When using testers like Leo Bodnar’s Lag Tester

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l337g0g0
Posts: 13
Joined: 14 Jul 2015, 19:13

When using testers like Leo Bodnar’s Lag Tester

Post by l337g0g0 » 15 Jul 2015, 09:24

How can you prevent it from trying to test in the middle of a frame?
Tv's/monitors have a set hrz, so it it sends the single to test half way threw a frame doesn't gain that half frames MS?

How do these devices avoid this?

Glide
Posts: 280
Joined: 24 Mar 2015, 20:33

Re: When using testers like Leo Bodnar’s Lag Tester

Post by Glide » 15 Jul 2015, 09:28

You measure the top point rather than the middle one.
That lag tester seems to be less useful these days, since it is fixed at 1080p60.
With most monitors being 1440p and televisions being 2160p, we really need a more flexible device.

l337g0g0
Posts: 13
Joined: 14 Jul 2015, 19:13

Re: When using testers like Leo Bodnar’s Lag Tester

Post by l337g0g0 » 15 Jul 2015, 09:36

I don't mean middle of the screen frame.
I mean the device sets of a que for the monitor to act on, then the monitor reacts to it and you get your number.

BUT what if the que sent out is in between a hrtz, doesn't the device gain those MS's cause the device can't register till the frame is put on the screen.
How does this device avoid the monitors default Herz?
Can it work around it? and how?

l337g0g0
Posts: 13
Joined: 14 Jul 2015, 19:13

Re: When using testers like Leo Bodnar’s Lag Tester

Post by l337g0g0 » 15 Jul 2015, 09:46

Like this?
https://www.youtube.com/watch?v=mHIoJWtGR_w

At 60 FPS the frames are coming every 16MS but the device is registering 3 MS.

How does the device override the monitors natural herz?

if the device sends a que out for it to pick up off the monitor at 3ms into a frame but the monitor only needs 3ms to acknowledge it.
Doesn't the monitor need another 10 ms (3MS + 3MS + 10MS = 16MS = 60 HERZ) before it can put a new frame on the screen to follow it's natural herz?

I hope this helps better explain what I'm after.


l337g0g0
Posts: 13
Joined: 14 Jul 2015, 19:13

Re: When using testers like Leo Bodnar’s Lag Tester

Post by l337g0g0 » 16 Jul 2015, 03:49

I'm not talking about the screen refreshing down the screen there for how can it be accurate. this is not my question.

I'm saying the device has to send a signal to the monitor to time how fast the monitor receives it.
But by default the monitor is cycling it's refresh/screen 60 FPS lets say.
That's 16 MS between screens, how can the device ask the monitor to refresh and the device and see 3ms?

The monitor can't even refresh that fast when it's refresh at it's 60 hertz, so how can the device send a signal and receve it from the screen in 3MS when the screens refreshing at 16ms???

Anyone here understand where I'm going with this?

Glide
Posts: 280
Joined: 24 Mar 2015, 20:33

Re: When using testers like Leo Bodnar’s Lag Tester

Post by Glide » 16 Jul 2015, 10:14

Most displays are "rolling displays" (or "scanned" displays) which draw the image from top to bottom.
So a display with zero processing delays would measure "0ms" at the top and "16.67ms" at the bottom at 60Hz.

A "global display" waits for the entire frame to be transmitted and then updates the screen simultaneously.
This screen might measure "17ms" at the top and bottom of the frame.

Latency is higher, but you avoid skew with horizontal motion.
CRTs, most LCDs and OLEDs are all rolling displays.
Plasmas, DLPs, and some LCD/OLED screens are global displays.

spacediver
Posts: 505
Joined: 18 Dec 2013, 23:51

Re: When using testers like Leo Bodnar’s Lag Tester

Post by spacediver » 16 Jul 2015, 12:08

oldschool flashtube tachistoscopes were also global "displays" :)

http://www.sykronix.com/researching/tscope.htm

l337g0g0
Posts: 13
Joined: 14 Jul 2015, 19:13

Re: When using testers like Leo Bodnar’s Lag Tester

Post by l337g0g0 » 16 Jul 2015, 19:58

You guys are missing my question.
I understand that the screen draws the image down the screen so it's slower at the bottom from the top.
I get this, this is not my question.
My question has nothing to do with that feature.

Within that screen the device sends a message to the screen that the device can register, what if it's half way threw a frame?
wouldn't the single the device asked the monitor to do so it can read it be delayed by half a frame of time, lets say 8.5 ms (half the frames time.

So the device sends the signal, has to wait 8.5 ms for the screen currently being displayed to be done, that adds 8.5 ms to the time on top of what ever reading the next frame gives the device.

Am i really bad at explaining my question?

Glide
Posts: 280
Joined: 24 Mar 2015, 20:33

Re: When using testers like Leo Bodnar’s Lag Tester

Post by Glide » 17 Jul 2015, 05:15

l337g0g0 wrote:Am i really bad at explaining my question?
Apparently. I have no idea what you're trying to ask now.

The device sends a video signal to the display, and then waits for the photodiode to register a signal. (the flash from the display drawing the image)
It then outputs the time difference between those two things.

I don't understand what this "waiting half a frame" stuff is.

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