Paradigm Touchscreen DPI and object size calculator

Introduction

Paradigm touchscreens (P-TS7) or monitors (used with VTS or P-TSI) have varying dots per inch (DPI), and if an object is created with the same pixel dimensions but used on screens with different DPI, the resulting size of the object displayed on screen will be also be different. For a consistent user experience you should size objects on different size screens to display with the same physical dimensions. You'll need to calculate each screen's DPI and enter that with a few other pieces of information into math formulas to determine what the object size should be in pixel dimensions within ControlDesigner.

Things you'll need to know:

• The screen resolution in pixels (example: 1366 wide x 768 high)
• The screen's size (diagonal dimension) in inches. (example: 18.5")
  • NOTE: the diagonal dimension may be slightly different than the manufacturer's model name/number may indicate. For example a P-TS18 has an 18.5" diagonal. It's best to measure the display (without including the bezel/border)
• Desired width and height of the object in inches (example: 1" x 5/8")

Math behind DPI and Object Size

The first step of calculating DPI is to find the diagonal pixel count (DCP) by applying the Pythagorean Theorem. The example will use the values from a P-TS18.

√(pixel width²) + (pixel height²) = DCP
Example: √(1366²) + (768²) = 1567.09

Next divide the DCP by the screen's diagonal dimension to determine DPI

DCP / Screen Size = DPI
Example: 1567.09 / 18.5 = 84.7

Lastly determine the object size (in pixels) by separately multiplying the the desired width and height (in inches) by the DPI. Since pixels only display in whole numbers, round the result up/down.

Width Inches * DPI = Width (Pixels)
Example: 2 * 85.7 = 169 pixels

Height Inches * DPI = Height (Pixels)
Example: 0.625 * 85.7 = 53 pixels

Thus an object that needs to be 2"x5/8" (0.625) on a P-TS18 must be 169 pixels wide by 53 pixels high. Contrast this to a P-TS7 which has a DPI of 133.28, resulting in an object that needs to be 267 pixels wide by 83 pixels high to have the same physical dimensions as the object on the P-TS18.

DPI and Object Size Calculator

Below is a calculator you can leverage to help figure out your object sizes. Enter the info in decimal form to all the fields and click [Calculate]. The [Reset] button will clear all values to default.