How to write frames into video after applying bounding box ?

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Bipasha Kundu 2021-11-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1597609-how-to-write-frames-into-video-after-applying-bounding-box

评论： Image Analyst 2021-11-28

I have a video file from where I need to track an object in each frame. I have successfully done that using (rectangle('Position',[st.BoundingBox(1),st.BoundingBo). I have total 300 frames from that video and I need to write the images containing bounding box within the for loop.

for k=1: nframes

. . .. . .. .. .. . .. . .. .. . . .. .. . .

obj=bwareafilt(~dilated1, 1, 'largest');

figure(1);

imshow(I);

hold on

st = regionprops(obj, 'BoundingBox' );

BB = st(1).BoundingBox;

K=rectangle('Position',[st.BoundingBox(1),st.BoundingBox(2),st.BoundingBox(3),st.BoundingBox(4)],...

'EdgeColor','r','LineWidth',2 );

end

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Answer 1

Image Analyst 2021-11-28

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https://ww2.mathworks.cn/matlabcentral/answers/1597609-how-to-write-frames-into-video-after-applying-bounding-box#answer_842209

在 MATLAB Online 中打开

Just burn them in. Like if you want it white

row1 = ceil(BB(2));
row2 = row1 + BB(4) - 1;
col1 = ceil(BB(1));
col2 = col1 + BB(3) - 1;
obj(row1:row2, col1) = 255;
obj(row1:row2, col2) = 255;
obj(row1, col1:col2) = 255;
obj(row2, col1:col2) = 255;
% Write this frame out to a new video file on disk.
writeVideo(videoWriterObject, obj);

See attached demos if you need more help in using writeVideo().

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Bipasha Kundu 2021-11-28

Hello Sir, this was helpful informations. because the position of the bounding box changes in every frame, i created a empty array as a placeholder at the beginning of the for loop. I was planning saving each frames into that array to write a video at the end. All of the frames are in grayscales. The problem i am runninh into after post processing when i save the image into an empty array, it not not saving with the boinding box.

placeholder = zeros([size(I,1) size(I,2) 1 nframes], class(I));

for k = 1:nframes

% processing binary image

A=pre processed original_frame

imshow(A);

hold on;

st = regionprops(obj, 'BoundingBox' );

BB = st(1).BoundingBox;

rectangle('Position', [BB(1),BB(2),BB(3),BB(4)], 'EdgeColor','b','LineWidth',2 );

placeholder(:, :, k) = A (k) ;

end

The bounding boxes are not being saved in the placeholder array and they did a mismatch of the sizes.

Image Analyst 2021-11-28

ExtractMovieFrames.m

Correct. And the reason is that your code above totally ignores my suggestion. Why aren't you assigning the rows and columns to obj, and using writeVideo() like I suggested?

You can save the image to a frame movie structure instead of saving just the bare image alone, if you want. That's how I did it in the attached demo where I built a movie from individual saved image files.

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