MATLAB: Color Tracking in MATLAB – RGB

color tracking

Hi,
I wrote code to track colors in MATLAB. The code plots three circles (Red, Blue, and Green) that follow the motion of colors moving on in front of the web cam (R, B, G). Red and blue work perfectly, but green does not. Any ideas? Here is my code after I set up the video acquisition:
 % Get snapshot of current frame
    snap = getsnapshot(vid);
    % Extract red by subtracting red from grayscale
    snap_red = imsubtract(snap(:,:,1), rgb2gray(snap));
    snap_blue = imsubtract(snap(:,:,3), rgb2gray(snap));
    snap_green = imsubtract(snap(:,:,2), rgb2gray(snap));
    % Filter out noise
    snap_red = medfilt2(snap_red, [3 3]);
    snap_blue = medfilt2(snap_blue, [3 3]);
    snap_green = medfilt2(snap_green, [3 3]);
    % Convert new snapshot to binary
    snap_red = im2bw(snap_red,0.18);
    snap_blue = im2bw(snap_blue,0.18);
    snap_green = im2bw(snap_green,0.18);
    % Remove pixles less than 300px
    snap_red = bwlabel(snap_red, 8);
    snap_blue = bwlabel(snap_blue, 8);
    snap_green = bwlabel(snap_green, 8);
    % Label all connected components
    bw_red = bwlabel(snap_red,8);
    bw_blue = bwlabel(snap_blue,8);
    bw_green = bwlabel(snap_green,8);
    % Properties for each labeled region
    stats_red = regionprops(bw_red, 'BoundingBox','Centroid');
    stats_blue = regionprops(bw_blue, 'BoundingBox','Centroid');
    stats_green = regionprops(bw_green, 'BoundingBox','Centroid');
    % Display new image
    drawnow
    % Puts red objects in rectangular box
    for object_red = 1:length(stats_red)
        bb_red = stats_red(object_red).BoundingBox;
        bc_red = stats_red(object_red).Centroid;
        plot(bc_red(1),-bc_red(2),'or')
        axis([0 300 -300 0])
    end
    hold on
    % Puts blue objects in rectangular box

    for object_blue = 1:length(stats_blue)
        bb_blue = stats_blue(object_blue).BoundingBox;
        bc_blue = stats_blue(object_blue).Centroid;
        plot(bc_blue(1),-bc_blue(2),'ob')
        axis([0 300 -300 0])
    end
    % Puts blue objects in rectangular box
    for object_green = 1:length(stats_green)
        bb_green = stats_green(object_green).BoundingBox;
        bc_green = stats_green(object_green).Centroid;
        plot(bc_green(1),-bc_green(2),'og')
        axis([0 300 -300 0])
    end
    hold off

Best Answer

Subtracting from the grayscale version of the image is a bad way to find the green, or any color for that matter. You need to look at the difference between the color you want and the average of the other two. For example this might give a better green signal:
greenDifference = abs(greenChannel - (redChannel + blueChannel)/2);
Then threshold on that. Cast them all to double first so you don't get any clipping.
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