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<table width="100%" summary="page for colorRamp {grDevices}"><tr><td>colorRamp {grDevices}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Color interpolation</h2>

<h3>Description</h3>

<p>These functions return functions that interpolate a set of given
colors to create new color palettes (like <code><a href="palettes.html">topo.colors</a></code>) and
color ramps, functions that map the interval <i>[0, 1]</i> to colors
(like <code><a href="gray.html">grey</a></code>).
</p>

<h3>Usage</h3>

<pre>
colorRamp(colors, bias = 1, space = c("rgb", "Lab"),
          interpolate = c("linear", "spline"), alpha = FALSE)
colorRampPalette(colors, ...)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>colors</code></td>
<td>
<p>colors to interpolate; must be a valid argument to
<code><a href="col2rgb.html">col2rgb</a>()</code>.</p>
</td></tr>
<tr valign="top"><td><code>bias</code></td>
<td>
<p>a positive number.  Higher values give more widely spaced
colors at the high end.</p>
</td></tr>
<tr valign="top"><td><code>space</code></td>
<td>
<p>a character string; interpolation in RGB or CIE Lab
color spaces.</p>
</td></tr>
<tr valign="top"><td><code>interpolate</code></td>
<td>
<p>use spline or linear interpolation.</p>
</td></tr>
<tr valign="top"><td><code>alpha</code></td>
<td>
<p>logical: should alpha channel (opacity) values be
returned?   It is an error to give a true value if
<code>space</code> is specified.</p>
</td></tr>
<tr valign="top"><td><code>...</code></td>
<td>
<p>arguments to pass to <code>colorRamp</code>.</p>
</td></tr>
</table>

<h3>Details</h3>

<p>The CIE Lab color space is approximately perceptually uniform, and so
gives smoother and more uniform color ramps. On the other hand,
palettes that vary from one hue to another via white may have a more
symmetrical appearance in RGB space.
</p>
<p>The conversion formulas in this function do not appear to be
completely accurate and the color ramp may not reach the extreme
values in Lab space.  Future changes in the <span style="font-family: Courier New, Courier; color: #666666;"><b>R</b></span> color model may change
the colors produced with <code>space = "Lab"</code>.
</p>

<h3>Value</h3>

<p><code>colorRamp</code> returns a <code><a href="../../base/html/function.html">function</a></code> with argument a
vector of values between 0 and 1 that are mapped to a numeric matrix
of RGB color values with one row per color and 3 or 4 columns.
</p>
<p><code>colorRampPalette</code> returns a function that takes an integer
argument (the required number of colors) and returns a character
vector of colors (see <code><a href="rgb.html">rgb</a></code>) interpolating the given sequence
(similar to <code><a href="palettes.html">heat.colors</a></code> or <code><a href="palettes.html">terrain.colors</a></code>).
</p>

<p>Good starting points for interpolation are the &ldquo;sequential&rdquo;
and &ldquo;diverging&rdquo; ColorBrewer palettes in the
<a href="https://CRAN.R-project.org/package=RColorBrewer"><span class="pkg">RColorBrewer</span></a> package.
</p>
<p><code><a href="../../stats/html/splinefun.html">splinefun</a></code> or <code><a href="../../stats/html/approxfun.html">approxfun</a></code> are used for
interpolation.
</p>

<h3>Examples</h3>

<pre>
## Both return a *function* :
colorRamp(c("red", "green"))( (0:4)/4 ) ## (x) , x in [0,1]
colorRampPalette(c("blue", "red"))( 4 ) ## (n)
## a ramp in opacity of blue values
colorRampPalette(c(rgb(0,0,1,1), rgb(0,0,1,0)), alpha = TRUE)(8)

require(graphics)

## Here space="rgb" gives palettes that vary only in saturation,
## as intended.
## With space="Lab" the steps are more uniform, but the hues
## are slightly purple.
filled.contour(volcano,
               color.palette =
                   colorRampPalette(c("red", "white", "blue")),
               asp = 1)
filled.contour(volcano,
               color.palette =
                   colorRampPalette(c("red", "white", "blue"),
                                    space = "Lab"),
               asp = 1)

## Interpolating a 'sequential' ColorBrewer palette
YlOrBr &lt;- c("#FFFFD4", "#FED98E", "#FE9929", "#D95F0E", "#993404")
filled.contour(volcano,
               color.palette = colorRampPalette(YlOrBr, space = "Lab"),
               asp = 1)
filled.contour(volcano,
               color.palette = colorRampPalette(YlOrBr, space = "Lab",
                                                bias = 0.5),
               asp = 1)

## 'jet.colors' is "as in Matlab"
## (and hurting the eyes by over-saturation)
jet.colors &lt;-
  colorRampPalette(c("#00007F", "blue", "#007FFF", "cyan",
                     "#7FFF7F", "yellow", "#FF7F00", "red", "#7F0000"))
filled.contour(volcano, color = jet.colors, asp = 1)

## space="Lab" helps when colors don't form a natural sequence
m &lt;- outer(1:20,1:20,function(x,y) sin(sqrt(x*y)/3))
rgb.palette &lt;- colorRampPalette(c("red", "orange", "blue"),
                                space = "rgb")
Lab.palette &lt;- colorRampPalette(c("red", "orange", "blue"),
                                space = "Lab")
filled.contour(m, col = rgb.palette(20))
filled.contour(m, col = Lab.palette(20))
</pre>

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