Enhance face details

Enhancing face details is needed when image is rather small or is heavily distorted with noise, compression artefacts or is blurred.
Face enhancement can be done when adding "face_enhance" option to enhancements.
"enhancements": ["face_enhance"]
Let's check the examples.
Input image
Upscaled 4x with face_enhance option
Upscaled 4x without face_enhance option