Thresholding

Compute a threshold to divide the values of a SpatRaster into two groups, and use that threshold to classify the raster.

# S4 method for class 'SpatRaster'
thresh(x, method="otsu", maxcell=1000000, combine=FALSE, 
      as.raster=TRUE, filename="", ...)

Arguments

x

SpatRaster

method

character. One of "mean", "median" or "otsu" for Otsu's method

maxcell

positive integer. Maximum number of cells to use to compute the threshold

combine

logical. If TRUE the layers of x are combined to compute a single threshold

as.raster

logical. If TRUE a classified SpatRaster is returned. Otherwise the threshold(s) are returned

filename

character. Output filename

...

additional arguments for writing files as in writeRaster

Value

numeric or SpatRaster

References

Otsu, N. (1979). A Threshold Selection Method from Gray-Level Histograms. IEEE Transactions on Systems, Man, and Cybernetics, 9(1), 62-66. doi:10.1109/TSMC.1979.4310076

See also

divide

Examples

s <- rast(system.file("ex/logo.tif", package="terra"))
thresh(s, "mean", as.raster=FALSE)
#>      red    green     blue 
#> 182.2855 185.3509 192.8046 
thresh(s, "mean", combine=TRUE, as.raster=FALSE)
#> [1] 186.8136


plot(thresh(s, "otsu"))