Dark Frame Insertion at VP - Compatible with PJs?

I'm not particularly interested in frame interpolation, but I am quite interested in dark frame insertion (DFI) - loss in brightness notwithstanding - as a means of reducing/eliminating the 'sample and hold' (SAH) induced motion blur that affects many current projectors (especially LCD/LCOS). While the latter do suffer from some inherent motion blur as a limitation of the technology, I would think the SAH component is probably more significant, and remedying that would get one closer to the look of actual projected film (nicely replicated by the naturally decaying phosphors in CRTs).

I know the Sony VW200 incorporates this at the projector level, but are there any video processors that feature DFI, and if so, would they work with the current crop of projectors?

I would think DFI at the VP level would be a relatively simple feature to incorporate - simply adding in a black frame/image once every 24 seconds (1/48th of a second separated from the native frame/image) should almost certainly be easier to implement than interpolating a detailed image at the same frequency.

DFI as articulated above would result in 1080p23.98 material encoded on disc being fed to the projector as 1080p47.96 (23.98 image frames/second, and 23.98 black frames/second). The key question is whether current projectors would be capable of accepting such a signal. I know that many (all?) will accept 1080p24, as well as 1080p60 and 1080p50 (PAL), but will they accept 1080p48 (shorthand for 47.96)? The JVC RS-2 for eg. does not spec 1080p48 among accepted digital video timings/resolutions, but it does list a number of other timings/resolutions for PC signals, and the fact (I think) that it accepts 1080p24 input and doubles (or quadruples) it to 1080p48 or 96 suggests that it should (perhaps with a minor firmware tweak?) be able to accept a 1080p48 digital video input. Certainly the latter would not present any bandwidth issues, since the projector happily accepts 1080p60. I no longer have a Lumagen HDP, but someone could verify this by using a Lumagen (or HTPC, etc.) to feed an RS-2 a custom 1080p timing.

To recap:

1. Are there any VPs that perform DFI?

2. Can most currently available projectors (I'm particularly curious about the RS-2) accept a 1080p48 'custom' timing?

Might not be an issue. If I'm not mistaken, the RS-2 displays 1080p24 at 1080p96 (it's doubled twice, i.e. effectively quadrupled). What this means is that both the image and dark frames within the 1080p48 input would be displayed (flashed) twice...which should go a long way towards ameliorating flickering.

Let me know if you disagree.

Good to know. If anyone's using a Lumagen or HTPC with an RS-2, can you confirm if the latter will accept 1080p47.952? If it does, the only question that remains is whether any commercially available VPs are capable of dark frame insertion. If not, I would think that an HTPC should be flexible enough to do so. Can anyone confirm that?

I don't think you understood what I'm driving at. Under the scenario I'm envisioning - and with native 1080p24 information encoded on disc - 1080p48 would be the output from the VP (dark frames inserted in between the native images) and thus the input into the projector. If it were then displayed 'as is' i.e. at 1080p48, then yes, one would detect significant flicker in the manner you've described. However (if I'm not mistaken), the RS-2 quadruples a 1080p24 input, and should thus double a 1080p48 input to display it as 1080p96 - the last (slightly flickery) scenario you've described, which may be quite acceptable if the reduction in 'sample & hold' derived motion blur is material.

EDIT...you are right, my response above is not correct...simple doubling of a flicker ridden 1080p48 input would do nothing to reduce flicker...see posts below

Good point re: desirability of on-board (the projector) implementation. However, given that I'm interested in enabling DFI in a a non-DFI enabled projector (eg. the RS-2), a video processor or HTPC seems to be the only viable route.

Excellent point about black insertion for subframe intervals, allowing one to dial in the ideal compromise between motion blur and flickering. I don't see why this couldn't also be done at the VP/HTPC level, though given the likely limits on max acceptable input resolutions/timings, as well as how they're handled (automatically doubled for eg.?) by the projector, such an approach would be far less flexible than if done on board the projector.

Once again, all of the above is academic unless we can affirmatively answer the following:

1. Does the RS-2 accept 1080p48 inputs

2. Are existing VPs or HTPCs capable of performing dark frame insertion on 1080p24 material?

N.B: Sub frame insertion would be even better - for eg. 2 image frames (same frame doubled) to every dark frames which should yield a perfectly acceptable 1080p72 signal, though I don't think most projectors with accept inputs north of 1080p60

Hmmm...you do have a point.

1080p24: ABCD, etc., etc.

1080p48 (w/ DFI performed by VP): AdBdCdDd, etc., etc.

In order to avoid the doubling of the 1080p48 signal w/in the projector to yield 1080p96 as you (and Erik Garci) describe (AAddBBddCCddDDdd), one would need to feed the projector a signal that would NOT automatically be doubled, but would still be high enough in frequency to avoid flicker. How about the sub-interval frame insertion postulated by Mark Peterson?

Yup, looks like they're trying to achieve the same thing.

It seems pretty clear that simply inserting a dark frame very 24 secs into native 1080p24 (ABCD) material results in 1080p48 (AdBdCdDd) with far too much flicker. Furthermore, having the projector double this 1080p48 does nothing to diminish the flicker.

I think Mark Peterson's really on to something with sub-interval dark frame insertion, and doubling 1080p24 into 1080p48 and then adding in a dark frame would give you 1080p72 (AAdBBdCCdDDd) material that should be far more flicker friendly. That said, I don't think the RS-2 will accept a 1080p72 input (1080p60 max?).

Perhaps its possible to go the interlaced route (with a higher custom refresh frequency) and then have the projector deinterlace?

Really? I would have thought a dark frame every 1/72nd of a second would not be an issue on the flicker front. Also, on the brightness front, it probably doesn't need to be completely black...perhaps a dark gray would better mimic the average interpeak brightness of CRT phosphors (given that they take a small amount of time to decay - and recover - from on to off).

Hmmm...that would mean you'd have this problem regardless of length of interval. i.e. even if the duration was 1/120th of a second, the frequency of the dark frame would still be 24Hz, and you'd still suffer from flicker. Is that correct?

If so, sounds like you'd need a 96hz signal (AaAaBbBbCcCcDdDd, etc.) to truly get at a low enough flicker...problem is that I don't think the RS-2 accepts a 96Hz signal.

I guess getting a VP or HTPC to do this is a bit of a pipe dream then?

Thanks for the clarification. Pity about the lack of devices capable of outboard DFI. If (and that's a big if) the RS-2 does accept a 1080p96 INPUT, I would have thought one could get an HTPC to convert ABCD (1080p24) to AdAdBdBdCdCdDdDd (1080p96) without too much trouble, but then again, I've never written any software.