---
name: "QwtColorMap"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtColorMap"
---

# QwtColorMap(3)

QwtColorMap is used to map values into colors.

## NAME

QwtColorMap - **QwtColorMap** is used to map values into colors.

## SYNOPSIS

`#include <qwt_color_map.h>`

Inherited by **QwtAlphaColorMap**, and **QwtLinearColorMap**.

### Public Types

enum **Format** { **RGB**, **Indexed** }\

### Public Member Functions

**QwtColorMap** (**Format**=**QwtColorMap::RGB**)\
 Constructor.  virtual **~QwtColorMap** ()\
 Destructor.  **Format** **format** () const\
 virtual QRgb **rgb** (const **QwtInterval** &interval, double value) const =0\
 virtual unsigned char **colorIndex** (const **QwtInterval** &interval, double value) const =0\
 QColor **color** (const **QwtInterval** &, double value) const\
 virtual QVector\< QRgb \> **colorTable** (const **QwtInterval** &) const\

## Detailed Description

**QwtColorMap** is used to map values into colors.

For displaying 3D data on a 2D plane the 3rd dimension is often displayed using colors, like f.e in a spectrogram.

Each color map is optimized to return colors for only one of the following image formats:

- •

  QImage::Format\_Indexed8\

- •

  QImage::Format\_ARGB32\

**See also:**

**QwtPlotSpectrogram**, **QwtScaleWidget**

## Member Enumeration Documentation

### enum QwtColorMap::Format

Format for color mapping

**See also:**

**rgb()**, **colorIndex()**, **colorTable()**

**Enumerator**

- *RGB*

  *The map is intended to map into RGB values.*

- *Indexed*

  *The map is intended to map into 8 bit values, that are indices into the color table.*

## Member Function Documentation

### QColor QwtColorMap::color (const QwtInterval & interval, double value) const` [inline]`

*Map a value into a color*

**Parameters:**

*interval Valid interval for values* \
 *value Value*

**Returns:**

*Color corresponding to value*

**Warning:**

*This method is slow for Indexed color maps. If it is necessary to map many values, its better to get the color table once and find the color using* **colorIndex()***.*

### virtual unsigned char QwtColorMap::colorIndex (const QwtInterval & interval, double value) const` [pure virtual]`

*Map a value of a given interval into a color index*

**Parameters:**

*interval Range for the values* \
 *value Value*

**Returns:**

*color index, corresponding to value*

*Implemented in* **QwtLinearColorMap***.*

### QVector\< QRgb \> QwtColorMap::colorTable (const QwtInterval & interval) const` [virtual]`

*Build and return a color map of 256 colors*

*The color table is needed for rendering indexed images in combination with using* **colorIndex()***.*

**Parameters:**

*interval Range for the values*

**Returns:**

*A color table, that can be used for a QImage*

### QwtColorMap::Format QwtColorMap::format () const` [inline]`

**Returns:**

*Intended format of the color map*

**See also:**

**Format**

### virtual QRgb QwtColorMap::rgb (const QwtInterval & interval, double value) const` [pure virtual]`

*Map a value of a given interval into a RGB value.*

**Parameters:**

*interval Range for the values* \
 *value Value*

**Returns:**

*RGB value, corresponding to value*

*Implemented in* **QwtAlphaColorMap***, and* **QwtLinearColorMap***.*

## Author

*Generated automatically by Doxygen for Qwt User's Guide from the source code.*