porting simple hlsl post effect doesn't give expected output

Hi, i have a simple HLSL post effect i want to use in UE (it is a cleared version of sweetFx Luma Curve )

Here what it (should) looks like

     UE without          -        UE With 

myOtherEngine without     -     myOtherEngine with

Did i made a classic mistake somewhere ? is there something specific to know ? i looked at docs and did what they said

other info :
I set it to postProcess + beforeToneMapping
added it to the process volume
the param is between 0 and 1 but our default value is 0.8

[my hlsl file][1]

[my Uasset file][3]

Thanks ! :slight_smile: