3D movie watching

3D spatial sight, 3D movies

The fact that we have the capacity for spatial sight, we can estimate the distance of objects from us and from each other relatively well, is the result of having two eyes, which, because of the distance separating them, see everything from slightly different angles. Our brain composes 3D sight from the two images “recorded” by our two eyes. A consequence of all of this is that with just one eye we unfortunately can’t have spatial sight, and 3D photos or movies can only be made with two cameras. The latter statement is contradicted by the fact that there are 3D movies currently on the market that were originally not recorded with two cameras, they were subsequently converted by computers. If someone experiences 3D first in such a converted movie, he will probably not be impressed, and it will be rather unpleasant to watch. Good examples for this are the “3D converted” versions of James Bond movies, starring Sean Connery, and the 3D Titanic which was prepared in a significantly better quality. The below website continuously catalogs ‘Real 3D’ and the subsequently converted ‘Fake 3D’ movies, in a list itemized by year. It’s worth browsing them, and getting acquainted with such concepts as hybrid 3D, in the case of which a computer generated view is 3D, but it was originally recorded with a 2D camera.
It’s surprising that, for example, the greatest movie hit of 2013, Ironman 3, is also only viewable in 3D thanks to computer technology…

3D Blu-ray (fullHD 3D)

We can thank the emergence of the Blu-ray disc data storage device not only for high resolution (more detail rich image and sound), but also for the spread of watchable home 3D. We could watch 3D movies even in the age of DVDs and VHS cassettes, with red-blue or green-magenta (anaglyph) glasses packaged with the movies, but the sight could only be considered interesting at best, not enjoyable. However, Blu-ray discs and the HDMI 1.4 standard together make it possible to transmit 48 full HD resolution images from the optical disc (in the case of a media-player, from the BD ISO file recorded on a hard disc or files with BD folder-structures) to our display. These 48 images are sufficient, so both of our eyes can watch 24 (more precisely 23.976) different images per second, and thus the experience of spatial motion picture can be created by our brain. More than these 2×24 images couldn’t even be transmitted via the HDMI 1.4 cable, so we can’t find 3D movies with 50 or 60 images per second speed on Blu-ray discs.

When on our website we discuss the concept of Blu-ray 3D, by that we mean the so-called frame packed picture format of BD players. In the case of these, the two full HD (1920×1080 pixel) frames, intended for the left and right eye, are displayed on top of each other (a 45 pixel-row separating stripe between them), and such 1920×2205 pixel images can be transmitted from the player in succession via the HDMI 1.4 cable. The task of the display equipment (TV, projector) is to “cut out” from these the two 1920×1080 pixel frames the images intended for the two eyes.

Half resolution 3D formats

However, 3D contents not only originate from Blu-ray discs, since there are already 3D TV channels that are operational, with land as well as satellite broadcasting. However, these DON’T use the Blu-ray 3D format, because currently it’s not possible yet to transmit the amount of data necessary for this via existing TV networks. Similarly, even a several years old, not 3D capable media-player can serve a 3D TV or projector, if we don’t insist on Blu-ray 3D format. This “not insisting”, in practical terms means that we forgo watching full HD image frames, and we don’t transmit more data than in the case of 2D contents. This may fundamentally be solved by two methods, the essence of which is the same: we place the images intended for the two eyes in a single full HD frame. It’s certainly predictable what kind of compromise this will entail.

Side-by-side (SBS) format. Let’s discard every second pixel-column of the full HD image frame! The result is a 960×1080 pixel resolution picture, and of course, in the case of 3D, two such pictures. This is great, so let’s place this “dumbed down” image frame for the left and right eye side-by-side next to each other, thus we receive a 1920×1080 pixel full HD image frame, which contains the information needed for both of our eyes. It’s true that the horizontal resolution is half of full HD movies, but it’s still better than in the case of DVDs (720 pixel), and the vertical resolution is unchanged. In exchange for this, the players don’t even realize that they aren’t transmitting a 2D picture frame, a larger bandwidth, the transmission of a higher amount of data is unnecessary. The display only needs to be prepared for vertically cutting the image in half, in the case of such SBS movies, to scale up (double) the 960 pixels to 1920, and to joyfully use the thus 1920×1080 picture intended for both eyes.

Top-bottom or top-and-bottom (TAB) format. The other option: let’s discard every second pixel-row of the full HD image frame! In this way the vertical resolution is halved, thus we can place two 1920×542 pixel resolution pictures on the top and the bottom of the full HD frame. In many instances this is a better choice than side-by-side, it’s enough to just consider wide screen (here we mean a screen even wider than 16:9, e.g. 21:9 movie screen) movies, which don’t contain 1080 pixel-rows anyhow, only let’s say 822. In this case we can already be glad that we didn’t lose half of the original row-resolution, only about 24% of it, meaning that the picture quality wasn’t reduced by as much compared to Blu-ray 3D, as in the case of side-by-side. The top-bottom format is clearly the winner, if we watch 3D movies on a passive 3D TV. Specifically on these TVs, in every pixel-row a filter layer is situated suitable for alternately the left and right “lens” of the passive glasses, meaning that in 3D mode they only display a 1920×540 pixel image to our eyes anyhow. Meaning that it’s to no avail if we transmit a Blu-ray 3D movie to them, the displayed end result will be exactly the same that can also be achieved with an average 2D player and the top-bottom format. Based on the above, on passive 3D TVs the side-by-side format is clearly the wrong choice (this is the reason why we hope that most 3D TV channels will apply the top-bottom format), since in the source the horizontal resolution is halved anyhow, while the TV also halves the vertical. Thus, we receive a 960×540 pixel picture, which is rather far from full HD, it’s even lower than HD (720p).

Both the side-by-side and the top-bottom formats are parts of the 3D standard (exactly because of TV broadcasts), therefore all 3D TVs and projectors have to be compatible with these. The newer types are capable of recognizing from the incoming signal, which format is needed, and they automatically switch to the appropriate mode, and a number of media-players also have the capacity to give the command necessary for switching to the appropriate mode to the display via the HDMI cable (e.g. if they find the necessary SBS or TAB marker in the file name). Such media-players also exits that have the ability to decode side-by-side and top-bottom videos by themselves, then they send these in the standard frame packing format, thus the TV believes that the source is Blu-ray 3D.

Active 3D, passive 3D

Wherever the 3D picture frames originate from, it must be ensured that those intended for our left eye can only be seen by the left, and those intended for the right, by the right. Aside from a few attempts that are still taking baby steps, the currently usable methods solve this problem by the means of some kind of glasses. They either apply some kind of a filter (in a passive method) to prevent the image intended for one eye from reaching the other, or they simply cover the eye (passive method). In the case of TVs the active method is the older one, while in the case of movie theatres it’s the passive.

Active methods became possible first when TV sets already had the capability to display at least 120 different images per second. Its implementation is relatively simple, when we just write it down: display the picture frame intended for the left eye on the screen, meanwhile the right lens of the “remote controlled” glasses should shut, meaning cover our right eye. This should last for 1/120 second, then we display the picture frame intended for the right eye and it should cover the left eye. This should be repeated 60 times per second, thereby the vibration of the “lens” opening and shutting in front of our eyes isn’t so disturbing. The “lenses” in the glasses are nothing else than simple LCD displays, which, of course, aren’t able to display either colors or hues, but they provide a black surface when affected by electricity, and more or less aren’t penetrated by light. In order for the glasses to be able to operate in a synchronized manner with the TV, they must be in constant contact, which may be achieved by infrared light or radio-waves (e.g. Bluetooth). A disadvantage of using infrared is that there can’t be any obstruction between the glasses and the signal transmitter built in the TV, since that interrupts the route of light – thus this is an obsolete method. Today’s modern glasses can be shut 100 or 120 times per second, which isn’t only necessary so we can watch a calmer image, it’s also required because of 24/23.976 Hz movies. Specifically, 60 isn’t divisible by 24, but 120 is, so at 120 Hz, 60, 30 and 24 frames/second speed movies can be played smoothly.

The passive method has been applied for decades in movie theatres, and this technology is continuously developing as well. Its greatest advantage compared to the active method is that in this case information is received by both eyes continuously. There are many people whose brain is unable to form a 3D image without this, therefore they can’t enjoy 3D with active glasses at all. Many are bothered even by the 120 Hz flashing, or at least it’s exhausting for them, it’s primarily unpleasant if aside from the one coming from the TV, another artificial light source (e.g. a light bulb operating from a 50 Hz current) also enters their field of vision through the active glasses. Its further great advantage is that brightness isn’t cut in half, thus contrast isn’t drastically reduced, since not just one half of the total amount of light from the TV enters our eyes. Even though brightness is diminished somewhat, since the light has to pass through various filters twice: once when it exits the TV screen or the projector’s lamp, and for a second time when it passes through the glasses in front of our eyes. The information intended for the left and the right eye is separated in an optical manner in the case of the passive method.

The simplest method that has been used for the longest time is polarization (see, e.g. here http://www.vilaglex.hu/Lexikon/Html/Polariza.htm). A simpler version of this is linear, while its more advanced version – which even tolerates tilting the head – is circular polarization (for further details see: Three dimensional television – Wikipedia, with the correction that, of course in our opinion, the polarization method isn’t the best for watching 3D movies:). In the case of TVs, the application of passive 3D technology has been common for a while as well, not only active TVs and glasses are available. In the case of passive TVs, the polar-filter is practically a film-layer that is applied to the screen’s surface and is about as thick as one pixel-row, the filters intended for the left eye and the right eye follow each other in an alternated way. As we have mentioned above, in the case of a full HD TV, in 3D, these TV sets are only able to display a 1920×540 pixel image for both eyes, but on the 4K resolution newer models displaying the full HD 3D image will not be a problem (in their case the 4K resolution will not be available in passive 3D mode).

3D and the size

Nowadays not only TV sets, but even computer monitors with the diagonal screen size of 68 cm are able to function in 3D mode. However, in our opinion the question is if there is a point in watching 3D in this size, and in what size there is a point in it at all. In our opinion, if at least a 1:1 size human figure isn’t displayable in 3D view, then 3D is only interesting at best, it’s not an extra experience. The essence of 3D would be – just as manufacturers advertise it – that we feel as if we were on the scene, in the middle of the action. However, this will not be possible even if our TV happens to be 1 meter tall. What we will see on it will be like a mock-up, a terrain model, on which toy cars and airplanes, tiny people are moving, but it will not be breathtaking if let’s say a 60 cm wide car is racing toward us… Therefore we would like to encourage everybody to try to acquire an at least 1.8 to 2 meters tall screen at home, if he wishes to get an extra experience out of 3D. Thus with the current options, practically only projectors and a projected image can be sufficient – just as what we are used to watching in a movie theatre.

Projection at home

3D projectors for your home are available for even under HUF 200 thousand (the price increases with quality, the sky is the limit, it can be HUF 10s of millions), of course with this the screen surface isn’t included, meaning that a screen or a special wall surface is also necessary. It’s also possible to spend HUF millions on a screen as well, unfortunately… If we purchase a projector with a quality level that we like, in 2014 it will very likely be 3D. However, this means that we also have to by active glasses for it separately, and that will not be cheap (considerably more expensive than the glasses for 3D TVs), and similarly to TVs, the projector also continuously alternates the image frames intended for each eye while the glasses cover the other eye. The first astonishment is experienced by most users, when they view a movie in 3D which they have previously seen on the new projector in 2D. Because of the reduced brightness and contrast the view will be (colors, lights, the quality of the image, of course not the 3D effect) only as good as could be achieved with a significantly cheaper projector in 2D. Thus, if someone spent a considerable sum for a projector, because of the quality it represents, he will not be happy to watch 3D, if that comes at the price of having to give up the picture quality that he is used to. We should also mention that if a 4-5 member family, possibly together with some friends, would like to watch 3D, they might easily spend nearly the price of the projector on active glasses, as a result of which, in the case of a larger company, there is a good chance that somebody will get a headache during the movie.

However, a passive method also exists on the market of home theater projectors, in the case of which the image is projected by two projectors, generally placed in a single house, with polar-filters, but currently these are all above HUF 10 million. Except for the one that you can get acquainted with on our website, furthermore this can be realized with any kind of projector suitable to You. Not insignificantly, for light projected in a polarized manner, such surface (screen) is required, in the case of which the polarization direction of light waves doesn’t change when they are reflected, otherwise they wouldn’t pass through the glasses appropriately. This can be achieved with the so-called silver screens, which are considerably more expensive than ordinary screens, or they may be painted wall surfaces on which exclusively polarized 3D can be watched. Meaning that if we wish to watch 2D with a projector, we have to use a different screen. Thus switching the two screens has to be accomplished, one of which, on top of this, also happens to be very expensive. There is no such problem if instead of polarization we use spectrum filtering!

Spectrum filtering by Dolby

From the point of view of the watchable quality of 3D, one of the most important parameters is to what degree the system allows light to enter one of our eyes that should be restricted to the other eye, meaning “interference”, even though in this case the term “light leakage” would be more accurate. In the case of horizontal/vertical polarization filtering, the contrast value is 200:1 between the two eyes, meaning that 200 times as much “intended” light inters e.g. our left eye as light which is only supposed to be seen by our right eye. Circular polarization - which is more widespread because it’s not sensitive to tilting our head – only has a ratio of 100:1, but this is still sufficient for 3D view. However, it’s evident that the separation isn’t perfect in either case, thus it depends on the individual how much it exhausts him that both his eyes can see the images intended for the other eye. Dolby Laboratories in the US, which is world famous in relation to audio formats, opened several of its own movie theatres in which it developed the audio technology according to its own sound system, to make the audio, not just the view, as high quality as possible. The so-called spectrum-filter method was first applied in their movie theatres, which already provides an interference ratio of 1000:1 between the two eyes. The patent of the application of spectrum-filters for 3D image display is also connected to this company. As its name suggests, the image is manipulated based on spatial-color and color-spectrum as well, like in the case of the Anaglyph, e.g. blue-red filter glasses in the past, but in this case the red, green and blue (RGB) components of light also pass through the filter (in the same range for both eyes), unlike in the case of the ancient method. The colors change slightly, thus they have to be compensated by the calibration of the projector, if the color correctness of the image is important. The size of the gamut displayable by the projector is slightly reduced after the application of the glasses (which in active 3D mode is reduced much more significantly, to less than half).

If we use the spectrum-filters with two projectors, we can achieve much greater brightness compared to an active projector: it’s not just that the projector’s brightness isn’t halved, but that of the two projectors is combined, and this is reduced slightly by the filters and the glasses. We achieve such a contrast ratio and brightness that the specific projector couldn’t display even in 2D. Further technical details and comparisons are available in the patent.