• Amarsaikhan, D., Douglas, T. (2004). Data fusion and multisource image
classification. International Journal of Remote Sensing, 25(17), 3529-3539.
• Behnia, P. (2005). Comparison between four methods for data fusion of ETM+
multispectral and pan images. Geo-spatial Information Science, 8(2), 98-103.
• Du, Q., Younan, N. H., King, R., Shah, V. P. (2007). On the Performance Evaluation
of Pan-Sharpening Techniques. Geoscience and Remote Sensing Letters, IEEE, 4(4),
518-522.
• Karathanassi, V., Kolokousis, P., Ioannidou, S. (2007). A comparison study on
fusion methods using evaluation indicators. International Journal of Remote
Sensing, 28(10), 2309-2341.
• Neteler, M, D. Grasso, I. Michelazzi, L. Miori, S. Merler, and C. Furlanello
(2005). An integrated toolbox for image registration, fusion and classification.
International Journal of Geoinformatics, 1(1):51-61 (PDF)
• Pohl, C, and J.L van Genderen (1998). Multisensor image fusion in remote sensing:
concepts, methods and application. Int. J. of Rem. Sens., 19, 823-854.
AUTHORS
Michael Barton (Arizona State University, USA)
with contributions from Markus Neteler (ITC-irst, Italy); Glynn Clements; Luca Delucchi
(Fondazione E. Mach, Italy); Markus Metz; and Hamish Bowman.
SOURCE CODE
Available at: i.pansharpen source code (history)
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© 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual