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Pan Sharpen Imagery / Image Fusion

Source: R/panSharpen.R
panSharpen.Rd

provides different methods for pan sharpening a coarse resolution (typically multispectral) image with a higher reolution panchromatic image. Values of the pan-chromatic and multispectral images must be of the same scale, (e.g. from 0:1, or all DNs from 0:255)

Usage

panSharpen(img, pan, r, g, b, pc = 1, method = "brovey", norm = TRUE)

Arguments

img

SpatRaster. Coarse resolution multispectral image

pan

SpatRaster. High resolution image, typically panchromatic.

r

Character or Integer. Red band in img. Only relevant if method!='pca'

g

Character or Integer. Green band in img. Only relevant if method!='pca'

b

Character or Integer. Blue band in img. Only relevant if method!='pca'

pc

Integer. Only relevant if method = 'pca'. Which principal component to replace. Usually this should be the first component (default). Only if the first component is dominated by something else than brightness it might be worth a try to use the second component.

method

Character. Choose method from c("pca", "ihs", "brovey").

norm

Logical. Rescale pan image to match the 1st PC component. Only relevant if method = 'pca'. If TRUE only min and max are matched to the 1st PC. If FALSE pan will be histogram matched to the 1st PC.

Value

pan-sharpened SpatRaster

Details

Pan sharpening options:

  • method='pca': Performs a pca using rasterPCA. The first component is then swapped for the pan band an the PCA is rotated backwards.

  • method='ihs': Performs a color space transform to Intensity-Hue-Saturation space, swaps intensity for the histogram matched pan and does the backwards transformation.

  • method='brovey': Performs Brovey reweighting. Pan and img must be at the same value scale (e.g. 0:1, or 0:255) otherwise you'll end up with psychodelic colors.

Examples

library(terra)
library(ggplot2)

## Fake panchromatic image (30m resolution covering
## the visible range (integral from blue to red))
pan       <- sum(lsat[[1:3]])
ggR(pan, stretch = "lin") 


## Fake coarse resolution image (150m spatial resolution)
lowResImg <- aggregate(lsat, 5)


## Brovey pan sharpening
lowResImg_pan <- panSharpen(lowResImg, pan, r = 3, g = 2, b = 1, method = "brovey")
lowResImg_pan
#> class       : SpatRaster 
#> dimensions  : 310, 287, 3  (nrow, ncol, nlyr)
#> resolution  : 30, 30  (x, y)
#> extent      : 619395, 628005, -419505, -410205  (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=utm +zone=22 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
#> source(s)   : memory
#> names       : B1_dn_pan, B2_dn_pan, B3_dn_pan 
#> min values  :  47.20757,  18.43627,  11.80072 
#> max values  : 191.12757,  87.47762,  85.39481 
## Plot 
ggRGB(lowResImg, stretch = "lin") + ggtitle("Original")
#> Warning: data length [3534] is not a sub-multiple or multiple of the number of columns [58]

ggRGB(lowResImg_pan, stretch="lin") + ggtitle("Pansharpened (Brovey)")
#> Warning: data length [88350] is not a sub-multiple or multiple of the number of columns [287]