I left the image uncropped and imported as a 16-bit TIFF into Gimp.

Finally the geometric correction module set to automatic 2-way correction straightened the ceiling beams but the resulting crop was again too constrictive. Also I activated the LensFun module to apply correction for the GR's 18.3mm f2.8 lens. So here's my retry in 2018 with DarkTable applying quite some heavy shadows/highlights protection. Also, correcting exposure burnt out the lamps and trying to protect them with a mask left telltale signs like halos or dark edges. Either I didn't get the lines straightened out just the way I wanted or when I did, the resulting crop left a very unsatisfying decentering on the circle of light. When I got back from London I made many attempts at dealing with the image but I never ended up being satisfied. The shot suffers from lens distortion, there is quite a bit of keystoning caused by me not holding the camera perfectly parallel to the floor and the exposure is correct for the lamps but the towering structures around that central lobby are badly underexposed. It would have been so much easier with an articulated LCD! I leaned back, standing in the middle of the lobby, knowing people were watching ('look mummy, that strange man is doing weird things') trying to lift my Ricoh GR above my head and line up the ceiling on the LCD. In the hotel lobby I looked straight up and saw the rain on the glass roof panels and the circle of incandescent lamps which contrasted the doom and gloom outside with very yellowish light. The weather was miserable and I was basically stuck in the hotel waiting for a business meeting across the street. Here's a shot I took in London some 3 years ago. Also, sometimes software progression has been to the point where I feel I can do so much more today than I could 3, 5 or 10 years ago merely because my toolkit has improved. I thought it'd be fun to revisit some older shots and see if I have learned anything over the past 3 years or if I can look at them with a fresh view to what could be done.

Darktable mask manager straight line