MATLAB plot image margin removal and aspect ratio keeping

Question

I have following code which basically trying to create a video based on a series images of size 256 X 256 X 3, where 3 is the RGB channls:

close all
clc

%% creating image volum
img = phantom(256);
img = repmat(img, [1,1,3]);

figure(1)
vidfile = VideoWriter('testVideo.mp4','MPEG-4');
open(vidfile);

%% loop to ceate images with different colors
for n = 1:120
    a = n/120;
    img(:,:,1) = img(:,:,2)*a;
    img(:,:,3) = img(:,:,2)*(1-a);
    imagesc(img), axis off
    set(gca, 'Position', [0 0 1 1])
    drawnow
    videoFrame(n) = getframe(gcf); 
    writeVideo(vidfile,videoFrame(n));
end

close(vidfile)

However, although I got rid of the margin, I cannot get the image aspect ratio right. The image looks like this:

The goal is to remove the margin of the plot and maintain the aspect ratio of the images. In this case, it should be a square image with size 256 X 256 that looks like this:

Any pointers? Some sample code would be very nice. Thanks!

Answer 1

I'm not sure exactly what you're looking for. The phantom dataset is square, but the phantom image does not occupy the whole dataset; instead, there is a margin on the left and right sides that is greater than on the top and bottom sides. Simply add one line of truesize to the data to plot it as-is will maintain the aspect ratio.

...
imagesc(img), axis off
set(gca, 'Position', [0 0 1 1])
truesize(gcf,[256,256]) % <<<< Just add this
drawnow
...

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

However, you need to do an additional step if you want a circular phantom without a margin.

img = phantom(256);
img = repmat(img(12:245,41:216), [1,1,3]); % <<<< I changed this line

figure(1)
vidfile = VideoWriter('testVideo.mp4','MPEG-4');
open(vidfile);

%% loop to ceate images with different colors
for n = 1:120
    a = n/120;
    img(:,:,1) = img(:,:,2)*a;
    img(:,:,3) = img(:,:,2)*(1-a);
    imagesc(img), axis off
    set(gca, 'Position', [0 0 1 1])
    truesize(gcf,[256,256]) % <<<< I changed this line
    drawnow
    videoFrame(n) = getframe(gcf); 
    writeVideo(vidfile,videoFrame(n));
end

close(vidfile)

That's a chubby phantom.