Refine hair and soft edges

A detail band is an outline you draw along a soft edge in Refine mask. Inside it, Cask Film keys the plate against a backing colour you pick, and adds that key to the matte where it exceeds it. A band only adds edge within Reach of the subject, so it never keys out a patch of background away from the subject.

A band’s outline is keyed and tracked like any shape. Its Edge settings apply to the whole layer and are not keyed.

Steps

1. Click the detail band button beside the Pen in the tool bar. Its tooltip reads Draw a detail band with the Pen. The Pen becomes the tool, and it draws bands until you click the button again.

2. Draw a closed outline along the edge: a little inside the subject and a little out into the hair. Click the first point to close it.

3. In the inspector, find the Edge section, marked Key · inside the band only. Until you pick a backing, the swatch is empty and Pick the backing colour shows in amber.

4. Click the eyedropper next to Backing. The tool bar reads Click the backing on the picture · Esc cancels.

5. Click a clean area of background close to the edge. The toast reads Backing colour · picked at f plus the frame.

6. Press 4 for the Trimap view: white is solid foreground, grey is the band, black is out. Press 5 for Comp and pick a backing swatch (checker, black, grey or white) that shows the edge clearly.

7. Tune the key:

   Setting	Default	What it does
   Balance	50%	Weights the backing’s other two colour channels when the key compares them. Adjust it until the hair holds and the background clears
   Choke	0 px	Positive shrinks the keyed edge. Negative grows it
   Soften	1 px	Blurs the keyed edge
   Reach	12 px	How far outside the subject the band may add edge. 0 keeps it inside the matte

8. Leave Decontaminate on (the default). It pulls the backing’s colour out of the soft edge pixels, so hair does not carry a green or blue fringe.

9. Click Done.

Each change in the Edge section is one undo step. A drag on a value is one step for the whole drag.

To keep part of the subject fully opaque inside a band, draw a shape over it and turn on Solid core in the inspector. It shows white in the Trimap view.

The weak-backing warning

When you pick a backing, Cask Film measures how much of the subject inside the band the key would remove. If a quarter or more would go, an amber warning under Backing says the backing is close to the subject’s colours and the key will be weak there. The band still keys. The warning tells you why the edge may come out thin.

Decontaminate after Done

On Done, decontamination moves into the Object mask itself. It applies when the Object mask is set to Cut out, in the preview and in export. The other modes ignore it. If several bands have Decontaminate on, the first visible one in the Layers list sets the colour that is removed.

Result

In the Comp view, the hair or soft edge sits over the backing swatch with its fine strands kept and no ring of background around the subject. After Done, the clip’s cut-out shows the same edge without a colour fringe.

If it doesn’t work

Symptom	Cause	Fix
The band changes nothing	No backing is picked. The empty swatch’s tooltip says No backing picked · the band keys nothing	Click the eyedropper and pick the backing
A ring of background is kept around the subject	Reach is too high for a busy background	Lower Reach
Long flyaway hairs are cut off	Reach stops short of them	Raise Reach. This works best on a clean, even backing
The amber weak-backing warning shows	The backing shares colours with the subject	Pick the backing again from a cleaner area, adjust Balance, or cover the problem part with a shape or paint
Edges still carry the backing colour after Done	Decontaminate is off, or the Object mask is not set to Cut out	Turn Decontaminate on, and set the Object mask to Cut out