Thresholding for sclera detection on CASIA database

Hi!

I would like to write a sclera matching algorithm and I have to my disposal the CASIA eye image database (version 1) to use. I've read that there exists a method of transforming the picture into grayscale and thresholding it according to hue, saturation and luminance (HSL) threshold to detect the sclera region. My question would be if anyone can tell me the thresholds to use as none of the papers mentions what values to use in order to have a precise sclera detection.

Answer 1

[Image Analyst]

The function you seek is rgb2hsv(). You would most likely threshold both the saturation channel and the value channel. The thresholds you would use depend on the overall brightness of your image. You can use my interactive thresholding application http://www.mathworks.com/matlabcentral/fileexchange/29372-thresholding-an-image to figure out what they would be. If you have control over the lighting in your scene then you can use the same threshold for all images. If the lighting level varies, then you will have to come up with some automatic algorithm that finds the proper spot on the histogram to do the thresholding.