How to extract videos after every 1 min interval and then how to subtract specific number of frames from background image.

The Code is :

clear all clc;
Z = imread('background.tif');
VR=VideoReader('traffic02.avi');
NumInFrames=get(VR,'NumberOfFrames');

count=0; 

for (frame=1:60:150)
diff1 =read(VR,frame)-Z;
idx=diff1==0;
out=sum(idx(:));
% if (diff1==0)
  %          count=count+1;
 %end
     break;

end

disp(out);

Answer 1

[Image Analyst]

I don't understand why your code is not doing what you want. Please clarify.

I attach my demo for an example.

[Chetan]

Can you please explain what is alpha and if it is threshold then why it is only 0.5?

Also how background image calculated?

[Image Analyst]

Alpha is a weighting of the current frame and the background frame. I set it at .5 so the new background is an equal proportion of this frame and the prior background. So this have an effect of making prior frames contribute less to the background, so 2 frames ago contributes .25, 3 frames ago contributes .125, and so on.

[Chetan]

Ok.

How to compare different videos?

ie In traffic situations, if density of vehicles on road is more then for that video will take more duration for greeen light.

Thanks in advance.

[Image Analyst]

I haven't done that. The Computer Vision System Toolbox has traffic monitoring capability - it's one of their demos.

I know in my town they switched a few years ago from traditional road sensor loops to a vision based system for controlling traffic signal timing. So there are companies out there with systems already perfected and ready to sell. So either buy one of those, or try to build a system yourself but be aware that you'll have established competition if you plan to sell your system commercially.

[Ilan Moshe]

Hi :)

How can I control the interval time between each frame. It seem that with your demo, we're getting 30 pics per sec, is'nt ?

If I want 1 pic per sec, how can I change it ?

thanks

[Image Analyst]

If you want to change the frame rate in a new movie you create, then

1. Create the VideoReader object
2. Create a new VideoWriter object
3. Specify the frameRate property of the VideoWriter object to be what you want (1 frame per second)
4. Read in the frames one by one from the the VideoReader object
5. Write the frames one by one to the ouput VideoWriter object
6. Close both the VideoReader object and the VideoWriter object

Answer 2

[Walter Roberson]

You need to pass read() the frame number, but instead you are trying to pass it a time in seconds. You need to get the FrameRate property and multiply that by 60 seconds to get the frame number.

Caution: in general, the frame rate will not necessarily be an integer, so the frames corresponding to "1 minute apart" will not necessarily always be the exact same number of frames apart. You can still use

for frame = 1 : 60*FrameRate : 1000

but you need to round() or ceil() the frame number to be sure it is integral. Another way is:

minutes = 0 : 5;   %capture ending at 5 minutes
framenums = unique(1 + floor(minutes * 60 * FrameRate));
for frame = framenums
  ...
end

The unique() avoids reading the same frame twice in a row for situations in which the FrameRate is less than two per minute.

[Image Analyst]

When he says

for (frame=1:60:150)

Why do you think that's the time in seconds rather than the frame number? Of course it's kind of weird that he'd read only 3 frames: frame #1, #61, and #121. Maybe he should do frame=1:NumInFrames to do all the frames.

[Walter Roberson]

I assume it is in seconds because the poster asked to read at 1 minute intervals. That would only correspond to 60 frames if the FrameRate was 1 per second exactly, which is not impossible but seems unlikely.