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Why does the screensaver get captured when I use GETFRAME on a MATLAB figure window while creating a movie using MATLAB 7.1 (R14SP3)?

Asked by MathWorks Support Team on 13 May 2011

I am creating an AVI movie by using GETFRAME to capture the figure window. However, if my screensaver gets activated while my code is executing, the screensaver gets captured instead of the MATLAB figure window.

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1 Answer

Answer by MathWorks Support Team on 13 May 2011
Accepted answer

This is the expected behavior of GETFRAME. GETFRAME captures the information that is visible on the screen, and hence will capture the screensaver image, or any other window or part of the window that is visible on top of the figure window.

To work around this issue, you may use any of the following alternatives.

1. You may directly use ADDFRAME to add the figure data to the AVI-file using the following algorithm:

 - Create an AVI object using AVIFILE.
 - Draw plots.
 - Use ADDFRAME with the handle to the figure to add the frame to the AVI object.

2. Alternatively, you could capture the figure data using the following algorithm:

 - Create an AVI object using AVIFILE.
 - Draw plots.
 - Use PRINT to export the figure to an image file.
 - Use IMREAD to read the image into MATLAB workspace.
 - Use IM2FRAME to create a frame.

3. Lastly, you may use HARDCOPY to copy the figure. HARDCOPY is an undocumented feature of MATLAB.

For example, for the "ZBuffer" renderer, you may use the following function to capture the figure data:

function cdata = zbuffer_cdata(hfig)
% Get CDATA from hardcopy using zbuffer
% Need to have PaperPositionMode be auto 
orig_mode = get(hfig, 'PaperPositionMode');
set(hfig, 'PaperPositionMode', 'auto');
cdata = hardcopy(hfig, '-Dzbuffer', '-r0');
% Restore figure to original state
set(hfig, 'PaperPositionMode', orig_mode); % end

For the "OpenGL" renderer you can write a similar code. This technique will not work for the "painters" renderer.

Next, replace the use of GETFRAME from your code with IM2FRAME as follows:

F = im2frame(zbuffer_cdata(gcf));

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