Processing Frames from a Video

I have a piece of code where I read an image and then do some processing with it. If I instead have an AVI file, is there a simple way to read the video file, select a chosen frame from it, and then analyse that frame as an image?

III0 = double(imread('Documents\sphereattempt.png'));

III1 = (III0(:,:,3)./(III0(:,:,1)+III0(:,:,2)+III0(:,:,3)));

figure(2);
contourf(flipud(min(max(movmean(movmean(III1,10,2),10,1),0.3),0.5)),[0.3:0.01:0.5]); 
axis equal; 
colorbar

set(gca,'Ydir','reverse')

Answer 1

[David K.]

The VideoReader object looks like the way to go. With the basic case being:

v = VideoReader('example.avi');
while hasFrame(v)
    frame = readFrame(v);
    % processing for each frame goes here
end

Where frame is an individual image. If you want to start from a specific time you can use

v.CurrentTime = 2.5; % time in seconds to start

then use readFrame to get the frame you want.

Something that may go wrong is shown on Supported Video Formats where there is a troubleshooting section talking about how there is a chance that you will need to install some other things if your specific avi format is not currently readable by your matlab install. I have not personally tried any of these methods to fix a format issue.

[Hollis Williams]

So in the processing section it would start

III0 = double(imread('frame'));  ?

[David K.]

Not quite. The readFrame function is taking the place of the imread function in your code. If the video is X by Y pixels and is in color. The output frame from

frame = readFrame(v);

should be a X x Y x 3 uint8 array. So III0 should be

III0 = double(readFrame(v));

to make them the same as your single image.