Performs LOCAL Otsu thresholding on an image, with a user-specified blocksize.
Updated 1 Sep 2016

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Performs LOCAL Otsu thresholding on an image; user can specify blocksize. Facilitates the threshold-segmentation of images with uneven illumination, without the need for background normalization.

SYNTAX: B = thresholdLocally(A,blksz,varargin)

THRESHOLDLOCALLY processes an image, calling graythresh on LOCAL blocks in an image. This facilitates easy thresholding of images with uneven background illumination, for which global thresholding is inadequate. Uses the Image Processing Toolbox function BLOCKPROC (R2009b).

A: Any image (or path/name of an image) suitable for processing with im2bw()
BLKSZ: (Optional) Block size of A, for determination of Otsu thresholding using graythresh(). In the form or [M,N]. Default is as determined by BESTBLK.
1) Any P-V pair accepted by BLOCKPROC.
2) FudgeFactor: a scalar value by which to multiply the local value returned by graythresh.

B: Output image

img = imread('rice.png');
thresholded = thresholdLocally(img);

Cite As

Brett Shoelson (2024). ThresholdLocally (, MATLAB Central File Exchange. Retrieved .

MATLAB Release Compatibility
Created with R2010b
Compatible with any release
Platform Compatibility
Windows macOS Linux

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Version Published Release Notes

Updated license

Minor change to replace default blocksize of [32 32] by that returned by function BESTBLK.

Fixed problem with screenshot. (Image was inappropriately rotated.)

Modified significantly to accept as optional inputs all parameter-value pairs accepted by BLOCKPROC, as well as an additional "fudge factor" parameter that allows one to scale the local graythresh value by a scalar multiple.