custom preview function for video data

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GEO GEP 2012-7-4

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https://ww2.mathworks.cn/matlabcentral/answers/42742-custom-preview-function-for-video-data

Hello, i m trying to write a custom preview function for processing video data. Due to camera constraints i can only use one resolution.. However video data within preview function can be processed at lower resolutions.

The problem is a strange axe flicker when subsampling/viewing the original video data for processing.. I was able to reproduce it by using a web camera and a simple script:

function test002
close all;clear all;
vid = videoinput('winvideo');
hFig = figure;
subsample=2;
vidRes = get(vid, 'VideoResolution');
imWidth = vidRes(1)/subsample;
imHeight = vidRes(2)/subsample;
nBands = get(vid, 'NumberOfBands');
hImage = image( zeros(imHeight, imWidth, nBands) );
setappdata(hImage,'UpdatePreviewWindowFcn',@mypreview_fcn);
preview(vid, hImage);
end
function mypreview_fcn(obj,event,himage)
data=event.Data;
subsample=2;
data_sub=data(1:subsample:end,1:subsample:end,:);
set(himage,'CData',data_sub);
end

Any ideas?? (tried doubleBuffering, and resizing figure)

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GEO GEP 2012-7-4

surprisingly substituing 'UpdatePreviewWindowFcn' by 'FramesAcquiredFcn' solves the flickering problem, but introduces lag due to (constant) memory access (one frame per trigger)

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