Count-rate image of the two NIRSpec detector arrays (SCA491 and SCA492) of an exposure of the TEST lamp acquired in imaging mode (MIRROR) with the MSA configured in a checkerboard pattern, more clearly visible in the enlargement. SCA491 is on the left (blue side) and SCA492 on the right (red side). The images of the fixed slits are in the center of the images. Areas of defective shutters that fail to open are clearly visible and, in some cases, a full row or column is fully closed. The dark round feature in SCA492 is an area of dead pixels. This image was acquired with the old set of detectors and old MSA module. The image was generated from NIRSpec raw data following the steps described in Sect. 4.