Undefined function 'preview' for input arguments of type 'struct'.

Hai I am using Back round subtraction method on frame.Now I want to see the preview of these frames.But Error is occured " Undefined function 'preview' for input arguments of type 'struct'. This is code:

if true
for i = 2:numFrames

    %fr = vid(i).cdata;
    % read in frame 
    fr= read(vid, i);

    fr_bw = rgb2gray(fr);       % convert frame to grayscale 
    fr_diff = abs(double(fr_bw) - double(bg_bw));  % cast operands as double to avoid negative overflow 
    threshHold=mean(fr_diff);%Experimetn
    for j=1:width                 % if fr_diff > thresh pixel in foreground 
        for k=1:height 
            if ((fr_diff(k,j) > threshHold)) 
                fg(k,j) = fr_bw(k,j); 
            else 
                fg(k,j) = 0; 
            end 
        end 
    end
     bg_bw = fr_bw; %store old frame to bg_bw variable

     imshow(fr_bw);
    figure(1),subplot(3,1,1),imshow(fr) 
    subplot(3,1,2),imshow(fr_bw) 
    subplot(3,1,3),imshow(uint8(fg)) ;
     z=i-1;

    q(z) = im2frame(uint8(fg),gray(256));            % put frames into movie
   preview((q(z)));

end end

Answer 1

[Guillaume]

preview does not appear to be a function of base matlab nor any of its toolboxes, so it must be a function that you've written yourself. Make sure that it is visible to matlab by adding its folder to matlab's path.

Answer 2

[Steven Lord]

There are a couple of objects in MATLAB that have preview methods. For instance, video input objects in Image Acquisition Toolbox have a preview method as do DatabaseDatastore objects in Database Toolbox and general datastore objects in MATLAB.

But there's no preview function or method for struct arrays.