Hi i made this tabi sock model but now I would like to know an easy way to add that seam like I did to the right, the right one is sculpted but retopology doesn't seem to work with such small seam channels at least with retopoflow. I tried knife project with a nurb curve but it just looks weird. I tried boolean which isn't like expected. Any help is much appreciated!
The easy way is to simply draw it on a bump map. Are you doing a 1mm flyby of your foot? Are you carefully lighting the scene for your tabi seam to catch dramatic shadows? Unless you are, geometry is pointless, save your verts for somewhere they matter.
But I dunno, maybe you're doing a foot flyby. The way to do it with geometry is to first fix the topo on your mesh-- you need an edge flow that follows the seams, something that is not yet present on your image. What you want is topo where there is some edge loop that you can cleanly select that represents the seam.
Once you have that topo, it's pretty trivial. Select your seam loop and start with a bevel-- mouse wheel up to get an extra edge loop in the center:
Ctrl numpad - to shrink your selection to only the central loop of the bevel, ctrl , to set pivot point to median, alt-s to scale along normals, scale to taste and confirm, and you have a seam.