@afre It doesn’t look they are talking about this tool you link since it’s about converting to shades of gray (which is obviously not what people are doing here).
@luluxXX Is the procedure you do in GIMP the Color > Satuation… tool, then setting “Scale” to 0.5? If so, the tool has an “Interpolation Color Space” where you can set “Native”, “CIE Lab/Lch” and “CIE Yuv”. Does’nt it answer the question since @David_Tschumperle says their own command is done in HSV colorspace?