Nvidia 3D Vision 120Hz Sync Pulse From Standard Monitor? - Page 1
Forum section: electronics / projects

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 12:37:02 am
content: Hello all. I bought some NVidia 3D vision 2 glasses which alternately shutter each eye on a 120Hz monitor to produce a 60Hz 3D image to the user. However, I tried it and without the sync pulse, my glasses don't shutter at the right time as the monitors. I kinda see the intended image but with strong double images.Does anyone have any suggestions for modifying my monitors (They use displayport if that is of any importance) to get a sync pulse? I'd ASSUME its just a TTL pulse every frame, but I could very well be wrong. Here is the pinout:I'm not afraid to bust out the Rigol and start sniffing signals, but I'd like some input first. Thanks!

author: helius
author_rank: Super Contributor
timestamp: June 13, 2017, 01:35:55 am
content: stereo glasses require hardware and software support. on the hardware side, the VESA stereo output in your diagram only exists on workstation-class cards. if your glasses are wireless, you also need an emitter module.on the software side, the application must be stereo-aware and change the camera position on every frame. this often involves quad-buffering.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 01:37:34 am
content: Quote from: helius on June 13, 2017, 01:35:55 amI've got the emitter module for the wireless glasses. I can get 3D images but the timing is a little off due to a lack of sync going to the emitter module

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 04:55:25 am
content: Quote from: blueskull on June 13, 2017, 04:10:51 amVery valid point. Hmm.....

author: helius
author_rank: Super Contributor
timestamp: June 13, 2017, 04:59:14 am
content: The stereo field signal is controlled by software, not by the monitor. I've seen hacks that use a parallel port pin with custom drivers.Note: even if you were guaranteed to never drop a frame and lock the framerate at 120, the monitor doesn't know which frame is left and which is right. Only the software knows that.

author: BrianHG
author_rank: Super Contributor
timestamp: June 13, 2017, 05:03:31 am
content: Quote from: blueskull on June 13, 2017, 04:10:51 am3D stereo drivers prepare a left & right frame simultaneously, then keep these 2 flipping as the next screen stereo set is being rendered. It's hard wired, you will never miss a v-sync cycling back and forth between the left and right eye. Nvidia's page-flipped stereo driver setting worked like this from day 1, over a decade ago up until today, and will continue to do so.Now, can your monitor display the 120 independent frames fast enough to no give a cross image residue from eye to eye? Is the monitor synchronous with the video card's video output without delay, or, 1 perfect v-sync delay? If you have and LCD display, will the polarizers of the glasses interfere with the monitor's polarizers?All these things need to work if you want to use that glasses connector...

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 05:16:30 am
content: Quote from: BrianHG on June 13, 2017, 05:03:31 amI can strobe the backlight at 120hz which eliminates ghosting as it lights in the middle of each frame. Maybe I just need to tap into that?

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 05:18:26 am
content: Quote from: blueskull on June 13, 2017, 05:17:21 amMy monitors claim a <1ms response time and can do 144hz, as well as backlight strobing at 120hz

author: helius
author_rank: Super Contributor
timestamp: June 13, 2017, 05:27:43 am
content: Quote from: iamdarkyoshi on June 13, 2017, 12:37:02 amYou assume too much. What use would a pulse every frame be to control shutter glasses? How do the glasses know which eye to blank from a pulse every frame?The VESA stereo signal is a square wave that is high when the left eye should be open.This took 30 seconds of searching.The monitor doesn't know anything about left and right frames unless it was designed with 3D stereo support with a compatible card. The left/right signal is not available in the monitor.

author: cdev
author_rank: Super Contributor
timestamp: June 13, 2017, 11:08:24 pm
content: I have simuleyes LCD glasses which originally used a VGA dongle that detected a white bar that was inserted into the bottom of the image for one eye.I would be interested in figuring out a way to use them again.The white marker seems like a good (compatible) way to identify which eye is which across multiple platforms without fuss.More info:http://www.cs.unc.edu/~stc/FAQs/Stereo/stereo-handbook.pdfTiming/Performance testinghttp://www.mtbs3d.com/phpBB/viewtopic.php?f=26&t=8489(VGA) hardwarehttp://www.vogons.org/viewtopic.php?f=46&t=45260http://www.epanorama.net/documents/pc/3dglass.htmlHomemade VGA passthrough devicehttp://stereo3d.com/vgapt.htm

author: cdev
author_rank: Super Contributor
timestamp: June 14, 2017, 12:03:33 am
content: Both Nvidia and AMD only officially support a subset of very high refresh rate monitors for use with their 3D visualization solutions.Glasses like mine support"white line code"or"blue line code"basically they use an area of solid color to tell the LCDs which eye is which.Quote from: blueskull onYesterdayat 23:17:21>Quote from: BrianHG onYesterdayat 23:03:31>Quote from: blueskull onYesterdayat 22:10:513D stereo drivers prepare a left & right frame simultaneously, then keep these 2 flipping as the next screen stereo set is being rendered. It's hard wired, you will never miss a v-sync cycling back and forth between the left and right eye. Nvidia's page-flipped stereo driver setting worked like this from day 1, over a decade ago up until today, and will continue to do so.Now, can your monitor display the 120 independent frames fast enough to no give a cross image residue from eye to eye? Is the monitor synchronous with the video card's video output without delay, or, 1 perfect v-sync delay? If you have and LCD display, will the polarizers of the glasses interfere with the monitor's polarizers?All these things need to work if you want to use that glasses connector...So tapping sync signal from monitor will work? That's good to know. As for latency, G2G time is usually <5ms for modern IPS, and <1ms for modern eSports optimized STN/MVA, so at 120Hz, I don't think there will be a huge issue.If nVidia dares to sell this technology, I guess they know to add blanking and some timing tricks to accommodate the slowest IPS on the market, or they are blowing up their reputation.

author: bktemp
author_rank: Super Contributor
timestamp: June 14, 2017, 03:51:10 pm
content: In addition to the response time of the LCD there is an even more important effect you need to care about: The screen refreshes from top to bottom during the active area of the video signal. And that takes most of the time. Only during the blanking interval there is no change of the image, but that time is very short (45 lines out of 1125 for typical 1080p timing, but it may be different because of the internal processing in the monitor itself).So depending on when you toggle the shutter glasses, there will be a port of the screen with good R/L seperation getting slowly worse towards the other end of the screen with basically R+L being visible to both eys.As far as I know 3D TVs using shutter glasses strobe the backlight for a very short time at a high brightness to compensate for that.I wouldn't recommend shutter glasses with LCD monitors that aren't specifically designed for this usage. I tried it with a cheap LCD monitor and it was next to useless because of the rolling screen refresh.DLPs probably work fine because of the high internal refresh rate.

author: BrianHG
author_rank: Super Contributor
timestamp: June 14, 2017, 08:27:10 pm
content: Quote from: bktemp on June 14, 2017, 03:51:10 pmCareful with some DLPs, they may say 120hz and 3d glasses support, but, unless you select the mode in the menu, the DLP will slow down the refresh rate to 60hz even if you feed 720p 120hz. This is because color quality drops at true 120hz since the DLP relies on Z time, pulse width modulation to create the actual shades of grey.This is not a problem with super high end 3 chip DLP projectors, but, if you had this equipment, I don't think this question would have shown up here.