# IBM Visualization Data Explorer User's Reference

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### Colormap

Category

Special

Function

Produces a color map.

Syntax Available only through the user interface.

Inputs

Name | Type | Default | Description
--- | --- | --- | ---
`data` | field | none | object used to derive min or max
`min` | scalar | min of data | minimum of color-map range
`max` | scalar | max of data | maximum of color-map range
`nbins` | integer | 20 | number of bins in the histogram
`colormap` | field or group | none | RGB color map to be used
`opacity` | field | none | opacity map to be used
`title` | string | "Colormap Editor" | title of editor

Outputs

Name | Type | Description
--- | --- | ---
`rgb` | field | RGB color field
`opacity` | field | opacity field

Functional Details

This interactive module allows the user to create color maps that are applied to data. Through inputs to the module (either the outputs of other tools or values set in its configuration dialog box), the Colormap Editor can be "data driven." If it is not data driven, then the attributes (such as `min` and `max`) are taken from values set by the user in the Colormap Editor.

Note: The Colormap Editor itself is invoked by double-clicking on the module's icon in the VPE window. The module's configuration dialog box is accessed from the `Edit` pull-down menu in the same window.

`data` | input can be used to derive the minimum and maximum values in the color and opacity maps. If this parameter is specified, a histogram of the "data" component becomes available in the Colormap Editor.
`min` | sets the minimum value used in the color and opacity maps. If this parameter is specified, it overrides the minimum value set by `data`. If neither `min` nor `data` is specified, the value is set in the minimum field of the Colormap Editor dialog box.
`max` | sets the maximum value in the color and opacity maps. If this parameter is specified, it overrides the maximum value set by `data`. If neither `max` nor `data` is specified, the value is set in the maximum field of the Colormap Editor dialog box.
`nbins` | specifies the number of data bins in the histogram displayed by the Colormap Editor. A value of 0 indicates that the histogram should not be computed. The histogram is accessible through the `Axis Display` in the `Options` pull-down menu in the Colormap Editor.
`colormap` | specifies the color map used to initialize the color-map portion of the Colormap Editor. For example, the map may be an imported `.cm` file, which contains both a color and an opacity map. If this file is passed to the `colormap` parameter, both maps will be used to initialize the maps in the editor. Alternatively, a simple map field can be passed to the appropriate parameter(s). Note that only the color information of the map is used to initialize the Colormap Editor; the "positions" component of the map (representing the data range to which the colors apply) are ignored. This is to allow a colormap to be used for any input data set which may be passed to the `data` parameter; the range of the map will be taken from `data`, rather than from the colormap. If you want to use the actual "positions" of the colormap, then simply use Mark to mark the "positions" component of the colormap, and pass the output of Mark to the `data` parameter of Colormap.
`opacity` | specifies the opacity map used to initialize the opacity-map portion of the Colormap Editor.
`title` | specifies the title of the Colormap Editor window.

Example Visual Programs

    UsingColormaps.net
    VolumeRendering.net

An example that uses a data-driven Colormap is:

    DataDrivenInteractors.net

See Also

AutoColor, Color

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