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Calculate pixel value threshold of a single-band image via Otsu's method
Source:R/threshold_otsu.R
threshold_otsu.Rd
Calculate Otsu's threshold value that separates a single-band (e.g. greyscale) image into two distinct classes.
The threshold value is determined by minimizing the combined intra-class variance.
library(terra)
is used to perform out-of-memory operations.
Arguments
- image
Single-band raster to be classified (
SpatRaster
object fromlibrary(terra)
), or a file path to the image to be imported (terra::rast()
will be used).- range
Numeric vector (of length 2) specifying the histogram range to be used for thresholding. Defaults to the minimum and maximum values of the imported raster.
- levels
Number of histogram bins used to calculate the threshold value, typically based on the bit depth of the image (e.g. 8-bit image has
2^8
=256
levels). Defaults to256
.
Value
Otsu's threshold value for the image (a single number), which can subsequently be used for image classification (e.g. convert continuous raster to binary raster).
References
Otsu, N. (1979). A threshold selection method from gray-level histograms. IEEE transactions on systems, man, and cybernetics, 9(1), 62-66. Pau, G., Fuchs, F., Sklyar, O., Boutros, M., & Huber, W. (2010).
EBImage—an R package for image processing with applications to cellular phenotypes. Bioinformatics, 26(7), 979-981.
See also
classify_image_binary()
to classify single-band image using Otsu's method. Callsthreshold_otsu()
internally.
Examples
if (FALSE) {
ndvi_mosaic <- system.file("extdata", "ndvi_mosaic.tif",
package="biodivercity")
terra::plot(ndvi_mosaic) # examine raster data
threshold_otsu(image = ndvi_mosaic)
}