Method for detecting moving cast shadows object segmentation

A method for detecting a uniform temporal change of illumination in a pixel between a first image and a second image, comprising:

• (a) determining a frame ratio within a change detection mask based on a first image and a second image, the change detection mask corresponding to a plurality of image regions of large difference between the first image and the second image;
• (b) comparing a local spatial variance of the frame ratio for each pixel with an illumination threshold;
• and
• (c) classifying each pixel as having a uniform temporal change of illumination when the local spatial variance is below the illumination threshold for that pixel.

A method for detecting borders of a moving cast shadow within a change detection mask having a border, the change detection mask corresponding to a difference between a first image and a second image, comprising:

• (a) obtaining a plurality of moving cast shadow border candidates from the border of the change detection mask;
• (b) performing, for each moving cast shadow border candidate from the plurality of moving cast shadow border candidates, the following substeps:
• (i) evaluating a spatial signal step width;
• and
• (ii) classifying the moving cast shadow border candidate as a moving cast shadow border when the moving cast shadow border candidate has a spatial signal step width exceeding a width threshold.

A method for detecting an image region changed by a moving cast shadow from a first image to a second image, comprising:

• (a) performing, for each pixel within a change detection mask, the change detection mask corresponding to a difference between the first image and the second image, the following substeps:
• (i) determining whether the pixel and a plurality of neighboring pixels include a static background edge;
• (ii) determining whether the pixel and the plurality of neighboring pixels are close to an edge with a spatial signal step width greater than a threshold, the signal step width being the difference between the first image and the second image;
• (iii) determining whether the pixel and the plurality of neighboring pixels have a uniform temporal change of illumination;
• and
• (iv) classifying the pixel as being changed by a moving cast shadow when at least two determinations from the group of determinations in steps (a)(i), (a)(ii) and (a)(iii) succeed for the pixel and the plurality of neighboring pixels.

A method for segmenting a moving object in front of a rigid background having a moving cast shadow, comprising:

• (a) determining a change detection mask based on a first image and a second image;
• (b) detecting an elimination portion of the change detection mask changed by the moving cast shadow to produce a remaining portion of the change detection mask;
• (c) combining the remaining portion of the change detection mask with an object mask of the first image, if available, to produce an object change detection mask;
• and
• (d) eliminating from the object change detection mask a portion corresponding to background uncovered by motion of the moving object to produce a mask of the moving object in the second image.

A method for segmenting and temporally tracking a plurality of moving cast shadows on a static background for a plurality of sequential image pairs, each image pair having a first image and a second image, comprising:

• (a) setting each pixel of a mask to a first value, the first value indicating no moving cast shadow;
• (b) performing, for each image pair from the plurality of sequential image pairs, the following substeps:
• (1) detecting a plurality of image regions changed by the moving cast shadows;
• (2) calculating a frame ratio by dividing each pixel of the second image by the corresponding pixel in the first image;
• (3) classifying each image region detected in said detecting step (1) into:
• (i) a first portion when the image region has a frame ratio greater than or equal to one, and
• (ii) a second portion when the image region has a frame ratio smaller than one;
• (4) setting to the first value in the mask each image region classified as the first portion in said classifying step (b)(1);
• and
• (5) setting to a second value in the mask each image region classified as the second portion in said classifying step (b)(2).