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Author
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Topic: HTI, Xenon, and Color Temperature
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Miguel Gimenez
Film Handler
Posts: 52
From: Grenoble, France
Registered: Feb 2010
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posted April 11, 2016 01:47 AM
Hey Alan, I am afraid I can't give you the projection feedback, but I can comment a little on this.
As a context information only: we have to take into account that the human eye luminosity perception is higher for green-blues (peak at greens) being the red ones the smallest one. This means that we always perceive cool lights/colors brighter than they are, or if you prefer, brighter than a warmer version of the same image with same actual luminosity (measured) than the cool sample.
Of course this is not against the actual lumens thrown by each lamp/projector. Which normally is higher for HTI than for halogens, talking in general.
This is the reason why screen/TVs/beamers manufacturers always adjusted their equipment by default for cool temperatures (normally even 9300 K !): they appeared cooler (in both senses ![[Wink]](wink.gif) ), and brighter to the potential purchaser.
Try to measure with a calibration probe a TFT screen adjusting temperature levels and, although the difference is there, the perceived brightness is much more. There is a nice article of Charles Poynton in his page, explaining the concepts behind this.
At side of that, I have concluded (please note that these are only my conclusions) that the Xeon/HTI was produced due to two facts mainly: the "need" to project for larger audiences AND to the people change of taste: progressively people were pushed to cooler looking screens, as explained above, and the 'world color tone' around us in our quotidian life has shifted from warmer tones to cooler ones (remember classic car colors, advertisements, illustration, clothes, lighting, etc), so a cooler light was considered more modern and more sales-safe...and warmer is perceived as worn-out, old-fashioned, and a grand-parent thing, at least for most people.
But for me the important point of all this, the key question, is with which light in mind were the prints made.
I have found some information through the years, about the process behind the Derann Disney prints, and -although I have not found final evidence of it yet, as there are several factors involved- it seems that they were done considering a color temperature between 3000 and 4000 k (closer to 3000). If so, then the 'best' way -related to color temperature- to project these copies is in a neutral controlled reflection screen, with a 3300K lamp, and if possible with a relatively neutral decorated room (or slightly shifted toward warm tones).
Alan, you say you worked in a lab (that's very interesting!), and you comment that the Xenon copies were timed differently, but you don't comment anything about the color tint. This seems to confirm me that these copies (not Xenon) were done all with the same tint, and that this tint "seems" the one for standard/halogen projection light. Did you ever had information about the color temperature balancing / timing or which were the origin of the films/masters?
I would love, though if someone could give more details about the film origin, ideally for the Derann Disney editions, to check or correct my information.
[ April 14, 2016, 05:21 AM: Message edited by: Miguel Gimenez ]
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Andrew Woodcock
Film God
Posts: 7477
From: Manchester Uk
Registered: Aug 2012
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posted April 11, 2016 05:25 AM
Going off Ugo Grassi's video on you tube showing his home cinema and his Xenon GS 1200, I'd have to agree Alan with your description of the sheer brilliance of the image projected with these, even on relatively small screen sizes.
I cannot say that the image lacks anything though on even on my halagon variants so long as it is completely dark when projected.
The Disney prints in particular really stand out on the big screen though due to the vibrant colours and the sheer colour palette used on these. Plus of course, the vast amount of contrast.
I'm guessing my Panasonic projector at 2200 lumens is something similar to what you're experiencing with a xenon, and the picture from this on Blu Ray is stunningly bright and beautiful.
One thing I did notice though, when a collector posted screenshots of another Disney favourite on film using a xenon, was that to my eyes, the screenshots posted appeared a little washed out or bleached almost compared to the screenshots of the same print from my halogen lamp. This could of course just be a difference in print, but for this particular title I'm referring to here, they were all renowned for their consistency and quality for both sharpness, contrast and indeed colour.
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"C'mon Baggy..Get with the beat"
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Miguel Gimenez
Film Handler
Posts: 52
From: Grenoble, France
Registered: Feb 2010
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posted April 11, 2016 04:28 PM
It could be another reason, but definitely a cooler light provide an increased perceived contrast, which is usually interpreted by the postprocess (ie, brain) as an increased (fake) sharpening effect in the limit zones (so no grain sharpening).
This is a known effect, but it has the downside that it is linked to cooler lights, so if you want it, you have to stand a cool light. These are reasons why all manufacturers pushed cool tints in their devices (and this includes tablets and mobiles, which abuse this effect, btw).
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Gary Crawford
Jedi Master Film Handler
Posts: 979
From: Manassas, VA. USA
Registered: Jun 2003
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posted April 12, 2016 06:47 AM
There are so many variables to picture quality. Here's another. At a recent film gathering someone with a GS xenon was showing super 8 prints ....prints which I owned also. The picture was hazy...somewhat bleached...no contrast. Evidently the owner of the machine didn't notice how bad it looked. I mentioned it and he took the lens out...and the rear element was filthy. It was diffusing the light badly. Once he cleaned it, picture was good and sharp with good contrast.
Then think of ALL the variables from the negative of the print, to how the print is timed, the stock for the print, the projection bulb, lens, AND screen, then the camera used to snap the stills..and its settings, lens, lens cleanliness, light in the room and bouncing off the ceiling. Then the program used to make the digital still and send it out....and the monitor we use to view the screenshot. It's a wonder anyone can pinpoint the cause of ANY color balance or sharpness issue.
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Miguel Gimenez
Film Handler
Posts: 52
From: Grenoble, France
Registered: Feb 2010
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posted April 12, 2016 04:29 PM
Well, a lot of concepts mixed up here. We are mixing luminosity, with saturation, with illuminant color spectrum, and all of that between perceived and measured.
'Livelier' is a relative term. We can have bluish looking image with tungsten light and warm image with xenon. It all depends on the light (illuminant) considered when balancing colors in the print.
Personally I never saw 'livelier' colors than at dawn or sunset, although luminosity is weaker than at noon, for example.
The same applies to photography, painting, and any other pictorial art.
That's the reason why I said that the 'key question' is 'with which light in mind were the prints made.'
...because, after all, you can compensate an image color to obtain what you want with any type of light spectrum illumination.
IMHO, regarding sharpness, I disagree about the influence of filament size. The light touches the film before the rays could be 'addressed' by the lens (aligned in divergence): halogen or Xenon lamps both throw a mess of light rays regardless of filament size: try to light something with them outside the projector (except if Xenon has some kind of lens inserted in the glass protection).
And even if they were aligned, it -theoretically- should be better for thicker filaments (more paralelism), but in practice there is a 'pollution' of rays that disguises the theoretical advantage of filament thickness, at the scale we are talking. Theoretically we could think a thinner filament has less crossed rays, but even without considering the rebound rays, it has higher dispersion...
I have been working with fresnel spots for years (and yet I do) in a portrait studio. Although a PJ does not use them, the basic principle behind is common. When you have the best defined contrast between shadows and lights is when you adjust the light to lens distance as flood (which is counterintuitive), i.e. when you have less dispersion and less crossed-rays (smaller angle).
Maybe some Xenon/HTI projectors have the bulb farer from the lens (not only the frame) than some halogen ones, depending on the characteristics of the lamp it could -theoretically- be a very slight increase of focus. But the small distances and smaller filament size, together with the scale we are talking about makes this irrelevant in practice, in my opinion.
In that regard it *could* be that if the Xenon lamps had some kind of pre-lens included in the same bulb and the distance to lens is increased considerably versus the halogen one, then that may lead, depending on the 'pre-lens', to a very slight increased sharpness. Although I would judge it very faint, which would mix with the perceived sharpness, which is also there, for sure.
I insist: the human eye contrast perception varies greatly depending of light wavelength and luminosity: as we know we have a non-linear brightness perception, when we project with higher lumens, the black is not shifted (or not too much) and highlights are pushed quite a lot vs an halogen one. This expand the efective dynamic range of the image and necessarily produces higher perceived contrast (eye's dynamic range is still wider), and, btw, perceived sharpness.
On the other hand I think that the point Brian has commented may have some influence too. To check, in any case.
So I think that, as Gary points out, there are a lot of factors that can influence it, perception, distance to film/lens, quality of lamp (more than size), etc.
Of course it could be that I may be completely wrong too ![[Big Grin]](biggrin.gif)
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