Method for detecting pixel outliers

In a digital image including a plurality of pixels, a method for identifying pairs of adjacent outlier pixels in a selected color space comprising:

• for each 3×3 patch of pixels in the image, calculating the minimum diameter of the 3×3 patch of pixels;
• for each pixel in the 3×3 patch, computing the distance to its nearest neighbor pixel within the 3×3 patch, as measured in the selected color space;
• comparing the computed distance from each pixel in the 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the minimum diameter;
• if the calculated distance to the nearest neighbor of a center pixel in the 3×3 patch is not both the largest distance to a nearest neighbor in the 3×3 patch and does not exceed the threshold, making a set of comparisons of the computed distance from non-center pixels in the 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the diameter, each comparison in the set made by ignoring a different one of the non-center pixels in the 3×3 patch;
• if in only one of the comparisons in the set, the calculated distance from the center pixel to its nearest neighbor is the largest distance to a nearest neighbor and exceeds the threshold:
• define a new 3×3 patch of pixels having the ignored pixel in the identified comparison as the new center pixel;
• for each pixel in the new 3×3 patch, computing the distance to its nearest neighbor pixel within the new 3×3 patch, as measured in the selected color space;
• comparing the computed distance from each pixel in the new 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the minimum diameter;
• if the calculated distance from the new center pixel to its nearest neighbor in the new 3×3 patch of pixels is the largest distance to a nearest neighbor and exceeds the threshold, identify the center pixel and the new center pixel as a pair of adjacent outlier pixels.