Cany143 wrote:
After merging multiple images in Lr, if there's any unintended curvature in the result, I'll right-click to 'Edit In' Ps. There, >Select >All >Edit >Transform >Warp and move/manipulate any of the top or side 'dots,' or left-click mouse to 'drag' one or more portions of the image, to the point that the curvature is eliminated. It only takes seconds, and admittedly it is done 'by eye' as opposed to anything formulaic, but it does work.
That's how I do it in PS.