Embedding a watermark in a coded signal
AssigneeKoninklijke Philips Electronics N.V.
InventorGerrit Langelaar
Life of this patent
Estimating the term…
Abstract
Method and arrangement for water(re)marking a compressed video signal by modifying selected DCT coefficients. To avoid that the bitrate is thereby reduced too much, selected variable-length codewords are represented by escape codes. In order to avoid that ESC codes increase the bitrate too much (an ESC code is 7-21 bits longer than the corresponding VLC word), the bitrate is controlled in units of small data chunks. While a VLC is processed, a table is filled with candidate ESC codes. The bitrate controller tries to make the difference between original and processed data chunks zero by re-encoding one VLC into an appropriate ESC code.
Claims10
A method of processing a compressed media signal, in which samples of said media signal are represented by variable-length code words (VLCs), the method comprising the steps of:
- decoding the VLCs of a sample;
- modifying a plurality of said decoded VLCs in accordance with a given signal processing algorithm;
- encoding the modified decoded VLCs into modified VLCs by a first coding method;
- encoding the modified decoded VLCs into at least one length of code by a second coding method;
- for each of the plurality of modified VLCS, selecting the modified VLC coded by the first or second method that has a length closest to the length of the corresponding unmodified VLC;
- and
- combining the selected modified VLCs and any unmodified VLCs.
A signal processing device for a compressed media signal comprises:
- a decoder operable to decode samples of a compressed media signal represented by variable-length code words (VLCs);
- means for modifying a plurality of the decoded VLCs in accordance with a given signal processing algorithm;
- a first encoder operable to encode the modified decoded VLCs into modified VLCs by a first coding method;
- a second encoder operable to encode the modified decoded VLCs into modified VLCs by a second coding method;
- memory means operable to buffer the modified decoded VLCs from the fist and second encoders;
- and
- a controller operable to select the modified VLC from either the first or second encoder closest in length to an unmodified VLC, for each of the plurality of modified VLCs.
Dependencies are inferred from the claim text.