Stretch — stretch • terra

Linear or histogram equalization stretch of values in a SpatRaster.

For linear stretch, provide the desired output range (minv and maxv) and the lower and upper bounds in the original data, either as quantiles (minq and maxq, or as cell values (smin and smax). If smin and smax are both not NA, minq and maxq are ignored.

For histogram equalization, these arguments are ignored, but you can provide the desired scale of the output and the maximum number of cells that is used to compute the histogram (empirical cumulative distribution function).

Usage

# S4 method for class 'SpatRaster'
stretch(x, minv=0, maxv=255, minq=0, maxq=1, smin=NA, smax=NA,
    histeq=FALSE, scale=1, maxcell=500000, filename="", ...)

Arguments

x: SpatRaster
minv: numeric >= 0 and smaller than maxv. lower bound of stretched value
maxv: numeric <= 255 and larger than maxv. upper bound of stretched value
minq: numeric >= 0 and smaller than maxq. lower quantile bound of original value. Ignored if smin is supplied
maxq: numeric <= 1 and larger than minq. upper quantile bound of original value. Ignored if smax is supplied
smin: numeric < smax. user supplied lower value for the layers, to be used instead of a quantile computed by the function itself
smax: numeric > smin. user supplied upper value for the layers, to be used instead of a quantile computed by the function itself
histeq: logical. If TRUE histogram equalization is used instead of linear stretch
scale: numeric. The scale (maximum value) of the output if histeq=TRUE
maxcell: positive integer. The size of the regular sample used to compute the histogram
filename: character. Output filename
...: additional arguments for writing files as in writeRaster

Value

SpatRaster

Examples

r <- rast(nc=10, nr=10)
values(r) <- rep(1:25, 4)
rs <- stretch(r)
s <- c(r, r*2)
sr <- stretch(s)