Experience with color calibration between lamps and lasers, and their matching.

[Christos Gartaganis]

I haven't conducted any measurements on an SP4K projector myself since we currently have only two installations in Athens and another one in Crete. Typically, a 3P laser projector should display three spikes, corresponding to each primary color. However, as Steve pointed out, there can be multiple spikes in the green and red regions. When time permits, I plan to take my own measurements using a spectroradiometer and share some photos here.

[James Gardiner]

I would also add that, to my understanding, there are also some mitigation techniques in the light-pipe area that help reduce speckle. I know Barco implements something along these lines, though I’m not certain whether Christie does the same.

I’ve often wondered why manufacturers don’t introduce a vibrating plate or mirror within the light pipe itself—essentially performing a similar function to screen vibrators, but from the projector side instead.

[Steve Guttag]

I believe these three are a Christie CP4415:

Red is clearly multi-spiked and centered around 640nm

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Green is also multi-spiked (and broader):

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I believe these three represent a Barco S4 RGB:

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And NEC (NC3541L...so an RBB with green phosphor wheel...which will be self evident):

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It's kinda wild on the blue (this is uncorrected or .1460, .0366)
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Green does correct to .280, 640...with a little help from its friends:

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It's corrected white is white-ish. .314, .351:

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To my eyes, the NEC looks cold/blue but I don't notice speckle. It's not a bad picture but despite the meter saying that is white, my eyes think it's on the cold side. The CCT is 6325K.

Compare that to an RGB laser system (should be a Barco S4) color corrected to 6359K:

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It seems improbable to me that these would make the same picture, color wise. But strict x/y coordinates and Y values (and CCT) they are essentially the same. They sure don't look the same to me, on screen.

The Christie and Barco are closer with the Christie, to my eyes, not as red. The meter says that the Christie corrected to 6217K:

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[Steve Guttag]

For those of you that might be curious about the SP2K laser (also phosphor wheel), we get more shenanigans to make it work. This is red:

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A typical phosphor created green:

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And a pretty typical blue:

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Put them together for a corrected white:
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The meter says 6368K.

For reference, corrected Xenon:

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(6298K)

[Christos Gartaganis]

I find it quite intriguing that Barco chose to use laser phosphor technology across all models in their new SP2K series of cinema projectors, while all the SP4K series models feature exclusively RGB laser technology.

[Steve Guttag]

It is going to be a cost thing, for sure. Green is expensive. The company that is going for 2K in 2026 is thinking cost. The average consumer has 4K in their home on screens MUCH smaller than any theatre, even when accounting for subtended viewing angles. So, if you have a cost conscious customer, why price yourself out with an RGB laser? Neither Christie (or Sharp) are going RGB on their smaller projectors either. It was only recently that Barco offered the SP2K in the "C" package (.98" imager) for the 21K lumen and 24K lumen projectors. Before then, that would have placed you in the 4K market for Barco.

[James Gardiner]

I’m personally a fan of phosphor based projectors. I’ve yet to see a pure RGB laser projector that mitigates speckle sufficiently, in some models from certain vendors it has been absolutely horrendous and frankly unacceptable. Fortunately, most of those models have now largely been phased out.

Looking at the images, it does seem that other vendors are starting to follow Barco’s lead. I’m also hearing that a new Sharp/NEC range may be arriving soon (All above the NC13XX), likely adopting multi-spike red or green, if not moving to a phosphor based approach.

[Harold Hallikainen]

Use of phosphors is interesting. I see it as making a fancy fluorescent lamp where the phospors are being excited with a laser instead of ultraviolet from mercury discharge. Since we need RGB, can a single laser be split to excite three different phosphors to generate RGB and not have any filters? Just use the phosphor glow to drive each DMD. Or do they use a phosphor mix to try to create white light, then filter that to RGB?

[Steve Guttag]

Thus far, what I've seen is using a blue laser to shine through the phosphor wheel prior to the integrating rod and prism. They are still trying to create white light prior to the prism breaking it into its color primaries.

[Ryan Gallagher]

Here is a fairly dumb laser question. So if you have to adjust laser power for a different zoom sizing for a unique aspect ratio... does that require separate color calibration?

My instinct is yes, but in my cursory experience with this visiting Barco Series 4 laser, I was not privy to where/how one sets the measured colors, was too busy ingesting festival content to watch much while Barco was doing that work. Not that we have the kit to do it without a tech handy.

It came up because because we zoomed larger for a F220 presentation to better fill our screen and be presented masked properly. We got everything sorted before studio tech arrived with a new top level preset for MediaPlayer_Flat_220. But conveniently we forgot a different zoom meant a brightness change. Luckily this tech wanted to shoot white first thing, and caught it, we added 5% laser power and they were happy. But in the back of my mind I'm wondering if laser power changes cause color shifts too. We were within 1% of our scope laser power, but being a flat format it was probably inheriting most things other than position and picture settings from the flat set of macros/settings prior? Or is color handled separately?

Tech/film folks were happy, just wondering if technically we missed an idealized step in building out a new format where color calibration is concerned.

[Steve Guttag]

Yes and no. Yes, technically, the color can shift as you adjust intensities as they don't go up/down together. However, the companies have calibrated their lasers to, mostly, track as you change intensity. This was not always the case. Furthermore, with HMI lamps, like with the NEC NC900C...you, absolutely, had to have separate color files based on the lamp intensity. Then again, its color quality wasn't all that great, to begin with and horrible if you took its notch filter out to get more "light."

[Marco Giustini]

Older lasers were also slow in changing brightness. Gen1 Christie would show some purple or cyan cast when brightness was changed abruptly (flat to scope and vice versa) and would take 30 seconds to stabilise, if even possible. Some of those systems were not rock stable on colours.

[Hong Sung Hyeok]

With the Christie Series 3, color calibration was incredibly cumbersome to achieve the correct white point. To obtain white values of 0.314 and 0.351, you had to carefully adjust the power of each individual R, G, and B laser. Furthermore, the Series 3 was particularly sensitive to ambient temperature; if the temperature was too high, it would confuse users every morning with absurd color tones.

With the release of the Series 4, things became more convenient as individual R, G, and B power adjustments were automated. However, whenever the regular maintenance season returned, the Christie Series 3s installed in the field still gave me a hard time.

[Marco Giustini]

I have a feeling you don't have a spectrometer which shows RGB with bars and allows you to set a white point? With that, it's just a matter of clicking on R-G-B on the UI until the relevant bars align
If you're looking at .314x.651 then it's a bit more cumbersome for sure

[Ryan Gallagher]

Yes and no. Yes, technically, the color can shift as you adjust intensities as they don't go up/down together. However, the companies have calibrated their lasers to, mostly, track as you change intensity. This was not always the case. Furthermore, with HMI lamps, like with the NEC NC900C...you, absolutely, had to have separate color files based on the lamp intensity. Then again, its color quality wasn't all that great, to begin with and horrible if you took its notch filter out to get more "light."

So I asked the same question of our Barco tech when he returned to collect the projector. 100% the Series 4 are supposed to "track" calibration values through their upper laser power ranges, but the caveat he mentioned, and would have impacted us, is that tracking does not work so well at the lower power ranges. We were at 40-46% laser power using the DP4K 25C, so definitely outside the easy to adjust range.

Henry Miranda was here too from WB, it was his feature where we had zoomed for F220 and had to put in a new laser power value after he measured. He did notice the color drift too, and was why he stopped me at 13.75fL cause another 1% power was putting it out of spec on color. To my eye I even saw the white color change after doing the initial +5% power adjustment. Everyone was totally happy, but good "gotchya" to be aware of.