In the beginning, there was ISO...
ISO, the International Organization for Standardization, is a network of 146 countries. Its main activity is to establish technical norms.
The flat screen norm is named ISO 13406-2. This 150 page massive volume indicates the guidelines to follow regarding dead pixels, contrast ratios, viewing angles etc. This norm also indicates the procedure to measure screen response time, representative of screen reactivity. It also determines how fast the screen displays pictures. The lower the response time (measured in milliseconds) the less afterglow a screen should have. Afterglow is a trail of light left behind bright objects in motion (it is particularly characteristic of old laptops).
The norm stipulates to obtain the overall monitor response time, add the measured rising and fall time. In practice, this involves measuring the change from a white to a black pixel and then the reverse. The extreme parts of the signal are then subtracted to keep the 10% to 90% part of the signal.
The ISO measurementWe followed the norm’s instructions. It’s not possible to directly obtain the measurement as the first operation is to calibrate a screen’s colors. This is imperative to do or the measurement could include “dark grey – light grey” instead of “black - white”. This situation could give radically different results from one setting to another.
Once calibrated (with the manufacturer’s brightness level), here are the results of each screen:
If this classification is compared to the visual test of games and films:
The order is completely reversed. First in the visual test, the Iiyama is last with the ISO measurement. The Samsung and Philips provide equivalent results. So if there was still a doubt, now we know that the ISO norm isn’t representative of a screen’s real quality and characteristics.
These results demonstrate another interesting point. Besides the LG, none of the screens gave its claimed response time, which means that panel manufacturers left the ISO norm or at least changed it. If we take a closer look at a screen’s specifications, the indicated response time often goes along with a “typ”. In this way it’s important to understand that a response time measurement isn’t from white to black and vice versa but between two grays. This changes results.
