how to find mean the value gray level 3 conditions

to find mean value of the figure in gray scale

I try to write code. in the picture above it error

Which I have the picture name 'IGray_crop'

in IGray_crop have very values.

So, I want to find mean the value is less than 20.

TT

Thank you ูู^^

[KSSV]

What error you get? YOu must specify the error.

[Ajaree Rattanaharn]

@KSSV

error like this

Answer 1

[KSSV]

Type error:

Matrix2(IGray_crop<20) 

Change m to M.