Increase contrast in a barco spk4k projector

[Ricardo David]

Hi guys,
WE installed a barco spk4k projector in out cinema and easy calibreated by barco guy, but my boss wants more contrast, how can i give more contrast?

[Tom Bert]

Hi David,

when you go to the "Accessories" section of the SP4K product page, you'll see some "HC" (= high contrast) lenses listed. E.g.:
(SP4K-C) https://www.barco.com/nl/product/sp4k-25#accessories
(SP4K-B) https://www.barco.com/nl/product/sp4k-35#accessories

Such a lens will boost your contrast to ~3000:1 (trading off of ~20% of brightness)

Note that there is also an SP4K model with 5000:1 contrast: https://www.barco.com/nl/product/sp4k-27hc

What projector are you using?

[Ricardo David]

Help guys,
I haver a high contrast Lens , we have 14fl in screen, should i oush ir more for Higher contrast?

[Ricardo David]

Hi, barco spk4k 12c with tld ultra 1.66 i think.

[Tom Bert]

This lens? https://www.barco.com/en/product/tld-ultra-116-149

[Ricardo David]

Thats correct,its that Lens.

[Ricardo David]

Ultra short trow, no HC.

[Ricardo David]

They are going to replace light engine too, One green stuck pixel, and i see a interference pattern in Bright color and on white teste patern of the projector.

[Marco Giustini]

"interference pattern" is likely Moire' and that won't be resolved by an engine swap. It's an effect given by the pixels of your projector and the perforation of the screen. You either replace the screen with one with smaller perforations (and you still won't be sure it will work) or you can try slightly defocussing the picture a bit to mitigate the issue. Another way is to zoom in/out the picture slightly and hope that the size of your pixels change just enough to stop showing moire on screen.

Re. the contrast, it's not an easy path. As Tom says, an HC lens will eat 20% of light so you first need to assess whether you can afford that - remember, a dim picture will look awful. I'd like to say that if you feel you don't have enough contrast then you chose the wrong projector.

[Sean McKinnon]

How dark is the room? How dark is the area around the screen? Basically the area around the screen should be a black hole with no shiny or reflective surfaces. What type of screen and gain are you using? a matte white or grey screen (in my opinion only) will make black look blacker and reflect less ambient light. House lights and aisle lights should be as dim as your local safety regulations allow and absolutely should not shine on the screen at all. What kind of glass are you using in your port? is it optical AR coated "water white" low iron content glass? Is it clean if the port glass isn't clean it will make blacks look milky. and finally was the "barco" guy actually from Barco or just a local dealer/tech they sent in. I have seen wide variation in the quality of the setup depending on the technician that does it.

[Randy Stankey]

I agree with Sean. Contrast, as perceived by the human eye, is relative.

I'm sure we've all seen the "Cornsweet Illusion" that asks the viewer to try to determine which of two squares in a diagram is darker but, in reality, both are the same.

Cornsweet-Illusion.png

It is the gradient running along the center of the diagram that confuses the eye. Cover the center of the image with a piece of paper and you'll see that the two squares are actually the same.

This effect is likely happening in your theater. Lighting conditions and the lightness/darkness of objects in the background can confuse your eye into thinking that your picture has less contrast than it actually does. Your technician from Barco could calibrate your projector six ways from next Sunday but, if conditions inside the auditorium aren't right, you'll just be pissing up a tree.

When I worked at Mercyhurst, it was a multi-purpose venue; a legitimate theater that also showed movies. The screen was hung from the fly system. I had, literal, cussing-swearing arguments with people who wanted to put things on the stage to "dress up the screen." The auditorium wasn't as dark as I wanted it to be because it wasn't originally designed for movies. The walls were light colored and, every time you opened the auditorium doors, light bled in from outside. I spent an inordinate amount of my time proverbially slapping down fuckwits who wanted to do things that would ruin the picture.

I remember reading a statistic which said that a light source, other than the projector, shining on the screen will degrade the picture by five percent for every one percent of brightness, relative to the projector. This means that a light that is only twenty percent as bright as the projector can completely obliterate the picture.

When we're talking about differences in contrast on the order of a fraction of a percent, a light source as dim as a cigarette lighter or an object in the field of view that is only slightly lighter than the background can easily ruin your picture.

I suggest going through your auditorium with a critical eye. Weed out all sources of stray light; not just things that shine on the screen but anything that a viewer can see from his seat. Ensure that the entire area around the screen is dead black. (Vantablack! )

Like Sean and others say, do everything you can to ensure that all the light from the projector is getting to the screen:

* Align the projector. (Should have been done... Check!)
* Make sure your lens is right. (Check!)

* Porthole glass? Is it the right kind of optical glass? Is it clean and installed properly?

That's the next thing I'd check. A bottle of Windex and some lint-free cleaning wipes might, very well, go a long way toward solving your contrast problem.

[John Thomas]

Do not use windex or any ammonia based product to clean optically coated glass.

[Randy Stankey]

Agreed. For optical glass, only use what the manufacturer recommends.

When I said "Windex" I mostly meant it in the generic sense.

However, I have never worked in a booth that had optical glass in the projection ports. A couple that I worked in, briefly, didn't have glass in the ports, at all. Just 18" square holes cut in the cement block wall. In all the rest, I actually used Windex® brand glass cleaner. Nothing else but good, old-fashioned, blue Windex but, as I said, none of my booths had optical glass.

[Stefan Scholz]

Think about the phenomena called limiting contrast. It is very important in viewing movie screens to have a matt black surrounding, a correctly masked image. The viewing mech compares to the dark part, which is used for reference. A black velvet masking is mandatory for the perceived "in image" contrast.

Secondly what Randy Stankey pointed out, stray light and direct visible bright spots has to go.
Port glass, Amiran on Optiwhite or Diamond on waterwhite. If fire rated is mandatorz, Pilkington projection glass. Not cheap, but ordinary window pane or standard Pyran Fire glass does not work in projection.

Third, the choice of a 0.98" chip projector with small light output is not the most clever way, the 1.4" chip machines offer a superior contrast out of the box. With the 0.98" chipset the HC lens does not really get the premium price tag resolved. Go for the good projector, if you want contrast. With Barco, that is the 27 HC model. That one offers a fine, outstanding image. Other brands eventually offer 1.4" machines in smaller light output as Barco does.
I was somewhat stunned looking on images presented by modern Laser presentation projectors, outperforming many theatre units out of the box. There must have been a technological improvement in DLP chip and optics design, to a point, that cinema ones loose.

[Mark Gulbrandsen]

Think about the phenomena called limiting contrast. It is very important in viewing movie screens to have a matt black surrounding, a correctly masked image. The viewing mech compares to the dark part, which is used for reference. A black velvet masking is mandatory for the perceived "in image" contrast.

Secondly what Randy Stankey pointed out, stray light and direct visible bright spots has to go.
Port glass, Amiran on Optiwhite or Diamond on waterwhite. If fire rated is mandatorz, Pilkington projection glass. Not cheap, but ordinary window pane or standard Pyran Fire glass does not work in projection.

Third, the choice of a 0.98" chip projector with small light output is not the most clever way, the 1.4" chip machines offer a superior contrast out of the box. With the 0.98" chipset the HC lens does not really get the premium price tag resolved. Go for the good projector, if you want contrast. With Barco, that is the 27 HC model. That one offers a fine, outstanding image. Other brands eventually offer 1.4" machines in smaller light output as Barco does.
I was somewhat stunned looking on images presented by modern Laser presentation projectors, outperforming many theatre units out of the box. There must have been a technological improvement in DLP chip and optics design, to a point, that cinema ones loose.

But talk to the people that actually matter, namely the colorists that actually grade each scene in.a movie and put it together as to the directors wishes. These people despise laser and they only use it if the job calls for it. They also make sure a particuluar job looks ok on the laser. But overall 95% of the time they are grading color and density by xenon.