Why the threshold is 0.90 used to obtain the white component from RGB channels ?

 vid = videoinput('winvideo',1, 'YUY2_1280x720');
 thresh = 0.90;
 % Set the properties of the video object
 set(vid, 'FramesPerTrigger', Inf);
 set(vid, 'ReturnedColorspace', 'rgb')
 vid.FrameGrabInterval = 5;
 %start the video aquisition here
 start(vid)
 % Set a loop that stop after 100 frames of aquisition
 while(vid.FramesAcquired<=100)
    % Get the snapshot of the current frame
    data = getsnapshot(vid);
    bwredFrame = imbinarize(data(:,:,1), thresh); % obtain the white component from red layer
    bwgreenFrame = imbinarize(data(:,:,2), thresh); % obtain the white component from green layer
    bwblueFrame = imbinarize(data(:,:,3), thresh); % obtain the white component from blue layer
    diff_im = bwredFrame & bwgreenFrame & bwblueFrame; % get the common region

Answer 1

[Guillaume]

You will have to ask whoever wrote that code why they chose that threshold.

Most likely, the answer will be : because it worked for my particular video

[Steven Lord]

According to Google it looks like this code is from a question posted to MATLAB Answers in 2017, almost exactly two years ago.

And I agree with Guillaume that it's probably a judgment call on the part of that author (or the person from whom they obtained that code) as to what constituted a "white enough" region of their particular video frames. If I were to run that example right now on the view outside my office window trying to detect the (storm) clouds, I'd need to adjust that threshold quite a bit.