diff --git a/csst_ifs_sim/csst_ifs_sim.py b/csst_ifs_sim/csst_ifs_sim.py
index cfef0fed129e245b41a2a0ba7ce6f841c5045023..c906376ea6db1bba25a5a5c175b61cd90ecef400 100644
--- a/csst_ifs_sim/csst_ifs_sim.py
+++ b/csst_ifs_sim/csst_ifs_sim.py
@@ -5251,6 +5251,9 @@ class IFSsimulator():
 
                     photons_blue.y = photons_blue.y/self.pixelscale + \
                         dy_blue+self.slice_blue['py'][k]
+                        
+                        
+                    photons_blue.y =2048-photons_blue.y 
 
                     blue_sensor.accumulate(photons_blue, blue_img)
 
@@ -5272,6 +5275,9 @@ class IFSsimulator():
 
                     photons_red.y = photons_red.y/self.pixelscale + \
                         dy_red+self.slice_red['py'][k]
+                        
+                        
+                    photons_red.y =3072-photons_red.y
 
                     red_sensor.accumulate(photons_red, red_img)