for loop for videos

Question

Nara Sixty Five 2021-11-28

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https://ww2.mathworks.cn/matlabcentral/answers/1597474-for-loop-for-videos

编辑： Drain Suburu 2021-11-29

i was wondering is there was an easy way to apply a for loop to frames on a video. i am trying to apply a mask on each frame (as if each frame were an image). i dont know if this is important, but i am applying my mask only to part of the image.

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Answer 1

Image Analyst 2021-11-28

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https://ww2.mathworks.cn/matlabcentral/answers/1597474-for-loop-for-videos#answer_841964

NumFrames is a field of video. Use it to construct a for loop over all the frames you want to process.

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Image Analyst 2021-11-28

在 MATLAB Online 中打开

Due to your lack of comments I'm not exactly sure what you're doing but I tried to repair your code as best I could in a short time:

% Create a VideoReader object.
video=VideoReader('rhinos.avi')
% Get the number of frames in the video.
frameCount= video.NumFrames
% Read first frame.
firstFrame = readFrame(video);
% Convert to gray scale if necessary.
[rows, columns, numberOfColorChannels] = size(firstFrame)
if numberOfColorChannels == 3
    firstFrame = rgb2gray(firstFrame);
end
% imhist(firstFrame);
% Threshold the frame to create a binary image.
x = [100 200];
y = [100 220];
% t = 255 * graythresh(firstFrame) % Automatic threshold.
threshold = 200;
% Extract image within the box.
Aroi = firstFrame(y(1):y(2),x(1):x(2));
imhist(Aroi);
% Threshold it.
Aroi = uint8(255 * Aroi<threshold);
% Assign binarized image to frame within the box.
firstFrame(y(1):y(2), x(1):x(2)) = Aroi;
imshow(Aroi);
for k = 1 : frameCount
    % Read next frame and convert to gray scale if necessary.
    thisFrame = readFrame(video);
    if ndims(thisFrame) == 3
        thisFrame = rgb2gray(thisFrame);
    end
    % Create lol - some cryptically named thing.
    % First find out rows and columns where the frame is pure white.
    [whiteRows, whiteColumns]=find(thisFrame==255);
    if isempty(whiteRows)
        break
    end
    % Call the findok() custom written function.
    [ok, thisFrame] = findok(whiteRows(1),whiteColumns(1), thisFrame,[]);
    ok = reshape(ok,2,length(ok)/2);
    % Assign results to this row of the lol matrix.
    lol(:, k) = sum(ok,2) / size(ok,2);
    % Display current frame and lol
    subplot(2, 1, 1);
    imshow(thisFrame)
    subplot(2, 1, 2);
    imshow(lol, []);
    drawnow;
end
hold on
scatter(lol(2,:),lol(1,:),'fill')

Image Analyst 2021-11-29

@Nara Sixty Five I see you removed your code. So I assume you no longer need my help. If you do however, I'm attaching all my video processing demos that I have so far.

Drain Suburu 2021-11-29

编辑：Drain Suburu 2021-11-29

Hi, sorry I am no longer using that account. Thanks for sharing these demos. If you can still help, my question remains. I posted it here with the code and vids.

https://www.mathworks.com/matlabcentral/answers/1598034-video-for-loops-with-masking

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