Signal and noise in fluorescence intensities. Representation of the first cycle of synthesis on five concatenated tiles of the phiX174 sequencing data. A. Projection of the intensity quadruples on the axes corresponding to the A and C channels and the G and T channels at cycles 1 an 15. The ellipses represent the Gaussian mixtures (centers and the line for one standard deviation are shown). B. Same data after de-correlation transformations (see Methods). Coloring reflects the mixture component with largest probability.