Skip to content

Adjusting the Render Settings

In the previous section, we saw how the Preview and 3D Tomography view can be used to show the tomographic 3D image of the core. The color and opacity of the core rendering are controlled by two functions, one that maps the attenuation of a voxel to a color, and another that maps it to an opacity.

You can control these two functions through the Render Settings, which are accessible via Show → Render Settings in the menu bar:

Show Render Settings

The Render Settings view will appear:

Render Settings

There are two modes in which you can manipulate the color and opacity function, Quick Mode and Detailed Mode, described in the sections below.


An alternative approach for adjusting the rendering of the tomography, suitable for advanced users, is offered by the Attenuation Segmentation toolbox, which allows the user to define regions of interest based on voxel attenuation histogram data.

Quick Mode

In the Quick Mode, which is the default, the currently used color and opacity function is shown at the bottom:

Quick Preview

The top X axis shows the attenuation scale and the Y dimension is the opacity. The color bar at the bottom shows the color function.

The above settings would color lighter minerals like quartz in almost fully transparent black (i.e. light gray), while heavier minerals like Barite would be colored in red. Very high attenuation minerals like silver would be colored in yellow.

Below is an example segment of core colored using these settings. The core is made of mostly lighter minerals (attenuation 0.5-2.0), with two main cross-cutting planar structures with heavier mineral particles (attenuation 5.0-10.0).

Color Example

Adjusting Color

In Quick Mode, there are two choices for the color function, either the gradual function from black to red to yellow described above, which is called Gray Fire, or a fixed Black function. You pick the color function using the Colors drop-down:

Quick Colors

Adjusting Opacity

To control the shape of the S-curve function that governs the opacity, use the Window / Level input control:

Window Level

By positioning the blue point in the white area, the shape of the S-curve opacity function can be controlled. Vertical movement of the point controls the steepness of the S shape, while sideways movement controls its extent across the attenuation scale.

For example, moving the point a little to the right, the S shape takes on a more elongated shape, suppressing (making transparent) more of the lighter minerals and allowing us to focus on the heavier components of the rock:

See Through

By default, the black, red and yellow points of the color function are positioned at attenuation 0, 10 and 20. By using the Keep Color Points under Window, they are instead placed equidistantly under the S shape (the "Window"):

Under Window

Notice how the color gradient from black to red to yellow is now kept underneath the S shape, the region of change for the opacity function. This option can be useful when you want to quickly "tune" both the color and opacity function to some specific attenuation range. In this case, from around 0.5 to around 8.0.

Detailed Mode

The default Quick mode is useful when you want to quickly adjust the color and opacity to something reasonable for the segment of core you're currently looking at. If you want greater control over the color and opacity functions, including the ability to save your settings as named "presets", you can use the Detailed mode, available through a button at the top:

Detailed Mode

Creating Presets

In Detailed mode, there's initially just a single built-in color / opacity preset called Gray Fire. To create a new one which you can edit:

  1. Click the Duplicate preset button next to the presets drop-down to duplicate the Gray Fire preset and use it as a starting point for your own:

    Duplicate Preset

  2. You will be prompted to enter a name and description for the new preset:

    Preset Name and Description

  3. Once the name is accepted with OK, the preset is created and the control points governing the color and opacity function of the preset become visible:

    Preset Created

Adjusting Color

Double-click a color control point in the color function (the bottom color bar). Doing so will bring up a color selection window where you can choose the color for the point. Click and drag a control point using the left mouse button held down to move it horizontally to a new position along the attenuation scale.

For example, using the preset created above, we can change the color of the red point to green and move it to the left:

Change Color

To insert a new point, click an empty spot along the color function. To remove a point, select it by clicking it once, then press Delete.


The mouse cursor must be hovering the color function area when Delete is pressed, in order for it to take effect.

Adjusting Opacity

Click and drag an opacity control point using the left mouse button held down to move it to a new position along the attenuation / opacity scale. Insert a new point by clicking an empty spot.

For example, to make the lighter material in our previous example more transparent and focus on the heavier parts, we can insert a new low opacity point at around attenuation 4.0:

Change Opacity

Remove an opacity point by clicking it once to select it and press Delete.


The mouse cursor must be hovering the opacity function area when Delete is pressed, in order for it to take effect.


You can zoom in the Opacity and Color windows by changing the horizontal (X) and vertical (Y) ranges. The horizontal and vertical ranges can be restored to show the whole function.

X Range Maximum X Range Reset

Importing and Exporting Presets

If you want to export a preset to a file, use the export button:

Export Preset

You will be prompted to pick a file name and location:

Export Filename

Confirm with Export and the file is exported. You can then share this file with your colleague, who can import it using the import button:

Import Preset