Premult
Multiply colour by alpha.
| Node | Premult |
|---|---|
| Menu | Merge › Premult |
| Names in each format | |
| .oink comp (JSON) | "type": "OC_N_premult" |
| .nk script | Premult (how .nk import works) |
| Python | nuke.createNode("Premult") |
| Assistant (MCP) | create_node(type="Premult") |
| Tab search | premult |
Inputs and outputs
| Port | Name | Type |
|---|---|---|
| input 0 | Image | image |
| output 0 | Image | image |
Knobs
Panel tab Premult, in panel order.
| Knob | Label | Type | Default | Range / values | .nk knob | Description |
|---|---|---|---|---|---|---|
channels | multiply | menu | rgb | rgba, rgb, alpha, all, none | Layer the op applies to: rgb, rgba, alpha, all, none, <layer> or <layer>.<ch> | |
alpha | by | menu | rgba.alpha | rgba.alpha, none | alpha | Channel to multiply / divide by (none = off) |
invert | invert | bool | false | invert | Multiply / divide by 1 - alpha |
Other knobs (Python, .nk and the assistant; not on the panel)
| Knob | Label | Type | Default | Range / values | .nk knob | Description |
|---|---|---|---|---|---|---|
gl_color | Viewer Controls Color | float ×3 | 0, 0, 0 | 0 to 1 | ||
postage_stamp_frame | Static Frame | int | 1 | -2147483648 to 2147483647 | ||
lifetimeStart | Lifetime Start | int | 0 | -2147483648 to 2147483647 | ||
lifetimeEnd | Lifetime End | int | 100 | -2147483648 to 2147483647 | ||
useLifetime | Use Lifetime | boolean | false | |||
cached | Cached | boolean | false | |||
bookmark | Bookmark | boolean | false | |||
dope_sheet | Dope Sheet | boolean | false | |||
clone_group | Clone Group | string | ||||
link_source | Link Source | string | ||||
link_overrides | Link Overrides | string | ||||
split_views | Split Views | string | ||||
mask_channel | Mask | string | none | Mask channel, e.g. rgba.alpha (none = no mask) | ||
invert_mask | Invert | boolean | false | invert_mask | ||
inject | inject | boolean | false | Copy the mask into mask.a for nodes downstream | ||
fringe | fringe | boolean | false | Only apply the effect at the edges of the mask | ||
unpremult | (Un)premult by | enum | none | none, rgba.alpha | ||
invert_unpremult | invert | boolean | false | (Un)premultiply by 1 - alpha | ||
mix | Mix | float | 1 | 0 to 1 | mix |
Examples
Open these from Help › Examples…, or from the ? menu in this node's Properties panel.
- Copy an alpha between streams (
examples/channel/copy_alpha.oink): Copy takes rgba.alpha from its A input (the CandleGlass render) and writes it into the B stream (the Desk photo), then Premult multiplies the colour by that alpha. The same pattern moves any channel between streams. - Premultiplied colour: Unpremult, grade, Premult (
examples/merge/premult_handling.oink): Colour corrections on a premultiplied render go between Unpremult and Premult, so edges keep their colour. PrismsLenses.exr is premultiplied with alpha 0 but rgb above 0 in places (glows); those pixels are left alone by Unpremult (alpha 0).