Session 2: Technical Issues for 3D Digital Cinema (Metadata, mainly about subtitles)
Richard Welsh, Dir., Digital Cinema Services,Dolby
Metadata impacts cinema, TV, PC, and mobile. It is a river of information that flows down to the sea; the consumer.
Issues include 3D subtitling work, workflow optimization, quality concerns, and standards work. Subtitle quality is critical in 3D. When you get subtitle placement wrong in a 3D image, your brain knows something is wrong and snaps you to attention about it.
In order to do subtitling well, he determines how they fit into the entire movie in multiple languages so they work with the story. You must analysis the stereo image. The subtitles must not clash with the image. (NOTE: Dolby discusses volume, where negative volume is behind the screen. The notation is opposite the +/- vergence convention.)
Depth metric (z) is dependent on physical separation, pixel separation, or percentage separation relative to display size, combined with the viewing distance from screen.
Block-based analysis helps supply automated information on where to place the subtitles in Z. You still must define the ‘safe area’ within the X/Y rectangle in which to place the subtitle.
Currently the practice is to render (e.g. burn) the subtitles into the picture.
He showed an Alice In Wonderland clip to demonstrate how anti-aliasing softens the edges of text to remove visual errors in diagonal lines/edges.
He then demonstrated Dynamic Move of subtitles on a whole-pixel and sub-pixel basis. The subtitles moved with the movement of the Cheshire Cat. Sub-pixel movement is only possible with anti-aliasing. SMPTE is currently discussing full-pixel vs sub-pixel subtitle movement.
Suitability of subtitle metadata
– a Depth Analysis Track is most useful in Post/Broadcast environment
– Subtitle Metadata is needed quickly, because proper quality 3D subtitling is a much more complex problem than 2D
– Depth compensation needs further research
– Window movement is interesting and useful
Bonus: send an email from a mobile device to NAB3DSummit@dolby.com and it will return 3 images for your mobile in anaglyph.