CRImage (version 1.20.0)

createBinaryImage: Thresholding

Description

Creates a binary image from a grayscale image by thresholding.

Usage

createBinaryImage(imgG,img=NULL,method="otsu",threshold=NULL,numWindows=1,whitePixelMask=c())

Arguments

img

An Image object or an array.

imgG

The grey valued Image object.

method

Either "otsu" or "phansalkar"

threshold

Fixed threshold

numWindows

Number of windows to use for threshold calculation.

whitePixelMask

Boolean mask of white pixels, if they should be excluded from thresholding

Value

The binary image.

Details

The functions returns the binary image resulting from the thresholding. If threshold is defined, all pixels smaller than this value will be fixed to 1 all other values will be set to 0. If threshold is undefined, the thresholding value is calculated automatically using 'otsu' or 'phansalkar' thresholding.

The function 'otsu' does Otsu thresholding on the grey level histograms of the image. The function 'phansalkar' does thresholding using the mean and standard deviation of a specified window. The thresholding is done on the RGB as well as the LAP color space and the results are ORed. The window size is dim(img)/numWindows. White pixel can be excluded from thresholding (e.g. if white is background) by defining a whitePixelMask

References

Neerad Phansalkar, Sumit More, Ashish Sabale, Dr. Madhuri Joshi, "Adaptive Local Thresholding for Detection of Nuclei in Diversly Stained Cytology Images," 2011 IEEE International Conference in Communications and Signal Processing (ICCSP), pp. 218, 10 Feb. 2011

Nobuyuki Otsu: A threshold selection method from grey level histograms. In: IEEE Transactions on Systems, Man, and Cybernetics. New York 9.1979, S.62-66. ISSN 1083-4419

Examples

f= system.file("extdata", "exImg.jpg", package="CRImage")
img=readImage(f)
#conversion to grayscale
imgG=EBImage::channel(img,"gray")
imgB=createBinaryImage(imgG,img=img,method="otsu",numWindows=4)
#white pixel mask
whitePixelMask=img[,,1]>0.85 & img[,,2]>0.85 & img[,,3]>0.85
#exclude white pixels from thresholding
imgB=createBinaryImage(imgG,img=img,method="otsu",numWindows=4,whitePixelMask)
#phansalkar threshold
imgB=createBinaryImage(imgG,img=img,method="phansalkar",numWindows=4)