Image registration method

A method of adjusting a displacement field relating positions of pixels between at least two images, the method comprising:

• receiving a first image and a second image, the received images being associated with an initial displacement field, each pixel of the first image and the second image being associated with a label;
• selecting a first pixel in the first image which maps to a second pixel in the second image based on a vector of the initial displacement field, the first pixel being associated with a first label and the second pixel being associated with a second label;
• determining a set of third pixels including the second pixel and a plurality of adjacent pixels to the second pixel, the third pixels being associated with third labels and a candidate shift vector with respect to the second pixel;
• determining a covariance score for each of the third pixels, the covariance score defining a statistical dependence between the first label and each of the third labels;
• determining an adjustment shift vector based on the covariance scores and the candidate shift vectors of the third pixels;
• adjusting the vector of the initial displacement field using the determined adjustment shift vector;
• and
• calculating a first histogram, a second histogram and a joint histogram, the first histogram comprising first marginal probability distribution values −P(ai) of labels associated with pixels in the first image, the second histogram comprising second marginal probability distribution values P(bj) of labels associated with pixels in the second image, the joint histogram comprising joint probability values P(ai,bj) of the labels associated with the pixels in the first image being mapped to the labels associated with the pixels in the second image;
• wherein the covariance scores are determined using joint probability values, first marginal probability distribution values, and second marginal probability distribution values.

A method of adjusting a displacement field relating positions of pixels between at least two images, the method comprising:

• receiving a first image and a second image, the received images being associated with an initial displacement field, each pixel of the first image and the second image being associated with a label;
• selecting a first pixel in the first image which maps to a second pixel in the second image based on a vector of the initial displacement field, the first pixel being associated with a first label and the second pixel being associated with a second label;
• determining a set of third pixels including the second pixel and a plurality of adjacent pixels to the second pixel, the third pixels being associated with third labels and a candidate shift vector with respect to the second pixel;
• determining a covariance score for each of the third pixels, the covariance score defining a statistical dependence between the first label and each of the third labels;
• determining an adjustment shift vector based on the covariance scores and the candidate shift vectors of the third pixels;
• adjusting the vector of the initial displacement field using the determined adjustment shift vector;
• and
• normalising the covariance scores wherein the adjustment shift vector is determined based on the normalized covariance scores, wherein the adjustment shift vector is defined using one of:
• a sum of the candidate shift vectors for the third pixels weighted by the corresponding normalized covariance scores;
• and
• an adjustment shift vector of one of the third pixels associated with the highest covariance score weighted by said highest covariance score being normalized.

A method of adjusting a displacement field relating positions of pixels between at least two images, the method comprising:

• receiving a first image and a second image, the received images being associated with an initial displacement field, each pixel of the first image and the second image being associated with a label;
• selecting a first pixel in the first image which maps to a second pixel in the second image based on a vector of the initial displacement field, the first pixel being associated with a first label and the second pixel being associated with a second label;
• determining a set of third pixels including the second pixel and a plurality of adjacent pixels to the second pixel, the third pixels being associated with third labels and a candidate shift vector with respect to the second pixel;
• determining a covariance score for each of the third pixels, the covariance score defining a statistical dependence between the first label and each of the third labels;
• determining an adjustment shift vector based on the covariance scores and the candidate shift vectors of the third pixels;
• adjusting the vector of the initial displacement field using the determined adjustment shift vector;
• calculating the covariance scores in advance for all pairs of labels for mapped pixels from the first image and the second image;
• and
• storing the calculated covariance scores in a look-up table indexed by a pair index associated with the pair labels.