I keep trying to convert a video grayscale but it gives me an error?

hi, i want to convert a video into grayscale, but it keeps giving me an error, specifically a "parse_input" error

my code:

%Create a multimedia reader video
readerobj = VideoReader('yourvideo.mp4', 'tag', 'myreader1');
readerobj.Width 
readerobj.Height
% Read in all video frames.
vidFrames = read(readerobj);

% Get the number of frames.
numFrames = get(readerobj, 'NumberOfFrames');

%creat an output video file
v = VideoWriter('peaks.avi');
%Set the output video framerate to the input frame rate
v.FrameRate = readerobj.FrameRate;
open(v);

% Create a MATLAB movie struct from the video frames.
for k = 1 : numFrames
     %get a frame from the video
     frame=vidFrames(:,:,:,k);
     
     
     frame = rgb2gray(frame);
     
     %write the frame to the output video file
     writeVideo(v,frame);
     
     %add the frame to a movie object
     mov(k).cdata = frame;
     mov(k).colormap = [];
     
     
     
     %if you want to save the frame
     %Create Filename to store
     
     
end
%close the output video file. This will finish writing he video file
close(v);
% Create a figure

hf = figure; 

% Resize figure based on the video's width and height
set(hf, 'position', [150 150 readerobj.Width readerobj.Height])

% Playback movie once at the video's frame rate
movie(hf, mov, 1, readerobj.FrameRate);

[Ameer Hamza]

What is the error message? How is vidFrames calculated?

[Ahmed Al-Qarqaz]

never mind someone solved it, but thanks anyway

Answer 1

[Image Analyst]

Instead of rgb2gray(), use read() and pass it the frame number. Should look something like this:

% Loop through the movie, writing all frames out.
for frame = 1 : numberOfFrames
	% Extract the frame from the movie structure.
	thisInputFrame = read(inputVideoReaderObject, frame);
	
	% Display it
	image(thisInputFrame);
        if ndims(thisInputFrame) == 3
            thisInputFrame = rgb2gray(thisInputFrame);
        end
	axis on;
	axis image;
	caption = sprintf('Frame %4d of %d.', frame, numberOfFrames);
	title(caption, 'FontSize', fontSize);
	drawnow; % Force it to refresh the window.
	
	% Resize the image.
	outputFrame = imresize(thisInputFrame, [outputVideoRows, outputVideoColumns]);
	
	% Write this new, resized frame out to the new video file.
	writeVideo(outputVideoWriterObject, outputFrame);
	
	% Update user with the progress.  Display in the command window.
	progressIndication = sprintf('Processed frame %4d of %d.', frame, numberOfFrames);
	disp(progressIndication);
	% Increment frame count (should eventually = numberOfFrames
	% unless an error happens).
	numberOfFramesWritten = numberOfFramesWritten + 1;
end

[Pamudu Ranasinghe]

I add some modifications to the above code of Image Analyst (MVP) and create it as a fuction to use

function RGB2GRAY_VIDEO(input_image_name,output_image_name,percentage_need)
% percentage_need --> if you need to convert Full video use 1
%                      0.5 for 50 % frams from total Frames
%                      Likewise 0.2 for 20% Frames
%                0 < percentage_need <= 1

% Sample Function call
% RGB2GRAY_VIDEO('Video_Input.mp4','Video_out.mp4',0.2)

%Create a multimedia reader video
readerobj = VideoReader(input_image_name, 'tag', 'myreader1');
readerobj.Width 
readerobj.Height

% Get the number of frames.
numFrames = get(readerobj, 'NumFrames');

%creat an output video file
v = VideoWriter(output_image_name);

%Set the output video framerate to the input frame rate
v.FrameRate = readerobj.FrameRate;
open(v);

outputVideoRows =readerobj.Height;
outputVideoColumns =readerobj.Width ;
Total_frames = numFrames;
numFrames = int8(Total_frames*percentage_need);
fprintf("%d Frames Needed from %d of Frames\n",numFrames,Total_frames);
% Loop through the movie, writing all frames out.
for frame = 1 : numFrames
    % Extract the frame from the movie structure.
    thisInputFrame = read(readerobj, frame);
    
    % Display it
    image(thisInputFrame);
    if ndims(thisInputFrame) == 3
        thisInputFrame = rgb2gray(thisInputFrame);
    end
    axis on;
    axis image;
    caption = sprintf('Frame %4d of %d.', frame, numFrames);
    title(caption, 'FontSize', 12);
    drawnow; % Force it to refresh the window.
    
    % Resize the image.
    outputFrame = imresize(thisInputFrame, [outputVideoRows, outputVideoColumns]);
    
    % Write this new, resized frame out to the new video file.
    writeVideo(v, outputFrame);
    
    % Update user with the progress.  Display in the command window.
    progressIndication = sprintf('Processed frame %4d of %d.', frame, numFrames);
    disp(progressIndication);
end
end