What image are you using? I made some tests and got different results. Correct me if I’m wrong but if you use a period of 3ms and a duty cycle of 100% then you should get a high pulse for the entire period, if you use 50% duty cycle you should get 1.5ms and so on.
I ran the code using 50%duty cycle and got 1.556ms. With 25% duty cycle I got 0.778ms. With 12.5% duty cycle I got 0.3737ms. So these values look pretty close to the theoric values. You can try with the code I’m using here Galileo/setPWM_GalileoGen2.ino at master · MakersTeam/Galileo · GitHub