can anyone explain this code? what is meant by imagesc?

 for a = 1:size(video,4)
     imagesc(video(:,:,:,a));    
 axis image off    
 drawnow;
 end;

[Stephen23]

"image with scaled colors":

https://www.mathworks.com/help/matlab/ref/imagesc.html

Note that your favorite internet search engine can find the MATLAB documentation just as easily as mine.

[sai likhitha GOdina]

please explain the enter code... i didn't understand that code

[Image Analyst]

The code is explained in the answers below. Did you see them?

[Adam]

I don't understand the relevance of your chosen tags so if you can't be bothered to give some helpful tags to guide people who might help you why do you expect other people to spend more time on your question than you do?!

doc for
doc size
doc imagesc
doc axis 
doc drawnow

take you to help pages for the various parts of that code. Just saying 'I don't understand' is the lazy approach. What in particular do you not understand, having read the documentation?

[Stephen23]

"...having read the documentation" and also tried the examples, so that you know what each function/operator does.

[sai likhitha GOdina]

please explain the for loop and then imagesc

[Jan]

@sai likhitha GOdina: Please do not post a question multiple times. Do you see my answer in your thread https://www.mathworks.com/matlabcentral/answers/332153-can-anyone-explain-this-code-this-code-is-related-to-my-project-crowd-density-estimation? It was a complete waste of time to type this, because Image Analyst has explained it already very good.

This is very basic Matlab code. Please read the Getting Started chapters of the documentation and https://matlabacademy.mathworks.com/ . It would not be efficient to explain the absolute basics in the forum, when there are very good tutorials available already.

Answer 1

[Image Analyst]

imagesc() is a display routine that scales the image to your display range (0-255) and displays it in the current (last used) axes. Your video is a 4-D array where the last index is the frame number. For RGB images I don't believe imagesc() does any scaling, though for gray scale images it does. So imagesc() is just like image() and imshow() for color images. I always use imshow() since for gray scale images imagesc() applies some weird colormap by default (though not for color images).

The third index is the color channel: 1 for red, 2 for green, and 3 for blue. This code does not have any comments and used not very descriptive variable names so it may be hard to understand what's going on. video(:,:,:,a) is the a'th frame of the video and it will be a full color RGB image. The colon means "all", so it's all rows, all columns, and all 3 color channels, which means a full color image.

The code could be written clearer like this:

% Get the total number of video frames.
totalNumberOfFrames = size(video,4)
% Loop over all frames displaying them as fast as possible.
for frameNumber = 1 : totalNumberOfFrames
    thisColorFrame = video(:, :, :, frameNumber);
    imagesc(thisColorFrame);    
    axis image off    
    drawnow; % force immediate repainting of the screen.
end

[sai likhitha GOdina]

thanks!

Answer 2

[Tom Pryke]

Its displaying the data contained in the array 'video' to whatever the current figure or axes object is. The 4th dimension of video contains the number of frames and the others presumably contain the image data.

[sai likhitha GOdina]

1:size(video,4) means?

[Guillaume]

You're asking extremely basic questions. Honestly, if you can't figure out for yourself what it means, you stand no chance of being able to write your own code.

Jan's provided a very good link in your identical question to the getting started tutorial. Grabbing a book on matlab from your favourite library would help as well.