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<title>GNU Octave: Color Conversion</title>

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<a name="Color-Conversion"></a>
<div class="header">
<p>
Previous: <a href="Plotting-on-top-of-Images.html#Plotting-on-top-of-Images" accesskey="p" rel="prev">Plotting on top of Images</a>, Up: <a href="Image-Processing.html#Image-Processing" accesskey="u" rel="up">Image Processing</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Color-Conversion-1"></a>
<h3 class="section">32.5 Color Conversion</h3>

<p>Octave supports conversion from the RGB color system to NTSC and HSV
and vice versa.
</p>
<a name="XREFrgb2hsv"></a><dl>
<dt><a name="index-rgb2hsv"></a>Function File: <em><var>hsv_map</var> =</em> <strong>rgb2hsv</strong> <em>(<var>rgb</var>)</em></dt>
<dt><a name="index-rgb2hsv-1"></a>Function File: <em><var>hsv_map</var> =</em> <strong>rgb2hsv</strong> <em>(<var>rgb</var>)</em></dt>
<dd><p>Transform a colormap or image from red-green-blue (RGB) space to
hue-saturation-value (HSV) space.
</p>
<p>A color in the RGB space consists of red, green, and blue intensities.
</p>
<p>A color in HSV space is represented by hue, saturation, and value
(brightness) levels.  Value gives the amount of light in the color.  Hue
describes the dominant wavelength.  Saturation is the amount of hue mixed
into the color.
</p>
<p><strong>See also:</strong> <a href="#XREFhsv2rgb">hsv2rgb</a>, <a href="Representing-Images.html#XREFrgb2ind">rgb2ind</a>, <a href="#XREFrgb2ntsc">rgb2ntsc</a>.
</p></dd></dl>


<a name="XREFhsv2rgb"></a><dl>
<dt><a name="index-hsv2rgb"></a>Function File: <em><var>rgb_map</var> =</em> <strong>hsv2rgb</strong> <em>(<var>hsv_map</var>)</em></dt>
<dt><a name="index-hsv2rgb-1"></a>Function File: <em><var>rgb_img</var> =</em> <strong>hsv2rgb</strong> <em>(<var>hsv_img</var>)</em></dt>
<dd><p>Transform a colormap or image from hue-saturation-value (HSV) space to
red-green-blue (RGB) space.
</p>
<p>A color in HSV space is represented by hue, saturation and value
(brightness) levels.  Value gives the amount of light in the color.  Hue
describes the dominant wavelength.  Saturation is the amount of hue mixed
into the color.
</p>
<p>A color in the RGB space consists of red, green, and blue intensities.
</p>
<p><strong>See also:</strong> <a href="#XREFrgb2hsv">rgb2hsv</a>, <a href="Representing-Images.html#XREFind2rgb">ind2rgb</a>, <a href="#XREFntsc2rgb">ntsc2rgb</a>.
</p></dd></dl>


<a name="XREFrgb2ntsc"></a><dl>
<dt><a name="index-rgb2ntsc"></a>Function File: <em><var>yiq_map</var> =</em> <strong>rgb2ntsc</strong> <em>(<var>rgb_map</var>)</em></dt>
<dt><a name="index-rgb2ntsc-1"></a>Function File: <em><var>yiq_img</var> =</em> <strong>rgb2ntsc</strong> <em>(<var>rgb_img</var>)</em></dt>
<dd><p>Transform a colormap or image from red-green-blue (RGB) color space to
luminance-chrominance (NTSC) space.  The input may be of class uint8,
uint16, single, or double.  The output is of class double.
</p>
<p>Implementation Note:
The reference matrix for the transformation is
</p>
<div class="example">
<pre class="example">/Y\     0.299  0.587  0.114  /R\
|I|  =  0.596 -0.274 -0.322  |G|
\Q/     0.211 -0.523  0.312  \B/
</pre></div>

<p>as documented in <a href="http://en.wikipedia.org/wiki/YIQ">http://en.wikipedia.org/wiki/YIQ</a> and truncated to 3
significant figures.  Note: The FCC version of NTSC uses only 2 significant
digits and is slightly different.
</p>
<p><strong>See also:</strong> <a href="#XREFntsc2rgb">ntsc2rgb</a>, <a href="#XREFrgb2hsv">rgb2hsv</a>, <a href="Representing-Images.html#XREFrgb2ind">rgb2ind</a>.
</p></dd></dl>


<a name="XREFntsc2rgb"></a><dl>
<dt><a name="index-ntsc2rgb"></a>Function File: <em><var>rgb_map</var> =</em> <strong>ntsc2rgb</strong> <em>(<var>yiq_map</var>)</em></dt>
<dt><a name="index-ntsc2rgb-1"></a>Function File: <em><var>rgb_img</var> =</em> <strong>ntsc2rgb</strong> <em>(<var>yiq_img</var>)</em></dt>
<dd><p>Transform a colormap or image from luminance-chrominance (NTSC) space to
red-green-blue (RGB) color space.
</p>
<p>Implementation Note:
The conversion matrix is chosen to be the inverse of the matrix used for
rgb2ntsc such that
</p>
<div class="example">
<pre class="example">x == ntsc2rgb (rgb2ntsc (x))
</pre></div>

<p><small>MATLAB</small> uses a slightly different matrix where rounding means the
equality above does not hold.
</p>
<p><strong>See also:</strong> <a href="#XREFrgb2ntsc">rgb2ntsc</a>, <a href="#XREFhsv2rgb">hsv2rgb</a>, <a href="Representing-Images.html#XREFind2rgb">ind2rgb</a>.
</p></dd></dl>






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<p>
Previous: <a href="Plotting-on-top-of-Images.html#Plotting-on-top-of-Images" accesskey="p" rel="prev">Plotting on top of Images</a>, Up: <a href="Image-Processing.html#Image-Processing" accesskey="u" rel="up">Image Processing</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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