Figure automatically scales by 2

Hi, I set my figure as below:

    figure(1)
    set(gcf,'units','pixels','position',[0,0,512,512]);

However, the popped figure window has resolution 1024x1024. When I try to get the result as a matrix:

    F = getframe (gcf,[0,0,512,512]);
    [img, ~] = frame2im (F);

I would like to get img with resolution 512x512x3, but I get its value as 1024x1024x3.

Is there anyway to solve this problem?

[xiaojuezi]

It seems to be my screen (retina). When I switched to a different screen, this gives the right plot. But how could I fix the figure size regardless the screen resolution?

[Tommy]

I apologize, I misunderstood the issue! MATLAB is 'DPI-aware' so when you plot your figure, it will be scaled according to your display.

Edit: If you are only concerned with keeping the resolution of img at 512x512, might this work?

newImg = img(1:end/512:end, 1:end/512:end, :);

I'd be surprised if this gave the same result as when you create the figure on your other screen (to be honest I'm not sure, I suppose it depends on how exactly MATLAB utilizes the extra space) but with this you could cherry-pick pixels to create a 512x512 image which at least captures the features of img.

[Walter Roberson]

https://www.mathworks.com/help/matlab/creating_guis/dpi-aware-behavior-in-matlab.html

For

• Windows® systems in which the display dots-per-inch (DPI) value is set higher than 96
• Macintosh systems with Apple Retina displays

When you set the Units property of a graphics or UI object to 'pixels', the size of each pixel is now device-independent on Windows and Macintosh systems:

• On Windows systems, 1 pixel = 1/96 inch.
• On Macintosh systems, 1 pixel = 1/72 inch.

(My Mac happens to be one of the last non-Retina models, so I am not affected by this... which also means that I cannot test work-arounds.)

[xiaojuezi]

Thank you all ! I think it is a problem of macos, when explicitly setting '-r72' or '-r96' for different os, the problem is solved.