Thank you Berbard! I'm trying to use that now.You can also generate a file with VituixCad :
A separate file should be created for each curve by erasing the other three colors with a simple application like Paint. It's a little tedious but it's feasible!
I just notice that you are the Author of REW.The digitising software will probably have an easier time if you can find an image with just the target of interest, those curves are so close in places it may struggle to distinguish them and lose the trace it is trying to follow.