MATLAB Answers

Deep P
0

histogram of a video file

Asked by Deep P
on 9 Oct 2017
Latest activity Commented on by Walter Roberson
on 26 Jul 2019
Hello,
Is it possible to plot a histogram of a video file? Please give me inputs.

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2 Answers

Answer by Walter Roberson
on 9 Oct 2017
 Accepted Answer

Use videoreader to open the video file, and readFrame() to read each frame. Process each frame to extract the information you want to take the histogram of. Calculate the histogram. Display it. Use drawnow() so it shows up. Proceed to the next frame.

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Deep P
on 10 Oct 2017
can u give the sample code please. Also I was referring to examples given in matlab documentation. https://www.mathworks.com/help/matlab/import_export/read-video-files.html can you please explain why we have to create a struct s and what is cdata and colormap there?
Also how to plot histogram of individual frame?
Thank you.
Walter Roberson
on 10 Oct 2017
That example code is creating an in-memory "movie" to be played. It happens that the in-memory movie display routine, movie(), works with a structure array of movie frames, where each frame independently can be RGB or grayscale or pseudocolor. The field named cdata is used to store the actual numeric frame data, and the field named colormap is used to store the pseudocolor colormap that applies to that one frame. When an rgb entry is being provided, the colormap field can be left as []
You do not have the same needs: you are not displaying images like that, you are displaying histograms.
Example:
filename = 'rhinos.avi';
obj = VideoReader(filename);
fig = figure();
ax = axes('Parent', fig);
while hasFrame(obj)
thisframe = readFrame(obj);
imhist(thisframe);
drawnow();
end

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Answer by sohab azhar on 25 Jul 2019

following code is showing eror in the line imhist(thisframe).

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sohab azhar on 26 Jul 2019
i want histgram of an video , i have tried many codes but all codes have some problems.
Walter Roberson
on 26 Jul 2019
So if I understand correctly, you need a program with the following properties:
  • must handle every possible kind of video in the world
  • must solve all of the bugs inherent in those formats, and all of the bugs from every program in the world that writes those videos
  • must have unlimited ability to create histograms from the videos, including being able to operate on all possible colorspaces
  • the program must already exist, or at the very least be available within a day from now, without you having to write any of the code
Good luck on that.

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