Your explanation is good, though a little long!Falkentyne wrote:Now, by increasing the vertical total, you are now INCREASING the size of the vertical synchronization area. Display-corner calls it "making the vertical synchronization phase LONGER". By doing this, you make the strobe pulse at the top start at the same spot, but the strobe pulse for the next frame start closer to the bottom, and in case of VT 1500, actually pushing the next phase just barely OFF the screen, because by extending the synchronization phase, the next strobe pulse is now offscreen and you have more of the screen area (1080 lines) visible without both crosstalk border pulses on the screen. You are not extending the SIZE of the screen vertically, pixel wise...just the synchronization. I think you can see that this also increases the pixel clock, since now the screen must "work harder."
Different people understand the concepts differently, but personally, I would fully decouple the concept of the signal timing from the concept of strobe timing, though one helps the other.
First, let's focus on the signal timing.
From the perspective of people who is familiar with the VHOLD adjustment from the old analog TV days -- The synchronization interval uses a number of dummy scanlines (black colored, no signal) which comprise the black bar you see. Vertical total is the total number of scanlines per refresh cycle (including synchronization scanlines between refreshes). Large vertical totals indeed puts a longer pause between refresh intervals (ala thickening the VHOLD bar, for those people familiar with VHOLD adjustment in analog TV days).
The time of the refresh cycle is maintained (e.g. 120Hz), but the time ratio of active picture refreshing, to pausing between refresh cycle, is adjusted. e.g. Ratio of 1500:1080 versus 1125:1080, when comparing VT1500 versus VT1080. The screen is scanned faster with larger vertical totals, but the vertical resolution is kept the same. So the active display area is scanned faster, followed by a longer pause between refresh cycles.
Next, let's explain how it relates to strobe timing:
The concept of a large vertical total is a workaround that works on the Z-Series to trick the BENQ Z-Series to scan the refresh quicker, so that there's more time for GtG pixel transitions to settle. When using VT1500, you have a full 2.3 milliseconds of pause between refresh cycles. Mathematically, that's the amount of time of the synchronization interval during VT1500, calculated as ((total - active)/total) of a refresh cycle, which is ((1500-1080)/1500ths of 1/120sec) = ~2.3 milliseconds. This 2.3 milliseconds is large enough to let most of an LCD finish refreshing (1-2ms GtG), which can be done in total darkness (between strobe flashes) to hide the vast majority of GtG pixel transitions, in order to reduce strobe crosstalk / double-image effect (incomplete GtG pixel transitions from the previous refresh cycle, leaking into the next strobe flash). Larger vertical totals means more time finishing an LCD refresh cycle unseen by human eyes (by hiding the majority of the ghosting / overdrive artifacts in the dark periods between strobe flashes). Larger vertical totals have less ghosting.
LightBoost already artifically internally scan-converts the signal (it does literally a kind of an equivalent of large vertical totals internally, via buffering the signal partially and doing an accelerated scan-out to the LCD).
To understand this better, it is useful to see a high-speed video of an LCD refreshing.
These videos are simply high speed video of a screen that's flickering between black then white (back and fourth)
from, www.testufo.com/flicker running in full screen mode.
Observe that an LCD refreshes via a top-to-bottom scan.
Older LCDs, not strobe compatible:
Observe older LCDs cannot finish refreshing before the next refresh cycle (strobe backlights won't work well)
Newer LCDs, strobe compatible:
Observe fast LCDs can finish refreshing before the next refresh cycle (strobe flash can be timed between refreshes).
Now you understand how LCDs refresh.
Now you can imagine that a longer pause between the top-to-bottom scans would be even better, reducing ghosting (strobe crosstalk) leaking between refresh cycles. The faster the "top-to-bottom" scan (via internal means such as LightBoost accelerated scanout, or via external means such as larger vertical total in the signal) subsequently followed by a longer pause between refreshes, makes it easier to finish GtG transitions between refresh cycles, reducing ghosting/overdrive artifacts during strobing.
