Fig. 5.

$R$ and $S$ values for the same muscle fiber under different imaging conditions. (a) Muscle fiber was imaged under different conditions by adjusting laser power, PMT gain, and averaging method. Laser power was doubled from image a to b; $R$ and $S$ had less than 3% difference. PMT gain was set from 1075, to 800, to 600 in images b, c, and d, and the dramatic changes in the average brightness (from 150 to 19) did not lead to major changes in $R$ and $S$ values (within 20%). Most confocal and two-photon microscopes have line and frame averaging methods to reduce noise level. Two-line average and two-frame average were used in image c, which has obvious improvement on image quality by comparing to image e, which had no average method used while other conditions were the same. The $R$ and $S$ difference is very small (within 10%).