The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 26, 1994
Filed:
Nov. 17, 1992
Adrianus Ligtenberg, Palo Alto, CA (US);
Storm Technology, Mountain View, CA (US);
Abstract
An enhancement to a standard lossy image compression technique wherein a single set of side information is provided to allow decompression of the compressed file. Certain portions of the image are selected (either by the user or automatically) for more compression than other portions of the image. A particular embodiment is implemented for use with the JPEG image compression technique. JPEG calls for subdividing the image into blocks, transforming the array of pixel values in each block according to a discrete cosine transform (DCT) so as to generate a plurality of coefficients, quantizing the coefficients for each block, and entropy encoding the quantized coefficients for each block. Techniques for increasing the compression ratio include subjecting each selected block to a low pass filtering operation prior to the transform, subjecting the coefficients for each selected block to a thresholding operation before the quantizing step, subjecting the coefficients for each selected block to a downward weighting operation before encoding them, or, where the entropy encoding uses Huffman codes, mapping coefficients to adjacent shorter codes.