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Question What kind of filter for extending colourspace?

jfinnie

Distinguished Member
Quite a few projectors these days have internal filters for extending their colourspace. I have an old trusty Sanyo PLV-Z800 which doesn't quite reach Rec.709 (particularly for green / hence cyans too). I wonder if this tech can be applied external to the projector to achieve similar results? What kind of filter could I buy off the shelf to achieve this?

Or is it much trickier because the filters have to be installed internally before the light reaches the panels, for example?

It doesn't matter if the image needs additional colour correction afterwards as I have a meter and an eecolor 3DLUT box that I can program whatever correction is required into; what I can't do at the moment is get more green than I have coming out of the PJ.
 

Peter Parker

Distinguished Member
You could try placing a green filter in front of the lens and recalibrate back to D65 and see what that does for the gamut. You'll probably lose around 30% or more lumens though, doing that.

Just buy a cheap filter, or a swatch of filters from the likes of Lees Filters, and then experiment. I don't know if it'll work as I can't test that myself right now, and it's not something I've tried before (I've used filters for increasing on/off contrast though), but you've not much to lose apart from the cost of a filter.

When I used FL-Day filters to increase the red deficiency of UHP lamps, I don't remember it increasing the gamut, so I've a feeling you may not get the result you're after, but it's worth a try if for nothing more than a learning exercise, plus, you can let us know the results you get.

I wonder if @Rickyj @ Kalibrate has noticed any gamut improvements as he's been adding filters to some of his projectors recently with great results, so he'll have first hand experience of what to expect.

Gary
 

jfinnie

Distinguished Member
That's exactly the quandry I'm in; I can't quite get my head around a filter increasing the gamut; yet it seems to be happening all over the place at the moment.

The projector is able to meet Rec709 more or less for red, but the level of red output for this PJ is low (and I guess most UHP lamps) - which has to get adjusted at the moment for Rec709 / D65. So in many ways the last thing I want is a greener picture!

One of the sister projectors in the family for mine - PLV-Z3000 - actually had one of these switchable gamut extending filters internally - from looking at the service manual it appears to be located just after the integrator in / out lenses - ie just in front of the lamp.
(http://cncms.com.au/SANYO-SMs/Commercial-Industrial/Projectors/LCD Projectors/plv-z3000/plv-z3000_draft.pdf, page 41)

I'm tempted to buy the part and crack the old dear open, but something external would be less hassle.
 

Peter Parker

Distinguished Member
That looks like an FL-Day filter that's often used to compensate for the UHP lamps lack of red. I wonder if placing it inside after the lamps and before the lens has a different effect to calibrating with it externally.

Gary
 

jfinnie

Distinguished Member
Useful info, thanks, found a few of your old posts on the subject. Definitely going to have a play with this :) I'm intrigued by the seemingly large difference this filter alone makes to the colour gamut
 

jfinnie

Distinguished Member
Panasonic (who deal with Sanyo spares) are happy to sell me the Cinema filter glass part from the higher-end projector for £25 including delivery. It is a square filter which would normally go into a geared holder, driven off a motor. With any luck it is big enough for the active area of the image on my projector, and I can just attach it by sticking it to a plain UV filter and then offering that up to the front of the lens. Should be here in the New Year. :)
 

Peter Parker

Distinguished Member
Let us know how you get on, though I've a feeling it should go inside to work as designed. Will you be brave enough to try that so you can compare? :)

Gary
 

jfinnie

Distinguished Member
I have the same suspicion too, but at £25 it piqued my interest - they used the same Cinema filter glass in both the PLV-Z3000 and PLV-Z4000 units. I might try it inside if outside yields no useful results and I still have the PJ in 3 or so months - the lamp will be spent by then and I'll be looking at spending more than what it cost me on a new lamp. I've already got the upgrade itch...
 

Peter Parker

Distinguished Member
Well, next year is going to hopefully see UHD BD available, and we'll know exactly what will be needed, so it's going to be difficult to decide what to get I reckon. :)

Gary
 

jfinnie

Distinguished Member
Well, today was a day of mixed emotions.

Brilliant! Package I'd forgotten about buying arrived from Germany.
Rubbish! One glass filter, inadequately packed, in 4 pieces, Oh well, at least one piece is big enough to mount to some card for test.
Wow! This piece of glass really does extend the green gamut way out past REC709, at the cost of a bit more than half the brightness. Calibrating the whitepoint with the filter in place doubles the contrast ratio of the PJ.

It does mean that the ridiculously green "dynamic" mode, with a little bit of tweaking, now seems to be useable, which will leave me with 14ftL at the screen.

I'm just running a quick 3DLUT for the EECOLOR to see what my tiny little slither of goodness looks like. I'd love to know what this filter glass is. If you put it on white card, it gives the card a distinct pink tinge. If you hold it at an angle, it becomes almost a mirror, reflecting back a slightly green image.

I'm not sure that even the complete piece of material is large enough to cover the whole projected frame, so it would be really good to work out what it is.
 

jfinnie

Distinguished Member
Yeah, I'm not sure it is like an FL-DAY. I have an (admittedly cheap) FL-DAY filter which doesn't do this weird colour flip.

It goes from green mirror to pinky depending on your angle with respect to it. See the following poor photos.

I'd love to know what it is as I probably need a slightly bigger piece of it for what I want to do.
DSC02386.jpg
DSC02387.jpg
DSC02388.jpg
 

Peter Parker

Distinguished Member
If you place both of then (one at a time) in front of the pj with a full white field, what is the difference between them when you measure them?

Although the FL-Day may not do the green reflection, does it have a similar overall effect?
 

jfinnie

Distinguished Member
No filter. New lamp, I don't plan to calibrate it properly til it has 100hrs or so on it, hence red is a bit high:

Screen Shot 2016-01-05 at 23.12.38.png


Sanyo Cinefilter - does extend the gamut:
Screen Shot 2016-01-05 at 23.12.46.png


Cheap FL-Day - does not notably extend the gamut:
Screen Shot 2016-01-05 at 23.12.52.png
 

Peter Parker

Distinguished Member
Have you got the CIE images to show the gamut differences? I'd be interested to see before and after changes for both filters if possible please. :)
 

jfinnie

Distinguished Member
I guess this is all potentially interesting for people wanting to achieve DCI-P3 on projectors which don't have a wide enough gamut as they stand.

Bear in mind I had the EEcolor 3DLUT in circuit when I ran this last night - so the "no filter" gamut is digitally cropped vs the native gamut of the projector to a best attempt at REC709. I was running out of time with what I wanted to try before going to bed. The gamut with the filter in place is much larger than shown, I will run it again this evening without the EEcolor.

No filter
nofilter.jpg


Sanyo cinema filter
cinefilter.jpg


Cheap FL-Day filter
cheapfldayfilter.jpg
 

Peter Parker

Distinguished Member
Thanks - I find it interesting so appreciate you taking the time to experiment and post the results. :)

Looking forward to seeing how big the filter gamut is before being altered.

Even if we can achieve a P3 gamut, can a pj map the colours to it correctly without P3 colourspace processing built in, or can an external scaler etc do that? I'm very rusty on calibration these days...

Cheers

Gary
 

jfinnie

Distinguished Member
I find it pretty interesting, too.
I guess it would be difficult to do with just a stand alone player. For PC playback it would probably not be too hard, using maybe the 3DLUT capability of madvr.
 

Peter Parker

Distinguished Member
Great stuff - thanks for posting. :)

These are the kind of things i used to do when I had the time and a set up to allow it. I hope to get back into it again later this year.

I guess the next thing is to try and get that brought back to 100% Rec709, and have images correctly mapped to it, and then try and get P3 encoded images mapped as accurately as possible to the expanded gamut.

Your next mission, should you choose to accept it.... ;)

Cheers

Gary
 

jfinnie

Distinguished Member
I did get it more or less to REC709 yesterday with a quick profile (~1400 patches) and a 3DLUT, though I think the colours are undersaturated a bit, need to have more of a play with some more time. Quick validation report attached.

Someone on AVSforum posted that it is a dichroic filter being used. It makes me think that using it outside the PJ isn't going to be totally satisfactory as dichroic filters (from my limited reading on the subject) have two behaviours that will be objectionable:

1) they reflect back the rejected wavelengths instead of absorbing them - I guess this means lots of green / blue light going back into the PJ, probably not a good thing.
2) the wavelengths of what does / doesn't travel through them shifts depending on the angle of incidence

Anyhow, something to play with for now. The slither of material I have won't quite cover the whole widescreen frame. A replacement will be with me... in another month's time...! :)
 

Attachments

  • Measurement Report 3.0.6.pdf
    184.2 KB · Views: 40

Peter Parker

Distinguished Member
If the colours look undersaturated, I wonder if something similar is happening to what would happen when people tried something similar with the JVC HD1 - that had oversaturated colours (reds and greens I think), but when the peaks were brought back to the correct locations, it also brought back the locations inbetween, so they were now less saturated than they should be, if that makes sense. A bit like drawing some dots on a piece of stretched elastic. As you relaxed the elastic, all the dots moved back, not just the one on the end.

If you angled the filter, would that help reduce the reflections?

Gary
 

jfinnie

Distinguished Member
I'm pretty sure the problem is that fully saturated colours are not bright enough compared to the measured peak white on the projector, just needs a bit of a fiddle, I was picking and choosing what to adjust as I didn't have much time, and was mostly interested in the gamut expansion.

The filter piece I have mounted to some board is only about 10mm x 30mm - if I angle it I'll have barely anything to project through. As it is I can only cover about 80% of the field. Hopefully if the replacement arrives intact from Japan I can test a bit more.

Anyhow, a lot of fun for £25 :)
 

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