Browse Prior Art Database

Subband Coding with Discrete Cosine Transforms

IP.com Disclosure Number: IPCOM000107938D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 52K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR

Abstract

Disclosed is a method for subband coding of data such as image data utilizing Discrete Cosine Transforms.

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This is the abbreviated version, containing approximately 71% of the total text.

Subband Coding with Discrete Cosine Transforms

      Disclosed is a method for subband coding of data such as image
data utilizing Discrete Cosine Transforms.

      Two common forms of image coding are based on either subband
coding or Discrete Cosine Transform (DCT) techniques. The former has
advantages wherein a low-frequency version of the image can be
isolated and handles with, say, greater reliability or separarely
when compatibility constraints are imposed (as in HDTV). DCT methods
are more generally accepted for high quality compression of images-
the so called visually lossless compression.

      We disclose here how to combine the two methods. A preferred
embodiment is discussed as a guiding example. We partition the image
to 8 x 8 blocks, and take the 8 x 8 quantized DCT of each
block. The quantization is a function of the desired quality and
average desired compression rate. The output of each block is
sectioned into four subblocks: the top-left 4 x 4  subblock, labeled
LL (low-low), the top-right 4 x 4  subblock, labeled LH (low-high),
the bottom-left 4 x 4 subblock, labeled HL (high-low), and the
bottom-right 4 x 4 subblock, labeled HH (high-high).

      The LL subblock may be in-turn subband coded again; the
remaining three subblocks are coded with any of the good lossless
coding techniques used in image processing, such as Huffman coding or
arithmetic coding (including Q-coding), utilizing a zig-zag pattern
as described in the JPEG standa...