Nathan Grout and Dr. Darl Larsen, Theatre and Media Arts
In the past year, there has been a wave of 3D films in theaters. These films utilize the latest digital technologies for production and distribution to provide a superior 3D experience. Similar quality levels, however, can be achieved on an independent/student production level. The resurrection of what is often considered an antiquated technique, anaglyphic 3D, levels the playing fields and provides low budget filmmakers a viable option for creating 3D films.
All 3D filmmaking operates by separating a pair of images that are displayed on the screen simultaneously so that each image is seen by one eye. This technique, called stereoscopic photography, mimics the independent vision of the viewers two eyes. The polarized lenses used in modern theatrical display can separate the two images so that each is seen by the correct eye based on the direction of the light waves. A similar effect can be achieved through color encoding of each eye’s video in opposite colors, such as red and cyan, a technique called anaglyphic 3D.
Thus, the main objective of post-production of anaglyphic 3D video is to combine the images of two cameras while encoding them in with the proper color information. Those involved in this process must be aware of the aesthetics of the combined image and the technical aspects of preserving pristine color information.
While some productions may utilize cameras that are set to film images that match exactly when combined in post production, it also common for productions to shoot footage that must be arranged in post production so that the two images overlap correctly. The aesthetic responsibility of composing the 3D image falls on those executing the post-production.
By shifting one image to the left or the right, the post-production artist determines where the two images align. At a certain distance from the camera, the two images will align perfectly, while objects at greater or lesser distances from the lens will be seen to have red and cyan borders. This point of alignment becomes what can be called the stereoscopic focal point. The stereoscopic focal point is flush with the surface of the screen on which the image is displayed rather than appearing to recede or extend from it. Control of the placement of the stereoscopic focal point by the post-production artist is imperative because distortion in color is minimal at the focal point. As a result, if the focal point is placed at or near the subject of the shot, the audience is will focus their attention on portions of the screen with minimal ghosting.
The quality of the anaglyphic image is not only determined by the aesthetic control of the placement of the focal point, but is also determined by the quality of the color encoding of the digital image. Distortions in the color of one of the images creates the potential of bleeding through the lens to the other eye. This intrusion of a second image in what is seen by an eye is called ghosting and can disorient the viewer.
Fortunately, all of the software technology needed to create quality anaglyphic video are readily available to student and low budget productions in the form of Apple’s Final Cut Pro and Adobe’s After Effects, two easily accessible and fairly affordable software packages. To create an anaglyph, the two channels of video are placed above each other on two tracks. The track from the left camera should be limited to the red channel, while the right channel is encoded using solely the blue and green channels. This can be achieved in Final Cut Pro using an RGB Balance filter and in After Effects by using a Levels filter. For optimum anaglyph brightness, the two images should be blended by setting the blend mode of the top image to screen. It is for this reason that Final Cut Pro and After Effects are ideally suited for anaglyph creation. Some film editing programs, like Avid, do not support advanced blend modes.
While using these techniques in Final Cut Pro is feasible for creating preview quality anaglyphs, finishing is better accomplished in After Effects. Final Cut is build to operate primarily in the YUV color space, while After Effects operates in the RGB color space. Since the RGB color space distinguishes color information based on the same colors used to distinguish the two channels of the anaglyphic image, it is ideally suited for anaglyph generation. (Even though Final Cut Pro can be set to render footage in the RGB colorspace, After Effects produces noticeably superior anaglyphs). A workflow for Final Cut editing and After Effects finishing might include exporting a left channel track and a right channel track, both aligned for anaglyph creation but without any color or blending effects. These “clean” video tracks would then be combined in After Effects for final output using 32 bit per channel color and the desired codec.
Codec choice is also key in outputting the cleanest anaglyph possible. Full color encoding is much preferable to encoding in any codec that compresses the color information using. The best codec options are (in order of increasing size) Apple’s ProRes 4444 codec, Uncompressed, and TIFF. All of these codecs, however, are very weighty because they do not compress the color information. Even high quality codecs that utilize relatively slight color compression, like Apple’s ProRes 422 and 422 HQ, show a marked degradation in image quality, most noticeable in bleeding of the cyan image through the red lens.
Since color is especially important in anaglyphic 3D, color choice on set and color correction in post-production become important. Colors more removed from red and cyan are more likely to appear appropriately when viewed through anaglyphic glasses. Thus, production design should emphasize grayscale colors, greens, blues, and yellows, while deemphasizing red. In as much as problematic colors still make their way into the image, it is the job of the colorist to reduce the intensity of those colors or shift their hue so that there appearance through anaglyphic glasses is minimized.
Proper concern for color choice, anaglyph composition, and output codec can lead to optimum quality home distribution. Codecs are the principle challenge in distribution of anaglyphic video. The highly compressed MPEG2 of DVDs and h.264 of Blu-Ray discs means that some of the color information necessary for clean anaglyph images is simply lost. Awareness of optimum anaglyph creation techniques combined with appropriate art design for anaglyphic video means that independently produced DVDs can easily compete with Hollywood films on DVD, as the latter are created for theatrical screens rather than being composed for home viewing.