Image processor, image processing method, and computer program

1. An image processing method for an image processor to track a first tracked target and a second tracked target in a movie, the first tracked target located at a first z-distance z1 and the second tracked target located at a second z-distance z2 at least a z-distance z3 from z1, the image processing method comprising:

a) calculating a depth image from an image frame making up a movie at time t, the depth image representing, as a pixel value on an image plane, a unique subject distance from an imaging device,

wherein the depth image is calculated for an entirety of the image frame;

b) acquiring a first tracking result for the first tracked target and a second tracking result for the second tracked target at time t−1,

c) determining a first processing area for the first tracked target and a second processing area for the second tracked target,

wherein the first processing area and the second processing area are determined based on a basis of movable ranges of the first tracked target and the second tracked target, respectively,

wherein the first z-distance and the second z-distance are used to adjust the movable ranges,

d) extracting a first picture area for the first tracked target from the image frame at time t by:

fitting the first tracking result at time t−1 to the depth image:

calculating an average z-distance Zt for all pixels within an area bounded by the first tracking result; and

extracting all pixels in the image frame which have values within a range of Zt−ΔZ<z1<Zt+ΔZ in the depth image to form the first picture area,

wherein ΔZ<z3;

e) extracting a second picture area for the second tracked target from the image frame at time t by:

fitting the second tracking result at time t−1 to the depth image:

calculating an average z-distance Zw for all pixels within an area bounded by the second tracking result; and

extracting all pixels in the image frame which have values within a range of Zw−ΔZ<z2<Zw+ΔZ in the depth image to form the second picture area;

f) generating a third tracking result for the first tracked target at time t using the first picture area;

g) generating a fourth tracking result for the second tracked target at time t using the second picture area; and

h) repeating steps a)-g) for an image frame at time t+1 to track the first tracked target and the second tracked target in the movie.

2. The method of claim 1 , wherein the wherein step c) further includes extracting a foreground area from the image frame using a background image prepared in advance.

3. The method of claim 1 , wherein the image frame is subjected to gray level reduction prior to steps d) and e).

4. An image processing method for an image processor to track a tracked target in a movie, the image processing method comprising:

a) calculating a depth image from an image frame making up a movie at time t, the depth image representing, as a pixel value on an image plane, a unique subject distance from an imaging device,

wherein the depth image is calculated for an entirety of the image frame;

b) acquiring a tracking result for the tracked target at time t−1,

c) determining a processing area for the first tracked target,

wherein the processing area is determined based on a movable range of the tracked target,

wherein a z-distance z1 of the tracked target is used to adjust the movable range,

d) extracting a picture area for the tracked target from the image frame at time t by:

fitting the tracking result at time t−1 to the depth image:

calculating an average z-distance Zt for all pixels within an area bounded by the tracking result;

and extracting all pixels in the image frame which have values within a range of Zt−ΔZ<z1<Zt+ΔZ in the depth image to form the picture area;

e) generating a tracking result for time using the picture area;

f) repeating steps a)-e) for an image frame at time t+1 to track the tracked target in the movie.