Do you Know Your Hyperstereo From Your Hypostereo?

The stereoscopic 3D world has introduced many new words to the production professionals, such as gigantism, depth budget and keystoning. Thanks to help from Sony Professional, 3D Focus is on hand to simplify the growing array for stereoscopic definitions. 

The 3D Focus glossary will be constantly added to and will soon be given a dedicated page.

The 3D Focus Stereoscopic 3D Glossary 

Alignment Plate - The plate that has all the adjustment gearing for picture alignment. Roll, Pitch and Z axis.

Beam Splitter - The mirror in the large box at the front of the mirror rigs. The “mirror” is in fact a 50/50 beam splitter allowing 50% of the light through to one camera and reflecting 50% of the light to the other.

Mirror Rig – A rig configuration using 2 cameras, where one camera is positioned vertically above or below the second camera. This configuration requires the use of a beam splitter to pass light to the vertical camera.

Under/Through -  The rig in its broadcast mirror configuration where the top camera is a full body Sony HDC-1500 and the bottom camera is an HDC-1500 utilisingT‐Block head adaptor, which remotes the CCD block from the main camera body.

P1 – Small bodied HD Camera designed for beauty cam and 3D applications. Known as HDC-P1 they can be used in place of HDC-1500 full bodied cameras. Although small this camera uses the same CCD as the HDC-1500R allowing cameras to be mixed.

Checkerboard– The ability to display the images from two cameras as one display, based on a checker or chess board layout. This enables very accurate colour balance between the two cameras.

2D to 3D conversion - allows the use of 2D images in a 3D production up to a certain level. Certain shots work well, others can actually have a negative effect.

3D Zoom control - One control that allows the cameraman to control zoom and focus on 2 cameras. Alignment process the process of aligning 2 cameras. This has 3 main areas when using the Element/Sony system.

• Optical alignment that ensures both lenses zoom into themiddle of the camera chip block.
• Mechanical alignment where the rig is adjusted mechanically so the 2 cameras are producing “identical” frames
• Digital alignment where any issues that could not be corrected mechanically are resolved using the 3D box

Anaglyph -  An outdated way of seeing 3D on a 2D monitor, using the red/blue colouring that everyone remembers from Jaws 3D, etc. There have been improvements along the way (Colour‐code for example) but it is still tiring to watch for any length of time. In production it is still used as a way of seeing 3D and also occasionally by convergence pullers who look at the red/blue image in 2D and judge the stereo within the picture.

Convergence - This refers to where in 3D space the physical screen plane is. The point of convergence is where an object within a frame appears as one (both images sit perfectly on top of each other) it is at this point that the screen plane is and objects in front will appear to be out of the screen and objects behind will appear to be into the screen.

Convergence Operator Control – The movement of the rig during filming and dictate under the Stereographer’s guidance the amount of 3D in any given shot. Also called Convergence Puller.

Depth Budget - This is the amount of “stereo” or 3D that is set prior to filming for the 3D department to adhere to, typically it is talked of as a percentage.

Difference Matte - Most Convergence Operators use a 2D screen displaying a difference matte to judge the amount of stereo in a frame. To do this one eye is displayed as a black frame one frame is displayed as a white one. When shown on top of each other there is a grey frame with differences displayed in black or white. One convergence puller described his job as “watching TV in letraset!”.

Dual Stream Record - Because the cameras produce 2 HD streams recording them can prove difficult. The Sony 5800, SRW1 and R1000 decks allow for these 2 streams to be recorded at  the same tape on the same tape or media with obvious benefits to sync.

Frame violation - Where an object breaks frame but causes an uncomfortable viewing experience. This can be either because the object is too close to the camera when compared to the rest of the frame or that it appears in one camera but not the other. These violations tend to happen on the camera that is not being monitored by the cameraman.

Horizontal shift - Difference between the 2 images. Good 3D relies upon perfectly aligned images from 2 cameras with slight and controlled horizontal differences.

Inter Ocular/Inter Axial - Commonly termed IO this refers to the physical distance between the centre of 2 frames, or loosely how far the cameras are apart. NB: it is the relationship between the Convergence and Inter Axial that determines the amount of 3D.

Keystoning - An effect caused by the act of convergence where one image when laid over the top of the other has slight differences in the corners of the frame. This is because the frame no longer sits “flat” but is slightly angled in comparison to the other.

Lens Tapping/Matching - A pre alignment procedure that matches 2 lenses as closely as possible.

Roll - Where one camera is not sitting completely square to the other and the images viewed from one camera on top of the other appear to be higher one side of the frame, then correct in the centre and then lower on the other side of the frame.

Stereographer - The lead person of the 3D crew. He/she oversees all the 3D alignment before the shooting begins and then during filming oversees the quality of the 3D output feeding comments to his crew.

Stereo Engineer - Looks at all the data being fed back from the various 3D boxes and “tweaks” within the 3D Box any issues that arise during filming.

Vertical/Y shift - A misalignment of the 2 frames vertically, where a horizontal line in frame (e.g. the roof of a stand) appears higher in one camera than another on the same rig. This is serious and is a major cause of viewing discomfort.

Z axis - The axis from front to back of a 3D image, i.e. into and out of the screen.

Parallax – separation on the screen plane between left and right images of an object. Determines the perceived depth of objects relative to the screen plane.

Negative Parallax – objects are perceived to be positioned within the viewer’s space (or “personal space”), i.e. in front of the screen plane.

Positive Parallax – objects are perceived to be positioned within the screen space (or “world space”), i.e. beyond the screen plane.

Zero Parallax – objects are positioned at the screen plane, and appear to be in two dimensions.

Depth Budget – the combined values of positive and negative parallax.

Screen Plane – the plane of the display  or the surface of the movie screen, TV screen, or computer screen.

Convergence – (or “toeing-in”), inward rotation of the lenses, to shift the parallax of the scene and the perceived depth of objects relative to the screen space.

Point of Convergence – the position on the set where the axes of the lenses exactly overlap, defining the position of the zero parallax plane or screen plane.

Divergence – the unnatural outward rotation of the human eyes to view images with an interocular that is larger than that of the average human eye (2.5”). Results in wall-eye.

Interocular – (or “interaxial”), horizontal displacement of the lenses of the cameras.

Hyperstereo – the effect of an interocular that is larger than that of the average human eye (2.5”).

Miniaturization – an artifact that results from use of wide-angle lenses or a larger interocular than that of the average human eye (hyperstereo).

Hypostereo – the effect of an interocular that is smaller than that of the average human eye (2.5”).

Gigantism – an artifact that results from use of a smaller interocular than that of the average human eye (hypostereo).

Orthostereo – the effect of shooting with parallel lenses and an interocular that approximates that of the average human eye.

Cardboarding – an artifact that results from the use of long focal length lenses.

Keystoning – (or “trapezoidal distortion”), an artifact that results from excessive convergence of the lenses.

Wall-eye – an uncomfortable condition that results from the attempt to fuse objects with strong positive parallax and a wider-than-normal interocular.

Dual Link– An abbreviation referring to dual simultaneous full frame HD left and right eye signals. This is carried by 2 video cables.

Side by Side Compression– A method of utilizing horizontal compression on the individual the left and right eye HD video frames to reduce their size, so that once combined left and right eye frames can be transmitted within a single HD video frame. This compression method enables 3D signals to be synchronously delivered using standard HD distribution equipment.

Side by Side Rig– A rig configuration using 2 cameras filming side by side.

RealD Cinema - is a digital stereoscopic projection technology made and sold by RealD Inc. It is currently the most widely used technology for watching 3-D films in theatres and is based on circularly polarized light. Glasses used for viewing are simple filter based units, known as “passive” glasses. These same glasses can be used with Sony professional displays as these are also RealD compatible.

Have we missed something? Let us know!

3D Focus would like to thank Sony Professional for their help with this 3D glossary. You can follow Sony Professional on their Facebook page.

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