CurtPalme.com Home Theater Forum

[amt_austin]

This may seem a little strange at first but bear with me:

I know the NEC XGs can technically do 1080p, but the caveats are:
-picture may be soft due to bandwidth limitations of the projector
-will need custom timings to get raster centered

These, IMO are why I personally would not run 1080p on the XG's. However, I was thinking of a way to get 1080p, while stacking to XG's, each running 1080i. Now, you are probably thinking, "umm, no, that does not make 1080p" -and you would be right. But what if we did the following:

Have a scaler take a 1080/24p input and drive two outputs. For each frame, it will send 4 interlaced frames to each of the projectors, for a refresh rate of 96 Hz. The idea here is for each of the four frames sent out, you want one projector to raster the even lines while another rasters the odd lines [at the same time] of the original frame, so in one pass, you get all of the lines of the original frame. In order to do this, you need to trick the projectors into rastering the right lines at the right time. So, you want one projector to start rastering from the top of the CRTs to the botton, even lines, then odd, then even, then odd (4 interlaced frames per original 24p frame). On the second projector, have the scaler send the image out starting from the bottom of the original frame, and have it raster from the bottom of the CRTs to the top (set it for floor mount instead of ceiling), rastering its even lines, then odd, then even, then odd. Yes, this seems incorrect, why would you raster even lines on both projectors at the same time? That would only get you an interlaced image. If both projectors were rastering from top to bottom, that would be correct, but since the 2nd projector is rastering from bottom to top, and rastering from a flipped original frame, it's even lines are actually the first projector's odd lines! So, what you should have is a 1080/96p from two XG projectors!

If this still does not makes sense, think of an original frame:

line 0: ---------------
line 1: ---------------
line 2: ---------------
line 3: ---------------

now have the first projector start with the even lines:

projector1:

projector 1 line 0: ----------------
<line 1 skipped>
projector 1 line 2: ----------------
<line 2 skipped>

at the same time, feed projector 2 the image, flipped, and even lines from the flipped image (which are the odd lines from the original image):

projector2: flipped line 0, original line 3: --------------
<line skipped>
projector2: flipped line 2, original line 1: --------------
<line skipped>

Don't forget! This projector is set up to raster from bottom to top, so it really displays (read from bottom to top):

<line skipped>
flipped line 2, original line 1: --------------
<line skipped>
flipped line 0, original line 3: --------------


And when you stack these on the same screen, you get:

projector 1 line 0: ----------------
projector 2 line 1: ----------------
projector 1 line 2: ----------------
projector 2 line 3: ----------------

You have to do this 4 times for each source frame, so or the next frame sent out to the projectors, the ratsered lines are alternated (pj 1 gets odd lines of original frame, pj 2 gets even lines of original frame). The third time, just like the first one, and the fourth time, just like the second frame sent out.


Now, I am betting there is not a scaler out there that does this, but I wonder if it could be done with a HTPC. I bet the good linux hacker could get it working!


I know it's seems crazy, but just think, double the light output, tons of bandwidth, no judder! And all done with reasonably priced projectors! Of course XG's are not the only ones that could make this work. I Imagine any 8" 1080i capable projector could pull it off.

[emdawgz1]

That is a HELL of a lot of work to go from 1080i to 1080p..... Id rather just do a 1080 blend. or just do a 720p stack.

but good luck w/ that it should be interesting to get it running!

[kschmit2]

You would need genlocked sources (some highest end video cards support that, but none of the consumer/gaminhg cards) to achieve that with full timings control incl. the order of the interlacing fields (none of the genlocked cards support that iirc).
And when you have devices capable of reliably doing that, you might as well invest into blending gear, as it won't really cost that much more, and will deliver a better picture in the end, since you can use more phosphor height and use progressive signals.

Kai