Combine red, green, and blue color bands to make a composite GRaster

This function takes as arguments three rasters typically representing red, green, and blue color bands, and returns a single raster with values based on their combination. Typically, this raster should be plotted in grayscale.

Usage

# S4 method for class 'GRaster'
compositeRGB(r, g = NULL, b = NULL, levels = 256, dither = FALSE)

Arguments

r, g, b

Either:

• One GRaster with one band each for r, g, or b representing red, green, and blue color bands; or

• r is single GRaster with 3 bands (R, G, and B bands), and g and b are NULL.

levels

Either a single value that is an integer, or a vector of integers: Number of levels of red, green, and blue intensities represented in r, g, and b. If a single value is supplied, it is assumed that all three have the same number of levels. If three values are supplied, then they correspond to the R, G, and B bands. The default is 256 (assume that R, G, and B rasters have values between 0 and 255).

dither

Logical: If TRUE, apply Floyd-Steinberg dithering. Default is FALSE.

Value

A GRaster.

See also

plotRGB(), terra::plotRGB(), GRASS manual page for module r.composite (see grassHelp("r.composite"))

Examples

if (grassStarted()) {

# Example data
madElev <- fastData("madElev") # elevation raster
madLANDSAT <- fastData("madLANDSAT") # multi-layer raster
madRivers <- fastData("madRivers") # lines vector

# Convert SpatRaster to GRaster and SpatVector to GVector
elev <- fast(madElev)
rivers <- fast(madRivers)
landsat <- fast(madLANDSAT)

# Plot:
plot(elev)
plot(rivers, add = TRUE)

# Histograms:
hist(elev)
hist(landsat)

# Plot surface reflectance in RGB:
plotRGB(landsat, 3, 2, 1) # "natural" color
plotRGB(landsat, 4, 1, 2, stretch = "lin") # emphasize near-infrared (vegetation)

# Make composite map from RGB layers and plot in grayscale:
comp <- compositeRGB(r = landsat[[3]], g = landsat[[2]], b = landsat[[1]])
grays <- paste0("gray", 0:100)
plot(comp, col = grays)

}