Pretty difficult indeed! I find it especially hard to get a nice contrast without an immense amount of posterization in the petals (and posterization of course kills contrast).
I decided to back off the contrast a bit from the initial one that I’d liked and add an instance of diffuse or sharpen (local contrast preset) after sigmoid to gain a bit of additional contrast.
That sounds interesting! I should read back through this thread, but what software are you working with? Something completely scratch-built or modified rawtherapee/darktable/G’Mic…?
Edit:
I thought this would be an interesting one to try the new sigmoid functionality in darktable (running 4.5+1093). I haven’t fully got my head around it yet, but seems to work well even in my hands.
While how a capture opened and edited with various apps looks is interesting, I like to look at an original image converted by RawDigger which allows no editing at all:
