How to sum up about 3-4 color frames and only show the brightest frame. Matlab

obj = VideoReader('C:\Users\Robotics\Pictures\Saved Pictures\Lightfile\Prelight.MOV');

for img = 1:obj.NumberOfFrames;
    filename = strcat('frame',num2str(img),'.jpg');
    b = read(obj,img);
    imwrite(b,filename);
end

I have this code that reads the file and get all frames, but I need it to sum up about 3-5 frames then take the brightest frame and store it. Can someone help please!!

[OCDER]

Can you explain what you mean to "sum up 3-5 frames and take the brightest frame"? The sum of 3-5 frames will always be the brightest frame.

Since an image is a matrix, you can simply add images together using matrix math, but use double format (im2double) so that the sum of 3-5 images doesn't exceed the maximum value given a number format (ex: uint8 max value is 255). Rescale all image intensities at the end to prevent flickering effects by inconsistent rescaling.

[Marqual Brown]

Okay, so if I have a video and its 30 seconds long with a flashing light going on and off . I would like the program to capture the frame when the light flashed then output the light that flashed. Each flash is going to have 10-12 frames with the light on but I want to capture the brightest frame of light.

Answer 1

[Walter Roberson]

The below code assumes that the frames are RGB.

The below code does not attempt to detect intervals of flash and determine the best out of the interval: it takes the frames frames_per_group at a time and determines the brightest of that group.

obj = VideoReader('C:\Users\Robotics\Pictures\Saved Pictures\Lightfile\Prelight.MOV');

frameidx = 0;
frames_per_group = 5;
frame_history = [];
frameidx_history = [];
while hasFrame(obj)
    frameidx = frameidx + 1;
    groupidx = groupidx + 1;
    b = readFrame(obj);
    frame_history = cat(4, frame_history, b);
    frameidx_history(end+1) = frameidx;
    if size(frame_history, 4) == frames_per_group
      maxbrightness = -inf;
      maxbrightnessidx = -inf;
      for K = 1 : frame_per_group;
        grayframe = rgb2gray(frame_history(:,:,:,K));
        thisbrightness = sum(grayframe(:));
        if thisbrightness > maxbrightness
          maxbrightness = thisbrightness;
          maxbrightnessidx = K;
        end
      end
      bestframe = frame_history(:,:,:,maxbrightnessidx);
      bestframeidx = frameidx_history(maxbrightnessidx);
      filename = sprintf('frame%04d.jpg', bestframeidx);
      imwrite(bestframe, filename);
      frame_history = [];
      frameidx_history = [];
    end
end

(Code not tested)

[Marqual Brown]

I have sorted through the code and I'm having the problem with the maxbrighnessidx. Not sure what the problem is?

[Walter Roberson]

Please expand on the difficulty?

[Marqual Brown]

What do you mean difficulty?

[Marqual Brown]

okay so I'm working on calculating lightning frames from a video. that's why I need to sum up the frames and get the brightest frame. then store the frame after its summed up.

[Walter Roberson]

The line

        bestframeidx = frameidx_history(maxbrigthnessidx);

should be

        bestframeidx = frameidx_history(maxbrightnessidx);

[Marqual Brown]

Thank you !!! Simple mistake. @Walter

[Marqual Brown]

I have another question, could this also work for an 360 degree camera!!

[Walter Roberson]

I do not know how a 360 degree camera might differ from a regular camera ? Is it just like a fish-eye lens with a single image, or is it multiple images at the same time?