Select ROI (Region Of Interest) from a video, and extracting rgb values

Hi,

I am wondering if there is a way that I can analyze a region of interest in a video and extract the rgb value in that video? Thank you.

Answer 1

[Nihal Reddy]

I understand you want to first select the Region of Interest(ROI) from a video and then extract RGB values from the selected ROI.

The first step would be to split the videos into frames and then select the region of interest using the “drawrectangle” function in each of the frames.

You can refer to following MATLAB documentation link for more details about “drawrectangle” function-

https://www.mathworks.com/help/images/ref/drawrectangle.html

As the second step, you can use the “imcrop” function to crop the selected ROI from the frames.

You can refer to following MATLAB documentation link for more details about “imcrop” function-

https://www.mathworks.com/help/images/ref/imcrop.html

To extract the RGB values from the selected ROI, the steps are as follows-

The imread function will read any image :

A = imread('myimage.jpg'); 

Then for the RGB values you can use the sample code below:

R = A(:,:,1);  
G = A(:,:,2);  
B = A(:,:,3); 

The red layer R is the first slice, blue B is the second slice, and green G is the third slice.

Answer 2

[Image Analyst]

See attached demos.

[Shu-An Hsieh]

Thank you! This is very cool! I am wondering in which part of the third code you can involve chosing a ROI inside.

[Image Analyst]

I don't. I just use the entire image. If you wanted to you could crop thisFrame to some rectangular region using indexing or imcrop().

thisFrame = thisFrame(row1:row1, col1:col2, :);

Or you could have a binary image with some irregular shape to use as a mask.

meanGrayLevels(frame) = mean(grayImage(mask));

[Shu-An Hsieh]

Thank you!

Another question I have is that how can you separate the rgb into separate plots? I try to use the subplot but it did not work.