Take MeituPic android for example:
How to realize the whitening and acne treatment of the local part of the picture?
How to accurately locate facial features in face recognition?
How can MeituPic be implemented in the same way as PS?
Functions such as simple coloring in part of the image?
This is not an android development problem, but a digital image processing problem. It is recommended that you look at books or web pages related to “digital image processing”.