GIMP Python-Fu script to create masks from OpenPose images.

gimp-openpose-mask.py

# GIMP Python-Fu script to create (rough) masks from OpenPose images.
# Not recommended for singe images, mainly useful for animations/batches.
# Requires a uniform black background to work.
# Edit input/output folders, then paste into Filters->Python-Fu->Console.
import gimpcolor
import os

in_dir = r"O:\example\raw" # Input folder
out_dir = r"O:\example\out" # Output folder
grow_size = 48 # Main mask size
feather_size = 96 # Feather radius ("softness")

def mask(img,dw):
	bg = gimpcolor.RGB(0,0,0)
	mk = gimpcolor.RGB(255,255,255)
	pdb.gimp_context_set_foreground(mk)
	pdb.gimp_context_set_background(bg)
	pdb.gimp_by_color_select(dw, bg, 32, 2, False, False, 0, False)
	pdb.gimp_selection_invert(img)
	pdb.gimp_selection_grow(img, grow_size)
	if (feather_size > 0):
		pdb.gimp_selection_feather(img, feather_size)
	pdb.gimp_bucket_fill(dw, 0, 0, 100, 0, False, 0, 0)

def run():
	for f in os.listdir(in_dir):
		p = os.path.join(in_dir,f)
		o = os.path.join(out_dir,f)
		if p.endswith(".png"):
			print(p)
			i = pdb.file_png_load(p, p)
			dw = pdb.gimp_image_active_drawable(i)
			mask(i,dw)
			pdb.file_png_save_defaults(i, dw, o, o)

run()
print("Complete")

Example output: