MalVeauX wrote in post #17868334
Otherwise, I just under or over-expose the backdrop so that it's completely black or completely white and it doesn't matter if it's wrinkled or not.
Yeah, that's what I do too. Control spill, or blow it out, slam it one way or the other in post. Or, if want to retain soft shadows or gradients, but you couldn't get it blurred out enough in camera--which is often impossible in a small space without compromising DoF of the subject--you can isolate the background and give it a healthy dose of Gaussian Blur or Lens Blur to eliminate just the wrinkle highlights. Or use a mix of blur and levels adjustment, like bringing down the white point on a dark grey background.
Admittedly, using an iron that has a vertical steaming function works best. I've done this to horribly wrinkled up sheets I wanted to flatten out because they had a pattern that would be noticeably distorted otherwise and difficult if not impossible to fix in Photoshop, but more often than not I use the MalVeaux technique on plain white or black backdrops.