Curves, HSL and grading

These are the tools for when the ordinary sliders are too blunt: they let you address one band of tone, or one band of colour, and leave the rest alone.

The tone curve

The curve maps input brightness to output brightness. A point dragged upward makes that range of tones lighter; dragged down, darker. Because you choose where the points sit, you can lighten shadows while leaving highlights untouched, which no single slider will do.

• The RGB curve moves brightness without changing hue. A gentle S makes contrast; lifting the bottom-left corner gives the faded, matte black that reads as film.
• The red, green and blue curves shift colour per tonal range. Lifting blue in the shadows is the classic cool-shadow look.

HSL

HSL splits the image into colour bands and gives each one three controls:

• Hue shifts that band toward its neighbours — nudging greens toward yellow to warm foliage, for example.
• Saturation makes that band alone stronger or weaker, which is how you desaturate a distractingly orange sign without touching the rest of the frame.
• Luminance brightens or darkens that band. Pulling blue luminance down is the standard way to deepen a sky.

Colour grading

Grading tints tonal ranges independently through colour wheels, each with a hue, a saturation and a brightness. Warm highlights against cool shadows is the split-tone that most cinematic looks are built on. Two extra controls sit underneath:

• Blend controls how much the ranges bleed into one another.
• Balance shifts where the boundary between them falls, biasing the effect toward the shadows or the highlights.

Black and white

The black-and-white mixer converts the image using per-colour weights, so you decide how bright each original colour becomes in grey. This is what separates a considered monochrome conversion from simply pulling saturation to zero: a red jumper and a green hedge can be identical greys until you weight them apart.

Curves reward small moves. A curve that looks dramatic on the graph is usually far too much on the photo — drag less than feels right, then compare against the original.

All of this can be confined to part of the image with a mask.