how to get the value of a certain pixel-region in video and analyze them?

I have a video of pills moving from left to right slowly. I want to draw a visual line in the original video and when the pills get through that line, the program automatically increase the pills-number by one, namely, n=n+1.

here is my code:

%read the video
      avi = aviread('sample.avi');    
      video = {avi.cdata};  
      pixels = double(cat(4,video{1:end}))/255;
      nFrames = size(pixels,4)

    %convert the video to gray scale

    for f = 1:nFrames           
      pixel(:,:,f) = (rgb2gray(pixels(:,:,:,f))); 
    end

    background=(pixel(:,:,1)+pixel(:,:,2)+pixel(:,:,3))/3;   %get a background picture

    %transfer the video to binary video and counting
    for l = 2:1:nFrames          
      dif(:,:,l)=(abs(pixel(:,:,l)-background));           
      bw(:,:,l) = im2bw(dif(:,:,l), 0.2);  
          **if (0==any(bw(:,314,l))) && (0~=any(bw(:,313,l)))
           n=n+1;
          disp(n)
          end**
    end

however I don't know why the condition "if (0==any(bw(:,314,l))) && (0~=any(bw(:,313,l)))" never get satisfied and the displayed "n" hence equals 0. I am badly in need of help. Thanks all of you.

Answer 1

[Image Analyst]

Reread the help on any for how it handles 2D matrices. Then try something like this:

dif = abs(double(pixel(:,:,l))-background);
bw = im2bw(dif, 0.2);  
if any(any(bw(:,314))) && ~any(any(bw(:,313)))

No need to have dif and bw be a 3D matrix depending on l (which is a bad choice for a variable name since "ell" looks like 1 ("one"). I'm still not sure about the "pixel" variable but I don't have time to look into it now.

[Stephen]

Thank you for your kind reply. In this program, I define "pixel" as the conversion result of the RGB video to gray video.Namely, the matrix of the gray video.