|Knowledge about all aspects of 3D displays and their application.|
|The method described below for parallel cameras will allow you to first compose the view you want and then to apply the method to capture the view stereoscopically. Given a set of simple measurements, the method calculates the stereoscopic camera inter-axial baseline, A, that will always result in a high quality 3D image. It is implemented for 35mm cameras in the Binocularity.org camera calculator spreadsheet (BCC) and further details are in this paper [Jones et al 2001].|
Two different spaces are important in 3D photography, the display/viewer space in which the image pair is viewed and the camera/scene space in which the image pair is captured. The method captures the depth seen by the camera and then reproduces it within a defined depth budget on your target 3D display. It provides a parameterization that gives you direct control over the stereoscopic composition of your final image.
Step one: consider the display/viewer space. The parameters required are shown in the diagram below, and remain fixed for as long you use the same target display.
The depth budget of the display is defined by N, the nearest point you wish depth in your picture to appear at, and F, which is the furthest point you want to depth to appear at. This depth budget is defined by human factors requirements and for desktop displays a comfortable but workable range is often just +/-50mm either side of the display surface. For displays that are viewed from further than two metres you can comfortably extend this to +/-1000mm or more.
The remaining parameters are: E, the viewer's eye separation, Z is the intended viewing distance from the viewer to the display and W is the width of the display.
Step two: consider the scene/camera space shown below. The first parameter is the zoom (focal length) of the camera, L. The other two parameters define the range of depth in the view seen by the camera, Nc, is the nearest point in the camera's field view while Fc is the furthest point seen by the camera.
Entering the parameters above into the Binocularity.org camera calculator spreadsheet will calculate the camera inter-axial baseline distance A. Using this value of A will ensure that the depth you see in your stereo photographs will not exceed the depth budget for the target display that you defined in the first step. This provides a repeatable way to help control your stereoscopic 3D compositions.
Note, because the camera axes are parallel there will be a small region of each image, on the left side of the left image and the right side of the right image, that need to be cropped as it has no corresponding region in the other image. The spreadsheet calculates this for you, and it is straightforward to apply in a stereo photo editing tool such as Stereophoto Maker.
An important compositional concern for stereophotography is the position of the zero disparty point in the scene, that is which part of the scene will be perceived to be on the screen plane when the image is viewed. If you apply the cropping as above then the zero disparity distance in the scene will be that calculated by the spreadsheet (Zc). If you want to alter the zero disparity point then, after you have taken the photograph, you can simply increase or decrease the cropping, Stereophoto Maker has tools to do this interactively.