[poisondeathray]

Alternatively, you can use smoothlevels and set the chroma processing to zero

By default, lato set it at 100 (from 0-200) or intermediate

e.g using stainlesss's (enough sssss's ? )test

ColorBars(pixel_type="YV12").Bicubicresize(480,360)
Levels(16,1.0,235,16,235,coring=false)  # Limiter dont work as required, results in luma Min = 10, not 16, so use Levels
A=Last
B=last.s.s.s.s.s.s.s.s.s.s.s.s.s.s.s
StackVertical(A.ColorYUV(analyze=true),B.ColorYUV(analyze=true))

#function s(clip c) { return c.ColorYUV(levels="TV->PC").ColorYUV(levels="PC->TV") }

function s(clip c) { return c.smoothlevels(preset="tv2pc", chroma=0).smoothlevels(preset="pc2tv",chroma=0) }