Convert live colour video into gray scale video?

Hi,

I am using MATLAB for image processing.I need to have a gray scale video saved in disk. Please can you help me to manipulate the following script in order to give a gray scale video.I changed the set(vid, 'ReturnedColorspace', 'rgb') to set(vid, 'ReturnedColorspace', 'grayscale'), but it shows error (Error using im2frame

Indexed movie frame must have a non-empty colormap).

imaqreset;
%warning('off','all'); %.... diable warining msg ...;
vid = videoinput('winvideo',1, 'YUY2_640x480');
set(vid, 'FramesPerTrigger', Inf);
set(vid, 'ReturnedColorspace', 'rgb');

% vid.FrameRate =30;
vid.FrameGrabInterval = 1; % distance between captured frames
start(vid)

aviObject = VideoWriter('myVideo.avi'); % Create a new AVI file
open(aviObject);
for iFrame = 1:50 % Capture 100 frames
% ...
% You would capture a single image I from your webcam here
% ...

I=getsnapshot(vid);
%imshow(I);
F = im2frame(I); % Convert I to a movie frame
writeVideo(aviObject,F); % Add the frame to the AVI file
end

close(aviObject); % Close the AVI file
stop(vid);

thanks

[Image Analyst]

You forgot to call rgb2gray()

[Koohyar]

Many thanks for your comments, please can you show me where should I call rgb2gray()? it goes to each frame? gray = rgb2gray(vid)?

Answer 1

[Amrtanshu Raj]

Hi,

You can modify your code like this to get the desired results.

CODE :

imaqreset; 
%warning('off','all'); %.... diable warining msg ...; 
vid = videoinput('winvideo',1, 'YUY2_640x480'); 
set(vid, 'FramesPerTrigger', Inf); 
set(vid, 'ReturnedColorspace', 'rgb'); 
% vid.FrameRate =30; 
vid.FrameGrabInterval = 1; % distance between captured frames 
start(vid) 
aviObject = VideoWriter('myVideo.avi'); % Create a new AVI file 
open(aviObject); 
for iFrame = 1:50 % Capture 100 frames 
% ... 
% You would capture a single image I from your webcam here 
% ... 
I=getsnapshot(vid); 
%changes made here
grayimg = rgb2gray(I); % Convert rgb image to grayscale img 
%imshow(I); 
F = im2frame(grayimg); % Convert grayimg to a movie frame 
writeVideo(aviObject,F); % Add the frame to the AVI file 
end 
close(aviObject); % Close the AVI file 
stop(vid); 

[Koohyar]

Hi Raj,

Thanks for this, but still shows error! does it work for you?

Error using im2frame

Indexed movie frame must have a non-empty colormap

Error in recording_video (line 19)

F = im2frame(grayimg); % Convert grayimg to a movie frame

[Koohyar]

my Matlab version is R2020a

[Amrtanshu Raj]

just change the

F = im2frame(grayimg);

to

F = im2frame(grayimg,gray);

[Koohyar]

Awesome! many thanks for your help, it works!

[almog haviv]

Allow an explanation of the code

[Image Analyst]

@almog haviv There are numerous comments all over. What lines are you confused about?