Ronin

Almost every free black-and-white LUT is a saturation slider at zero, and that one shortcut is why so much amateur monochrome looks flat. Pulling saturation out collapses every colour onto the standard luma weights, which are dominated by green: a blue sky and green foliage arrive at nearly the same grey, a dark costume melts into the hedge behind it, and the frame turns to mud. Nothing in the grade afterwards can pull them apart, because by then they are the same number.

Ronin is a channel mix instead, weighted toward red, which is what an orange filter did on panchromatic stock for most of the twentieth century. One decision buys three things at once: blue sky goes dark so cloud detail separates instead of blowing out, green foliage drops well below a lit face, and skin goes bright and smooth because blemishes and veins are red. Measured against a plain desaturation, the separation between mid skin and foliage goes from 0.235 to 0.350. Separation is the whole game in monochrome, since there is no colour left to carry it, so it has to be built into the mapping rather than found later.

Two honest notes. It cannot invent drama that the lighting never created: a LUT maps each pixel value to another value, so if the costume and the sky reach it as the same grey they leave as the same grey. Give it a real lighting ratio, a dark subject against a bright ground, a directional key, and it renders hard; on flat midday footage it will be tasteful and quiet, and that is the footage talking, not the look. And one thing it only partly solves: a deep skin tone against green foliage is nearly the same grey under a plain desaturation, and Ronin improves it about sevenfold but still leaves it close. Backlight that shot, or put a lighter background behind it.