DCI Christie Warp Files (for the uninitiated?)

[Ryan Gallagher]

Due to having the pleasure of witnessing a 4K Laser with Warp correction in our steep theatre yesterday, a couple conceptual questions arise:

1. When did DCI loosen their stranglehold on disallowing any pixel level geometry correction other than cropping in DCI setups? If they did?

2. We ran our 2k as a live backup, but in aligning to the primary's bottom/top masking, our resulting scope image was narrower than their Mystique warp corrected scope image. What is the origin of this difference? They used our normal scope side masking position, before changing the 2k size we had a taller image.

My instinct was to either blame our periscope mirrors relationship, or the fact their warp correct was perhaps doing more than simply keystone correcting, it was also correcting the vertical stretch resulting from our steep angle? (And in doing so has to sacrifice some horizontal and vertical size overall). Additional lens shift down was required after enabling the warp, that was my primary clue.

3. Why they make twist/warp licensing it so darn expensive? This is free if not standard tech/features with any Non-DCI large venue projector. Or were our visiting techs just citing the "full price" for the top of the line Mystique license for multi-projector arrays etc etc (Said 17,000$ for the Mystique license). The "automatic" features of Mystique make sense to charge good money for, but the underlying warp stuff is pretty standard non-DCI projector tech.

If curious, we left our 2k backup within their masking, and removed my keystone cropping because the un cropped image was still within the side masking. The other option would have been to match their width with my keystone crop still in play, and add top and bottom crop until we fit the masking. That probably would have "looked" better, but with tons of crop sacrificing. But backup was of course not needed.

[Ryan Gallagher]

After typing that I realized that any "normal" keystone correct mode in a projector also impacts image vertical size. Dealing with DCI primarily of late has warped my brain into thinking about removing keystone by only manipulating the image's horizontal size.

[Ryan Gallagher]

I found the 2021 warp conversation. Good read, thanks folks!
http://www.film-tech.com/vbb/forum/m...dci-projectors

[Marcel Birgelen]

Christie has a somewhat convoluted way of licensing their image warping technology, but it's one of their money makers, so convoluted licensing schemes are to be expected. Interesting to know: If you have a CineLife(+) projector, your projector is already using warping under the hood for color convergence...

But what you need to do warping beyond this color convergence, is software to create those warp files. There are currently two pieces of software that can do this: Christie Twist and Christie Mystique. Christie Twist is a free solution for manual warping, but it does not support the DCI-line of projectors... (There are also paid upgrades of Twist, but those are not needed for single-projector setups.)

Mystique DOES support a limited range of Christie's DCI projectors and it's certainly not free. The licensing happens on a "per projector" level, as in the license type limits the number of projectors you can control and what features are available. The camera solution is another upgrade, called the Guardian.

To me, $17k for a single projector license sounds a bit steep, especially if it's only for the Mystique license. The Essentials Edition, which should suffice in your case, should be ±$5k. Still, without further knowledge about what's included or not in this $17k, it's hard for me to judge that figure.

Due to having the pleasure of witnessing a 4K Laser with Warp correction in our steep theatre yesterday, a couple conceptual questions arise:

1. When did DCI loosen their stranglehold on disallowing any pixel level geometry correction other than cropping in DCI setups? If they did?

I don't think this was ever in the DCI specs. E.g. DCI always allowed for scaling and none-square anamorphic scaled setups are also "within spec". The problem is that anything beyond simple linear scaling requires quite some processing power inside the secure enclosure. Most vendors initially simply implemented TI's standard ICP design and that didn't support anything beyond simple scaling.

There is a section about the delivery format that forbids anything but "square pixels" inside the container itself.

Update: You're using a periscope mirror setup in conjunction with laser? I've never seen such a setup being used with laser. You don't have any problems with color convergence in that room?

[Marco Giustini]

Not sure what you mean with "narrower", you mean horizontally or vertically? I believe you might mean vertically: if the projector is raked, your picture would stretch vertically, deforming it and affecting linearity. Mystique has a way to correct that, as long as the keystone correction.

I really dislike those corrections. They cripple picture resolution. Sometimes they're the lessen of the two evils but they should be avoided as much as possible. If you don't believe me, play a 4K test pattern WITH and WITHOUT mystique. I feel there was a very good reason for DCI to forbid those types of picture manipulation!

[Ryan Gallagher]

Update: You're using a periscope mirror setup in conjunction with laser? I've never seen such a setup being used with laser. You don't have any problems with color convergence in that room?

No no. Periscope setup is on the 2k in the booth. The visiting 4k Laser was on scaffolding just outside the booth without mirrors. The hush box/chassis rake angle was EXTREME though... I'd guess 30deg. And that was with maximum lens shift down for scope. We would want a little lens shift wiggle room in a permanent setup because we drive some weird aspect content here on occasion. So there is some debate whether mirrors would be required still. Personally I have no idea if laser sources play well with optical periscope mirrors. Periscope lenses do exist for non-DCI projectors though, so I assume it's possible.

If we were to invest in such a projector it would go in the booth, and there is a slight question of ceiling height clearance at that chassis angle, we might have to move our portglass down, which risks hands and heads. The licensing costs question was more academic. The warp file creation would probably be done one time against the Custom full raster, and used on every channel, as such I'm not sure "we" would need to own the Mystique license, just pay someone to do it once.

Marco, yeah definitely saw both with and without test patterns in the setup process. I know it is a compromise, but our situation has always been a compromise. It definitely produced better results than our 2k with the periscope. Even with the periscope we still have about 12" of side keystone crop in flat. Without the warp file on the laser it would have been more like 2.5 feet on each bottom corner, aspect depending. I guess the benefit of 4k and laser sub-pixels is that it's easier to make the argument for sacrificing some of those pixels.

Narrower "after" matching vertical size, if we had matched top edge size i think "taller" would have been the correct term. ;-) But note our 2k is not raked at the chassis much at all, but is raked by way of the periscope setup. So I assume that "can" introduce vertical too. Without the warp file the 4k rake produced even more vertical stretch, so I assume our 2k mirrors are helping there, just not fully corrected.

[Marco Giustini]

Get a flashlight with a defined beam - not your mobile LED light - and shine the light on a wall while perpendicular. Now angle the flashlight to mimic a projector: the beam is not round anymore, it's elliptical. That happens when your projector is raked.
Mystique can compensate for that as well - it's optional - so to restore the proper vertical height, or linearity if you want. As a result, if you match your uncorrected 2K projector to the corrected 4K height, the width of the two will be different.

That's where I'm not sure I'd use all those options. Yes, they make your picture "nicer" geometrically but the price is less resolution.

[Ryan Gallagher]

That's where I'm not sure I'd use all those options. Yes, they make your picture "nicer" geometrically but the price is less resolution.

You haven't seen how bad our geometry is uncorrected. ;-) If we were to upgrade I don't think we would opt for another periscope system knowing that mystique and warp files are now an option.

[Marco Giustini]

And that's exactly why DCI banned those features in the first place!

[Carsten Kurz]

DCI never banned such features. They only demanded scaling to be performed without introducing visible image artifacts.


from DCI spec 1.4:

'Should electronic image resizing or scaling be used to support a constant height projection or constant width projection theater environment, then it is required that the image resizing or scaling does not introduce visible image artifacts. It is intended that the projector project the full horizontal pixel count or the full vertical pixel count of the image container.'

Yes, there is no strict formal definition of 'visible' or 'non-visible' image artifacts.