# MergeExpression

> Per-channel expressions of A and B.

| Node | MergeExpression |
|---|---|
| Menu | Merge › MergeExpression |
| **Names in each format** | |
| .oink comp (JSON) | `"type": "OC_N_mergeexpression"` |
| .nk script | `MergeExpression` ([how .nk import works](/docs/nuke-users/nk-import)) |
| Python | `nuke.createNode("MergeExpression")` |
| Assistant (MCP) | `create_node(type="MergeExpression")` |
| Tab search | `mergeexpression`, or its initials `me` |

![MergeExpression properties](/shots/nodes/mergeexpression@2x.webp)

## Inputs and outputs

| Port | Name | Type |
|---|---|---|
| input 0 | B | image |
| input 1 | A | image |
| input 2 | mask | image |
| output 0 | Image | image |

## Knobs

Panel tab **Mergeexpression**, in panel order.

| Knob | Label | Type | Default | Range / values | .nk knob | Description |
|---|---|---|---|---|---|---|
| `temp_name0` | temp_name0 | text |  |  | `temp_name0` |  |
| `temp_expr0` | temp_expr0 | text |  |  | `temp_expr0` |  |
| `temp_name1` | temp_name1 | text |  |  | `temp_name1` |  |
| `temp_expr1` | temp_expr1 | text |  |  | `temp_expr1` |  |
| `temp_name2` | temp_name2 | text |  |  | `temp_name2` |  |
| `temp_expr2` | temp_expr2 | text |  |  | `temp_expr2` |  |
| `temp_name3` | temp_name3 | text |  |  | `temp_name3` |  |
| `temp_expr3` | temp_expr3 | text |  |  | `temp_expr3` |  |
| `channel0` | channel0 | text | `rgba.red` |  | `channel0` |  |
| `expr0` | = expr0 | text |  |  | `expr0` |  |
| `channel1` | channel1 | text | `rgba.green` |  | `channel1` |  |
| `expr1` | = expr1 | text |  |  | `expr1` |  |
| `channel2` | channel2 | text | `rgba.blue` |  | `channel2` |  |
| `expr2` | = expr2 | text |  |  | `expr2` |  |
| `channel3` | channel3 | text | `rgba.alpha` |  | `channel3` |  |
| `expr3` | = expr3 | text |  |  | `expr3` |  |
| `mask_channel` | mask | menu | `none` | none, rgba.alpha, rgba.red, rgba.green, rgba.blue |  | Mask channel, e.g. rgba.alpha (none = no mask) |
| `inject` | inject | bool | `false` |  |  | Copy the mask into mask.a for nodes downstream |
| `invert_mask` | invert | bool | `false` |  | `invert_mask` |  |
| `fringe` | fringe | bool | `false` |  |  | Only apply the effect at the edges of the mask |
| `unpremult` | (un)premult by | menu | `none` | none, rgba.alpha |  |  |
| `invert_unpremult` | invert | bool | `false` |  |  | (Un)premultiply by 1 - alpha |
| `mix` | mix | float | `1` | 0 to 1 | `mix` |  |

### 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 |  |  |  |  |
| `channels` | Channels | string | `rgba` |  |  | Layer the op applies to: rgb, rgba, alpha, all, none, <layer> or <layer>.<ch> |


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Sources: opencomp_core/nodes/color/expression.py, opencomp_electron/src/components/properties/knobSchema.ts, opencomp_core/nk/mapping.py