Measurements between grays
Afterglow mainly affect games and movies. With games or other activities, screen pixels constantly change from one color shade to another, such as light green to dark green, red, blue, etc.
If we take a closer look at pixels, we see that they are made up of three sub pixels, a red, green and blue. Each sub-pixel is a liquid crystal cell with a color filter. So it’s possible to assimilate these sub-pixels to gray cells with color applied at the last moment to obtain colors on the screen.
In this line of thinking, it would be interesting to add the measurement of response times in changing from grey to white and grey to another color. We only kept the 10 – 90 % part of the signal. Results were interesting in that response time doubles depending on the colors tested.
How to interpret the graph
The Y axis represents response time measured by adding rising + fall time.
The X axis starts at 0 and goes up to 255, with increments of 32. The indices represent different colors, where 0 = black, 255 = white and all intermediate values correspond to different shades of grey.
The Z axis only includes three values, 0 (black), 128 (average grey), and 255 (white). These are the reference colors.
For example with the Iiyama screen, the 24 millisecond time found at the intersection of the color 0 and 96 was measured in this test: color 96 to 0 black (rising time) + 0 black to 96 (fall time).
Some of the graph’s response times appears at 0. This happens when two colors are identical or when the difference is too small to get an accurate measurement. For this particular case we put the response time at 0 and the result is ignored.
Finally, each graph is followed by a table for further interpretation. Included is the response time following the ISO norm and our measurement, which is the average of all response times found between gray. Min and Max are the minimum and maximum response time measured in the test.
Iiyama AS4314UTG
Measured response time follows a certain logic. Smaller response times were measured from 0 (black) and they increase when the final color is lighter.
Response time measured varied from 24 to 56 milliseconds with an average of 38 milliseconds.
LG L1920B
IPS screens have the reputation of having a similar response time between all colors. We realize here that this is partly true. The gap between “min and max” is reduced compared to other technology, but the maximum response time is still almost two times larger than the minimum.
The LG screen seems faster than the Iiyama. This time the average response time is 30 ms.
Philips 190S5
TN technology is well known to be the least stable. Our measurements confirm this reputation and the gap between the minimum and maximum response time is almost three times more.
Samsung SyncMaster 193P
Measurements are quite stable but also high, whether from black, white or average grey. The highest response times were with intermediate grays.
Results compilationWith response times between colors, ratings are already different from the one obtained following the ISO norm.
It is closer to the visual test results, but still not the right one. Even if the LG screen’s min max response times are inferior to the Iiyama screen’s, the Iiyama remains the fastest for games.
Also it would seem illogical to find the same response time for the Iiyama and Philips. With the first screen it’s possible to play UT2004, while with the other it’s much more difficult.
Finally, the measured response time doesn’t really provide useful results. Measurements from white to black and between grays don’t resemble the visual test’s results. So why can’t we evaluate a screen’s performance with such a method?
