Color Maps in Raven Workbench

Color maps (or palettes) in Raven are used to map numerical power values in a spectrogram to specific colors. This document explains how color mapping works technically and how to configure it in the application.

Color Maps and the Color Bar are available in Raven Expedition and Raven Annotate.

How it Works

Technical Implementation

Raven uses a ColorMap model to translate power levels (typically in dB) into colors for display. Each color map defines a Lower Limit and an Upper Limit.

• Lower Limit: Any power value at or below this limit is mapped to the first color in the palette.
• Upper Limit: Any power value at or after this limit is mapped to the last color in the palette.
• Dynamic Range: The difference between the Upper and Lower limits.

Values between the limits are mapped to intermediate colors, typically using linear or cubic spline interpolation.

Brightness and Contrast

Instead of setting limits directly, Raven often uses Brightness and Contrast settings (scaled 0-100 in the UI) to calculate them:

1. Center Calculation: The "center" of the color range is determined by Brightness. Increasing brightness lowers the center value, making more of the spectrogram appear "brighter" (using colors from the upper end of the palette).
2. Range Calculation: The "width" of the color range is determined by Contrast. Increasing contrast narrows the dynamic range, making the transition between colors sharper.

The mathematical relationship is:

• Center = BrightnessOffset + (1 - Brightness) * BrightnessRange
• Range = (1 - Contrast) * ContrastRange
• Lower Limit = Center - Range / 2
• Upper Limit = Center + Range / 2

How to Use Color Controls

1. Using the Color Toolbar

The Color Toolbar provides quick access to common adjustments. It is typically located at the top or side of the main window.

• Brightness Slider: Adjusts the overall brightness of the spectrogram.
• Contrast Slider: Adjusts the color contrast.
• Color Map Dropdown: Select from various pre-defined palettes (e.g., Jet, Grayscale, Viridis, Inferno).
• Invert Button: Reverses the color order of the current palette.
• Spectrogram Parameters (Gear Icon): Opens the Spectrogram Parameters dialog for technical FFT settings.

2. The Color Bar

The Color Bar is a visual legend shown directly next to a chart that shows how power levels map to colors. It also displays the current Lower and Upper limits.

Toggling the Color Bar

The Color Bar visibility can be toggled in multiple ways:

1. View Menu: Go to the View menu and select Color Bar.
2. Toolbox Panel: In the Annotation Toolbox, go to the Selection Editor tab and click the Gear icon (Settings). Under the Chart Configuration section, you can check or uncheck the Color Bar option.
3. View Configuration Dialog: Open the View Configuration dialog from the View menu or the toolbar and toggle the Color Bar checkbox.

3. Color Bar Configuration Dialog

For precise control over the color mapping, you can open the Color Bar Configuration dialog.

Opening the Dialog

1. Go to the View menu.
2. Select Color Bar… (or right-click on the Color Bar itself if visible).

Dialog Features

• Brightness & Contrast Sliders: Identical to the ones in the toolbar.
• Floor & Ceiling: These allow you to set the Lower Limit ("Floor") and Upper Limit ("Ceiling") directly in dB units.
• Transfer Function Plot: A line chart showing how input values map to the color scale.
• Live Preview: A small color bar within the dialog that updates in real-time as you move the sliders.

Once you are satisfied with the settings, click Apply to update the spectrogram.