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<a href="#libvips-freqfilt.description" class="shortcut">Description</a>
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<h2><span class="refentrytitle"><a name="libvips-freqfilt.top_of_page"></a>freqfilt</span></h2>
<p>freqfilt</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<a name="libvips-freqfilt.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis"><span class="returnvalue">int</span> <a class="link" href="libvips-freqfilt.html#vips-fwfft" title="vips_fwfft ()">vips_fwfft</a> (<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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freqfilt.html#vips-invfft" title="vips_invfft ()">vips_invfft</a> (<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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freqfilt.html#vips-freqmult" title="vips_freqmult ()">vips_freqmult</a> (<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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freqfilt.html#vips-spectrum" title="vips_spectrum ()">vips_spectrum</a> (<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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freqfilt.html#vips-phasecor" title="vips_phasecor ()">vips_phasecor</a> (<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>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.description"></a><h2>Description</h2>
<p>
</p>
</div>
<div class="refsect1">
<a name="libvips-freqfilt.details"></a><h2>Details</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="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>in</code></em> :</span></p></td>
<td>input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>output image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
<td>
<code class="literal">NULL</code>-terminated list of optional named arguments</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error.</td>
</tr>
</tbody>
</table></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="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>in</code></em> :</span></p></td>
<td>input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>output image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
<td>
<code class="literal">NULL</code>-terminated list of optional named arguments</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error.</td>
</tr>
</tbody>
</table></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="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>in</code></em> :</span></p></td>
<td>input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>mask</code></em> :</span></p></td>
<td>mask image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>output image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
<td>
<code class="literal">NULL</code>-terminated list of optional named arguments</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error.</td>
</tr>
</tbody>
</table></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="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>in</code></em> :</span></p></td>
<td>input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>output image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
<td>
<code class="literal">NULL</code>-terminated list of optional named arguments</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error.</td>
</tr>
</tbody>
</table></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="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>in1</code></em> :</span></p></td>
<td>first input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>in2</code></em> :</span></p></td>
<td>second input image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>output image</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>...</code></em> :</span></p></td>
<td>
<code class="literal">NULL</code>-terminated list of optional named arguments</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error.</td>
</tr>
</tbody>
</table></div>
</div>
</div>
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