Tony359 ha detto:
Se l'immagine è scura, non è un problema di Dolby o di RealD ma di aver scelto una sala con schermo troppo grande
NON TUTTI i proiettori supportano il triple flash (144hz)
Per chi non vede niente, solo roba sdoppiata, e nessuno si lamenta... Purtroppo non è la prima volta che leggo e purtroppo molti pensano che il 3D sia quello ed escono "delusi"
avremo anche noi un 2K con il 3D. Presumibilmente un CMC4 della Cinemeccanica. I sistemi 3D - per il discorso di luminosità - non si possono installare su schermi molto grossi
Ciao Tony,
ti ringrazio per il tuo intervento molto interessante sull'argomento:
Non sono un esperto, ma un semplice appassionato e curioso, il Cinemeccanica di cui parli è il CMC4 D2, capace di offrire valori di luminosità di oltre 42.000 Lumens con lampada Xenon da 6.500 Watt ?
il Cinemeccanica CMC4 supporta perfettamente senza compromessi i 144hz ?
Il Cinemeccanica in questione è veramente ecellente/ottimo nella performance sia per le proiezioni in Digitale 2K che per quelle in 3D ?
Ho dei parenti a Firenze, conosco la sala 6 del Ex Warner Village, pensi che lo schermo della sala sia troppo grande per le preizioni in 3D, o il Cinemeccanica CMC4 è sufficentemente luminoso per le proiezioni 3D ?
Il sistama della Dolby ha il vantaggio per gli esercenti di poter utilizzare uno normale schermo per le proiezioni 2D, ma alla fine quale è il più performante coinvolgente tra il Dolby3D, il RealD e l' XpanD ???
Se dipendesse da te... quale delle tre soluzioni (Dolby3D, RealD, XpanD) consiglieresti/scegliresti per conto del gestore del Cinema in cui lavori ?
Fare un istallazione 3D tanto per fare, o per potersi solo fregiare del logo 3D, ma senza garantire allo spettatore determinati standard qualitativi, è una presa in giro... quindi, non sarebbe meglio spendere qualcosa in più (fare un buon investimento), ma garantire allo spettatore una esperinzia in 3D di ecellente qualità, adottando il sistema 3D migliore, abbinato ad una più che acettabile luminosità e coretta gestione dell'impianto... in modo tale che al prossimo film in 3D che esce, ed anche a quello succesivo, la gente ritorni in sala..?
Qui ci sono alcune considerazioni, anche negative sulle tecnologie adottate per le proiezioni in 3D:
I've experience plenty of crosstalk in Imax. The reasons are many.
First of ALL. The finest polarized performance theoretically ever attainable today is linear and something like 99.998% efficient. That means that you still will always, even under best ever theoretical conditions, would be watching with your "wrong eye" 0.002% of the "wrong image" (a double image).
That may seem like little, but the eye is a remarkable photon catcher So this amount of ghosting is the very least theoretical for a polarized (linear, circular is quite worse, Dolby is even better) system.
But, of course, such performance in real life is not usual. Most linear systems have a practical performance of about 250:1 contrast ratio. That means that, say in a spot on the screen shared by the left and right image, the right image is 251 times brighter than the same part in the other eye, you would start to appreciate the "ghost" spot of light. (Circular is about 100:1)
DCinema has a contrast ratio of 2000:1, so plenty of oportunities to see plenty of light from the wrong eye enter the wrong filter on the glasses while not being overshadowed by the right amount of light from the right image.
The main reasons for excessive ghosting in ANY movie presented polarized are:
-Bad screens. The surface has to be metallic for a reason. Dust is usually not metallic.
-Bad filters. Most effective polarizers are also the ones the degrade fastest. They need to be changed "often".
-Bad alignment or theater geometry. Filters (projector) needs to be perfectly leveled for linear systems, as need to be filters in the glasses. The projector should maintain a good angle for the incident light to bounce off the screen to the audience in a good geometry.
-Audience tilting their heads (in ear-shoulder direction). Circular is mosly inmune to this. In practice, circular also benefits from straight heads for reasons of residual analyzing polarization.
-Fingerprints or oils on the glasses, or otherwise degraded glasses filters.
That affects all films, making ghosting worse than it needs to be.
But the "practical" reason for a lot of ghosting is bad cinematography on some movies. They are shot with so much parallax (i.e. the left and right views so far apart in many parts of the image), that fusion of both images is far more difficult, leading to all sort of problems and worsening of any inherent ghosting.
Also, movies with inherent lots of contrast (i.e. a white star field in a black space background) and lots of parallax (i.e. things very far into or out of the screen), make the limitation of each projection setup more evident.
I saw Space Station 3D in Imax and don't recall it being particularly ghost-trouble film. But I've seen so many 3D films my memory is but a big blur.
A lot of Imaxes were shot with their "small" integrated 3D camera which allowed for very little error. I used it once myself during a training seminar in LA, and it was quite a little piece of equipment (that I would never considering using for real-world projects other than Imax, of course).
RealD systems are now trying to avoid these pitfalls by pre-processing the movie to get rid of contrast above their perception threshold in parts of the scenes with large parallax (lots of "3D"). From IEEE "Cancellation of image crosstalk in time-sequential displays of stereoscopic video".
quote:In this paper, we propose a method to reduce such crosstalk. We present a simple model for intensity leak, we assess model parameters for a time-sequential LCS/CRT system and we propose a computationally efficient algorithm to eliminate the crosstalk. Since the full crosstalk elimination implies an unacceptable image degradation (reduction of contrast), we study the tradeoff between crosstalk elimination and image contrast. We describe experiments on synthetic and natural stereoscopic images and we discuss informal subjective viewing of processed images. Overall, the viewer response has been very positive; 3-D perception of many objects became either much easier or even effortless. Since the proposed algorithm can be easily implemented in real time (only linear scaling and table look-up are needed), we believe that it can be successfully used today in various stereoscopic applications suffering from image crosstalk.
That paper is from the year 2000 when LCS shutters were thought to be the future and none of this DCI stuff existed, but it applies somewhat to the same problem.
Other random quotes that may apply:
quote:In the Real D system, the encoding takes place at the projector using an electronically controlled polarizer, which Real D calls the "Zscreen™." Images are decoded when the audience wears complimentary decoding polarized glasses. To allow head movement without upsetting the decoding quality of the glasses, Real D uses only circularly polarized filters in its system. Polarization alone, however, does not offer sufficient protection from crosstalk, also referred to as extinction ratio, with stereoscopic images. The audience experiences such crosstalk as a ghost in the motion picture. To enhance the ability of its polarization method to reject ghosting, Real D employs a "ghost busting" technique, which requires pre-processing of the images prior to projection. In its early systems, Real D's ghost-busting is applied prior to distribution. In future systems, ghost-busting will be applied in real-time by means of a processing box in the playback system.
quote:While Real- D is very popular with audiences and gaining acceptance, the silver screen used
in the process can cause a ghosting highlight from one eye to the other that reads like a
second offset limit. To solve this, a "ghost-busting' pass is done for the REAL D version,
which mathematically subtracts the bright highlights of the primary eye from the secondary
eye. This cancels out the effect, but leaves the left eye with strangely dark hot spots. For
this and reasons of stereoscopic adjustment and minor softening from beam
splitters/mirrors, the untreated primary eye is used as the standard DVD or TV version.
You don't want ghosting? Tell your theater to order an Imax Infitec (Dolby) color-corrected print, replace their current polarizer filters with Infitec's, double the light output to compensate for light loss, and buy Infitec glasses instead.
for many technical reasons, it may help in many cases, as a temporary measure to reduce ghosting, to sit as centered and as far back in the theater as you can and to wear two pair of 3D glasses, one on top of the other.
...
. Certo, le cose da sistemare ci sono ancora secondo me: le scene in rapido movimento, per esempio, e tutto ciò che non è a fuoco, risultano essere ancora troppo confusionari e fastidiosi da guardare. Anche il livello di luminosità percepita è da migliorare, anche se in questo film si assesta comunque a livelli accettabili ed è comunque meglio del sistema Dolby. In sostanza, quest'esperienza è stata molto più positiva rispetto alle precedenti. Tutto ciò, sicuramente, è anche merito di un film che riesce a sfruttare molto di più i lati positivi della visione stereoscopica piuttosto che enfatizzare quelli negativi (come invece avviene con le produzioni 3D di Disney). Concludo consigliando a tutti gli appassionati di guardarlo, non tanto per la storia in sè, ma per essere partecipi di tutti i progressi che gradualmente si stanno raggiungendo con questa tecnologia. La proiezione 3D mi piace moltissimo e condivido sempre di più l'opinione di James Cameron che vede in tutto questo la più grande rivoluzione dai tempi dell'introduzione del colore. A questo punto, sono davvero curioso di provare la soluzione di XpandD che vede occhialetti attivi al posto di quelli passivi. Vi saluto sperando di leggere al più presto altre opinioni... 
