JaccardSimilarity[ref,pred]

gives the Jaccard Similarity between 1 and 0 of segmentations ref and pred for class equals 1.

JaccardSimilarity[x,y,class]

gives the Jaccard Similarity of segmentations ref and pred for class.

JaccardSimilarity[x,y,{class,..}]

gives the Jaccard Similarity of segmentations ref and pred for the list of gives classes.