REPORT: Input lag Part 26
From purely logical considerations, all measurements made to date can be estimated in advance. As long as none of the remaining error sources take effect, the ideal photo method should deliver the lowest values of the three photo methods and thereby demonstrate the lowest fluctuations, which is expressed in a small deviation. Since here, figures that are "visible just now" are evaluated, the "minimum estimate ", which has been created with the oscilloscope with the aid of the photo receiver will come closest to this time n. The comparative diagram confirms these considerations roughly:
Comparative overview of all measurement processes.
Nonetheless, the question as to what exactly should be measured is a difficult one: the time until any change on the monitor is visible or only the time the electronics require until the respective pixel is controlled? As a first approximation, this difference was determined for the Samsung 2494HM and is reflected in this special case in a complete denomination. Whilst a total lag of five to six milliseconds was established via photo receiver, including the response time of the panel, it takes just 0.6 milliseconds until a pixel changes its condition in a measurable manner. The measurement could also be refined further by tapping the voltage applied to the respective transistors on an open monitor, which completely excludes the sluggishness of the liquid crystals.
However, without a doubt, it is visible that there is a great difference between the pure signal processing time and the time the monitor requires to display a change in the screen content.
The ideal input lag measurement method, also referred to as the ideal photo method, measures a value the ideal case that covers about half of the response time of the panel and thus indicates the value from which the image content changes visibly. However, through refresh rates and the nature of the signal preparation and output within the graphics cards, additional delays can arise which may separate the results from the real values by up to 16 ms – in extreme cases, even after an average value has been found.
Thus, it is not an option to achieve a precise value for the image processing time in the monitor using a camera. It is only possible to indicate approximate areas in which the input lag of the monitor is likely to be encountered, but subject to a rather large error.
An evaluation of the input lags of monitors using the photo method should thus lead to sorting into rough classes such as the following:
- probably less than 1 frame lag / less than 16 ms lag
- probably one to two frames lag / 16 ms to 32 ms lag
- the lag is probably greater than two frames / greater than 32 ms.
Only the last class should demonstrate clearly noticeable lags in daily usage.
Values which have been arrived using the old methods to date cannot be compared with these values, since their systematic errors alone often exceed the values from the new method multiple times.
It would be ideal for customers if the manufacturers themselves would take on the obligation to determine the actual input lag of the monitors. On the one hand, manufacturers, unlike the test editor, are technically suitably equipped for such a test and are therefore in a position to carry this out, but on the other, erroneous measurement results would not be allowed to make customers more unsure and would make models look worse than they actually are.
This should be equally in the interests of all manufacturers and at the same time, those of the customers.
In the automotive sector, in addition, guide values should be implemented which would establish a maximum image signal processing time before these may be displayed for visual aid measures. Here, the input lag of the monitor used is only one value of many which must be considered, but it is still not something which cannot be ignored.
Here, the personal contribution of the following persons (listed alphabetically and separated by company) deserves particular mention:
Michael Busche (Tektronix Deutschland – Organisation of the trial period)
Bernhard Schmidt-Peltzer (Tektronix Deutschland – Product rollout, triggering)
Trevor J Smith (Tektronix EMEA)
Winfried Schultz (Tektronix Deutschland)
Steffen Prein (Femto – CEO; Measurement of the lag of the OE-200-Si)