---
name: "plscmap1a"
section: "3plplot"
platform: "linux"
package: "plplot-doc"
version: "5.15.0+dfsg2-15"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/plscmap1a"
---

# plscmap1a(3plplot)

Set semitransparent cmap1 RGBA colors.

## NAME

**plscmap1a** - Set semitransparent cmap1 RGBA colors.

## SYNOPSIS

**plscmap1a**(*r*, *g*, *b*, *alpha*, *ncol1*)

## DESCRIPTION

Set semitransparent cmap1 colors (see the PLplot documentation) using RGBA vector values.  This function also sets the number of cmap1 colors.  N.B. Continuous cmap1 colors are indexed with a floating-point index in the range from 0.0-1.0 which is linearly transformed (e.g., by [**plcol1**(3plplot)](/plcol1/3plplot.md)) to an integer index of these RGBA vectors in the range from 0 to *ncol1-1*.  So in order for this continuous color model to work properly, it is the responsibility of the user of [**plscmap1**(3plplot)](/plscmap1/3plplot.md) to insure that these RGBA vectors are continuous functions of their integer indices.

Redacted form: **plscmap1a(r, g, b, alpha)**

This function is used in example 31.

## ARGUMENTS

- *r* (**PLINT\_VECTOR**(3plplot), input)

  A vector that represents (using unsigned 8-bit integers in the range from 0-255) the degree of red in the color as a continuous function of the integer index of the vector.

- *g* (**PLINT\_VECTOR**(3plplot), input)

  A vector that represents (using unsigned 8-bit integers in the range from 0-255) the degree of green in the color as a continuous function of the integer index of the vector.

- *b* (**PLINT\_VECTOR**(3plplot), input)

  A vector that represents (using unsigned 8-bit integers in the range from 0-255) the degree of blue in the color as a continuous function of the integer index of the vector.

- *alpha* (**PLFLT\_VECTOR**(3plplot), input)

  A vector that represents (using PLFLT values in the range from 0.0-1.0 where 0.0 corresponds to completely transparent and 1.0 corresponds to completely opaque) the alpha transparency of the color as a continuous function of the integer index of the vector.

- *ncol1* (**PLINT**(3plplot), input)

  Number of items in the *r*, *g*, *b*, and *alpha* vectors.

## AUTHORS

Many developers (who are credited at http://plplot.org/credits.php) have contributed to PLplot over its long history.

## SEE ALSO

PLplot documentation at http://plplot.org/documentation.php.