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Niblack Thresholding

Source: R/ximgproc.R
niBlackThreshold.Rd

niBlackThreshold performs thresholding on an Image object using Niblack's technique or some of the popular variations it inspired.

Usage

niBlackThreshold(
  image,
  max_value = 255,
  threshold_type = "binary",
  block_size = 31,
  k = 0.5,
  method = "Niblack",
  r = 128,
  target = "new"
)

Arguments

image

An 8-bit (8U) single-channel Image object.

max_value

Non-zero value assigned to the pixels for which the condition is satisfied (default: 255). It is used only if threshold_type is set to "binary" or "inverse".

threshold_type

The name of the threshold type to use. It can be any of the following:

  • "binary":each pixel is replaced by `max_value` if its value is above the threshold, and by zero otherwise (the default).

  • "inverse":each pixel is replaced by zero if its value is above the threshold, and by `max_value` otherwise.

  • "truncate":each pixel is replaced by `threshold` if its value is above the threshold, and is unchanged otherwise.

  • "to_zero":each pixel is replaced by zero if its value is below the threshold, and is unchanged otherwise.

  • "to_zero_inverse":each pixel is replaced by zero if its value is above the threshold, and is unchanged otherwise.

block_size

Size of a pixel neighborhood that is used to calculate a threshold value for the pixel (default: 31). It must be an odd number greater than 1.

k

A user-adjustable parameter used by Niblack and inspired techniques. For Niblack, this is normally a value between 0 and 1 that is multiplied with the standard deviation and subtracted from the mean.

method

A string indicating the binarization method to use. It can be any of the following:

  • "Niblack (the default)"

  • "Sauvola"

  • "Wolf"

  • "Nick"

r

A user-adjustable parameter used by Sauvola's technique. This is the dynamic range of standard deviation.

target

The location where the results should be stored. It can take 3 values:

  • "new":a new Image object is created and the results are stored inside (the default).

  • "self":the results are stored back into image (faster but destructive).

  • An Image object:the results are stored in another existing Image object. This is fast and will not replace the content of image but will replace that of target. Note that if target does not have the same dimensions, number of channels, and bit depth as image, an error may be thrown.

Value

If target="new", the function returns an Image

object. If target="self", the function returns nothing and modifies

image in place. If target is an Image object, the function returns nothing and modifies that Image object in place.

See also

Image, threshold, autothreshold

Author

Simon Garnier, garnier@njit.edu

Examples

balloon <- image(system.file("sample_img/balloon1.png", package = "Rvision"))
balloon_gray <- changeColorSpace(balloon, "GRAY")
balloon_th <- niBlackThreshold(balloon_gray)