System and method for recompressing a jpeg image using requantization
View Patent ↗A system and method for recompressing a JPEG image using requantization is described. DCT transform coefficients for a compressed JPEG image are statistically analyzed to generate a stored numeric error representation. Local minimizers are determined from the stored numeric error representation with selective rounding. A new quantization matrix Q 1 is selected from the local minimizers bounded by a target quantization matrix Q bound . The compressed JPEG image is recompressed using the new quantization matrix Q 1 .
1. A system for recompressing a JPEG image using requantization, comprising:
a matrix module statistically analyzing DCT transform coefficients for a compressed JPEG image to generate a stored numeric error representation, determining local minimizers from the stored numeric error representation with selective rounding, and selecting a new quantization matrix Q 1 from the local minimizers bounded by a target quantization matrix Q bound ; and
an image recompression module recompressing the compressed JPEG image using the new quantization matrix Q 1 .
2. A method for recompressing a JPEG image using requantization, comprising:
statistically analyzing DCT transform coefficients for a compressed JPEG image to generate a stored numeric error representation;
determining local minimizers from the stored numeric error representation with selective rounding;
selecting a new quantization matrix Q 1 from the local minimizers bounded by a target quantization matrix Q bound ; and
recompressing the compressed JPEG image using the new quantization matrix Q 1 .
3. A system for constructing a new quantization matrix for use in recompressing a JPEG image, comprising:
an intermediate constant module determining an intermediate constant k computed in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
a matrix module defining a new quantization matrix Q 1 , comprising a plurality of quantizers q 1 , from an initial quantization matrix Q 0 , comprising a plurality of quantizers q 0 , each such quantizer q 1 computed in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
is
odd
;
kq
0
+
1
,
if
k
>
0
and
k
is
even
.
;
and
a recompression module recompressing a JPEG image using the new quantization matrix Q 1 .
4. A system according to claim 3 , further comprising:
a compression module compressing the JPEG image using a lossy JPEG compression mode.
5. A method for constructing a new quantization matrix for use in recompressing a JPEG image, comprising:
determining an intermediate constant k computed in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
defining a new quantization matrix Q 1 , comprising a plurality of quantizers q 1 , from an initial quantization matrix Q 0 , comprising a plurality of quantizers q 0 , each such quantizer q 1 computed in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
is
odd
;
kq
0
+
1
,
if
k
>
0
and
k
is
even
.
;
and
recompressing a JPEG image using the new quantization matrix Q 1 .
6. A method according to claim 5 , further comprising:
compressing the JPEG image using a lossy JPEG compression mode.
7. A system for constructing a new quantization matrix for use in recompressing a JPEG image with selective rounding, comprising:
an intermediate constant module determining an intermediate constant k computed in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
a matrix module defining a new quantization matrix Q 1 , comprising a plurality of quantizers q 1 , from an initial quantization matrix Q 0 , comprising a plurality of quantizers q 0 , each such quantizer q 1 computed in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
>
0.
;
and
a recompression module recompressing a JPEG image using the new quantization matrix Q 1 while rounding each half integer value towards zero.
8. A system according to claim 7 , further comprising:
a compression module compressing the JPEG image using a lossy JPEG compression mode.
9. A method for constructing a new quantization matrix for use in recompressing a JPEG image with selective rounding, comprising:
determining an intermediate constant k computed in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
defining a new quantization matrix Q 1 , comprising a plurality of quantizers q 1 , from an initial quantization matrix Q 0 , comprising a plurality of quantizers q 0 , each such quantizer q 1 computed in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
>
0.
;
and
recompressing a JPEG image using the new quantization matrix Q 1 while rounding each half integer value towards zero.
10. A method according to claim 9 , further comprising:
compressing the JPEG image using a lossy JPEG compression mode.
11. A system for recompressing a JPEG image using requantization, comprising:
a JPEG image stored as compressed image data quantized per an initial quantization matrix Q 0 comprising a plurality of initial quantizers q 0 ;
a quantization matrix generator defining a target quantization matrix Q bound comprising a plurality of target quantizers q bound , computing an intermediate constant k in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
,
and constructing a new quantization matrix Q 1 comprising a plurality of quantizers q 1 from the initial quantization matrix Q 0 by computing each such quantizer q 1 in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
is
odd
;
kq
0
+
1
,
if
k
>
0
and
k
is
even
.
;
and
an image recompression module requantizing the compressed image data using the new quantization matrix Q 1 .
12. A system according to claim 11 , wherein the JPEG image comprises a color image, further comprising:
a component separation submodule separating the color image into separate color components; and
a quantization submodule requantizing each such color component using the new quantization matrix Q 1 .
13. A system according to claim 11 , wherein the JPEG image comprises a grayscale image, further comprising:
a quantization submodule requantizing the grayscale image using the new quantization matrix Q 1 .
14. A system according to claim 11 , further comprising:
a partition submodule partitioning the JPEG image;
a transformation submodule transforming each partition using a DCT; and
a quantization submodule quantizing the transformed partitions using the quantization matrix Q 0 .
15. A system according to claim 11 , wherein the JPEG image is compressed using one of baseline sequential encoding and DCT-encoding.
16. A method for recompressing a JPEG image using requantization, comprising:
storing a JPEG image as compressed image data quantized per an initial quantization matrix Q 0 comprising a plurality of initial quantizers q 0 ;
defining a target quantization matrix Q bound comprising a plurality of target quantizers q bound ;
computing an intermediate constant k in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
constructing a new quantization matrix Q 1 comprising a plurality of quantizers q 1 from the initial quantization matrix Q 0 by computing each such quantizer q 1 in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
is
odd
;
kq
0
+
1
,
if
k
>
0
and
k
is
even
.
;
and
requantizing the compressed image data using the new quantization matrix Q 1 .
17. A method according to claim 16 , wherein the JPEG image comprises a color image, further comprising:
separating the color image into separate color components; and
requantizing each such color component using the new quantization matrix Q 1 .
18. A method according to claim 16 , wherein the JPEG image comprises a grayscale image, further comprising:
requantizing the grayscale image using the new quantization matrix Q 1 .
19. A method according to claim 16 , further comprising:
partitioning the JPEG image;
transforming each partition using a DCT; and
quantizing the transformed partitions using the quantization matrix Q 0 .
20. A method according to claim 16 , wherein the JPEG image is compressed using one of baseline sequential encoding and DCT-encoding.
21. A system for recompressing a JPEG image using requantization with selective rounding, comprising:
a JPEG image stored as compressed image data quantized per an initial quantization matrix Q 0 comprising a plurality of initial quantizers q 0 ;
a quantization matrix generator defining a target quantization matrix Q bound comprising a plurality of target quantizers q bound , computing an intermediate constant k in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
,
and constructing a new quantization matrix Q 1 comprising a plurality of quantizers q 1 from the initial quantization matrix Q 0 by computing each such quantizer q 1 in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
>
0.
;
and
an image recompression module requantizing the compressed image data using the new quantization matrix Q 1 by rounding each half integer value towards zero.
22. A system according to claim 21 , wherein the JPEG image comprises a color image, further comprising:
a component separation submodule separating the color image into separate color components; and
a quantization submodule requantizing each such color component using the new quantization matrix Q 1 .
23. A system according to claim 21 , wherein the JPEG image comprises a grayscale image, further comprising:
a quantization submodule requantizing the grayscale image using the new quantization matrix Q 1 .
24. A system according to claim 21 , further comprising:
a partition submodule partitioning the JPEG image;
a transformation submodule transforming each partition using a DCT; and
a quantization submodule quantizing the transformed partitions using the quantization matrix Q 0 .
25. A system according to claim 21 , wherein the JPEG image is compressed using one of baseline sequential encoding and DCT-encoding.
26. A method for recompressing a JPEG image using requantization with selective rounding, comprising:
storing a JPEG image as compressed image data quantized per an initial quantization matrix Q 0 comprising a plurality of initial quantizers q 0 ;
defining a target quantization matrix Q bound comprising a plurality of target quantizers q bound ;
computing an intermediate constant k in accordance with the equation:
k
=
⌊
q
bound
q
0
⌋
;
constructing a new quantization matrix Q 1 comprising a plurality of quantizers q 1 from the initial quantization matrix Q 0 by computing each such quantizer q 1 in accordance with the equation:
q
1
=
{
q
0
,
if
k
=
0
;
kq
0
,
if
k
>
0.
;
and
requantizing the compressed image data using the new quantization matrix Q 1 by rounding each half integer value towards zero.
27. A method according to claim 26 , wherein the JPEG image comprises a color image, further comprising:
separating the color image into separate color components; and
requantizing each such color component using the new quantization matrix Q 1 .
28. A method according to claim 26 , wherein the JPEG image comprises a grayscale image, further comprising:
requantizing the grayscale image using the new quantization matrix Q 1 .
29. A method according to claim 26 , further comprising:
partitioning the JPEG image;
transforming each partition using a DCT; and
quantizing the transformed partitions using the quantization matrix Q 0 .
30. A method according to claim 26 , wherein the JPEG image is compressed using one of baseline sequential encoding and DCT-encoding.