Digital image compression
AssigneeCanon Kabushiki Kaisha
InventorsWoei Chan, James Philip Andrew, Andrew James Dorrell
Life of this patent
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Abstract
A method of reconstructing an image, where the input image data is preferably part I or part II compliant JPEG2000 coded data, or pixel data of the original image. The method selects (810) an output resolution R, and then determines a number of sub-passes to extract from each block code based on the selected resolution. The method then extracts (830) the determined sub-passes and the remaining sub-passes are discarded. The method then reconstructs 840 the image from the extracted sub-passes. The reconstructed image can be in the form of the selected resolution of the original image, or it can be in the form of compressed image data of the selected resolution of the original image.
Claims53
A method of transcoding a first image file to a second image file, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the method comprising:
- selecting a parsed form of the single image codestream:
- locating, by using the table, those codestream segments associated with the selected parsed form;
- locating, by using the table, those codestream header data associated with the selected parsed form;
- and
- writing the located codestream header data and codestream segments as a single codestream of the selected parsed form to the second image file.
A method of generating a first image file from an original image, the method comprising the steps of:
- generating a single codestream representative of the original image, wherein said single codestream comprises a plurality of different forms of the image;
- and
- generating a first image file, wherein the first image file comprises segments of the single codestream and segments of codestream header data associated with different parsed forms of the original image, and a table comprising references associated with the different parsed forms of the original image for referencing segments of codestream header data and segments of the single codestream.
A method of decoding a first image file to provide an image, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the method comprising:
- selecting a parsed form of the single image codestream:
- locating, by using the table, those codestream segments associated with the selected parsed form;
- locating, by using the table, those codestream header data associated with the selected parsed form;
- constructing a single codestream of the selected parsed form from the located codestream header data and codestream segments;
- and
- decoding the constructed single codestream to produce an image of the selected parsed form.
A method of transcoding a first coded representation of an original image to provide a second coded representation of a reduced resolution of said original image, wherein said original image was previously encoded using a S-level DWT and blocks of DWT coefficients were previously coded in sub-passes to provide said first coded representation, the method comprising the steps of:
- determining a desired reduced resolution level J of the first coded representation, wherein J is less than S;
- determining a number of sub-passes to extract from each coded block of the first coded representation based on a predetermined image quality at said desired resolution level J;
- and
- extracting those determined sub-passes to form said second coded representation of the original image, wherein a reconstructed image of the second coded representation of the original image is not significantly degraded visually compared with a reconstructed image of the first coded representation at said desired resolution level J.
A method of encoding an original image to provide a coded representation of the original image, the method comprising:
- transforming said original image with a S-level DWT transform to produce a plurality of subbands of DWT coefficients;
- quantising the DWT coefficients of each subband according to a quantisation table;
- dividing each subband into one or more codeblocks of quantised DWT coefficients;
- entropy encoding said codeblocks to form a number of coded sub-passes;
- and arranging said coded sub-passes into a number of block layers, wherein the codeblocks in resolution levels greater than resolution level l make no contributions to block layers 0,1 . . . ,l, so as to enable a reconstruction of a resolution of the original image of just visually acceptable quality
A method of decoding a coded representation of an original image, wherein said original image was previously encoded using a S-level DWT transform and blocks of DWT coefficients were previously coded in sub-passes to provide said coded representation, the method comprising:
- determining a desired reduced resolution level J to decode, wherein J is less than S;
- determining a number of sub-passes to discard for each coded block based on a predetermined image quality at said resolution level J;
- discarding said determined sub-passes from said code blocks;
- and
- decoding those sub-passes not discarded to reconstruct said image at said desired reduced resolution level J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution level J using all said sub-passes.
A method of reconstructing an image, said image being encoded using a S-level DWT, wherein S is an integer and wherein blocks of DWT coefficients are coded in passes, the method comprising:
- determining a desired resolution J to decode, wherein J is less than S;
- determining a number of sub-passes to extract for each block code based on said resolution;
- extracting determined sub-passes from said block codes;
- and
- reconstructing said image from said extracted sub-passes at the desired reduced resolution J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution J using all said sub-passes.
Apparatus for transcoding a first image file to a second image file, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the apparatus comprising:
- means for selecting a parsed form of the single image codestream:
- means for locating, by using the table, those codestream segments associated with the selected parsed form;
- means for locating, by using the table, those codestream header data associated with the selected parsed form;
- and
- means for writing the located codestream header data and codestream segments as a single codestream of the selected parsed form to the second image file.
Apparatus for generating a first image file from an original image, the apparatus comprising:
- means for generating a single codestream representative of the original image, wherein said single codestream comprises a plurality of different forms of the image;
- and
- means for generating a first image file, wherein the first image file comprises segments of the single codestream and segments of codestream header data associated with different parsed forms of the original image, and a table comprising references associated with the different parsed forms of the original image for referencing segments of codestream header data and segments of the single codestream.
Apparatus for decoding a first image file to provide an image, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the apparatus comprising:
- means for selecting a parsed form of the single image codestream:
- means for locating, by using the table, those codestream segments associated with the selected parsed form;
- means for locating, by using the table, those codestream header data associated with the selected parsed form;
- means for constructing a single codestream of the selected parsed form from the located codestream header data and codestream segments;
- and
- means for decoding the constructed single codestream to produce an image of the selected parsed form.
Apparatus for transcoding a first coded representation of an original image to provide a second coded representation of a reduced resolution of said original image, wherein said original image was previously encoded using a S-level DWT and blocks of DWT coefficients were previously coded in sub-passes to provide said first coded representation, the apparatus comprising:
- means for determining a desired reduced resolution level J of the first coded representation, wherein J is less than S;
- means for determining a number of sub-passes to extract from each coded block of the first coded representation based on a predetermined image quality at said desired resolution level J;
- and
- means for extracting those determined sub-passes to form said second coded representation of the original image, wherein a reconstructed image of the second coded representation of the original image is not significantly degraded visually compared with a reconstructed image of the first coded representation at said desired resolution level J.
Apparatus for encoding an original image to provide a coded representation of the original image, the apparatus comprising:
- means for transforming said original image with a S-level DWT transform to produce a plurality of subbands of DWT coefficients;
- means for quantising the DWT coefficients of each subband according to a quantisation table;
- means for dividing each subband into one or more codeblocks of quantised DWT coefficients;
- and
- means for entropy encoding said codeblocks to form a number of coded sub-passes and for arranging said coded sub-passes into a number of block layers, wherein the codeblocks in resolution levels greater than resolution level l make no contributions to block layers 0,1 . . . ,l, so as to enable a reconstruction of a resolution of the original image of just visually acceptable quality.
Apparatus for decoding a coded representation of an original image, wherein said original image was previously encoded using a S-level DWT transform and blocks of DWT coefficients were previously coded in sub-passes to provide said coded representation, the apparatus comprising:
- means for determining a desired reduced resolution level J to decode, wherein J is less than S;
- means for determining a number of sub-passes to discard for each coded block based on a predetermined image quality at said resolution level J;
- means for discarding said determined sub-passes from said code blocks;
- and
- means for decoding those sub-passes not discarded to reconstruct said image at said desired reduced resolution level J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution level J using all said sub-passes.
Apparatus for reconstructing an image, said image being encoded using a S-level DWT, wherein S is an integer and wherein blocks of DWT coefficients are coded in passes, the apparatus comprising:
- means for determining a desired resolution J to decode, wherein J is less than S;
- means for determining a number of sub-passes to extract for each block code based on said resolution;
- means for extracting determined sub-passes from said block codes;
- and
- means for reconstructing said image from said extracted sub-passes at the desired reduced resolution J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution J using all said sub-passes.
A computer program for transcoding a first image file to a second image file, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the computer program comprising:
- code for selecting a parsed form of the single image codestream:
- code for locating, by using the table, those codestream segments associated with the selected parsed form;
- code for locating, by using the table, those codestream header data associated with the selected parsed form;
- and
- code for writing the located codestream header data and codestream segments as a single codestream of the selected parsed form to the second image file.
A computer program for generating a first image file from an original image, the computer program comprising:
- code for generating a single codestream representative of the original image, wherein said single codestream comprises a plurality of different forms of the image;
- and
- code for generating a first image file, wherein the first image file comprises segments of the single codestream and segments of codestream header data associated with different parsed forms of the original image, and a table comprising references associated with the different parsed forms of the original image for referencing segments of codestream header data and segments of the single codestream.
A computer program for decoding a first image file to provide an image, wherein the first image file comprises a single codestream and a table comprising references associated with different parsed forms of the single codestream for referencing segments of codestream header data and segments of the single codestream, the computer program comprising:
- code for selecting a parsed form of the single image codestream:
- code for locating, by using the table, those codestream segments associated with the selected parsed form;
- code for locating, by using the table, those codestream header data associated with the selected parsed form;
- code for constructing a single codestream of the selected parsed form from the located codestream header data and codestream segments;
- and
- code for decoding the constructed single codestream to produce an image of the selected parsed form.
A computer program for transcoding a first coded representation of an original image to provide a second coded representation of a reduced resolution of said original image, wherein said original image was previously encoded using a S-level DWT and blocks of DWT coefficients were previously coded in sub-passes to provide said first coded representation, the computer program comprising:
- code for determining a desired reduced resolution level J of the first coded representation, wherein J is less than S;
- code for determining a number of sub-passes to extract from each coded block of the first coded representation based on a predetermined image quality at said desired resolution level J;
- and
- code for extracting those determined sub-passes to form said second coded representation of the original image, wherein a reconstructed image of the second coded representation of the original image is not significantly degraded visually compared with a reconstructed image of the first coded representation at said desired resolution level J.
A computer program for encoding an original image to provide a coded representation of the original image, the computer program comprising:
- code for transforming said original image with a S-level DWT transform to produce a plurality of subbands of DWT coefficients;
- code for quantising the DWT coefficients of each subband according to a quantisation table;
- code for dividing each subband into one or more codeblocks of quantised DWT coefficients;
- and
- code for entropy encoding said codeblocks to form a number of coded sub-passes and for arranging said coded sub-passes into a number of block layers, wherein the codeblocks in resolution levels greater than resolution level l make no contributions to block layers 0,1 . . . ,l, so as to enable a reconstruction of a resolution of the original image of just visually acceptable quality.
A computer program for decoding a coded representation of an original image, wherein said original image was previously encoded using a S-level DWT transform and blocks of DWT coefficients were previously coded in sub-passes to provide said coded representation, the computer program comprising:
- code for determining a desired reduced resolution level J to decode, wherein J is less than S;
- code for determining a number of sub-passes to discard for each coded block based on a predetermined image quality at said resolution level J;
- code for discarding said determined sub-passes from said code blocks;
- and
- code for decoding those sub-passes not discarded to reconstruct said image at said desired reduced resolution level J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution level J using all said sub-passes.
A computer program for reconstructing an image, said image being encoded using a S-level DWT, wherein S is an integer and wherein blocks of DWT coefficients are coded in passes, the computer program comprising:
- code for determining a desired resolution J to decode, wherein J is less than S;
- code for determining a number of sub-passes to extract for each block code based on said resolution;
- code for extracting determined sub-passes from said block codes ;
- and
- code for reconstructing said image from said extracted sub-passes at the desired reduced resolution J, wherein said reconstructed image is not significantly degraded visually compared with an image reconstructed from said coded representation at said desired resolution J using all said sub-passes.
Dependencies are inferred from the claim text.