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This topic comprises 2 pages: 1 2
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Topic: Definition of "dual digital"?
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 05-31-2009 01:10 AM
They mean they are using two projectors instead of one. Imax, i.e., does it this way (with dual-projectors).
This could hold the following (practical) advantages over SOME single projector systems, specially when playing 3D titles:
-Potentially brighter picture, by using two projection lamps instead of one. This could also allow for a potentially larger screen as well, i.e.
-No "3D flicker" (no temporal disparities). This is a slight defect that occurs on single projectors when one eye is seeing one thing that is different in time from what the other eye "remembers". In short: it gives some people some eye fatigue/headaches/weird feelings sometimes. Dual projectors or Sony 3D single projector do NOT need to have this effect.
-Potentially higher quality picture, with double the color resolution (4:4:4 instead of 4:2:2) and larger color gamut (12 bits against 10 bits). Sony 3D single projection system also has this advantage.
-Potentially, a dual projection system could be made to have less ghosting (3D double-images) than some single projection systems. But some single projection systems, like Dolby, can be as good or even better in this department.
-For 2D applications, the screendoor "artifact" could be less visible. Sitting close to the screen, it may be apparent the black space between the pixels, called the "screendoor", on many projectors. By using two projectors together, their screen-door effect could be less apparent by "blurring" together.
But dual-projection can have its dissadvantages. I.e. if both projectors are not calibrated/adjusted perfectly, the images in 3D may appear assymetrical. They need to match in color, brightness (i.e. lamp aligment and output), etc. It's not possible to align the images 100.00% identically, so there is always some (very) minor keystone disparities between the images, etc.
Also, specially if placed side-by-side instead of one on top of the other, they could show assymetries in silver screens 'cos of the hotspots being (slightly) different for each image.
And, of course, it can cost twice as much as a single projection to buy and run (i.e. two lamps/double the electricity).
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 05-31-2009 09:52 AM
Master Image also offers passive polarization filters:
http://masterimage.co.kr/new_eng/product/system_02.htm?pos=22
You could, indeed, use linear polarization instead of circular like it has been the preferred method in the past (i.e., Imax Prime ![[Razz]](tongue.gif) ). It would have a slight advantage in brightness, ghosting and cost over circular. With the drawback that is more sensitive to geometrical angle-dependant performance (i.e. patrons need to keep their heads perfectly leveled or ghosting starts to appear, worse for larger screens or steep projection angles, etc).
4:4:4 and 4:2:2 are terms used in the video industry to refer, in short, to how the video signal is sampled. The video signal usually travels in 3 components, like 3 signals, which could represent each primary color (i.e. Red Green Blue) or a multi component signal (i.e. luminance+2 channels of chrominance).
What it means, in short, is having X number of pixels in one channel, typically the luminance channel (Y or the "black and white image") and a relative number of pixels on the other two channels (i.e. the "color difference channels"). So for 4:2:2 it could mean, i.e., that for each 4 pixels on each scanning line in the first channel, there are 2 pixels in each one of the other 2 channels horizontally and another 2 in the next scanning line.
There are many variations of this and sometimes the notation is not all that ... there. But it's a way to talk about "stuff" in the image, like color, having more or less resolution than other "stuff" in the same image, like some other color channel or luminance, and how the (sub) samples are located in the image vertically and horizontally compared to the main (not sub-sampled) channel.
Here it's better explained:
http://en.wikipedia.org/wiki/Chroma_subsampling
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