MATLAB: Why matlab calls (pixel per inch “PPI”) a (dot per inch “DPI”)

MATLAB

why matlab uses the DPI abbreviation for a something called the screen pixels per inch unit,

the DPI term indicates to a something related to printing terminology which is dot ink per inch unit,

is it a mistake or there is an explaination for this?

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the DPI term indicates to a something related to printing terminology which is dot ink per inch unit,

Although it did certainly have that meaning, historically most electronic displays were CRT (Cathode Ray Tubes), and historically those used round-ish pixels created by steering an electron beam, so historically it was dots per inch for displays.

Technology for displays now varies quite a bit. Quite a lot of the technologies use dots of various forms. There are not a lot of display technologies around for which "dot" is technically wrong.

Dots Per Inch is mostly used to refer to physical limitations, whereas Pixels Per Inch is mostly used to refer to logical arrangements. For example my physical display is normally 2560 x 1440, but I can configure it for 1600 x 900 pixels per inch, with the graphics card automatically scaling . As that is a 1.6 ratio, the implication is that the hardware might have subpixels that are not user addressible. Hypothetically individual sub-pixels on the hardware might not have enough brightness or clarity, or there might be too much leak between adjacent wells to make the sub-pixels useful, but having the same level going to multiple sub-pixels in an area might overcome those problems, allowing a variety of pixel sizels (visible units) to be overlayed on hardware dots.

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MATLAB: GUI written without GUIDE: How to make sure layout remains consistent across different displays (different resolutions)

figures and all uicontrols and uipanel can be placed by normalized units. Be sure to specify the Units before the Position.

Fonts, on the other hand, are absolute sizes (points), so when you move to a smaller display text can come out too big for the area you allocated. Accounting for this often requires that you allow a variable-sized area and use the textwrap() function. Key trick: if you put text inside a text control and then ask for the Extent property of the control, the result will be how wide the control would need to be to include all of the text. You will find yourself writing a routine that tosses the desired text into a temporary (invisible) control just to find out how big of a space you need for it so you can determine the Position to use for your real control.

Once you start allocating variable amounts of space for text areas, you will need to start positioning (and sizing) your other controls relative to those spaces. In combination with the fact that it's a real pain to program human-readable position information in normalized units, this will likely lead you to start writing layout routines, especially to position a box to the top right side of another box, and to position a box to the left and underneath another box. You may occasionally need to position in other relative coordinates.

Note that it is not just for different resolutions that you might want to do this. You might also want to do this if you offer the user a choice of fonts or font sizes.

MATLAB: In MATLAB, how to obtain information about the screen resolution and screen size

MATLAB uses certain APIs in order to get information about the size and resolution that the system is using. The information returned is made available to the user through the Root properties 'ScreenSize' and 'Units'. The following example demonstrates how to use these properties:

%Sets the units of your root object (screen) to pixels
set(0,'units','pixels')  
%Obtains this pixel information
Pix_SS = get(0,'screensize')
%Sets the units of your root object (screen) to inches
set(0,'units','inches')
%Obtains this inch information
Inch_SS = get(0,'screensize')
%Calculates the resolution (pixels per inch)
Res = Pix_SS./Inch_SS

On the test machine used for this example, this was the result:

 Res =
        Inf       Inf   96.0000   96.0000

This means that my screen has a resolution of 96 pixels per inch in both the x and y directions.

You can confirm these numbers on a Windows 2000 machine by right-clicking on the desktop and selecting Properties -> Settings -> Screen Area. This will display the number of pixels per inch which should match the number obtained by the command:

Pix_SS = get(0,'screensize')

NOTE: Sometimes inaccuracies creep into the results you may get. This is due to the fact that the system may return incorrect information. If you begin to notice this, you can compensate by updating the video drivers or switching the resolution of the monitor. However, this is rare.

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MATLAB: GUI written without GUIDE: How to make sure layout remains consistent across different displays (different resolutions)

MATLAB: In MATLAB, how to obtain information about the screen resolution and screen size

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