Comparing contrast (Kohler illumination type vs Coaxial illumination type)

Evaluation environment
Coaxial tube:  Kohler illumination type    /   Critical illumination type 
Objective lens: PEIR Plan 10X
Camera:BU406M(2048 x 2048, 5um)
Light source: SIS-150-AIR + band pass 1100nm
Inspecting object: Mirror

<How to calculate the contrast>
(The average brightness in red square – The average brightness in blue square)  /  ( The average brightness in red square + The average brightness in blue square)

<Original image /  Kohler illumination type>                                                                                             

Mean of brightness in red square : 169.169375
Mean of brightness in blue square : 26.015625
Contrast : 0.7334259804800574

<Original image /  Critical illumination type>   

Mean of brightness in red square :155.194375

Mean of brightness in blue square :  33.10875

Contrast : 0.6483462502281893

Result :
Comparing each contrast values, Kohler illumination type allows to show higher contrast image.