how to limit this shader effect to 0-40srgb?

[geextahslex]

Hi, could someone be so nice and help me to put a srgb treshold (smoothstep) into this shader? This is a S-Curve (sigmoid) contrast shader. I would like to apply the effect only in the sRGB 0-40/80(smoothstep) range

#define Thresh 15/255.
#define w 10/255.
#define CoefLuma vec4(0.2126, 0.7152, 0.0722, 0) //sRGB, HDTV
smoothstep(Thresh + w, Thresh - w)

S-Curve

//!HOOK OUTPUT
//!BIND HOOKED
//!DESC sCurve (sigmoid)

#define S 0.25 

vec4 hook(){
    vec4 c0 = HOOKED_texOff(0);
    
    c0.rgb = mix(c0.rgb, 1/( 1.0 + exp(-14*c0.rgb +7) ), S);
    return c0; 
}

Thank you :)

[geextahslex]

//!PARAM S
//!DESC sCurve Strength
//!TYPE float
//!MINIMUM 0
//!MAXIMUM 1
0.15

//!HOOK OUTPUT
//!BIND HOOKED
//!DESC sCurve (sigmoid)

#define EFFECT_END             vec3(70.0) // stop applying the effect here
#define EFFECT_END_RAMP_SIZE   vec3(40.0) // smooth out the edge of the effect

// #define S vec3(0.15)

vec4 hook()  {
    vec4 orig = HOOKED_tex(HOOKED_pos);
    vec3 effect = mix(orig.rgb, 1/( 1.0 + exp(-14*orig.rgb +7) ), S); //your desidered effect.
    
    //effect = vec3(0.0); 
    
    vec3 mmix = smoothstep(EFFECT_END - EFFECT_END_RAMP_SIZE*0.5, 
                           EFFECT_END + EFFECT_END_RAMP_SIZE*0.5, 
                           orig.rgb * 255.0);
    
    vec3 out_color = mix(effect, orig.rgb, mmix);
    
    return vec4(out_color, orig.a);

}