panSharpen: Pan Sharpen Imagery / Image Fusion

Description

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)

Value

pan-sharpened SpatRaster

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.

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

Run this code

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
## Plot 
ggRGB(lowResImg, stretch = "lin") + ggtitle("Original")
ggRGB(lowResImg_pan, stretch="lin") + ggtitle("Pansharpened (Brovey)")

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