using peekdata or getdata for live video stream

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Kassidy Lundy 2018-1-16

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评论： Kassidy Lundy 2018-1-18

Hi,

I'm having a lot of trouble processing frames from a continuous feed in real time. I want to first get the pixel data from each 100th frame using either the peekdata function or the getdata function. However, my code only seems to return the information for one frame rather than every hundred frames. This is what I came up with so far:

    while isrunning(vid) == 1
    if mod(vid.FramesAcquired,100) == 0 
           for i = vid.FramesAcquired/100
           Frame100(i) = peekdata(vid,1); 
           regionsprops(Frame100(i));
end
end
end

Does anyone have any insight?

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回答（1 个）

Walter Roberson 2018-1-16

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peekdata() returns a height by width by bands by frames numeric matrix. You are trying to store that matrix into a single location Frame(i) . That is going to cause an error unless you have set your ROI to be a single pixel on a greyscale image.

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Walter Roberson 2018-1-17

编辑：Walter Roberson 2018-1-17

https://www.mathworks.com/help/imaq/peekdata.html

"The number of frames available to peekdata is determined by recalling the last frame returned by a previous peekdata call, and the number of frames that were acquired since then."

This implies that if you want to peek a frame you cannot peek with a lower frame count and then go back to peek with a larger count to get more of the recent frames.

But I think I am getting confused here. What is the state of the Running property at the time you are trying to do the peekdata ?

Kassidy Lundy 2018-1-18

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Hello!

I apologize for asking any questions that should have obvious answers but thank you for putting the potential issues with the if statement into context. Does that mean that there is no fool proof way to do any analysis of every nth frame? Should I possibly consider doing something like this (I'm mostly way off base):

if mod(vid.FramesAcquired,100) == 0
data = peekdata(vid,100);
% find the nearest 100th frame
framevalue = vid.FramesAcquired-mod(vid.FramesAcquired,100);
%find average of frames
avgdata (framevalue,:) = mean(data);
analysis = regionprops(avgdata(framevalue,:));

As for the running property is, there is live video input coming in so the variable "vid" is running during the time that I am trying to process the incoming frames.

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