How to combine different saturation sliders?

i'm not sure understand how lr4 combines values global saturation slider , local adjustments. 2 questions in bold @ bottom.

i made following experiments:

1) start color raw image, process version 2012, untouched.

2) bring down global saturation -100

3) add graduated filter saturation +100 (i added, say, sharpness -100 see precisely side filter being applied)

i expect half of picture colored , half b&w. instead filter totally ineffective (i.e. produces absolutely no effect, can see rotating it). conjecture total saturation not "additive" (i.e. -100+100) maybe "compound" (i.e. product of 1+p/100). if true, slider equal -100 bring saturation minimum. let's see if holds true:

4) set global saturation -100. value of filter saturation ineffective

5) set filter saturation -100 , global saturation 0. (say) in photo sky blue on left , grey on right.

6) move global saturation -50 +100: grey sky changes! a... less saturated grey sort of... super-saturated grey (more blilliant , yellow?).

so conjecture false , looks filter applied first, , global value applied last, ignoring filter possibly did (so if filter turned blue grey, "saturate" grey).

a) documented anywhere?

b) in particular, if want desaturate everything, except small area, have paint complement of area saturation -100 which feels quite unnatural (i'd painting on small area). there workaround?

thanks,
mh

mycroft.holmes wrote:

 

in particular, if want desaturate everything, except small area, have paint complement of area saturation -100 which feels quite unnatural (i'd painting on small area). there workaround?

one simplistic variation: paint adjustment brush on entire picture desired -100 saturation.

 

then switch brush erase mode, , are - in effect - painting saturation, each new brush stroke.

 

[that's if determined have effect in first place... ]

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