get(gca,'D​ataAspectR​atio') does not refelct the real pixel ratio, and does not upate after stretching the figure window in default auto mode.

Hi, I am using imagesc to show a matrix and want to get the aspect ratio of pixels at that time:

C = [0 2 4 6; 8 10 12 14; 16 18 20 22];
imagesc(C)
a = get(gca,'DataAspectRatio') % [2.0000    1.5000    1.0000] looks not close enough to real display.
aMode = get(gca,'DataAspectRatiomode') %auto

% however, after set the aspect ratio to its original value, the display changed:
set(gca,'DataAspectRatio',a)
% The initial aspect ratio value [2.0000    1.5000    1.0000] is more close to the 2nd image.

C = [0 2 4 6; 8 10 12 14; 16 18 20 22];
imagesc(C)
a = get(gca,'DataAspectRatio') % [2.0000    1.5000    1.0000]
aMode = get(gca,'DataAspectRatiomode') %auto
% I stretch the window, then retrieve the ratio again, but it still the same

a = get(gca,'DataAspectRatio') % [2.0000    1.5000    1.0000]

Why the initial retrieved aspect ratio does not reflect the displayed image and it does not update?

Thanks.

Answer 1

[Walter Roberson]

set(gca,'DataAspectRatio',a)

when you set the DataAspectRatio then DataAspectRatioMode is set to 'manual' -- but the mode must be 'auto' in order for stretch-to-fill behaviour to be active. This is pointed out clearly in daspect