Custom processing within a video preview window

Hi,

I'm trying to perform custom processing on a video preview. However, I'm having trouble utilizing the FramesAcquiredFcn. Although I don't get any errors, the video preview is always the same, unprocessed video preview.

vid = videoinput('pointgrey',1,'Mono8_640x480');
vidRes = get(vid, 'VideoResolution');
imWidth = vidRes(1);
imHeight = vidRes(2);
nBands = get(vid, 'NumberOfBands');
himage = image( zeros(imHeight, imWidth, nBands) );
setappdata(himage,'FramesAcquiredFcn',@mypreview_fcn);
%If I change the name of my processing function (from @mypreview_fcn to anything else, eg @mypreview), I still get no errors, and the same video. Therefore, I tried dropping the handle, @, and just put the name of my function, but this yields an error of "Error using mypreview_fcn Too many output arguments." If I place an output argument into mypreview_fcn, then I get an error that the variable "event" is undefined when I thought it is supposed to be an argument supplied by the preview function.
preview(vid,himage);

my preview function is shown below:

function mypreview_fcn(obj, event, himage)
data = event.Data;
w_s = 5;
SC = stdfilt(data(:,:,1),ones(w_s))./imfilter(double(data(:,:,1)),fspecial('average',w_s),'symmetric');
set(himage,'CData',SC);
end

Please let me know if you have any thoughts, it would be greatly appreciated. Thank you!

Answer 1

[Walter Roberson]

set(vid, 'FramesAcquiredFcn',@mypreview_fcn);

[RPA]

Hi,

Thank you for your response. I inserted your line into my code, but I'm finding that regardless of what I put after the "@" symbol, the preview remains the same, even if I put a function that doesn't exist. The code after incorporating your line looks like this:

vid = videoinput('pointgrey',1,'Mono8_640x480');
vidRes = get(vid, 'VideoResolution');
imWidth = vidRes(1);
imHeight = vidRes(2);
nBands = get(vid, 'NumberOfBands');
himage = image( zeros(imHeight, imWidth, nBands) );
set(vid, 'FramesAcquiredFcn',@mypreview_fcn);
setappdata(himage,'FramesAcquiredFcn',@mypreview_fcn);
%If I change the name of my processing function (from @mypreview_fcn to anything else, eg @mypreview), I still get no errors, and the same video. Therefore, I tried dropping the handle, @, and just put the name of my function, but this yields an error of "Error using mypreview_fcn Too many output arguments." If I place an output argument into mypreview_fcn, then I get an error that the variable "event" is undefined when I thought it is supposed to be an argument supplied by the preview function.
preview(vid,himage);

Perhaps there is something I am missing about the handle (@) syntax. Please let me know if you have any ideas about this. Thank you again!

Answer 2

[Petter Hagqvist]

Very late answer, but I encountered this myself and also found the solution. It might help someone looking for the answer in the future.

You need to add:

start(vid);

Only calling preview() doesn't seem to be enough.