How to make imshow function faster in the for loop?

I want to generate a video in the figure window with its original sound, and I extracted total of 6600 frames from the video and saved them in the folder 'VideoFrames' with name 'p1' to 'p6600'.

Below in the for loop I call imshow to display each frame as they "become" the video, but they still are not at the same pace as the sound.

The imshow function takes most of time to run in the profiler, so it's necessary to improve the step of displaying images.

Below is the part of code:

[Y, Fs] = audioread('FruitVideo.mp4'); 
sound = audioplayer(Y, Fs); % get the audioplayer object
for j = 1:6600 % total frames are 6600
        % get each frame image by using the path name & file in index
        imageData = strcat('D:\ProgramFiles\MATLAB\InterDir\NetVideos\VideoFrames\p', num2str(j), '.bmp');
        % read each frame image
        framImage = imread(imageData);
        % display each frame in the loop
        imshow(framImage);
        % After #40 of frame, playing the sound, 
        % but the images still generates slower than the sound
        if j == 40
           sound.play;
        end
end

Answer 1

[Walter Roberson]

To make imshow() faster...

Don't call imshow()

Seriously: imshow() has a lot of overhead.

Instead, call image() once and record the handle. Then each iteration through the loop, set the CData property of the image() object to the new data to be displayed.

Reminder: store your directory name in a variable, and use fullfile() to create the path.

imageData = fullfile(ImageDirectory, "p" + i + ".bmp");

[William Wang]

Thanks for this help!

I tried for image() getting object, and I notice that bmp format might have different return type of array making image() to display differently.

The format of image file matters, so I might need a little conversion of the file data, or can I use ".jpg" instead?

[Walter Roberson]

[Y, Fs] = audioread('FruitVideo.mp4');
ImageDirectory = 'D:\ProgramFiles\MATLAB\InterDir\NetVideos\VideoFrames';
sound = audioplayer(Y, Fs); % get the audioplayer object

for j = 1:6600 % total frames are 6600
        % get each frame image by using the path name & file in index
        imageData = fullfile(ImageDirectory, "p" + j + ".bmp");
        % read each frame image
        framImage = imread(imageData);
        % display each frame in the loop
        if j == 1
          h = image(framImage);
        else
            h.CData = framImage;
        end
        drawnow()
        % After #40 of frame, playing the sound, 
        % but the images still generates slower than the sound
        if j == 40
           sound.play;
        end
end