Detect colour ratio on ROIs individually

Hello boys and girls,

I have a study on selecting 4 ROIs and calculating the red colour ratio on an object.
I build a process flow in the attached JPEG file.
I’m a noob python and opencv user.

Is there anyone who can help me about my study?

Dear all,

I’ve completed the study by myself.
Anyone who needs it, I’ll be happy to share. Just please let me know.