An Efficient Caption Insertion Scheme for MPEG Video in MC-DCT Compressed Domain

Jongho NANG  Seungwook HONG  Ohyeong KWON  

IEICE TRANSACTIONS on Communications   Vol.E84-B   No.8   pp.2292-2300
Publication Date: 2001/08/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Multimedia Systems
multimedia system,  MPEG,  video coding,  watermark,  

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The (cinema) caption processing that adds descriptive text on a sequence of frames is an important video manipulation function that a video editor should support. This paper proposes an efficient MC-DCT compressed domain approach to insert the caption into the MPEG compressed video stream. It basically adds the DCT blocks of the caption image to the corresponding DCT blocks of the input frames one by one in the MC-DCT domain as in [6]. However, the strength of the caption image is adjusted in the DCT domain to prevent the resulting DCT coefficients from exceeding the maximum value allowed in MPEG. In order to adjust the strength of the caption image adaptively we need to know the exact pixel value of the input image. This is a difficult task in DCT domain. We propose an approximation scheme for the pixel values in which the DC value of a block is used as the expected pixel value for all pixels in that block. Although this approximation may lead to some errors in the caption area, it still provides a relatively high image quality in the non-caption area, whereas the processing time is about 4.9 times faster than the decode-captioning-reencode method.