Technical explanation for a "double image" effect in 30 fps games on current HDTVs

Cheers again.

Bad deinterlacing and crazy upscaler softness are my two biggest fears with moving away from beloved CRTs (lag is third, but I believe Samsung's have good low latency gaming modes). I have RGB scart cables for most of my stuff, and can get or make some for the rest.

One thing I like about the Samsung LCDs is that they still have a VGA connector on most of them, so I can link up my Dreamcast and VGA mod my Xbox. The death of the PC/VGA connector is quite sad when you think that RF and composite are still hanging on. Most of the Panasonic Plasmas that everyone raves about have no VGA, 1 scart, and 1 s-video connector.

I know it's OT, but this thread has been pretty useful in helping me chose a TV upgrade path!
 
Might I suggest a medical explanation?

It could be palinopsia, everyone sees afterimages to some extent, some can just have stronger afterimages or simply be able to notice them better than others. Or even HPPD (But let's not go there).

Also monitor response rates and their ability to remove traces of the previous frame would play a strong role.

On my Gateway FPD1775W I've never properly notice the phenomenom OP said, in moving scenes in 30fps games though I find it a bit difficult to notice the details in the scenery but it's quite subte and doesn't bother me.
 
Dungeonscaper said:
Might I suggest a medical explanation?

It could be palinopsia
Click to expand...
I don't think so, Agent Scully, because posters have described seeing this on some particular TVs, but not on others. If it was a medical reason for it, you'd expect the behavior to exhibit itself all the time and not just on a few isolated instances... :)
 
function said:
Cheers again.

Bad deinterlacing and crazy upscaler softness are my two biggest fears with moving away from beloved CRTs (lag is third, but I believe Samsung's have good low latency gaming modes). I have RGB scart cables for most of my stuff, and can get or make some for the rest.

One thing I like about the Samsung LCDs is that they still have a VGA connector on most of them, so I can link up my Dreamcast and VGA mod my Xbox. The death of the PC/VGA connector is quite sad when you think that RF and composite are still hanging on. Most of the Panasonic Plasmas that everyone raves about have no VGA, 1 scart, and 1 s-video connector.

I know it's OT, but this thread has been pretty useful in helping me chose a TV upgrade path!
Click to expand...

My Samsung Plasma TV (something like b 850) has a kick-ass scaler and latency in game mode is almost non-existent. Lovely image quality as well. I really like that thing. It's also a really pretty tv.
 
On old CRTs there was a period of time between one frame being displayed and the next appearing; you could catch it with a fast shutter speed on your camera (despite the phosphor glow). Plus, the image scanned from the top down, so I guess this could have helped temporally separate the image a little more. Perhaps that helped to alleviate the "double image" effect. Even at 100 or 120hz I didn't really have a problem with double image - 120fps looked a lot smoother than 60fps sure, but the huge issue shown in the photos above certainly wasn't there.

On a 600hz plasma the time interval between one frame being displayed and the next appearing could be very, very small and the problem of them both seeming to appear simultaneously should be much greater, especially if you have very little blur on the display device to hide the transition (newer LCDs seem a lot more responsive). On a 30 or 60 hz camcorder (or particularly a camera phone with a smaller aperture and longer, er, "exposure"?) the image should really show up. And I guess the lower the frame rate, the greater the change in the image between updates, so the more apparent the double image should be.

I'll take a stab as the differences between TVs and say that it's probably related to how fast they switch images and how they handle the transition (panel response, maybe flashing a different intermediate, tv generated screen screen up in-between).

CRTs are still pretty awesome. If only they weren't so damn big.
 
Sigfried1977 said:
My Samsung Plasma TV (something like b 850) has a kick-ass scaler and latency in game mode is almost non-existent. Lovely image quality as well. I really like that thing. It's also a really pretty tv.
Click to expand...

Just had a look a the Samsung Plasmas. They look super, but unfortunately the full HD ones are out of my price range. Tempted to try a 1024 x 768 one but people would laugh at me. :(
 
Consoles allow a lot of control over when you flip buffers - the 360 will even tell a game how far down the front buffer the output "scan" is so the game can decide whether to tear or wait for the next refresh (the PS3 probably does the same). I'm not aware that PC drivers allow this level of control, which might explain why games don't offer a "cap at 30, tear in the top or bottom 10%, otherwise wait for sync option".
 
Rage PC has a smart v-sync option now, though it needs a certain driver for nV cards.

If your graphics driver supports [swap-tear] extension and you set VSync
to SMART then RAGE will synchronize to the vertical retrace of
your monitor when your computer is able to maintain 60 frames per
second and the screen may tear if your frame rate drops below 60 frames
per second.
Click to expand...
I'm guessing nV decides how it determines when to enable/disable v-sync, but it's something.
 
AlStrong said:
Rage PC has a smart v-sync option now, though it needs a certain driver for nV cards.

I'm guessing nV decides how it determines when to enable/disable v-sync, but it's something.
Click to expand...

Yeah, that's a start then. I guess the next thing would be to add would be a driver level "virtual refresh" so you could use a 30hz sync on a 60hz monitor or a 30, 40 or 60 hz sync on a 120 hz monitor. Tie that to smart v-sync and gaming would become a lot smoother and more consistent on all manner of PCs.

MS should really consider adding this stuff to the DX standards.
 
function said:
Yeah, that's a start then. I guess the next thing would be to add would be a driver level "virtual refresh" so you could use a 30hz sync on a 60hz monitor or a 30, 40 or 60 hz sync on a 120 hz monitor. Tie that to smart v-sync and gaming would become a lot smoother and more consistent on all manner of PCs.

MS should really consider adding this stuff to the DX standards.
Click to expand...
There already is a framerate limiter on nvidia drivers and in some cases it does work nicely. :)
 
function said:
On a 600hz plasma the time interval between one frame being displayed and the next appearing could be very, very small and the problem of them both seeming to appear simultaneously should be much greater, especially if you have very little blur on the display device to hide the transition (newer LCDs seem a lot more responsive).
Click to expand...
Plasma displays are binary coded, the real frame rate is 600/8 = 75 Hz (although most of them can probably run at 72 Hz too for film mode).

Any way the real effect is probably judder ... and the video and screenshots probably have more to do with shutter time overlapping frame updates.
 
i tried fable 3 and wow.. that game have horrible doubling. tried 720 and upscaled 1080 in xbox, the doubling still there.

if i remever right, old ps2 game called shadow collosus also have doubling. that game run lower than 20fps
 
ChrisT said:
Hi!
The problem is especially evident on plasma tvs, even the Panasonic top ones (G series, V series), as on plasmas, the doubled image is very sharp.
Click to expand...

Hello. I've bought Panasonic P46G30 recently and this double image in 30 fps games is evident. I am really disappointed - I bought this TV for low input lag and high motion resolution, but this double image is really terrible and there are just few games running in 60 frames per second. As far as I know (based on some interviews with developers and UE4 creators) it will be also true for next-gen consoles (most games will be native 1080p with advanced graphics, physics and animation but in 30 fps) which is not nice for plasma users :(

Thowllly said:
Way back in the day 3dfx (I think?) released a little program to show this effect.
30 fps on 60hz screens give this double effect. 60fps on 60hz screen and the effect disappears. 60fps with 120hz refresh and the effect is back, but the distance between the double objects is halved.
Very obvious on CRTs, I guess plasmas flicker like the CRTs used to do, and some LCDs also turn off the backlight between frames.
I happens when your eyes tries to track an object moving across the screen. Your eyes moves in a smooth motion while the object blinks into excistence twice in each position (for 30fps games). Relative to your moving eyes these manifest as two different objects, separated by the distance your eyes moves in 1/60 of a second. If the game runs at 20fps you get triple objects and so on.
On displays that does not dim between frames the object just get blurred instead (while it should be perfectly sharp as long as your eyes can keep up with it)
It's a bit hard to explain without visual aids, maybe somebody can explain better, but it's all actually very simple...
Click to expand...

Sounds logical, but if it would be only related to how brain and eyes work people would not be able to get photos of this effect. And there are photos on the internet. I was also able to take a picture which shows this effect, although in real life it looks a little bit different but still similar. BTW photos I have taken shows that plasma "flickers" - becomes darker/brighter - some photos are really dark or with wierd colors, but my camera settings were fixed so it must be what is going on on screen.
 
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