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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>VIPS Reference Manual: freqfilt</title>
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                  <a href="#libvips-freqfilt.description" class="shortcut">Description</a></span><span id="nav_hierarchy"> <span class="dim">|</span> 
                  <a href="#libvips-freqfilt.object-hierarchy" class="shortcut">Object Hierarchy</a></span>
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<div class="refentry">
<a name="libvips-freqfilt"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="libvips-freqfilt.top_of_page"></a>freqfilt</span></h2>
<p>freqfilt — fourier transforms and frequency-domin filters</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="libvips-freqfilt.stability-level"></a><h2>Stability Level</h2>
Stable, unless otherwise indicated
</div>
<div class="refsect1">
<a name="libvips-freqfilt.functions"></a><h2>Functions</h2>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="functions_return">
<col class="functions_name">
</colgroup>
<tbody>
<tr>
<td class="function_type">
<span class="returnvalue">int</span>
</td>
<td class="function_name">
<a class="link" href="libvips-freqfilt.html#vips-fwfft" title="vips_fwfft ()">vips_fwfft</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">int</span>
</td>
<td class="function_name">
<a class="link" href="libvips-freqfilt.html#vips-invfft" title="vips_invfft ()">vips_invfft</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">int</span>
</td>
<td class="function_name">
<a class="link" href="libvips-freqfilt.html#vips-freqmult" title="vips_freqmult ()">vips_freqmult</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">int</span>
</td>
<td class="function_name">
<a class="link" href="libvips-freqfilt.html#vips-spectrum" title="vips_spectrum ()">vips_spectrum</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<span class="returnvalue">int</span>
</td>
<td class="function_name">
<a class="link" href="libvips-freqfilt.html#vips-phasecor" title="vips_phasecor ()">vips_phasecor</a> <span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.object-hierarchy"></a><h2>Object Hierarchy</h2>
<pre class="screen">
</pre>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.includes"></a><h2>Includes</h2>
<pre class="synopsis">#include &lt;vips/vips.h&gt;
</pre>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.description"></a><h2>Description</h2>
<p>To and from Fourier space, filter in Fourier space, convert Fourier-space
images to a displayable form.</p>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.functions_details"></a><h2>Functions</h2>
<div class="refsect2">
<a name="vips-fwfft"></a><h3>vips_fwfft ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_fwfft (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in</code></em>,
            <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> **out</code></em>,
            <em class="parameter"><code>...</code></em>);</pre>
<p>Transform an image to Fourier space.</p>
<p>VIPS uses the fftw Fourier Transform library. If this library was not
available when VIPS was configured, these functions will fail.</p>
<p>See also: <a class="link" href="libvips-freqfilt.html#vips-invfft" title="vips_invfft ()"><code class="function">vips_invfft()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.7.8.2.7"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>in</p></td>
<td class="parameter_description"><p>input image </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>...</p></td>
<td class="parameter_description"><p><a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.4.7.8.2.8"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-invfft"></a><h3>vips_invfft ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_invfft (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in</code></em>,
             <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> **out</code></em>,
             <em class="parameter"><code>...</code></em>);</pre>
<p>Optional arguments:</p>
<p><em class="parameter"><code>real</code></em>
: only output the real part</p>
<p>Transform an image from Fourier space to real space. The result is complex.
If you are OK with a real result, set <em class="parameter"><code>real</code></em>
, it's quicker.</p>
<p>VIPS uses the fftw Fourier Transform library. If this library was not
available when VIPS was configured, these functions will fail.</p>
<p>See also: <a class="link" href="libvips-freqfilt.html#vips-fwfft" title="vips_fwfft ()"><code class="function">vips_fwfft()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.7.8.3.9"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>in</p></td>
<td class="parameter_description"><p>input image </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>...</p></td>
<td class="parameter_description"><p><a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.4.7.8.3.10"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-freqmult"></a><h3>vips_freqmult ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_freqmult (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in</code></em>,
               <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *mask</code></em>,
               <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> **out</code></em>,
               <em class="parameter"><code>...</code></em>);</pre>
<p>Multiply <em class="parameter"><code>in</code></em>
 by <em class="parameter"><code>mask</code></em>
 in Fourier space.</p>
<p><em class="parameter"><code>in</code></em>
 is transformed to Fourier space, multipled with <em class="parameter"><code>mask</code></em>
, then
transformed back to real space. If <em class="parameter"><code>in</code></em>
 is already a complex image, just
multiply then inverse transform.</p>
<p>See also: <a class="link" href="libvips-freqfilt.html#vips-invfft" title="vips_invfft ()"><code class="function">vips_invfft()</code></a>, <a class="link" href="libvips-create.html#vips-mask-ideal" title="vips_mask_ideal ()"><code class="function">vips_mask_ideal()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.7.8.4.7"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>in</p></td>
<td class="parameter_description"><p>input image </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>mask</p></td>
<td class="parameter_description"><p>mask image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>...</p></td>
<td class="parameter_description"><p><a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.4.7.8.4.8"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-spectrum"></a><h3>vips_spectrum ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_spectrum (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in</code></em>,
               <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> **out</code></em>,
               <em class="parameter"><code>...</code></em>);</pre>
<p>Make a displayable (ie. 8-bit unsigned int) power spectrum.</p>
<p>If <em class="parameter"><code>in</code></em>
 is non-complex, it is transformed to Fourier space. Then the
absolute value is passed through <a class="link" href="libvips-conversion.html#vips-scale" title="vips_scale ()"><code class="function">vips_scale()</code></a> in log mode, and <a class="link" href="libvips-conversion.html#vips-wrap" title="vips_wrap ()"><code class="function">vips_wrap()</code></a>.</p>
<p>See also: <a class="link" href="libvips-freqfilt.html#vips-fwfft" title="vips_fwfft ()"><code class="function">vips_fwfft()</code></a>, <a class="link" href="libvips-conversion.html#vips-scale" title="vips_scale ()"><code class="function">vips_scale()</code></a>, <a class="link" href="libvips-conversion.html#vips-wrap" title="vips_wrap ()"><code class="function">vips_wrap()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.7.8.5.7"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>in</p></td>
<td class="parameter_description"><p>input image </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>...</p></td>
<td class="parameter_description"><p><a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.4.7.8.5.8"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-phasecor"></a><h3>vips_phasecor ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_phasecor (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in1</code></em>,
               <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *in2</code></em>,
               <em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> **out</code></em>,
               <em class="parameter"><code>...</code></em>);</pre>
<p>Convert the two input images to Fourier space, calculate phase-correlation,
back to real space.</p>
<p>See also: <a class="link" href="libvips-freqfilt.html#vips-fwfft" title="vips_fwfft ()"><code class="function">vips_fwfft()</code></a>, <a class="link" href="libvips-arithmetic.html#vips-cross-phase" title="vips_cross_phase ()"><code class="function">vips_cross_phase()</code></a>,</p>
<div class="refsect3">
<a name="id-1.4.7.8.6.6"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>in1</p></td>
<td class="parameter_description"><p>first input image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>in2</p></td>
<td class="parameter_description"><p>second input image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output image</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>...</p></td>
<td class="parameter_description"><p><a href="http://library.gnome.org/devel/glib/unstable/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.4.7.8.6.7"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</p>
<p></p>
</div>
</div>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.other_details"></a><h2>Types and Values</h2>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.see-also"></a><h2>See Also</h2>
image
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