How can I update values from a variable that updates constantly to a table?

Basically, I am looking at a video with 1200 frames. I have a function which only picks out the frames of interest (e.g. frame 61,101,175,etc...). How do I plot all the values of 'frame' on a table? (Keep in mind that the value of 'frame' updates!)

[Bob Thompson]

I'm assuming you have some kind of loop that views each frame so you can identify which ones are of interest. Could you not just add an if statement to that loop which saves the value of frame to an array?

[ESIDOR PASHAJ]

Hi Bob. That's correct. I tried to do that but instead of saving all the different values of 'frame', it only saves one (the last one). I would appreciate if you could help with some code as I'm pretty new to Matlab. Thanks

[Bob Thompson]

What Walter Roberson posted is basically what I was thinking. Essentially, within your for loop for all frames you will want to have a condition such that IF an interesting frame is found THEN an index value is increased, and the data for the frame is stored as that new increased index in your storage array.

By having the index increase within the if statement it should only increase when an interesting frame is found, rather than for all frames in the movie. This will help keep your array of interesting frames short, but the increasing index will ensure the data is added to the array, rather than overwriting.

Answer 1

[Walter Roberson]

number_of_frames - 1200;
interesting_frames = cell(number_of_frames, 1);
interesting_frame_numbers = zeros(number_of_frames, 1);

interesting_frames_found = 0;

for frame_number = 1 : number_of_frames
   thisframe = ... get frame #frame_number from video object
   if frame_is_interesting(thisframe)
      interesting_frames_found = interesting_frames_found + 1;
      interesting_frames{interesting_frames_found} = thisframe;
      interesting_frame_numbers(interesting_frames_found) = frame_number;
   end
 end

   interesting_frames(interesting_frames_found+1:end) = [];
   interesting_frame_numbers(interesting_frames_found+1:end) = [];

[Walter Roberson]

Note that I pre-allocate here to the maximum size, and then shorten down to the size actually used. If you knew a maximum smaller number of "interesting" frames you could use that. The overhead per cell entry is about 104 bytes so cells are not free -- but a wasted cell is a lot more efficient than having to copy all of the data around because you were expanding an array on the fly.