add contrast ability [feature request]

Expected behavior of the wanted feature

Hi, I want to ask for a native contrast option. I don't mean the default "contrast" or "brightness" they just change the white and black point. I mean change contrast without clipping whites or crushing blacks. At the moment I am using butterw sCurve glsl shader but having a native mpv solution would be nice.

Thank you

I use hook LUMA to not affect colors/saturation

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

#define S 0.15 

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

Alternative behavior of the wanted feature

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Log File

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Sample Files

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The issue does not name a repository file, test, or entry point. Begin by locating mpv's existing contrast and brightness handling, then compare its behavior with the provided LUMA sCurve shader. Done should mean a native contrast option that changes contrast without clipping whites or crushing blacks and does not alter color saturation.