fix header bug: no gain and gain order, fix led bug

ObservationSim/sim_steps/readout_output.py

@@ -12,6 +12,11 @@ def add_prescan_overscan(self, chip, filt, tel, pointing, catalog, obs_param):
                                     pre2=chip.prescan_y,
                                     over1=chip.overscan_x,
                                     over2=chip.overscan_y)
+
+    if obs_param["add_dark"] == True:
+        ny = int(chip.npix_y/2)
+        base_dark = (ny-1)*(chip.readout_time/ny)*chip.dark_noise
+        chip.img.array[(chip.prescan_y+ny):-(chip.prescan_y+ny),:] = base_dark
     return chip, filt, tel, pointing
 
 def add_readout_noise(self, chip, filt, tel, pointing, catalog, obs_param):