Koninklijke Philips Corporation N.v.

Armand V Wemelsfelder

Wiebe De Haan

Richard Cees Spiero

Jan Van Der Meer

Graphic images that overlay a transmitted video signal are provided in the form of bitmaps that allow any character or font size to be displayed. A color-look-up-table (CLUT) at a receiver is defined that maps 'm' inputs to a combination of color and luminance values for display. One or more map tables are provided that allow pixel colors to be encoded using fewer than 'm' bits, the map tables providing an &#x201c;m&#x201d; bit output for accessing the CLUT. The provider of the graphic images can also specify a required minimum number of CLUT colors for rendering the images; if this minimum is greater than &#x201c;m&#x201d;, the image is not rendered. The use of map tables provides compatibility between a variety of encoding techniques and a variety of rendering devices, without requiring different CLUTs to be transmitted for each different color encoding format.

Subtitling transmission system

A method of simultaneously transmitting a video signal and encoded data representing graphic images is disclosed. The invention is particularly applicable for transmitting multilingual subtitles with a video program. The graphic images are rectangular regions within the active video area. They are transmitted in the form of bitmaps. The invention not only allows any character font or size to be displayed, but also the definition of e.g. a program provider's logo. The encoded data includes a time stamp to specify the time at which a subtitle is to be displayed. Preferred embodiments of the invention include the transmission of color-look-up-table (CLUT) data and a compatibility code indicating a required minimum number of entries of said color-look-up-table. For receivers with a CLUT having more entries than necessary, a map table is a for mapping the pixel data width to the input witdh of the relevant CLUT. The method is applicable to Direct Video Broadcast systems wherein the video signal is MPEG2 encoded and the graphic images are accommodated in a private data stream of an MPEG2 Transport Stream.

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Hilversum, Netherlands

Armand V Wemelsfelder