Changing one part of the frame

Primary against secondary

A primary correction applies to the whole image. Everything so far has been primary.

A secondary applies to part of it — one colour, one region, one object. Two mechanisms produce the selection: a qualifier, which selects by colour, and a window, which selects by shape.

Qualifiers, and what they actually do

A qualifier builds a mask from ranges of hue, saturation and luminance. Pick a colour with the eyedropper, widen the ranges until the thing you want is selected, and the node applies only inside that selection.

Standard uses: pulling down an over-saturated red shirt, changing the colour of a sign, warming skin without warming the background, taking the green out of foliage that is competing with the subject.

The procedure that works:

1. Turn on the highlight view, which shows the selection as a matte — white where selected, black where not. You cannot judge a key by looking at the graded result.
2. Sample the colour, then widen hue, then saturation, then luminance, one at a time.
3. Add blur to the matte. A hard-edged key always looks cut out; two or three pixels of blur solves it.
4. Add a little denoise to the matte if it is crawling.
5. Restrict it with a window if it is also selecting something elsewhere in the frame.

Where qualifiers fall apart, and why

The chroma subsampling lesson at the start of this course pays off here.

A qualifier builds its mask from colour information. In 4:2:0 footage — every phone, every consumer camera — colour is recorded at half the horizontal and half the vertical resolution. So the mask is being built from a quarter as much information as the picture has, and the edges come back blocky, stepped and unstable between frames.

On 4:2:2 or 10-bit footage, qualifiers work well. On 8-bit 4:2:0, expect to blur the matte heavily and to restrict the correction to something subtle. A large hue change on a 4:2:0 key will show its edges.

This is not a failure of the software and no setting fixes it. It is the file.

Windows

A window is a drawn shape — circle, rectangle, polygon, or a freehand curve — with a softness setting.

Standard uses: a vignette, brightening a face, darkening a bright window behind a subject, drawing attention to one part of the frame.

The softness setting is the whole craft. A hard-edged window is visible as a shape. Set softness high enough that you cannot see where it ends, then raise the adjustment inside it until it does something. Almost every window in professional work is softer and subtler than a beginner's.

The principle worth holding: a good window is one the viewer never notices. If somebody can see that you brightened the face, it is too strong or too hard.

Tracking

A static window on a moving subject is useless, so windows track.

Resolve's tracker analyses the movement of what is inside the window and moves the window to follow, supporting pan, tilt, zoom, rotate and perspective. In practice you place the window on the first frame, press track forward, and check the result.

When it fails — the subject leaves frame, something crosses in front, the movement is too fast — you can switch to frame-by-frame keyframing, or track in reverse from a later frame, or split the shot at the problem point and track the halves separately.

The tracker is in the free version and it is good. It is one of the clearest cases where free Resolve is doing something that used to cost thousands.

Combining a window and a qualifier

The most useful secondary technique. Draw a window around the general area, then qualify inside it.

Example: you want to warm somebody's face. A skin-tone qualifier alone will also select the wooden table and the brick wall. Draw a loose tracked window around the head, qualify skin inside it, and the selection is only the face.

In Resolve, both the window and the qualifier feed the same node's key, and the node's key controls let you combine them.

When not to bother

Secondaries are where grading time disappears. Before spending forty minutes on a key, ask whether the shot is on screen for three seconds in a piece nobody will pause.

The honest order of value: correction and matching first, because everyone perceives those; a simple look second; secondaries last, and only where something is actively distracting. A distracting bright object behind a subject is worth a window. A slightly over-saturated jumper is not.

Today

Draw a soft circular window on a face, raise the brightness inside it by a small amount, and toggle it. Then raise the softness until you cannot tell where it ends.