No difference between font size units 'pixels' and 'points'

I noticed when changing the font size of a figure it makes no difference if one chooses pixels or points as units. Is this a known issue or intended?

figure(1)
set(gcf,'Position',[10 10 800 800])
peaks;
fontsize(16,'pixels')

figure(2)
set(gcf,'Position',[10 10 800 800])
peaks;
fontsize(16,'points')

left: figure 1, font size = 16 px; right: figure 2, font size = 16 pt; created using MATLAB Desktop

Interestingly, creating the same figures using the code above in the New Desktop for MATLAB produces 33% bigger font sizes given in points compared to pixels (consistent with the points/pixels size conversion).

left: figure 1, font size = 16 px; right: figure 2, font size = 16 pt; created using New Desktop for MATLAB

[Epsilon]

Hi Jakob,

I could not reproduce this issue in R2024b. I am getting distinct sizes.

Is there something I am missing ?

[Bruno Luong]

Point is 1/72 inche and Pixels unit is OS dependent according to the documentation

"Pixels.

Starting in R2015b, distances in pixels are independent of your system resolution on Windows and Macintosh systems:

• On Windows systems, a pixel is 1/96th of an inch.
• On Macintosh systems, a pixel is 1/72nd of an inch.

On Linux systems, the size of a pixel is determined by your system resolution."

'points'Points. One point equals 1/72nd of an inch.

So On Windows 1 pixel = 72/96 = 0.75 point (test match on my PC), or 1 point = 1.333 pixel.

The code in the question has font larger on the second figure on my PC as well, as expected.

On Mac pixel = 72/72 = 1 point

[Jakob Weis]

Thanks! That makes sense, I am indeed working on a Mac. Interesting, too, that the New Desktop seems to handle pt/px differently.

[Bruno Luong]

Perhaps the New Desktop redefines the pixel unit differently. I don't know New Desktop myself.

Answer 1

[DGM]

I'm not sure how it's doing the scaling internally, but my guess would start here:

% units per em
sz = 16; 

% units per inch
pxpin = get(0,'ScreenPixelsPerInch'); % px/in
ptpin = 72; % pt/in

% inches per em 
szinpx = sz/pxpin

szinpx = 0.1600

szinpt = sz/ptpin

szinpt = 0.2222

That would tell us that on this system, the rendered sizes should differ, but measuring the exact height of 1 em is a bit of a chore unless you know what text features are 1 em high. Instead, we can just measure the ratio of character heights.

% expected ratio of on-screen sizes
ptpin/pxpin

ans = 0.7200

On my machine, the calculated ratio seems to be quite close to the size ratio I can measure from screenshots.

If your reported display resolution were 72, then the rendered sizes would be the same. It seems that would be expected on a Mac.

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