Image analysis – Image compression or coding – Transform coding
Reexamination Certificate
1998-04-06
2001-07-10
Tran, Phuoc (Department: 2621)
Image analysis
Image compression or coding
Transform coding
C382S240000, C382S247000, C382S166000
Reexamination Certificate
active
06259819
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compression of digital image data and in particular to a method of encoding a raw bitmap of a low resolution version of an original image directly into a compressed bit stream. Further, encoding a raw bitmap into the pressed bit stream is achieved without substantially affecting the compression efficiency or computational efficiency of the compression and/or decompression of the digital image.
BACKGROUND ART
In general, digital age compression comprises encoding an entire image, either as a whole or in a block-wise manner, to produce a bit-stream of data representing the image. Often the size, measured in bits, of the bit-stream representing the image is reduced, by the compression process, when compared with the number of bits required to represent the digital image in an uncompressed format.
An advantage of compressing a digital image is that a compressed digital image data physically occupies less storage space on a storage device (eg. RAM, Disk or Magnetic Tape storage). Another advantage lies in a transmission of the digital images; a reduced bit-stream, typically as a result of compression, requires less transmission time than does the transmission of the digital image in an uncompressed format. At least one drawback of storing or transmitting a digital image in a compressed format is that the compressed image requires processing or decompressing before it can be displayed on a display device. Consequently, a compressed digit image cannot be displayed without investing costly time to decompress the compressed image. When browsing through a multitude of images, which are stored in a storage device or transmitted to a user in compressed format, having to decompress each image and display the image to find a select one of the images can pose a difficulty. In particular, the processing time required to decompress each image can render the browsing slow and cumbersome.
A number of hierarchical techniques for image coding are known which involve coding a lower resolution version of an image within a bit stream of a higher resolution version of the image. However, to display the lower resolution version of an image the compressed image or coded bit stream must be decoded. Typically the lower resolution version of an image can not be gleaned off the coded bit stream in a form substantially ready for display without decoding the entire, or part of the image. Further, with many of the known techniques, a low resolution version of an image in an uncoded format (ie. a format substantially ready for display) cannot be embedded in a bit stream of a coded higher resolution version of the image without substantially affecting the compression efficiency, computational efficiency or decoding complexity.
In addition, for known techniques where a first (low resolution) image is stored together with a second (high resolution) image, the first image typically being a small size likeness of the second image, the first image generally duplicates information already inherent in the second image. For example, a digital image can be duplicated and the duplicate image sub-sampled to provide a small likeness (lower resolution) of the digital image. The digital image is compressed and the small duplicate likeness can be stored in an uncompressed format together with the compressed digital image. The small duplicate likeness of the digital image makes available a representation of the digital image readily displayable on a display device without a requirement to decompress the entire digital image. However in current techniques the small duplicate likeness of the digital image is typically stored as an independent stream of data and not as an uncompressed portion of a digital image. Thus with the known techniques, at least, some disadvantages lie in a requirement to store duplicate information inherent to a digital image, which reduces the compression efficiency.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is disclosed a method of providing a thumbnail-size colour digital image in a bit stream of a larger size colour digital image, the bit stream of the larger digital image being in a compressed format, and comprising a thumbnail size image in a substantially uncompressed format, the method comprising the steps of:
converting input colour values of the larger colour image from a first colour format to corresponding values in a Luminance, Chrominance-blue, Chrominance-red (Y,Cb,Cr) colour format;
applying a transform to the corresponding values to decompose the larger digital image into a DC subband and one or more higher frequency subbands;
outputting to the bit stream the DC subband in an uncompressed format; and
encoding at least one of the one or more higher frequency subbands into the bit stream in a substantially compressed format, wherein the DC subband represents the thumbnail-size colour digital image in the bit stream,
In accordance with a second aspect of the present invention there is disclosed a method of compressing a digital image, the digital image comprising pixels represented in primary colour red, green and blue (RG) format, the method comprising the steps of:
converting R, G and B components of the pixels from the RGB format to components in Luminance, Chrominance-Blue, Chrominance-Red (YCbCr) format, the converting including sub-sampling of the Cb and Cr components;
decomposing using non-integer based processing each YCbCr component of the pixels of the digital image into a DC subband and a plurality of higher frequency subbands;
encoding into a bit stream the DC subband for each component as a substantially uncompressed raw bitmap image; and
encoding into the bit stream the plurality of high frequency subbands as a compressed bitmap image.
In accordance with a third aspect of the present invention there is disclosed a method of compressing a digital image, the dig image comprising pixels represented in primary colour (RGB) format, the method comprising the steps of:
converting the pixels from the RGB format to Luminance, Chrominance-Blue, Chrominance-Red (YCbCr) component format;
decomposing using a non-integer based discrete wavelet transform each component of the YCbCr format of the digital image into a DC subband and a plurality is of higher frequency subbands;
converting the DC subband into RGB format;
encoding into a bit stream tee convened DC subband for each primary colour as a substantially uncompressed raw bitmap image; and
encoding into the bit stream the plurality of high frequency subbands as a compressed bitmap image
A number of other aspects of the invention including apparatus configured to perform one or more of the methods and corresponding computer readable media are also disclosed.
REFERENCES:
patent: 5563960 (1996-10-01), Shapiro
patent: 5739920 (1998-04-01), Nakajima et al.
patent: 5748786 (1998-05-01), Zandi et al.
patent: 5880856 (1999-03-01), Ferriere
patent: 5982938 (1999-11-01), Dube
“Coding of Still Pictures”, Boliek et al., ISO/IEC JTC 1/SC 29/WG 1, Jun. 30, 1995.
Andrew James Philip
Chen Linda
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Phuoc
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