With the huge financial and critical success of films such as Avatar and Alice in Wonderland it is clear that 3D has finally come of age. The quantum leap in viewing experience has galvanized audiences across the world, but what exactly is 3D? How does it work? And what are the processes involved from start to finish?
Depth cues create an impression of 3D in 2D images
Understanding how the eyes and brain work is the basis for an understanding of 3D. There are actually eight depth cues our eyes and brains use to estimate depth and create a 3D image of the world around us.
We use focus to estimate where objects are relative to one another. Perspective makes objects grow smaller, the further away they are.
Lighting and shading help us estimate the relative shape and position of objects. Colour intensity and contrast allows us to estimate objects near to us with more intense colour from those a long way off with less saturated colour. Objects in front hide objects behind, something we call occlusion. These five depth dues have been used for hundreds of years by artists, illustrators and designers to give the illusion of depth in diagrams, drawings and paintings.
The sixth depth cue, relative movement has been used by film directors and videographers to show depth in movies and television programmes.
However it is the last two cues, vergence and stereopsis that provide us with the most powerful depth cues. Vergence is the effect where our eyes slightly converge towards one another when we focus on an object near to us. Stereopsis is the small difference between what our left eye sees and our right eye sees.
Our brains have an amazing ability to build a convincing 3D image from vergence and stereopsis something that conventional 2D film and television cannot take advantage of!
If you think 3D is new, think again! 3D entertainment has been around for over 100 years. In Victorian times the Stereoscope was phenomenally popular, with many people building large collections of 3D images. Viewmaster was first sold in the late 1930s and used mainly as a toy to view 3D images from favourite movies.
Autostereogram pictures, now generally called Magic Eye pictures, have also been around for many years. These early examples of 3D dispel the myth that 3D has only been feasible in the digital age. The truth is that 3D has existed in some form or another since 1890, yet, as innovative as these early examples were, they never achieved lasting mass market adoption.
So now that you know everything about 3D images, let’s move on to 3D video.
3D Cameras are set apart the same distance as human eyes
3D video works by making use of two cameras to simultaneously record a scene. The cameras are set apart at the about same distance as the human eyes, creating two separate images. When these images are combined in to a single image, shown on a special display using special 3D glasses, it is possible to create the illusion of depth that we know as 3D. The glasses split the single image back into an image for each eye and fool the brain into seeing 3D.
An important part of viewing 3D is the concept of parallax. This is the difference in the apparent position of an object viewed along two different lines of sight for each eye. Parallax is divided into positive (where the object appears behind the screen), zero (where the object appears on the screen) and negative (where the object appears in front of the screen). An understanding of how parallax affects the end result is crucial for any cameraman wishing to produce user friendly 3D content.
Another key consideration for the creation of good 3D is how the cameras interact together. Vertical or rotational misalignment, unmatched zoom tracking, poor focus, incorrect colour matching and excessive convergence can all break the 3D illusion. Much of this can now be done automatically with Sony’s unique MPE-200 SIP (stereo image processor) technology which is able to correct these issues in real time. Indeed the Sony SIP really is the stereographer’s dream, a technical and craft box of tricks specifically designed to help the stereographer both in live production and in post.
Even after the images have been acquired there are still a number of things which need addressing in post production. It is crucial that any mixes, fades and wipes remain frame accurate. Fast cuts and zooms can produce an uncomfortable viewing experience as the audiences’ eyes as they are constantly having to refocus. Stereographers will need to be keenly aware of this to ensure that the 3D experience is a success.
Anaglyph technology filters the two images, cyan and red
There are five methods in which 3D can be displayed. Anaglyph technology filters the two images, cyan and red and simply combines them together into one image. It requires no special display or projector, and has been popular for many years due to its simplicity. Even today anaglyph is popular in posters leaflets and other printed material. However true colour is difficult to recreate and it is not popular now for cinema and television.
An alternative approach is to use linear polarised technology. Here, the left image is vertically polarised and the right image is horizontally polarised. Linear polarising glasses split the combined image back to one for each eye. There are, however, significant downsides to this solution: it requires a special display or projector and the viewer’s head must be absolutely straight, making it impractical for use in cinemas or televisions.
Another display solution is the use of circular polarised technology. Very similar to linear polarising technology except that circular polarising filters are used in the display and glasses, one clockwise and the other anti-clockwise. The benefit of this solution is that the viewers head position is unimportant. Like the linear solution, however, a special display or projector is required. Circular polarising technology, championed by RealD, is popular in cinemas because the glasses are cheap and easy to clean between each performance. It is also popular in professional monitors because it produces a good 3D image on broadcast monitors. Circular polarising makes the image slightly darker and cinemas will often use silvered screens and turn the lights down a little more during performances to compensate for this.
Regarded by some as the modern equivalent to anaglyph, the third system uses narrow band filters to filter the images for each eye down to its primary colours. The colours used in each eye are slightly different. Therefore by wearing a special pair of filtering glasses it is possible to split the combined image back into one for each eye. This system is popular in cinemas, but will probably not become popular in the home, because it requires a filter on the screen which makes normal 2D television viewing darker.
Active LCD shuttered glasses
Active LCD shuttered technology offers a unique solution for the home. It utilises an infra-red signal from the television to synchronise a pair of active glasses. The screen shows the left image while the left eye is open and the right eye is closed, and the right image while the right eye is open and the left eye closed. A smooth image is maintained by switching quickly between the left and right images and eyes. The technology offers great 3D separation a wide viewing angle and the same bright image whether watching in 2D or 3D. The glasses are powered and more expensive than polarised glasses. So this technology is more appropriate for the home where people tend to look after their glasses, rather than in the cinema where glasses would be broken or go missing, batteries would need replacing and the glasses would need to be cleaned between each performance.
So that’s it: a brief overview of the science and processes behind the creation of 3D content. Complex? Yes, of course it is. The adoption of 3D by broadcasters will require adaptations to the existing broadcast workflow as well as the learning of new skills. Sony will be providing support in both these areas, in terms of new technologies and training.
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