Image Acquisition Toolbox

Alpha Blending Streamed Image Pairs

This example shows how to capture streaming images from an image acquisition device, perform on-line image processing on each frame and display the processed frames.

The result is an alpha blend of two images, one a stationary pendulum, the other a pendulum in motion, making moving features appear transparent.

This example requires Image Processing Toolbox™.

Step 1: Capture A Background Image

Log and display a snapshot of the background with no moving features.

% Access an image acquisition device.
vidobj = videoinput('winvideo', 1, 'RGB24_320X240');

% Using the preview window, properly position the camera.
preview(vidobj)
pause(1)

% Capture an image with no moving features.
background = getsnapshot(vidobj);

% Display the background image in a figure window.
imshow(background);

Step 2: Process Logged Data

Using the acquired image data, perform on-line image processing, and display the processed images in a figure window.

For each streamed image frame, calculate the linear combination between that frame and the background image. The linear combination effectively alpha blends the two images so any moving features appear transparent.

% Set the object into motion.
pause(2);

% Configure the figure to produce flash-free rendering.
fig = gcf;
fig.DoubleBuffer = 'on');

% Configure the acquisition.
vidobj.FramesPerTrigger = 20;

% Start the acquisition.
start(vidobj)

% While logging data, perform a linear combination between
% the current and background images.
current = getdata(vidobj, 1);
transparent = imlincomb(0.5, current, 0.5, background);

% Display the processed image.
imshow(transparent);

% Repeat for all remaining images.
while (vidobj.FramesAvailable > 0),
    % Perform a linear combination between the current and background images.
    current = getdata(vidobj, 1);
    transparent = imlincomb(0.5, current, 0.5, background);

    % Display the processed image.
    imshow(transparent);
end

% Once the video input object is no longer needed, delete
% it and clear it from the workspace.
delete(vidobj)
clear vidobj