Method and apparatus for representing and searching for colour images
A method of representing a colour image comprises selecting a region of the image, selecting one or more colours as representative colours for the region and, for a region having two or more representative colours, calculating for each representative colour at least two parameters related to the colour distribution in relation to the respective representative colour and using said parameters to derive descriptors for the image region.
1. A method of searching for colour images stored in data storage means using a control unit, the method comprising:
inputting a query relating to colour of an image,
comparing, using the control unit, said query with descriptors for stored images derived in accordance with a method that includes:
representing a colour image comprising two or more colours as dominant colours for an image and, for each dominant colour,
calculating variance of colour distribution of the image in colour space relative to the dominant colour,
representing the image in terms of colour space value of each dominant colour and value of respective colour variance; and
forming a descriptor including the color space value of each dominant colour and the respective colour variance value; and
using a matching function and selecting and displaying, using the control unit, at least one image for which the matching function indicates a close match between the query and at least part of the image,
wherein the matching function is based on
D
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where
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and
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where
D is the similarity measure;
F 1 represents the first descriptor;
F 2 represents the second descriptor;
i and j index the representative colours;
x and y index the descriptors;
N 1 is the number of dominant colours in the first descriptor;
N 2 is the number of dominant colours in the second descriptor;
P 1i is the ith weight in the first descriptor;
P 2j is the jth weight in the second descriptor;
l, u and v represent colour components; and
c and v are the dominant colour values (mean values) and variances respectively.
2. A method as claimed in claim 1 wherein inputting a query comprises selecting a query image region and obtaining descriptors for said image region and wherein the matching function uses the descriptors for the query and for the stored images.
3. A method as claimed in claim 1 wherein a query is selected from a plurality of images displayed on display means.
4. A method as claimed in claim 1 wherein inputting a query comprises selecting a single colour value.
5. A method as claimed in claim 1 wherein inputting a query comprises specifying one or more component distributions.
6. A method as claimed in claim 1 wherein a query is input using only some of the components of the colour space.
7. An apparatus for searching for an image comprising:
an input device for inputting a query relating to colour of an image;
a comparator for comparing said query with descriptors for stored images, said descriptors for stored images comprising two or more dominant colour values and two or more respective colour variance values; and
a processor for selecting and displaying at least one image for which a matching function indicates a close match between the query and at least part of the image,
wherein the matching function is based on
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1
,
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2
)
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∑
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=
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N
1
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2
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,
where
f
xiyj
=
1
2
π
v
xiyjl
v
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v
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exp
[
-
(
c
xiyjl
v
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+
c
xiyju
v
xiyju
+
c
xiyjv
v
xiyjv
)
/
2
]
and
c
xiyjl
=
(
c
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-
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=
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=
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c
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=
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xiv
-
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)
2
,
v
xiyjv
=
(
v
xiv
+
v
yjv
)
,
where
D is the similarity measure;
F 1 represents the first descriptor;
F 2 represents the second descriptor;
i and j index the representative colours;
x and y index the descriptors;
N 1 is the number of dominant colours in the first descriptor;
N 2 is the number of dominant colours in the second descriptor;
P 1i is the ith weight in the first descriptor;
P 2j is the jth weight in the second descriptor;
l, u and v represent colour components; and
c and v are the dominant colour values (mean values) and variances respectively.
8. A computer-readable medium having stored thereon a plurality of executable instructions, the instructions comprising instructions to
receive an input relating to colour of an image;
compare said query input with colour descriptors for images stored in a data store to determine similarity between the query and said stored images; and
select and display at least one image, for which a matching function indicates a close match between the query and at least part of the image,
wherein the matching function is based on
D
(
F
1
,
F
2
)
=
∑
j
=
1
N
1
∑
i
=
1
N
1
p
1
i
p
1
j
f
1
i
1
j
+
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i
=
1
N
2
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j
=
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2
p
2
i
p
2
j
f
2
i
2
j
-
∑
i
=
1
N
1
∑
j
=
1
N
2
2
p
1
i
p
2
j
f
1
i
2
j
,
where
f
xiyj
=
1
2
π
v
xiyjl
v
xiyju
v
xiyjv
exp
[
-
(
c
xiyjl
v
xiyjl
+
c
xiyju
v
xiyju
+
c
xiyjv
v
xiyjv
)
/
2
]
and
c
xiyjl
=
(
c
xil
-
c
yjl
)
2
,
v
xiyjl
=
(
v
xil
+
v
yjl
)
,
c
xiyju
=
(
c
xiu
-
c
yju
)
2
,
v
xiyju
=
(
v
xiu
+
v
yju
)
,
c
xiyjv
=
(
c
xiv
-
c
yjv
)
2
,
v
xiyjv
=
(
v
xiv
+
v
yjv
)
,
where
D is the similarity measure;
F 1 represents the first descriptor;
F 2 represents the second descriptor;
i and j index the representative colours;
x and y index the descriptors;
N 1 is the number of dominant colours in the first descriptor;
N 2 is the number of dominant colours in the second descriptor;
P 1i is the ith weight in the first descriptor;
P 2j is the jth weight in the second descriptor;
l, u and v represent colour components; and
c and v are the dominant colour values (mean values) and variances respectively.