Projector pixel response times

[Fat Tone]

Does anyone know how to compare pixel response times for projectors? I'm interested in a DLP model (http://www1.euro.dell.com/content/pr...pecstab#tabtop) for displaying stereo images, but I can't see from the specs how this might compare with any other technology.

TIA

T.

[Jammrock]

DLP doesn't really have a "pixel response time" in the traditional sense of the term. DLP is a bunch of really small mirrors that flip around really fast in synch with a color wheel to produce the picture. Because DLPs are designed for TV, or HDTV, you can be garauntee a 60Hz refresh rate on a good quality 720 p DLP projector, but I doubt they design the projectors to operate any faster than that. So that's ... approximately 17 ms.

Jammrock

[Fat Tone]

Cheers. We will need it to run at 100 or 120Hz to give 50 or 60Hz stereo using shutter glasses!

[Jammrock]

Cheers. We will need it to run at 100 or 120Hz to give 50 or 60Hz stereo using shutter glasses!

afaik, only CRTs can pull that off. You would have a better chance of getting a more accurate answer if you posted at AVSforums.

Jammrock

[xortam]

You have to be careful with the video processing time that may delay the video on digital displays. Samsung DLPs have had quite a problem with A/V synch (sometimes referred to as lip-synch delay). 'Athletic' gamers have had troubles with the delay of their console game video on Samsung DLPs.

Some of the newest TI DLP DMD chips also will multiplex two pixels per mirror (referred to as wobulation). The color wheel speed may increase in time (limited by heat, noise, and processing speeds) as well as increases in the mirror flip frequency thus increasing the bandwidth of the DLP engines.

[xortam]

You can read up on TI's DLP engine and DMD in their white papers hosted at their site.

[magician]

Cheers. We will need it to run at 100 or 120Hz to give 50 or 60Hz stereo using shutter glasses!

Actually, you don't need more then 50Hz to pull that off. You see, TV standards (PAL/NTSC) was designed that way (50/60Hz) because of poor phosphore persistence in early cathode tubes, so there was impossible for electron ray to reach the bottom of the screen without loosing brightness of scanned lines at the begginning. Therefore "interlaced" was adopted as a work around.

Cinema actually uses only 24 fps for smooth motion picture reproduction, but introduces doubling of frames (48 fps), by shatter operation, for entirely different reason (eye sensitivity for high brightness/contrast flashes). Considering all facts, I think that you could achieve desired effect with no more then 48/50 fps in moderately darkned room (avoid high dynamics/brightness). If that failles, maybe you could try same DIY modding of projection system by adding additional shatter in the front of the lense, but it ought to be perfectly synchronised so... maybe you'll be better with 100Hz projector.

[xortam]

There's been interest in the past of seeing large 1080p60 displays used for 3D stereo applications (30 fps per eye). We're now seeing DTVs based on various technologies, including DLP, which support 1080p60 while some only support 1080p24.

BTW, film at 24fps relies on smoothing techniques to reduce the jerkiness of slower frame rates.

[magician]

...
BTW, film at 24fps relies on smoothing techniques to reduce the jerkiness of slower frame rates.

I'm not sure I'm following you?

Was you refearing to frame interpolation in speedup effect?

BTW: Actually only about 18 fps is needed for smooth motion perception, but 24 fps is picked because of an audio synch issues.

Movie camera takes whole, discreet snapshots of time-space, so in a fast action scenes "natural" smoothing (blurring) occurres within each frame, if exposure time is long enough (depends on lighting conditions and film sensitivity).

For slow motion effect you just speedup filming frame rate and reproduce it with regular 24 fps, while for speeding effect you decrease filming rate and reproduce it again at regular 24 fps. Sometimes they interpolate intermediate frames to smoothout some special effects.

Please note that frame rate needed for smooth motion perception and smooth visual perception is two different things, but both depend on exposure times.

Edit: clarifications added.

[Wombat]

No, even fast motion appears bad at 24fps on movie screens.