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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>freqfilt: VIPS Reference Manual</title>
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                  <a href="#libvips-freqfilt.description" class="shortcut">Description</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>
<acronym title="The intention of a Stable interface is to enable arbitrary third parties to
develop applications to these interfaces, release them, and have confidence that
they will run on all minor releases of the product (after the one in which the
interface was introduced, and within the same major release). Even at a major
release, incompatible changes are expected to be rare, and to have strong
justifications.
"><span class="acronym">Stable</span></acronym>, unless otherwise indicated
</div>
<div class="refsect1">
<a name="libvips-freqfilt.functions"></a><h2>Functions</h2>
<div class="informaltable"><table class="informaltable" 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.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="vips-fwfft.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" 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><code class="literal">NULL</code>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="vips-fwfft.returns"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</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>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><em class="parameter"><code>real</code></em>
: only output the real part</p></li></ul></div>
<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="vips-invfft.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" 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><code class="literal">NULL</code>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="vips-invfft.returns"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</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="vips-freqmult.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" 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><code class="literal">NULL</code>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="vips-freqmult.returns"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</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="vips-spectrum.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" 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><code class="literal">NULL</code>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="vips-spectrum.returns"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</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="vips-phasecor.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" 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><code class="literal">NULL</code>-terminated list of optional named arguments</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="vips-phasecor.returns"></a><h4>Returns</h4>
<p> 0 on success, -1 on error.</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>
<a class="link" href="VipsImage.html" title="VipsImage">image</a>
</div>
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