Method and apparatus for extracting pixel values

Details Method and apparatus for extracting pixel values Method and apparatus for extracting pixel values

H - Electricity

04

N

H04N 7/30 (2006.01) G06T 9/00 (2006.01) H04N 7/26 (2006.01)

Patent

CA 2470346

The invention provides a method and apparatus for extracting the luminance and chrominance values of pixels encoded according to MPEG or JPEG encoding using a forward discrete cosine transform (DCT). The invention applies theoretical work to mathematically analyse the forward DCT used in MPEG encoding to derive a set of equations which directly relate a pixel value in an encoded image to one or more of the DCT coefficients obtained via the forward DCT transform in the usual image encoding process. These predetermined equations are used in the invention to allow for extremely fast and computationally efficient extraction of pixel values directly from the DCT coefficients of an encoded pixel block, without having to undergo an inverse DCT transform. The invention is expected to be of use in any application where it is desirable to extract original images from MPEG and JPEG encoded versions in a fast and efficient manner.

L'invention concerne un procédé et un appareil destinés à extraire les valeurs de luminance et de chrominance de pixels codés selon un codage MPEG ou JPEG par transformation en cosinus discrets directe (TCD). L'invention applique un travail théorique afin d'analyser mathématiquement la TCD directe, utilisée dans le codage MPEG, afin de dériver un ensemble d'équations qui relient directement une valeur de pixel d'une image codée à un ou plusieurs coefficients TCD, obtenus lors de la transformation TCD directe, dans le processus de codage de l'image normale. Ces équations déterminées sont utilisées dans l'invention afin de permettre une extraction, extrêmement rapide et efficace sur le plan du calcul, des valeurs de pixel directement à partir des coefficients TCD d'un bloc de pixels codés, sans avoir à réaliser une transformation TCD inverse. L'invention est censée s'appliquer dans toute application dans laquelle il est souhaitable d'extraire des images originales de versions, à codage MPEG ou JPEG, d'une manière rapide et efficace.

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