Detecting white color in moving video

What change I have to do in given code below to detect white color from video and get it's brightness.

 snap_red = imsubtract(snap(:,:,1), rgb2gray(snap));

Answer 1

[Image Analyst]

See my demo http://www.mathworks.com/matlabcentral/fileexchange/28512-simple-color-detection-by-hue It would be something like this

hsvImage = rgb2hsv(double(rgbImage));
h = hsvImage(:,:,1);
s = hsvImage(:,:,2);
v = hsvImage(:,:,3);
whitePixels = s < 0.2 & v > 0.8;

or something like that.

whitePixels is a binary image, or "mask". Feel free to modify the parameters.

See my demo where I track a green Sharpie pen.

[KDN]

Thanks nice work, but I am getting error while running video.

[Image Analyst]

It works for me. Was that for my demo video, or for one of yours? If you put a breakpoint on this line and execute it,

% Setup other parameters
numberOfFrames = videoObject.NumberOfFrame;

what does it say numberOfFrames is? Is the videoObject a valid object?