For every project with multitouch screens, the technical question of the optimum resolution should be clarified at an early stage. After all, the user of the multitouch screen is only an arm’s length away from the image surface and not up to several meters away, as is usual with a passive screen such as a television. So what needs to be considered so that the screen’s resolution does not appear pixelated to the user, who is used to the highest resolutions from his smartphone?.
Calculation of the optimal resolution
There are two essential variables to consider in the calculation: First, the viewing distance, that is, how many cm distance between the eye and the screen. Secondly, the pixel density, i.e. how many pixels the screen has per unit area.
Apple has created a quasi-standard with the definition of its “Retina display”. The goal is to increase the pixel density until the human eye is no longer able to recognize individual pixels from a typical viewing distance. The viewer should therefore have the impression of a “perfect picture”. Accordingly, Apple achieves or even exceeds the Retina resolution in its products like the iMac 5K or the iPhone 7.
Recommended resolution for multitouch screens
If you apply this principle to a multitouch screen with a viewing distance of about 80 cm, it’s clear: you can’t achieve Retina resolution with pixel densities that are common today. A 55-inch full-HD screen, for example, only has a pixel density of 40 ppi (pixels per inch). This only achieves about 37% of the Retina standard. The pixels are clearly visible for the user. As a result, texts look pixelated and pictures or videos do not appear clear either. Such a screen is therefore out of the question for a high-quality multitouch table, for example.
Ultra-HD 4K resolution should be standard for multitouch tables
An ultra-HD screen, with twice as many pixels on the same area, still comes to 80 ppi, which is about 74% of the Retina standard. That is not perfect, but already relatively close. A user has to look very closely at a viewing distance of 80 cm to recognize individual pixels. Fonts appear sharp and pictures as well as videos detailed.
Since the pixel density decreases again with larger screens, such as 65 inches, and this size is also disproportionately more expensive than 55 inches, these should only be used in a multi-touch tablet in justified cases. It won’t be too long until new screen generations also enable a double pixel density in large formats at affordable prices. Then, multitouch screens will also meet the Retina standard 100% and more.
(The infographic on resolution and pixel density for multitouch screens is part of the large multitouch infographic from Garamantis).