Figure 2

Camera and light source timing . The CCD camera is triggered by the falling edge of a 2KHz TTL signal (Black). The light source switching is triggered by the rising edge of a 1 KHz TTL signal (Red). Output from the light source was captured using a photo-diode, the output of which is shown in blue. The different amplitudes indicate the 2 different wavelengths of light supplied by the source. Odd numbered frames record fluorescence during stable illumination, while even numbered frames capture the transition period between the two wavelengths; these even numbered frames are deleted in post-processing.