Stereo3D Image Balance

Introduction

It is crucial to not only have 3D material with the least amount of geometric disparity as possible but to also have the images matching in their colour correction, white balance and exposure. This stereoscopic image calibration is achieved with the Stereo3D Image Balance plug-in.

Initial Setup

The Clip Coupler plug-in, as with all the plug-ins in the Stereo3D suite, can be applied to an already pre-existing multiplexed stereo pair (left & right video files married together) that is any number of 3D formats (side-by-side, over-under, etc) as well as be applied to a single left or right eye file and then be coupled with the correct adjacent left or right video clip.

To access the Geometry plug-in go to:

Video Filters → Dashwood Stereo3D Toolbox → Stereo3D Image Balance

Once applied to the clip, the clips render status will appear red in the FCP timeline unless set to Unlimited-RT. To access the menu to change the timeline’s render settings click on the RT button on the far left of the timeline. Select Unlimited-RT and the clips render status will turn orange, indicating that Final Cut Pro will process as much of the un-rendered effect in real-time as permitted by the video card. Typically the more VRAM that FCP has access to, the closer to real-time it will display the un-rendered clip. If an external 3D Monitor is being used for playback, then Playback Video Quality should be set to High and Playback Frame Rate can be left at Dynamic.

Luminance and Chroma Correction

Every sensor reads light slightly different and every lens is unique. Depending the type of stereoscopic camera rig and how attentive the camera team was during production, there can sometimes be disparities between the images based on exposure, white balance and a variety of other aspects. These issues must be address before final output. Beam splitter rigs will always cut up to 1.5-stops of light from the camera that is shooting through the mirror.

Luminance
There are seven sliders for each eye for luminance. In order to more accurately match the images, side-by-side should be selected as the output mode (discussed in S3D Output Options of this Guide). To match the luminance values, the waveform monitor is very helpful and it can be accessed by clicking Tools → Video Scopes →Waveform. Two similar waveforms will appear beside one another and Luminance sliders in the Image Balance plug-in can now be manipulated to match the corresponding waveforms.

Overall Exposure adjusts either the left or right eyes overall brightness or darkness. It mimics the behaviors of changing the scenes iris level, besides affecting the depth-of-field. If the footage was acquired on a beam splitter rig that has one of the cameras shooting through the mirror, then the Overall Exposure slider should be used to gain back the light lost.

Contrast will adjust the intensity of distinction between the low luminance values and high luminance levels within the scene. Adjusting the slider to the left will decrease the difference between these values and moving the slider to right will increase the range between the darkness and brightness of the scene.

Input Level Low adjusts the amount of black and dark luminance values that are passed through the filter for front end processing.

Input Level High adjusts the amount of white and high luminance values that are passed through the filter for front end processing.

Output Level Low increases the amount of output of black and low luminance values after the video is passed through the initial filter.

Output Level Mid increases the amount of output of mid luminance values after the video is passed through the initial filter.

Output Level High increases the amount of output of white and high luminance values after the video is passed through the initial filter.

Chroma
The chroma sliders (17 in total) allow for RGB adjustment of the individual files in the stereoscopic pair.

Image Balance Features

S3D Input
Please refer to either Clip Coupler or Geometry Plug-in manuals for details on how to use the S3D Input and for brief definitions of the various 3D formats.

Click the links below.

http://www.dashwood3d.com/help/stereo3d-clip-coupler/

http://www.dashwood3d.com/help/stereo3d-geometry/

Input Squeezed (Only available when using Side-by-Side input types)
This option tells Stereo3D Toolbox whether or not the side-by-side footage is squeezed into one full resolution composition or if it is two full resolution compositions coupled in the same file.

Swap Inputs
The naming hierarchy of left & right 3D files can sometimes be incorrect depending on the accuracy of the Data Management Technologist’s file handling and the labeling of the physical cameras on a Beam-Splitter Rig. This naming error will be evident if the footage is viewed on a 3D display, as the background will be perceived to be floating in front of objects that should be in the foreground and vice-versa. When incorrectly labeled the left and right eye video will be reversed and thus the human eye will be receiving incorrect information. If the viewer is unsure if the footage is named properly, then by clicking Swap Input back and forth while playing the footage, the 3D will either be comfortable to watch or slightly straining to view. If the footage is comfortable to watch and the objects within the scene are positioned in the proper location in 3D space (foreground objects appearing at the front or “popping” off the screen & background objects appearing in the back or “behind” the screen) when Swap Input is selected, then this indicates that the footage has been named incorrectly.

View
At any point during the image balancing process the original look of the left and right file can be viewed by accessing the View drop-down menu and selecting on either Final Corrected Images or Original.

S3D Output Options

The various stereoscopic 3D output modes available in Stereo3D Toolbox can be accessed underneath the S3D Output Mode Tab. Side-by-side, Line by Line Interlaced and Above Below are the three output modes are most commonly found finishing formats besides exporting separate left and right video tracks or upgrading to a DCP for a cinema release.

These formats are discussed in the Clip Coupler Guide.

Swap Outputs
It is sometimes necessary to swap the output as some 3D Monitors interleave their polarized signals differently, amongst other reasons. If ever needed, the Swap Outputs checkbox can be selected after the convergence and stereoscopic settings have been changed.

Flip Flop
Cameras shot on certain beam splitter rigs need one or both of the cameras to be flipped or flopped in order for the perspectives to match.
Flip will rotate the image 180º so that it is upside down from it’s native position.
Flop will change the images perspective so that is a mirror image of it’s native position as though it has been rotated 180º along the z-axis.