Method for run-length encoding of a bitmap data stream

US7657109B2 · kind B2 · utility

Assignee

• Thomson Licensing · FR

Inventors

• Dirk Gandolph · Hannover, DE
• Jobst Hörentrup · Hannover, DE
• Axel Kochale · Springe, DE
• Ralf Ostermann · Hannover, DE
• Hartmut Peters · Barsinghausen, DE

Key dates

• Filing date: May 6, 2004
• Grant date: Feb 2, 2010
• Expiry date: Mar 8, 2026

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04N21/4884
• WIPO field: Audio-visual technology
• WIPO sector: Electrical engineering

Abstract

Subtitling aims at the presentation of text information and graphical data, encoded as pixel bitmaps. The size of subtitle bitmaps may exceed video frame dimensions, so that only portions are displayed at a time. The bitmaps are a separate layer lying above the video, e.g. for synchronized video subtitles, animations and navigation menus, and therefore contain many transparent pixels. An advanced adaptation for bitmap encoding for HDTV, e.g. 1920×1280 pixels per frame as defined for the Blu-ray Disc Prerecorded format, providing optimized compression results for such subtitling bitmaps, is achieved by a four-stage run length encoding. Shorter or longer sequences of pixels of a preferred color, e.g. transparent, are encoded using the second or third shortest code words, while single pixels of different color are encoded using the shortest code words, and sequences of pixels of equal color use the third or fourth shortest code words.