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Apparatus and methods for re-compression having a monotonic relationship between extent of compression and quality of compressed image

  • US 8,805,109 B2
  • Filed: 04/14/2011
  • Issued: 08/12/2014
  • Est. Priority Date: 04/29/2010
  • Status: Expired due to Fees
First Claim
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1. A computerized method for generating a quantization matrix usable for independent disjoint block-level recompression of an image, the image generated by independent disjoint block level compression of a precursor image using at least one first quantization matrix, the method comprising:

  • providing a second quantization matrix;

    updating, using a processor, the second quantization matrix to provide a monotonic relationship between a compression extent and a compression quality when performing independent disjoint block-level recompression of the image using the second quantization matrix, including, for at least one (row, column) position, performing the following, giving rise to the quantization matrix;

    calculating a ratio between values located at the position in the first quantization matrix and in the second quantization matrix;

    calculating a rounding of the ratio;

    calculating a rounding error, being a difference between the ratio and the rounding; and

    if the rounding error fulfills an unacceptability criterion, decreasing, using the processor, the value at the position in the second quantization matrix.

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