NCD values shown as a heatmap for all pairs of image frames in the z-stack of three selected defocused image stacks from the same experiment. Color code blue specifies pairs of frames with lowest NCD values and red specifies highest NCD values. In each heatmap, the lowest z frame is in the lower left, the highest z frame is in the upper right. Analysis illustrates that off-diagonal NCD values range from 0.6 (most similar images) to 1 (red, most dissimilar images). Along the diagonal NCD equals zero (blue). Note the diversity of similarity relationships among the frames of each z-stack.