“Edge violation is a visual artefact that can arise when part of an object is visible at the edge of one image pair but not at the other,” explained Cel-Soft founder and managing director Robin Palmer. “The brain normally compensates for edge violation when viewing the real world, as it does with many other inherent defects of human visual perception. Viewing through a television or cinema frame, however, it can become confused.”
An example of edge violation can be seen in the diagram above which shows a street lamp located on the extreme left in the foreground. With the cameras converging on the middle ground, only the right-hand camera is able to display the entire lamp post.
Viewed in 2D the supporting pillar is only partly onscreen. The rest of the pillar is perceived as being behind the frame. If the shot is viewed in 3D and the post is in front of the screen plane, then some of it appears to be levitating.
In this example, the occlusion gives the viewer the impression that the post is behind the frame, but the parts visible to both eyes create the 3D illusion of the post being in front. This conflict can causes eyestrain, headaches or even nausea.
“Edge violation can be fixed in postproduction, but is best handled if you are alerted to the problem during the initial shoot,” Palmer added. “Spotting where edge violations are occurring takes a practiced eye as they may not be as obvious as the lamp post. The search window has to be very wide as edge-violation objects are likely to be close to the cameras and therefore to have large horizontal disparities. If these match in any position, they are not edge violators.”
Using the latest version of Cel-Scope3D, edge violation can be displayed automatically in several ways. Alarm messages can be superimposed on the analyzer’s display screen as soon as the violations are detected. Additionally, the offending objects are visually yellow-highlighted on the depth map display. With the logging option, edge violations can be automatically logged by timecode in a report, along with over 30 user settable parameters and checks.
The automatic edge violation detection feature is additional to the depth spectrogram, which was introduced at IBC2011 in September. The depth spectrogram allows the depth dynamics to be viewed and makes spotting 2D-to-3D converted material very easy by its signature.
Cel-Scope3D 1.4 can analyze file-based content as well as live or recorded signals in dual-stream or multiplexed formats. It allows stereoscopic camera alignment to be performed quickly and accurately. Footage and edits in a wide range of file formats can be viewed and assessed in real time. Disparities are analyzed and displayed as clear and intelligible graphics on 2D or 3D monitors. Anaglyph display, user presets and on-screen-alarms are all provided.
Cel-Scope3D generates live displays which can be scaled and arranged as six or eight windows on one or two PC monitors. Left and right channels can be viewed simultaneously together with actual depth dynamics. Each graphic window can be set to show waveform, vectorscope and histogram graphics as well as differences in video parameters between each channel. Geometry issues can be identified using built-in real-time image manipulation. Quality-control tests can be performed on live stereoscopic video sources in any 720P, 1080 or 2K formats from industry standard capture cards and input devices or from file playback.
Cel-Soft’s products are available as software-only systems, or as complete turnkey systems running on workstations or laptops for field use.