The spectra of the object images have to be corrected of fibre thoughput. To do it, a sky image is used. In absence of a sky image, we can use a flat image.
This operation is done with the msresp1d task. A 2D output image (hereafter, fibresens) with a constant value per each fibre (corresponding to its sensibility; all the values are around the unity) is obtained (e.g.: msresp1d "" flatim "" fibresens).
Then, we divide the object image by the fibresens with the imarith task.