How can a DCI Projector have a dead pixel?

[Lyle Romer]

I saw Project Hail Mary at the Regal Sawgrass in Auditorium Digital Cinema Forum This is a recently renovated auditorium with really nice motorized recliners and was upgraded to laser projection. There was a black spot in the image that was noticeable anytime there was something bright in the area. I can't think of anything that could cause this other than a dead pixel but I also can't comprehend how a 3 chip projector can have a completely dead pixel. Shouldn't a dead pixel on one chip just make the color be off?

[Marcel Birgelen]

A single dark pixel is a rarity, because as you indicated: chances of exactly the right mirror on three different DMDs getting stuck in "off" position should be almost zero. Also, I presume this is a 4K machine and spotting a single dead pixel on a 4K machine, especially on a rather dark movie like Project Hail Mary is pretty hard. So, I think there was some other kind of contamination, although it's interesting where that could've happened in the light path... You're sure it wasn't a hole in the screen?

[Lyle Romer]

I don't "think" it was a hole in the screen but maybe dirt in the light path could explain it.

[Dave Macaulay]

Is it really dead or just missing one colour? All three is not likely at all. I don't know of any surface where the completed image is in focus to have a piece of dirt the size of one pixel be a black spot on screen.
A hole in or a dark spot on the screen seems most probable if it is true black

[Lyle Romer]

Is it really dead or just missing one colour? All three is not likely at all. I don't know of any surface where the completed image is in focus to have a piece of dirt the size of one pixel be a black spot on screen.
A hole in or a dark spot on the screen seems most probable if it is true black

It was easily visible any time there was a bright part of the image over it, it looked like it was black but the shape looked too regular to be a hole in the screen. Somebody would have had to climb a ladder and deliberately cut it with a straight edge and tape measure.

[Mike Blakesley]

Maybe it is a hunk of something stuck to the screen. We had somebody heave a huge wad of chewing gum up there once.

[Ioannis Syrogiannis]

That makes more sense than something in the light path. And that is because a speckle in the light path would either be indistinguishable, or manifest as a dark/discolored area.

[Martin McCaffery]

I agree with Mike. Early in the days of digital I went and saw something at a Carmike theatre. There was this red dot on the screen that was really visible in bright scenes. I thought it was a dead pixel, until I went up to the screen after the show and saw a red gummy bear stuck to the screen. God knows how long it was there, but I did notify the manager on my way out.

[Marcel Birgelen]

I think we can exclude a DMD issue and something in the optical path from the shortlist. Anything with sharp defined corners should be close to the focus plane, which is the surface of the DMD, which would require the same anomaly being present three times at exactly the right spot. We've all seen how dust particles look like and if they're visible at all, they usually manifest as vague blobs.

Lyle himself indicated that it didn't look like an issue with the screen, although I agree with others here that it's sometimes hard to judge.

One possibility that remains is an electrical or software defect, although I'm not sure what would possibly trigger the blackout of one or more pixels, there might be possible avenues. For example, I remember a time where the subtitling engine crapped out and this resulted in a black and white pixel-soup "stuck" at the bottom third of the screen, overlapping the picture itself.

[Marco Giustini]

I had that before and it was determined it was LASER damage. There were clearly a bunch of dead pixels on all three DMDs - which is very much impossible. DMDs can be easily damaged by a laser pointer aimed at the lens. There is a true story where a company installed 60 DLP projectors at a show and another company was installing laser heads. At some point they realised all 60 projectors had laser damage on their DMDs.

The recommendation at that time was to... close the dowser between shows

[Marcel Birgelen]

That makes some sense indeed... Still, a laser is monochromatic light, you'd expect almost all of it landing on either the green or red DMD... Also, the fact that a DMD can be damaged via a laser pointer reverse through the lens is pretty scary, given the fact that it's used to have a killer light-source hammering on it from the other side...

[Ryan Gallagher]

The recommendation at that time was to... close the dowser between shows

this is why physical shutters will always be needed in mixed use venues. I was disappointed to learn Barco Series 4 4K does not have one. If we have a laser show we cover the lenses as well.

[Jim Cassedy]

One of the auditoriums at my venue recently had a 'stuck' green pixel. No amount of
running through alternating test patterns or full color screens could get rid of it.
Fortunately, the stuck pixel was near an upper corner of the screen, so it wasn't too
visible, but one you noticed it, you couldn't 'un-see' it. The projector ( a Barco SP4k-
12C laser) was under a year old so a Barcoguy came out and put in a new light
engine at no cost since it was still under warranty.

[Marcel Birgelen]

this is why physical shutters will always be needed in mixed use venues. I was disappointed to learn Barco Series 4 4K does not have one. If we have a laser show we cover the lenses as well.

The idea is that you shut-down the light engine, which kills all the light on-screen. That's the advantage of those laser-diode based light sources, you don't have to ignite the light source like xenon or a carbon arc and it immediately produces the desired output.

I'm not sure if Barco or other manufacturers deem the dowser to be sufficiently safe as a protection against stray laser light sources.

I've been thinking about how something like a laser-pointer could damage three DMDs and I'm pretty sure that any "street legal" laser won't do this. But a professional laser show using a powerful RGB/white laser easily exceeds 500mW often going up to 30W or more for indoor use and even more for outdoor, which could certainly fry one or more pixels on three DMDs at the same time if it hits from the outside. For big venue shows I remember using a "professional cardboard contraption" to avoid lasers hitting our projectors, although they say that at the speed those usually scan, they cannot do much harm...

[Ryan Gallagher]

The idea is that you shut-down the light engine, which kills all the light on-screen. That's the advantage of those laser-diode based light sources, you don't have to ignite the light source like xenon or a carbon arc and it immediately produces the desired output.

Apparently implementation and intent are pretty far apart. Barco advised we only use the "dowser" within a black, to avoid a bunch of visible weirdness on screen as the DMD mirrors move out of their storage position. So not as "immediate" as one would hope.