Stereo Rendering (CineRender)
Use Stereo Rendering settings to define all properties having to do with the creation of two or more images whose perspectives are slightly offset.
In recent years, advances in technology have made it possible to display 3D images and movies true to color and free of fatigue for the human eye. Most techniques record two images of the same scene from slightly offset perspective views (those of the left and right “eyes”). These two images must then be displayed to the viewer in a way that the left eye only perceives the left image and the right eye the right image (which is done using specially designed glasses). The rest is done more or less automatically: the brain combines these two images into a single image.
Two images with different perspectives are combined to create a stereoscopic image.
Topics in this Section
Special settings are available if you want to make the 360° view of a Spherical Camera into a stereoscopic view. The left and right eye views will be combined to a single image (left = top; right = bottom).
Check the Spherical Camera option to access the special Stereo Rendering options for a spherical camera.
If you are not using Spherical Camera: See Options with a Non-Spherical Camera.
•Mono: No stereoscopic images will be rendered.
•Parallel: Both cameras will be arranged with parallel axes of view.
•Toe-in: Both cameras’ axes of view will cross. The point of intersection can be defined using the Focal Distance.
The various Stereo modes with the camera axes (the cameras are rotated internally for rendering panoramas)
The primary difference between the two stereo modes lies in the definition of the null parallax, i.e., the distance from the camera at which no parallax is generated.
Note: Parallax is the apparent displacement of an object when seen from two different points.
•If Toe-In is selected, the null parallax will be defined using the Focal Distance setting and cannot be subsequently modified.
•If Parallel is selected, the null parallax is infinite and can be subsequently modified (by moving the left and right perspectives).
Define how the two stereo images should be arranged, or which one (left or right) should be rendered alone.
This value defines the distance between both cameras/eyes. The default distance of 6.5 cm represents the average distance between human eyes.
Eye to Neck Distance
Depending on which target model is rendered, you can define the horizontal distance from the neck to the eyes (see image above). If the Eye to Neck Distance is set to 0, the camera’s rotational point will no longer lie at the center of both cameras.
If Stereo Mode is set to Toe-In, you can use this setting to define where the null parallax should lie. Objects that lie in front of this point and face the camera’s direction of view will protrude out of the monitor towards the viewer; objects that lie behind this point will more or less “sink” into the monitor.
Top Pole Smoothing/Bottom Pole Smoothing
For technical reasons, stereoscopy cannot be rendered correctly around the poles. To prevent unwanted artifacting, the stereo effect can be gradually faded in these regions. In most cases, this can be done with no problem because the visually important elements mostly occur horizontally around the camera’s location (and not vertically above or below it).
The smoothing can be defined separately for top and bottom poles. In the region in which the smoothing takes place, the views will be equalized with the left and right cameras until they are identical with the maximum possible smoothing.
Smoothing, using the defined Smoothing Angle, will take place from the start to the pole using one of two methods:
•Linear: Smoothing occurs with linearly increasing strength, i.e., abrupt deployment
•Exponential: Smoothing occurs with exponentially increasing strength, i.e., gradual deployment.
–Use Top/Bottom Pole Exp settings to affect the Exponential option.
If you are not using the Spherical Camera option, the following Stereo Rendering options are available.
•Mono: This is the normal camera mode without stereoscopy.
•Symmetrical: Use this mode to render normal stereoscopic images. A double camera will be assumed and each camera will be assigned half of the defined Eye Separation value, left and right, respectively.
Depending on the parameters defined, both cameras will be positioned as follows on the Camera object’s X axis:
•Left: left camera is set to 0, right camera is set to + distance between eyes
•Right: left camera is set to -distance between eyes, right camera is set to 0
This value defines the distance between the left and right eye. The default value of 6.5cm reflects the average distance between a human’s eyes. Normally, this value should be as small as possible. Greater values will produce a correspondingly larger spatial view but it will also become more strenuous for the viewer to view the scene.
Exception: if a scene, e.g., a landscape, is depicted that lies far away from the camera.
Even though several options are available, most of them are only there for compatibility reasons. For stereoscopic double images, you should always (with the exception of special circumstances) set Placement to Off Axis.
Each example in the image below uses a double camera only.
Depending on placement, both (or several) cameras will be oriented differently.
•Parallel: This is the simplest stereoscopic camera arrangement. Both cameras are positioned parallel to each other (the image axes are also parallel). Stereoscopic images with this type of arrangement only depict objects that lie in front of the projection plane. Hence, the null plane CANNOT be moved by modifying the Zero Parallax value. This is in contrast to other following three modes.
•Off Axis: Basically the same camera arrangement as Parallel, but with an offset, which means that the image axes are no longer parallel; they intersect. The zero parallax lies at this point of intersection (see next setting, Zero Parallax). Objects can be depicted to lie spatially either in front of or behind the projection plane (i.e. in or in front of the monitor).
Tip: This mode is recommended for stereoscopic double images because it delivers the best results for the widest range of applications.
•On Axis: When this mode is selected, both cameras are rotated so their Z axes intersect with the zero parallax. This reflects approximately how the human eye works but is not recommended for the creation of stereoscopic images because a vertical parallax can result. This mode is also referred to as “toe-in”.
•Radial: This mode is similar to On Axis, except that both cameras don’t lie on the Z axis but rather on an arc (whose center point lies on the point of intersection of both cameras’ zero parallaxes).
The zero parallax is a virtual plane that lies vertically to the camera’s angle of view and defines where the projection plane lies, i.e., the plane that represents the monitor screen at its depth. Objects that lie in front of this plane in the direction of the camera protrude spatially out of the monitor in the direction of the viewer; objects that lie behind this plane lie “within” the monitor.
Choose either an Auto value of 70 or 90, or choose Manual to enter separate Left Plane and Right Plane values.
If you want to play it safe, select 90 and place all visible objects in the direction of the camera and behind this plane.
The Auto Planes do not affect rendering! They only serve as visual references that you can adjust manually. If you determine via test renderings that the optimal spatial impression within a given distance from the camera has been achieved (objects that, for example, lie too close to the camera – while the zero parallax is positioned far away – can only be seen with great effort by the human eye), then you can define these planes accordingly and can place objects in the view correctly, within the restricted space that results.
The options 70 and 90 represent a parallax of 70 and 90 arc seconds, respectively, for the near plane. These values are described in technical literature as values at which the human eye can perceive spatially with normal effort. Therefore, objects should lie behind this near plane.
A formula exists that defines the maximum parallax (distance between red and cyan (anaglyph)):
P = tan a * D
where P = Parallax, D = Distance of the viewer from the projection plane (e.g., the monitor), a = Angle between 2 points that the eye can comfortably perceive (this should be max. 1.5° or somewhat less).
For an average distance between eyes and monitor of 50 cm, an average reference value of 13 mm results.
Calculate Stereoscopic Images
Define how the stereoscopic images should be rendered and saved.
•Merged Stereoscopic Image: A stereoscopic image will be rendered using the left and right eye views only and no other channels. This is the mode with which you will normally render.
In contrast to stereoscopic techniques that use 2 channels, multi-channel techniques let you render multiple camera views, which can then be edited as channels (or streams) using external applications. Auto-stereoscopic playback devices can then be used to view these images with two matching channels (which can change depending on the angle of view).
•Individual Channels: Several camera views can be rendered, depending on the number of channels defined. Channel 1 will always be the left eye perspective and channel X will always be the right eye perspective. If Channels is set to greater than 2 additional views will be rendered between these views. Select this mode if you want to subsequently create a stereoscopic image, either in the Picture Viewer or using an external application.
At left a stereoscopic setup with 2 channels, at right a stereoscopic setup with 5 channels.
•Individual Channels and Merged Image: In addition to the left and right eye views (or any number of additional intermediate camera views), a combined, stereoscopic image will be created out of a combination of these views.
•Single Channel: Only the channel defined by the Single Channel value will be calculated. This mode is recommended if you – for whatever reason – only want to render a single camera view.
Define which channel should be rendered. 1 will always render the left eye view. The value defined for Channels will be the right eye view. in-between values will represent the intermediate camera views, as described here: see Placement.
Enable this option if the normal camera view should be calculated in addition to the stereoscopic views.
Stereo Rendering Mode: Anaglyph, Side-by-Side, Interlaced
This is the most well known method, which has been used in movie theaters since the 50s. An image’s color information is separated using 2-color glasses (previously red-green, today most commonly red-cyan). Advantage: simple, affordable glasses. Disadvantage: color range is in part very limited.
• Method: Set the color of the stereoscopic image. A problem with the anaglyph technique is that some colors cannot be displayed without straining the viewer’s eyes (red when using red-cyan coding). Recommendation: Use Optimized, because it offers the least strenuous “viewing experience”.
The different available methods (Full with anaglyph colors red-blue). “Mono” = Stereo Rendering OFF. Models by DOSCH Design.
The following list is arranged according to the quality that can be expected from anaglyph images, from worst to best:
–Full: The oldest (and lowest quality) method of anaglyph display; the display is dark and monotone. This mode is designed for use with the Red-Blue or Red-Green anaglyph techniques.
–Gray: The anaglyph image will appear as a gray-scale image through the glasses (not designed for use with red-blue or red-green). For brighter images use Full.
–Half Color and Color: These modes allow only a limited color reproduction compared to the other options. Blue, green and yellow tones can be reproduced very well when the common red-cyan code is applied. If Color is selected, “retinal rivalry” can occur, i.e., red surfaces (red-cyan) will cause the left eye to pass on maximum color intensity to the brain and the right eye will only see “black”. This is irritating and strenuous for the eyes. This effect can be minimized by selecting Half Color. However, red will then be darkened to such a degree that it can no longer be recognized as such.
–Optimized: This mode is similar to Half Color, but offers better color reproduction and minimizes the retinal rivalry effect.
•System: Define the color of the stereoscopic color coding here when using Anaglyph mode. Both colors should be the same as the lenses of the 3D anaglyph glasses you will be using. If your client does not supply you with color information, use Red-Cyan.
–Use Custom option to define the individual colors for the stereoscopic color coding (however, it will then be difficult to find a matching pair of glasses…). If Method is set to anything but Full, you will only be able to define the left eye color. The left color must be the same as the color of the left lens of the glasses. The right eye color will automatically be set to the left eye’s complimentary color.
Left and right images are switched and squeezed into a normal image size. Some televisions use this technique for HD 3D because the transmission band width is the same as the HD band width. The terminal device must be able to decode these double images and display them sequentially (most commonly in combination with shutter glasses). Disadvantage: reduced resolution, expensive technology (special hardware required).
•Alignment: This mode defines whether or not both image parts should be arranged next to each other (horizontally or vertically).
•Left Mirror X/Left Mirror Y/Right Mirror X/Right Mirror Y: Use these checkbox options to mirror the image halves along the X or Y axes.
This method requires a monitor with a polarization filter and glasses with polarized glass. Since both images are coded into a single image (e.g., left eye all even, right eye all uneven lines), the resolution is halved. Advantage: affordable glasses, good color reproduction. Disadvantage: special monitor required, reduced resolution.
Define whether the coding should take place via offset lines (Horizontal) or columns (Vertical). Checkerboard is a combination of both modes.
Additional Parallax (pixel)
Moves the image halves by the defined value in pixels. This can be used to increase the stereoscopic effect.
If enabled, the left and right image halves will be swapped.
A few guidelines for achieving good stereoscopic images
There are several rules that should be followed when creating stereoscopic images. This is necessary so they can be easily viewed without any unnatural effects or fatigue for the viewer’s eyes. Hence, the following guidelines should be followed.
•Depth of Field: It is generally suggested that a larger depth of field (i.e. little blur) be used. A common 2D technique is to take the background out of focus using a slight depth of field. A blurred wall behind a sharp object makes this surface look flat. Such techniques are in contrast to stereoscopic techniques.
•Distance from object(s): The 3D effect depends a lot on how far the viewer is from the projection plane (monitor, screen, paper, etc.). The farther away the viewer is from the projection plane, the stronger the 3D effect will be (the perceived impression of depth between an object that is near and one that is far away)! This should be taken into consideration when creating a stereoscopic zone.
•Ghosting is when one eye perceives the image information of the other eye (leads to irritation). This is especially noticeable in images with high contrast (anaglyph images in particular are prone to this). Therefore, you should avoid such contrasts in your images if at all possible. Very small parallax values can also reduce ghosting.
•It is often irritating for the eye when objects are cut off at the edge of an image (if they do not lie on the projection plane). However, because there are always objects that lie on the edge of an image, it shouldn’t necessarily be the most important object in the image, the one that is currently the center of attention, that is being cut off.
•For videos it is important to give the eye time to adjust to strong parallax changes (between different settings). Short, fast cuts should then be avoided.
•Avoid exaggeration: Chain saws constantly flying towards the viewer or similar scenes can be fatiguing for the eye. Such visual gimmicks should be used sparingly or be well thought out.