PMT gain and offset adjusting

Gain (voltage) on PMT has a 0 to 1000 V adjustable range. Offset of PMT has -100 to 100 range for tuning, lower value has higher cut-off and higher value has lower cut-off.
Combination of gain and offset adjustment on PMT produces a preliminary optimized image with balanced intensity and background noise from which further operation can be done.
The default value for Gain and Offset after LCS launch is zero. They must be changed from default. Raise Gain from zero while lower offset to control background. Otherwise, most probably, you get a black screen.
During adjusting, pay attention to the hardware legend for gain and offset reading. It is better to maintain Gain at the range of above 600 V by lowering offset value a little bit (usually within negative range). Higher PMT voltage give less secondary emission noise (shot noise), but too high PMT voltage gives out more dark current thus more background, while too high offset cut away too much signal and reduce dynamic range of the image.

Since these two parameters counteract each other, it is important to find an appropriate balance point. You might get similar image intensity at a combination of 700 V gain and -20 offset, or 1000 V gain and -100 offset, but obviously, the former has better image quality while the latter suffers from high noise due to high voltage and low dynamic due to high cut-off. Similarly, +100 offset combined with 200 V gain is not good either since you have more shot noise due to low voltage while too much background due to low threshold. So, avoid using this pair at their extreme value.

While turning the corresponding knobs on the control box to adjust gain and offset, keep your ear alert: When you hear a beep sound, it is a warning that you reach one of its end. You can get better result by drawing both gain and offset back from extreme to middle range to find a new balance point. It is not advisable that you push one parameter very hard to the end while draw it back by using another parameter at its end too, and get bad side effects from both.

Keep in mind: Raising gain (voltage) on PMT can amplify weak signal but also amplify noise; raising offset on PMT (threshold) can cut off background noise but signal is equally affected,  the SNR and image quality won't improve. To improve image quality, approaches which increase photon number has to be used, such as average, accumulation, slow scan speed, lower scan format for bigger pixel size and longer pixel time, larger pinhole size, etc..