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Facts:

  • We know that a system needs high data transfer speed if it works with +120 Hz refresh rate and +1080p resolution(This mostly requires DVI dual link).
  • We know that in a 3-D system with shutter, the method is to flash for Right and Left eye arbitrary.

    Respresentative image

For right eye, shutter shuts the left eye and display shows the image for right eye and then for the left eye, shutter shuts the right eye and opens up the left eye and display shows for the left eye and on and on goes like this. This is how 3-D visual is done with shutter.

Now, there are several 3-D systems out there in the market. The most popular one is lightboost setup:

Lightboost system requirements

As the lightboost released on the market many monitor vendors also released +120 Hz monitors with lightboost support(such as VG248QE the most popular one).

Before I reveal my question, I feel like I have to explain technical details of DVI dual link and LCD driver a little bit. There are some missing parts of them which I could not understand.

This is DVI dual link pinouts:

DVI dual link Pinouts

I found this on the adress: http://www.alciro.org/alciro/conectores_26/conector-DVI-interfaz-visual-digital_269_en.htm

explained as follows:

The DVI connector is divided mainly into three areas:

TMDS. (Transition Minimized Differential Signaling) or Transition Minimized Differential Signal similar to communication systems balanced. Marked on the figure by the brown color has four twisted pair cables one for each primary color video red, green and blue. Each two pairs have a mass of specific protection marked in dark brown. The video signal is synchronized with a pair of twisted wires in light brown line has its own mass. With a video link can transmit high-definition HDTV signal (1920 × 1080) at 60 Hz (139 MHz) for better definitions and better refresh the DVI connector includes a second link in combination with the former provides resolutions higher than HDTV HDTV (1920 × 1080) at 85 Hz (2 × 126 MHz) or WQXGA (2560 × 1600) at 60 Hz (2 × 135 MHz), among others. Pug & Play. Marked in blue has a number of lines that highlight the DDC (Display Data Channel), serial connection with pin I2C Bus SDA (data) and SCL (clock). Are used to detect and display settings when connecting to a computer. Analog. Analog system, marked in green features a pin (pin) for each RGB primary color red, green and blue analog sync with the digital connector makes it compatible with the analog system, reaching a bandwidth of 400 MHz

Pin description of DVI

So, 3-D visualization method seems not that hard. Send the pixel datas for Left eye than send the datas for Right eye and on... Communication protocol also seems not that hard! You simply send the datas not encapsulated as you can see below:

DVI dual link communication block scheme

As you see, with DVI, we send datas bit by bit and the LCD driver of the monitor decodes received data. So, my question is this: Why do I need lightboost(Or any other 3-D vision product)? What lightboost(3-D stereo feature of it) actually does? Why don't we just use the same communication with monitor and simply send preconstructed Left and Right pixel datas to the monitor and then it decodes the data and do the same job as in lightboost?

To open up my question a bit more, I have to indicate where my question actually relies. It is between the graphic board and the monitor. You see, lightboost requires both graphic board and monitor lightboost compitable. What does it mean? In lightboost 3-D mode, does communication between graphic board and the monitor change? If so, why? Why doesn't the graphic card first construct 3-D content and send them in the same way before? For instance, when try to use lightboost on some other machine with old graphic cards, I get the warning that the graphic card does not have 3-D stereo feature. If 3-D content is already prepeared(like 3-D movie or anmation), why can't I use any graphic card(which can drive 120 Hz 1080p) to send them to the monitor? After all, the method looks simple:

(1)drive pixels with left eye data, then strobe backlight

(2)drive pixels with right eye data, then strobe backlight

then it goes like 1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2....

Why do I need 3-D stereo? What 3-D stereo feature does? How it effects the communication between the monitor and the graph card? Are there primarily differences in the hardware structures of graphic cards which have 3-D stereo feature and which don't have? If there are, what are they? I firstly, wonder about these. I could not reach any detailed documentation about the topic.

Secondly, say it has to be done in that way, communication between the monitor and the G.board(via DVI dual link) has to change in 3-D mode. Then why is that?What changes? In what way they manage to switch to 3-D mode? I firstly, want to know the reason for this and secondly, what is the method for this.

Thank you already.

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Why do I need lightboost(Or any other 3-D vision product)?

You do not need Lightboost or any other 3D product to display 3D content that is visible with shutter glasses.

You can just send alternating right and left fields and as long as you have a way to sync the shutters in the glasses to the corresponding fields, the user will see 3D. (Assuming you do it fast enough!)

Back in the good-old days, we would use the vertical retrace time to alternate the fields by just redrawing the bit-mapped graphics screen. We would send a signal out the audio jack to control the LCD shutters and sync the glasses. Ugly, but it worked!

Heck, the (amazing!) Vectrex displayed stereo 3D images by using a spinning disk with a slot in it. There was a little sensor in the glasses that told the display when the slot was going to be over each eye, and the CPU would then draw the next field just in time for the slot to reveal it.

(It was actually so much cooler than this simplified explanation! It could even do color on a monochrome screen because there were alternating colored filters over the slot in the spinning wheel. One of the greatest hacks I've ever seen!).

What lightboost(3-D stereo feature of it) actually does?

Lightboost is a clever idea to make 3D content viewed though shutter glasses look brighter. Normally when you look at a monitor without glasses, both of your eyes are open and collecting light all the time.

When you use 3D shutter glasses, the shutters alternate opening and closing. No light gets to either eye when both shutters are closed, so any light the monitor produces during this time is wasted. The more time both shutters are closed, the dimmer the display looks to your eyes.

So why not just have the one shutter open at exactly the moment the other closes so there is never a moment when both are closed? While this is the ideal goal, in real life shutters do not open and close instantly and screens to do update instantly. As you reduce the time when both shutters are closed between fields, at some point each eye starts to see images meant for the other eye or intermediate images. This usually looks like blurring.

With Lightboost, the back-light in the monitor actually turns off between fields. You can not see what is on the screen when the back-light is off, so as long as there is a full-formed image on the monitor and one shutter is completely open and the other is completely closed at the moment the back-light strobes, there will not be any blurring visible no matter how long the shutters stay open.

I think Lightboost also takes advantage of the fact that you can run the back-light at a higher brightness for a short duration than you could run it at continuously.

The net effect is that more light gets from the monitor to your eyes with Lightboost, so the image looks brighter.

Why don't we just use the same communication with monitor and simply send preconstructed Left and Right pixel datas to the monitor and then it decodes the data and do the same job as in lightboost?

You could just send pixel data, but to get Lightboost to pulse exactly when your shutter is open you will need to replicate the protocol, which is non-trivial.

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  • \$\begingroup\$ Thank you for such detailed answer. I may I ask about something else? vg248e asus monitor claims that it has 1 ms rise time. Is this issue process related or design related? Because, I also tested many lcd's, none of them has below 1.5 ms rising or falling time. Do you know some methods to minimize rise time of lcd's? \$\endgroup\$ – Alper91 Dec 18 '15 at 18:10
  • \$\begingroup\$ It depends on what you are trying to do. You can increase the response time on LCD's by overdriving the pixels during changes, but that has some downsides. If you are using a monitor with Lightboost, as long as the pixel is able to change fully before the next back-light strobe, then there will be no visible motion blur. \$\endgroup\$ – bigjosh Dec 18 '15 at 18:27
  • \$\begingroup\$ Sorry for delay. I thought that when I accept this answer bounty will automatically be given. \$\endgroup\$ – Alper91 Dec 18 '15 at 23:01

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