Color Picker

Overview

The Color Picker is a dockable panel that replaces Nuke's built-in color chooser with a full-featured, HDR-capable swatch manager. It stores palettes persistently, supports drag-and-drop to and from Nuke knobs, viewer color sampling, palette extraction via K-means++ clustering, and import/export in industry-standard formats.

Opening the Picker

There are two ways to open the Color Picker:

• Panes menu — Panes → NELSIG → Color Picker. The panel can be docked into any Nuke pane layout.
• Hotbox — If the Hotbox tool is installed, the Color Picker is available as a quick-launch entry from the radial menu.

Swatch Management

Adding swatches

• HDR Picker — Click the + button to open the HDR color picker dialog and choose any color, including values above 1.0.
• Drag from Nuke — Drag a color value from any Nuke knob directly onto the swatch grid.
• Viewer sample — Sample a pixel or area from the Nuke viewer and add it as a swatch in one click.
• Extract from viewer — Run K-means++ palette extraction to generate a group of representative swatches from the current viewer image.

Editing swatches

Double-click any swatch to re-open the HDR picker dialog with the current color pre-loaded. The swatch updates in place when you confirm.

Deleting swatches

Right-click a swatch and choose Delete, or select one or more swatches and press Delete.

Groups & Tabs

Swatches are organized into groups, displayed as tabs along the top of the panel.

Creating a group

Click the + tab button at the end of the tab bar to create a new group. You will be prompted for a name.

Managing groups

• Switch — Click a tab to display its swatches.
• Reorder — Drag tabs left or right to rearrange them.
• Rename — Double-click the tab label to edit the name inline.
• Duplicate — Right-click the tab → Duplicate Group.
• Delete — Right-click the tab → Delete Group. A confirmation dialog prevents accidental loss.

Data format

Groups and swatches are stored as JSON. Each swatch records its RGB values as 32-bit floats (linear), preserving the full HDR range. See Data Storage for the file location.

HDR Color Picker Dialog

The HDR picker opens as a modal dialog whenever you create or edit a swatch. It provides precise control over the full dynamic range.

Hue / Saturation wheel

Click or drag on the circular wheel to set hue and saturation simultaneously. The wheel updates dynamically to reflect the current gain level.

Gain slider

The vertical gain slider uses an exponential scale from 0 to 50, giving fine control in the 0–1 SDR range while still reaching extreme HDR highlights.

Slider modes

Toggle between three slider-bank modes using the buttons above the sliders:

Additional controls

• Dynamic gradients — Each slider track renders a real-time gradient showing how the color changes along that axis.
• Mouse wheel — Scroll on any slider or the gain bar for fine incremental adjustments.
• Hex input — Type a hex code (e.g. #FF6600) into the text field for exact SDR values.
• Old / New swatches — A split preview shows the original color alongside the new selection so you can compare before committing.

RotoPaint Integration

The Color Picker has dedicated shortcuts for RotoPaint workflows:

• Ctrl+click a swatch — Sets the color as the current brush color on the active RotoPaint node.
• Alt+click a swatch — Applies the color to the currently selected stroke in the RotoPaint curve list.

Smart Color Apply

When you click a swatch (without modifiers), the picker intelligently detects the selected node type and applies the color to the most appropriate knob:

Viewer Color Sampling

Point sampling

Click the eyedropper button, then click a single pixel in the Nuke viewer. The sampled value is added as a new swatch with full 32-bit float precision in linear color space.

Area sampling

Drag a rectangle in the Nuke viewer to sample an area. The picker averages up to 2500 pixels within the bounding box to produce a representative color.

Technical details

• Uses nuke.activeViewer().node()['colour_sample_bbox'] to read the sampling region.
• Pixel values are read with node.sample('red', x, y) etc., returning true 32-bit float values in linear space.
• The sampled color is stored without any view transform applied — what you see in the swatch is the raw linear value.

Extract Palette from Viewer

How to use

1. Frame the image you want to analyze in the Nuke viewer.
2. Click the Extract Palette button in the Color Picker toolbar.
3. Choose the number of colors to extract (default: 6).
4. The extracted colors appear as a new swatch group.

K-means++ algorithm

The extraction uses K-means++ clustering to find the most representative colors in the image. K-means++ improves on standard K-means by choosing smarter initial centroids, producing more consistent and perceptually meaningful palettes.

Use cases

• Extracting a color script from reference images.
• Building a palette that matches plate photography.
• Quickly generating harmonious swatch sets from texture maps.

Match Color

Match Color creates a Grade node that transforms one color into another, useful for quick color matching between elements.

Workflow

1. Right-click a swatch — Choose Match Color from the context menu. This swatch becomes the target color.
2. Sample the source — Click or drag in the viewer to pick the color you want to transform from.
3. Live preview — A Grade node is created immediately and connected to the selected node. The viewer updates in real time as you adjust.
4. Validate — Click Apply to keep the Grade node, or Cancel to remove it.

Grade node structure

The generated Grade node uses:

• Gain — Scales the source color to match the target brightness.
• Multiply — Adjusts per-channel ratios to match hue and saturation.
• Label — Automatically set to [NELSIG Match Color] for easy identification.

Color Harmonies

Right-click any swatch and choose Generate Harmonies to create a set of color-theory-based companion colors. The generated swatches are added to the current group.

Drag & Drop

From picker to Nuke

• Drag to a knob — Drop a swatch onto any color knob in the Properties panel to set its value.
• Drag to the DAG — Drop a swatch onto empty space in the node graph to create a Constant node with that color.

From Nuke to picker

Drag a color value from any Nuke knob and drop it onto the swatch grid to add it as a new swatch.

Technical format

Drag data uses the MIME type application/x-nuke-color encoding RGB as three space-separated floats (e.g. 1.0 0.4 0.15), preserving full HDR range.

Import / Export

Supported formats

Importing

Click the Import button and select a file. You are prompted to choose an import mode:

• New group — Creates a fresh tab with the imported colors.
• Replace — Replaces all swatches in the current group.
• Merge — Appends imported colors to the current group, skipping duplicates.

Exporting

Click the Export button, choose a format, and save. The entire current group is exported. For JSON, all groups can be exported at once.

Color space handling

Internal storage is always linear (scene-referred). When exporting to 8-bit formats like GPL, colors are converted to sRGB with gamma encoding. When importing from sRGB sources, the inverse transform is applied automatically.

Keyboard & Mouse Reference

Swatch actions

HDR picker dialog

Tab bar

Troubleshooting

Data Storage

All swatches and group definitions are persisted to a single JSON file:

~/.nuke/nelsig_color_picker_data.json

The file is written automatically whenever you add, edit, delete, or reorder swatches. It is human-readable and safe to version-control or copy between machines.