A 3D world on a 2D screen
The visual cues in a 2D video help our brain to understand the depth information in the scene, but we don’t see things in 3D. To see objects in front of a screen and behind it, we need additional cues that can only be captured by using two cameras.
Depth cues in 2D video include Focus, Perspective, Occlusion, Lighting and Shading, Colour Intensity and Contrast and Relative movement. These are explained in the below table.
When video is captured by a suitably positioned pair of cameras, there are two additional depth cues:
Stereo (also called Stereopsis) is the most important factor in true 3D. It is the way the brain interprets the difference between images taken from a slightly different viewpoint to give a true 3D experience.
Vergence is the angle your eyeballs move though relative to each other to look directly at an object in 3D space. Your eyes diverge (move apart) as an object moves away, and converge (move together) as it moves towards you. This movement helps your brain to position images in 3D space.
Creating a 3D image
To create a stereo image, you need to have two cameras positioned horizontally about the same distance apart as the eyes on your face. This is called the inter-ocular distance, or inter-axial distance when you are talking about cameras, and it is normally about 65mm. The two images will have slightly different information in them, because each has been taken from a different viewpoint.
Moving the cameras’ lenses apart will increase the sense of depth, and turning the camera lenses towards each other or apart moves the whole scene forwards or backwards. These settings must be used carefully because if they are taken to extremes, they can cause discomfort to the viewer.
How to handle 3D and how to avoid mistakes
All the settings and adjustments on the stereo pair of cameras need to be matched, including
• Lens Type
• Focal Length
• White Balance
Slight camera miss-alignments can be corrected later using Sony’s MPE-200 image processor, but it is still important to get things right at the time of image capture. Correct focusing on both cameras is essential as mistakes cannot be corrected later. Sony’s camera control systems can be linked to make it easy to manage a stereo camera pair.
In live and post production, cuts, mixes and transitions must be done identically on both parts of the stereo pair. Sony’s 3D workflows make it easy to handle a stereo pair of video feeds as if they were one.
Titles should always be in front of the nearest object to the viewer to look natural. Objects in front of the screen can cause problems when they move off the screen, breaking the 3D illusion.
Understand and create
3D production can be simple as long you understand the basic principles. Configure the right and left cameras in a stereo pair identically, and process the right and left videos in the same way at all stages. Don’t create conflicts between traditional and stereoscopic depth cues by using extreme 3D settings, and aim for a natural 3D effect that viewers can enjoy in comfort.