Method and apparatus for tracking moving objects in spatial differential frame pictures
View Patent ↗Each frame of time-series pictures shot by a camera is converted to a spatial differential frame picture by the following equations: H ( i,j )=Σ| G ( i+di,j+dj )− G ( i,j )|/( Gi,j, max/ G max), I=G max/{ 1+ exp(−0.02( H−80))}, where Σ denotes a sum over di=−1 to 1 and dj=−1 to 1, Gi,j,max denotes the maximum pixel value of 3×3 pixels having its center at the i-th row and j-th column, and Gmax denotes the assumable maximum value 255 of the pixel value G(i, j). Moving objects at a time t is discriminated based on a correlation between spatial differential frame pictures at times (t−1) and t and a discrimination result of moving objects included in the spatial differential frame picture at the time (t−1).
1. A moving object tracking method of processing first time-series pictures to track moving objects therein, the method comprising the steps of:
(a) generating second time-series pictures by converting the first time-series pictures to respective spatial differential frame pictures, a pixel of the spatial differential frame pictures having a value ‘I’ associated with a differential value between a value of the pixel and values of its neighboring pixels, the value ‘I’ being associated with a value ‘H’ proportional to a value obtained by dividing the differential value by a maximum value among the value of the pixel and the values of the neighboring pixels; and
(b) discriminating moving objects at a time t 2 based on a correlation between one of the spatial differential frame pictures at a time t 1 adjacent to the time t 2 and another of the spatial differential frame pictures at the time t 2 , and also based on a discrimination result of moving objects included in said one of the spatial differential frame pictures at the time t 1 .
2. The moving object tracking method according to claim 1 , wherein, if the value H is within a predetermined range, then the value I is determined by an approximate linear transformation of the value H, or else, the value I is determined by converting the value H to a value which is suppressed so as not to exceed an assumable maximum value Gmax of a pixel of the spatial differential frame picture.
3. The moving object tracking method according to claim 1 , wherein in the step (b),
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
4. The moving object tracking method according to claim 2 , wherein on the basis of a sigmoid function
f ( H )=1/{1+exp[−β( H−α )]},
the value I=Gmax·f(H) is determined,
where H is said proportional value, and α and β are positive constants.
5. The moving object tracking method according to claim 2 , wherein the object map at the time t 2 is produced by the steps of:
assuming that a block i in the object map at the time t 2 has an identification code IDi and a moving vector Vi;
calculating a unit correlation between an image of the block i in the spatial differential frame picture at the time t 2 and an image of a box in the spatial differential frame picture at the time t 1 , the box being determined by moving a box of the block i by a vector−Vi; and
calculating a total sum of the unit correlations over all blocks at the time t 2 so as to produce the object map at the time t 2 at a maximum value among the total sums.
6. The moving object tracking method according to claim 4 , wherein the constant β is a value in a range of 0.05 to 0.50.
7. The moving object tracking method according to claim 4 , wherein in the step (b),
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
8. A moving object tracking apparatus of processing a first time-series pictures to track moving objects therein, the apparatus comprising:
a picture recording section for storing the first time-series pictures;
a picture conversion section for generating second time-series pictures by converting the first time-series pictures to respective spatial differential frame pictures, and for storing the generated second time-series pictures into the picture recording section, a pixel of the spatial differential frame pictures having a value ‘I’ associated with a differential value between a value of the pixel and values of its neighboring pixels, the value ‘I’ being associated with a value ‘H’ proportional to a value obtained by dividing the differential value by a maximum value among the value of the pixel and the values of the neighboring pixels; and
a picture processing section for discriminating moving objects at a time t 2 based on a correlation between one of the spatial differential frame pictures at a time t 1 adjacent to the time t 2 and another of the spatial differential frame pictures at the time t 2 , and also based on a discrimination result of moving objects included in said one of the spatial differential frame pictures at the time t 1 .
9. The moving object tracking apparatus according to claim 8 , wherein the picture conversion section, determines the value I by an approximate linear transformation of the value H if the value H is within a predetermined range, or else, the picture conversion section determines the value I by converting the value H to a value which is suppressed so as not to exceed an assumable maximum value Gmax of a pixel of the spatial differential frame picture.
10. The moving object tracking apparatus according to claim 9 , wherein in the picture processing section,
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
11. The moving object tracking apparatus according to claim 8 , wherein the picture conversion section, on the basis of a sigmoid function
f ( H )=1/{1+exp [−β( H −α)]},
determines the value I=Gmax·f(H), where H is said proportional value, and α and β are positive constants.
12. The moving object tracking apparatus according to claim 11 , wherein the constant β is a value in a range of 0.05 to 0.50.
13. The moving object tracking apparatus according to claim 12 , wherein in the picture processing section,
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
14. The moving object tracking apparatus according to claim 11 , wherein in the picture processing section,
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
15. he moving object tracking apparatus according to claim 8 , wherein in the picture processing section,
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .
16. The moving object tracking method according to claim 15 , wherein the picture processing section:
assumes that a block i in the object map at the time t 2 has an identification code IDi and a moving vector Vi;
calculates a unit correlation between an image of the block i in the spatial differential frame picture at the time t 2 and an image of a box in the spatial differential frame picture at the time t 1 , the box being determined by moving a box of the block i by a vector−Vi; and
calculates a total sum of the unit correlations over all blocks at the time t 2 so as to produce the object map at the time t 2 at a maximum value among the total sums.
17. The moving object tracking apparatus according to claim 8 , wherein in the picture processing section,
each of the spatial differential frame pictures at the times t 1 and t 2 is divided into blocks each including a plurality of pixels;
the moving object discrimination result at the time t 1 is an object map at the time t 1 which includes an identification code of a moving object assigned to at least one of the blocks, said one including a portion of the moving object, and also includes a moving vector of said at least one of the blocks; and
an object map at the time t 2 is produced to discriminate a moving object at the time t 2 .