In ADM we are looking to interrogate the finest detail of the displayed image, so the element being examined is an individual pixel. The calculation must then consider the size of the pixel – so we must include vertical resolution in our calculation.
Our variables for ADM, then, are:
- Image height (IH)
- Farthest viewer (FV); and
- Vertical image resolution (IR)
A constant called the Acuity Factor (AF) helps simplify the calculation, with AFADM = 3438 and is a result of simplifying quite complex trigonometric calculations.
The closest viewer for ADM is defined only by the horizontal limits, so image offset is not considered. Your screen should be sited to afford viewers an opportunity to self-select a comfortable viewing position.
As with BDM calculations, the formula can be rearranged to solve for whichever is the missing term, so to calculate image height:
Rearrange the terms to solve for FV:
Rearrange again to identify required minimum resolution for a given image and FV:
- Image Height = 1500mm
- Vertical image resolution = 1080 pixels
- FV = 1500 x 3438 / 1080 = 4775mm
TIP: AVIXA publishes calculators online at https://www.avixa.org/standards/discas-calculators/