Using your webcam and MATLAB to take pictures

Hey all,

I’ve been messing around with some topics which had me implement some intermediate tools in MATLAB that might just be useful to some of you. Sharing is caring.

Using your webcam and MATLAB to take pictures

For this example you’ll need the Image Acquisition Toolbox and Image Processing Toolbox (the latter only for color space conversion operations). I needed to have a quick way to take pictures from the video feed, so after a couples of minutes fooling around the internet, copying snippets here and there it resulted in

%% Snapshot Acquisition

%data
buffer = {};

%Video acquisition
vInput = videoinput('winvideo',1);
set(vInput,'FramesPerTrigger',1);

% Create a customized GUI.
fHandle = figure('Name', 'Snapshot Taker');
set(fHandle,'WindowButtonDownFcn','buffer = store_image(vInput,buffer);');
uicontrol('String', 'Close', 'Callback', 'close(gcf);delete(vInput)');

% Create an image object for previewing.
vidRes = get(vInput, 'VideoResolution');
nBands = get(vInput, 'NumberOfBands');
hImage = image( zeros(vidRes(2), vidRes(1), nBands) );
preview(vInput, hImage);

In this example, I invoke videoinput('winvideo',1) because my webcam happened to be device number 1 connected to winvideo adapter. This will likely be the rule for most of us, but in case you’re unaware of which adapter should you use, run imaqhwinfo to get more information on all the adapters available to your system. Use then imaqhwinfo(<your_adpator_name>) to check if there are available devices on it. Note that there is a store_image function which is called every time the mouse button is pressed on top of the video feed figure.

function buffer = store_image(vidObject, buffer)

    frame = getsnapshot(vidObject);
    
    %change color space
    frameRgb = ycbcr2rgb(frame);
    
    figure;
    image(frameRgb);
    buffer = [buffer;{frameRgb}];
end

This function receives the video object and the cell array with previously taken pictures, and returns the latter with a new picture appended. It opens a new figure with each snapshot taken. When you are satisfied, you may want to save each image to an individual file. To do that run the following snippet

%Dump buffer as files
for n= 1:numel(buffer)
    I = rgb2gray(buffer{n});
    imwrite(I,['calibration_data/image_',num2str(n),'.tif'],'tif');

end

Notice that in the end I actually store my images in grayscale, so simply remove the line invoking rbg2gray in case you want colored pictures. Finally, here’s a screenshot on how things should like on your screen if everything went as expected.