:topic: Color Mapping Controls

.. index::
   triple: DREAM3D-NX; Quad View; Color Mapping

.. _QuadViewColorMapping:

Color Mapping Controls
#######################

**In this section we describe how to configure the data array coloring
and slab projection settings in the Quad View module.**

The **Controls Panel** on the right side of the Quad View module
provides a set of controls for selecting which data array to display,
how to map it to color and opacity, and how each slice plane is
projected. All four windows use the same color mapping simultaneously.

.. figure:: Images/40_ColorMapping/ColorMappingControls.png
   :alt: Color Mapping Controls

   Color Mapping Controls in the Controls Panel

Thick Slab Mode
=================

The **Thick Slab** checkbox enables slab projection mode in Windows
2–4. Instead of displaying a single thin slice through the data, each
window renders a projection through a slab of voxels, which can reveal
features that are not fully visible in a single slice.

When **Thick Slab** is enabled, three blend mode options become
available to control how values are combined across the slab depth:

-  **Mean Blend**: Each pixel shows the average value of all voxels
   sampled along the projection ray through the slab.
-  **Min Intensity Blend**: Each pixel shows the minimum value
   encountered along the projection ray. This is useful for
   highlighting low-intensity structures.
-  **Max Intensity Blend**: Each pixel shows the maximum value
   encountered along the projection ray. This is commonly used in
   medical imaging to highlight high-intensity structures such as
   bright vessels.

Data Array Selection
======================

The **Array** drop-down selects which cell data array in the loaded
geometry is used for coloring the slice planes and volume rendering.
Only arrays associated with the geometry's cell data are listed.

The **Component** drop-down selects which component of the array is
displayed. For single-component (scalar) arrays this shows ``Scalar``.
For multi-component arrays (for example, vector or tensor data) the
drop-down lists:

-  **Magnitude** as the first entry — selecting it computes
   :math:`\sqrt{\sum_i c_i^2}` over all components per voxel and uses
   the resulting scalar field for coloring and volume rendering.

-  Each individual component, listed by index, so a single component
   can be selected for display.

.. figure:: Images/40_ColorMapping/ArrayComponentDropdowns.png
   :alt: Array and Component Drop-Down Selectors

   Array and Component Selectors

.. figure:: Images/40_ColorMapping/MagnitudeComponentOption.png
   :alt: Magnitude Component Option

   Component drop-down expanded for a multi-component array, with
   Magnitude shown as the first entry above the per-component indices.

.. note::

   When switching between arrays the per-array color preset, opacity
   transfer function, and custom data range are preserved. Returning to
   a previously displayed array restores its color customizations
   without re-applying defaults.

Color Preset Toolbar
======================

Below the array and component selectors is a row of action buttons for
managing the color transfer function:

-  **Reset** (|reset|): Reverts the color and opacity transfer function
   to the default state for the current color preset.

-  **Edit** (|colorpreset|): Opens the **Select Preset** dialog so you
   can browse and apply a named color preset (for example, *2hot*,
   *Black-Body Radiation*, *Blue Orange*) to the color map. Favorite
   presets can be starred for quick access and filtered via the search
   bar at the top of the dialog.

.. figure:: Images/40_ColorMapping/ColorPresetPicker.png
   :alt: Select Preset Dialog

   The Select Preset dialog opened by the **Edit** button.

-  **Invert** (|invert|): A toggle button. When active (pressed), the
   currently selected color map is reversed so that the minimum value
   maps to the color that would normally correspond to the maximum, and
   vice versa. Click the button again to release it and restore the
   original color map order.

-  **Scale to Data** (|scaletodata|): Sets the data range minimum and
   maximum to the actual minimum and maximum values found in the
   selected array and component across the full dataset.


.. figure:: Images/40_ColorMapping/ColorPresetToolbar.png
   :alt: Color Preset Toolbar

   Color Preset Toolbar

Opacity and Color Transfer Function Editor
============================================

The large interactive graph in the Controls Panel combines three
elements into a single view:

-  **Histogram bars** showing the distribution of voxel values in the
   active data array. The bars are colored according to the active color
   map so that the relationship between value and color is immediately
   visible.

-  **Opacity curve** (a line with draggable control points) mapping each
   data value to an opacity level (0 = fully transparent, 1 = fully
   opaque).

-  **Color gradient bar** (bottom strip) showing the current color
   transfer function, with draggable color control points.

.. figure:: Images/40_ColorMapping/TransferFunctionEditor.png
   :alt: Opacity and Color Transfer Function Editor

   The Histogram, Opacity Curve, and Color Bar

The **?** button above the editor opens its navigation help without
covering the histogram. Use **Alt/Option + scroll wheel** to zoom around
the pointer (a plain wheel is passed to the surrounding Controls Panel),
or use **Ctrl/Command+=** and **Ctrl/Command+-** to zoom around the chart
center. Left-drag empty chart space to pan.

Right-click for **Zoom In**, **Zoom Out**, **Reset View to Data**, **Box
Zoom Mode**, and **Reset Min/Max**. Press **Z** to enter Box Zoom (shown
by a mode label and crosshair cursor), drag a selection rectangle, and
press **Escape** to cancel. A successful selection automatically returns
to Pan mode; a selection that is too small leaves Box Zoom active for
another attempt. Editable points and range handles take priority when the
pointer is over them, and editing is suspended while Box Zoom is active.

Opacity Curve Interaction
---------------------------

**Add a control point**
   Double-click in the histogram area at the desired data value and
   opacity level. A new control point is inserted.

**Move a control point**
   Left-click and drag a control point. Interior points can be moved
   both horizontally (data value) and vertically (opacity). The first
   and last points are locked horizontally and can only be moved
   vertically.

**Remove a control point**
   Middle-click on a control point to remove it. The first and last
   points cannot be removed.

Color Bar Interaction
-----------------------

**Add a color control point**
   Double-click in an empty area of the color bar. A new point is
   created at the clicked position and a color picker dialog opens so
   you can choose its color. If you cancel the dialog, the point is
   removed.

**Edit a color control point**
   Double-click on an existing color control point to open the color
   picker and change its color.

**Select a color control point**
   Single-click on a color control point to select it (shown with a
   blue highlight ring). Press **Enter** or **Return** to open the
   color picker for the selected point.

**Remove a color control point**
   Select the point then press **Delete** or **Backspace**, or
   middle-click the point. The first and last color points cannot be
   removed. A minimum of two color points is always maintained.

**Deselect**
   Left-click (without dragging) on empty space in the histogram area to
   deselect the currently selected color point.

Range Lines (Custom Data Range)
---------------------------------

Two vertical yellow lines with triangular handles at the top of the
histogram define the active data range. The region outside the range
lines is dimmed. Dragging a range line rescales the color and opacity
mapping so that the full color gradient is compressed into the range
defined by the two lines.

**Drag a range line**
   Left-click and drag one of the yellow handles or lines to adjust
   the minimum or maximum of the custom range. All four windows update
   in real time as you drag.

**Reset range**
   Right-click the histogram and select **Reset Min/Max** to restore
   the range lines to the full data extent.

Keyboard and Mouse Reference
------------------------------

The following table summarizes all mouse and keyboard interactions
in the histogram/opacity editor:

+-------------------------------+----------------------------------------------------+
| Input                         | Action                                             |
+===============================+====================================================+
| Left-click + drag point       | Move an opacity or color control point             |
+-------------------------------+----------------------------------------------------+
| Left-click + drag range line  | Adjust custom data range boundary                  |
+-------------------------------+----------------------------------------------------+
| Left-click + drag empty space | Pan the visible histogram range                    |
+-------------------------------+----------------------------------------------------+
| **Alt/Option** + scroll wheel | Zoom the histogram view in/out (centered on        |
|                               | cursor position)                                   |
+-------------------------------+----------------------------------------------------+
| **Ctrl/Command+=** or **+**   | Zoom in around the chart center                    |
+-------------------------------+----------------------------------------------------+
| **Ctrl/Command+-**            | Zoom out around the chart center                   |
+-------------------------------+----------------------------------------------------+
| **Z**                         | Toggle Box Zoom Mode                               |
+-------------------------------+----------------------------------------------------+
| Left-drag in Box Zoom         | Zoom to the selected rectangle, then return to Pan |
+-------------------------------+----------------------------------------------------+
| **Escape**                    | Cancel Box Zoom and restore Pan mode               |
+-------------------------------+----------------------------------------------------+
| Double-click histogram area   | Add a new opacity control point                    |
+-------------------------------+----------------------------------------------------+
| Double-click color bar        | Add a new color control point (opens color picker) |
+-------------------------------+----------------------------------------------------+
| Double-click color point      | Edit color of existing point (opens color picker)  |
+-------------------------------+----------------------------------------------------+
| Middle-click on point         | Remove an opacity or color control point           |
+-------------------------------+----------------------------------------------------+
| **Delete** / **Backspace**    | Remove the selected color control point            |
+-------------------------------+----------------------------------------------------+
| **Enter** / **Return**        | Open color picker for selected color point         |
+-------------------------------+----------------------------------------------------+
| Left-click empty space        | Deselect the selected color point                  |
+-------------------------------+----------------------------------------------------+
| Right-click                   | Open the navigation and range context menu         |
+-------------------------------+----------------------------------------------------+

**Reset View to Data** restores navigation zoom and pan. **Reset
Min/Max** separately restores the yellow editable range handles to the
full data extent. Hovering over histogram bars shows the data value and
bin count at the pointer.

.. note::
   While the editor or its help popup has keyboard focus,
   **Ctrl/Command+=** and **Ctrl/Command+-** control chart zoom instead of
   the application font size.


.. |colorpreset| image:: Images/40_ColorMapping/Preset.svg
.. |invert| image:: Images/40_ColorMapping/invert.svg
.. |scaletodata| image:: Images/40_ColorMapping/ScaleToData.svg
.. |reset| image:: Images/40_ColorMapping/Reset.svg