dot (pixel) pitch and resolution for a LCD monitor - accessibility question

[moniia]

I would like to understand the relation between LCD monitor parameters and physical real world size of objects on the monitor. This has something to do with accessibility, because some monitors display too small font to read comfortably.

On wiki there is the following information:

1280x1024 19" monitor has 0.294 pixel pitch and 86.3 pixels per inch
1920×1080 23" monitor has 0.265 pixel pitch and 95.8 pixels per inch

If I display the same object on both monitors, which one will be larger? I mean real world size, measured by a real world ruler. As an example, let's say After Effects panel's text, E.g. "Effects & Presets". On which monitor this text will be physically larger?

My first thought was that on the lower resolution, 19" monitor the text will be larger. But I am not sure about the pixels per inch part (ppi) which is greater in case of the 23" monitor. In Windows in Control Panel, when changing font dpi from 96 to 120, the font becomes physically larger. So, maybe greater ppi means physically larger font/object, and this would mean that the 23" monitor will display larger objects.

[jagabo]

1280x1024 19" monitor has 0.294 pixel pitch and 86.3 pixels per inch
1920×1080 23" monitor has 0.265 pixel pitch and 95.8 pixels per inch

If I display the same object on both monitors, which one will be larger?

The 19" monitor.

Consider an object that is 86 pixels wide. It will appear as 1 inch wide on the 19" monitor (86 pixels / 86 pixels per inch). But only 86/96" wide on the 23" monitor. That's assuming you're using an operating system that doesn't correct for the pitch of the monitor (Windows).

In Windows in Control Panel, when changing font dpi from 96 to 120, the font becomes physically larger.

Because you're telling it your monitor is 120 DPI so it draws the text larger to make it the same size as the same text on a 96 DPI monitor. Since the pitch of your monitor isn't changing that text will look bigger.

[moniia]

Thanks for explaining!

[jagabo]

By the way, pixel pitch is in millimeters:

86 pixels * 0.294 millimeters per pixel ~= 25 millimeters ~= 1 inch

[AlanHK]

If I display the same object on both monitors, which one will be larger? I mean real world size, measured by a real world rule

It depends on whether the object's size is defined in pixels or a real world unit.

If it's a 500 pixel square jpeg, it will be about 10% smaller at 95.8 pixels/inch than 86.3.

But most text is defined by curves (Truetype, Opentype) and measured in points (1/72 inch), not pixels. So higher dpi means that text is the same size, but will have finer resolution.
But some text, particularly that designed specifically for screens, is bitmapped, and scaled in pixels, So higher resolution makes it smaller.

However; it doesn't end there: the operating system is "aware" of what the screen resolution is and has a default set of fixed pixel size screen fonts that it uses depending on the screen resolution.
And you can usually override that if you want to. (In Windows, r-click on the desktop and choose "Properties".)
You can have large text at high screen resolution if you want.


Applications may just use the operating system defaults for their own text, or may have their own defaults.

To finish where I started: the answer is: it depends.

[jagabo]

But most text is defined by curves (Truetype, Opentype) and measured in points (1/72 inch), not pixels. So higher dpi means that text is the same size, but will have finer resolution.

Windows assumes a 96 dpi monitor. If you attach a monitor with a different pitch it doesn't know unless you tell it. So my 46" HDTV shows text with the same number of pixels as my 23" monitor (both are 1920x1080). But everything is twice as big on the HDTV.