Originally Posted by borf
That's perfectly valid if taken by itself. Like you said, hz don't matter if the duty cyle is long
The only reason you need 72hz is because the duty cycle must be short
to avoid blur. So within the context of this theoretically motion-perfect LCD i'v been talking about, you need 72hz (minimum) to avoid flicker.
The following are my theories:
Firstly, what I was trying to establish with my last post is that the best way to display any given source with a set frame rate, sans interpolation of frames or another method to increase the number of unique frames, is to display each frame for the time necessary to have a high enough duty cycle to avoid flicker in one single duration, if this is possible. This is in opposition to what is the mainstream practice which involves repetition of frames, because current tech is incapable of actively altering duty cycle; it is set in stone, determined only by hz, because of the physical properties of the tech, namely fall time in a CRT. Here is a practical example: I'll continue to use 24fps. In order to display 24fps/hz with a 10% duty cycle you must display each individual frame/hz 0.00416(repeating) seconds. In this case that time is also equal to the hold time. Conversely with 24fps displayed at 72hz each hz must be displayed for 0.00138(repeating) seconds in order to accomplish a 10% duty cycle. This figure, however, does not represent the hold time as each frame is displayed 3 times meaning the hold time is equal to 0.00138+0.00138+0.00138 which is 0.00416(reapeating). Because hold time is equal to the 24fps example motion handling should be the same. Duty cycle is also equal, meaning the screen is lit for the same percentage of time and flicker is also equal.
The reason I went into such meticulous detail is because this also relates to my second point, that being that if duty cycle is actively managed hz has no bearing on flicker and that duty cycle does not have to be "long", it just has to be optimal. Duty cycle, as it relates to flicker, will also be optimal regardless of hz
. In this scenario the number of unique frames will determine hold time and thus be the sole factor in determining blur. In LCD this could be accomplished with backlight scanning provided you have a fast enough rise and
fall time. Another example: for this scenario let us say that 10% is optimal duty cycle for flicker simply because it will be easy to work with mathematically. As stated previously with 10% duty cycle 24hz's hold time will be 0.00416(repeating). Duty cycle could be either lowered or raised according to preference; lower duty cycle and hold time is lowered meaning motion handling is greater but more flicker will be evident. The most optimal scenario is one that involves optimal duty cycle for flicker with enough unique frames to lower hold time to the desired motion handling level. If the desired hold time is 1/240th of a second, and 10% is optimal duty cycle the number of fps needed is equal to 24(1/24=0.0416*0.1 is equal to 1/240. If flicker is
evident at 10% duty cycle more unique frames would be needed, e.g. if 50% duty cycle is required the number of unique frames required to meet the quoted sufficiently low hold time is equal to 120(1/120=0.0083*0.5 = 1/240)