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<h2><span class="refentrytitle"><a name="libvips-freq-filt.top_of_page"></a>freq_filt</span></h2>
<p>freq_filt — fourier transforms and frequency-domin filters</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="libvips-freq-filt.stability-level"></a><h2>Stability Level</h2>
Stable, unless otherwise indicated
</div>
<div class="refsynopsisdiv">
<a name="libvips-freq-filt.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include <vips/vips.h>
enum <a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType">VipsMaskType</a>;
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-create-fmask" title="im_create_fmask ()">im_create_fmask</a> (<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><span class="type">int</span> xsize</code></em>,
<em class="parameter"><code><span class="type">int</span> ysize</code></em>,
<em class="parameter"><code><a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType"><span class="type">VipsMaskType</span></a> flag</code></em>,
<em class="parameter"><code>...</code></em>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-disp-ps" title="im_disp_ps ()">im_disp_ps</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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-flt-image-freq" title="im_flt_image_freq ()">im_flt_image_freq</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><a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType"><span class="type">VipsMaskType</span></a> flag</code></em>,
<em class="parameter"><code>...</code></em>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-fractsurf" title="im_fractsurf ()">im_fractsurf</a> (<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><span class="type">int</span> size</code></em>,
<em class="parameter"><code><span class="type">double</span> frd</code></em>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-freqflt" title="im_freqflt ()">im_freqflt</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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-fwfft" title="im_fwfft ()">im_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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-invfft" title="im_invfft ()">im_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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-invfftr" title="im_invfftr ()">im_invfftr</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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-phasecor-fft" title="im_phasecor_fft ()">im_phasecor_fft</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>);
<span class="returnvalue">int</span> <a class="link" href="libvips-freq-filt.html#im-rotquad" title="im_rotquad ()">im_rotquad</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>);
</pre>
</div>
<div class="refsect1">
<a name="libvips-freq-filt.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-freq-filt.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="VipsMaskType"></a><h3>enum VipsMaskType</h3>
<pre class="programlisting">typedef enum {
VIPS_MASK_IDEAL_HIGHPASS = 0,
VIPS_MASK_IDEAL_LOWPASS = 1,
VIPS_MASK_BUTTERWORTH_HIGHPASS = 2,
VIPS_MASK_BUTTERWORTH_LOWPASS = 3,
VIPS_MASK_GAUSS_HIGHPASS = 4,
VIPS_MASK_GAUSS_LOWPASS = 5,
VIPS_MASK_IDEAL_RINGPASS = 6,
VIPS_MASK_IDEAL_RINGREJECT = 7,
VIPS_MASK_BUTTERWORTH_RINGPASS = 8,
VIPS_MASK_BUTTERWORTH_RINGREJECT = 9,
VIPS_MASK_GAUSS_RINGPASS = 10,
VIPS_MASK_GAUSS_RINGREJECT = 11,
VIPS_MASK_IDEAL_BANDPASS = 12,
VIPS_MASK_IDEAL_BANDREJECT = 13,
VIPS_MASK_BUTTERWORTH_BANDPASS = 14,
VIPS_MASK_BUTTERWORTH_BANDREJECT = 15,
VIPS_MASK_GAUSS_BANDPASS = 16,
VIPS_MASK_GAUSS_BANDREJECT = 17,
VIPS_MASK_FRACTAL_FLT = 18
} VipsMaskType;
</pre>
</div>
<hr>
<div class="refsect2">
<a name="im-create-fmask"></a><h3>im_create_fmask ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_create_fmask (<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><span class="type">int</span> xsize</code></em>,
<em class="parameter"><code><span class="type">int</span> ysize</code></em>,
<em class="parameter"><code><a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType"><span class="type">VipsMaskType</span></a> flag</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>
This operation creates a one-band float image of the specified size. The
image must be square, and the sides must be a power of two. The image has
values in the range [0, 1] and is typically used for multiplying against
frequency domain images to filter them.
</p>
<p>
All masks are created with the DC component at (0, 0), so you might want to
rotate the quadrants with <a class="link" href="libvips-freq-filt.html#im-rotquad" title="im_rotquad ()"><code class="function">im_rotquad()</code></a> before viewing. The DC pixel always
has the value 1.0.
</p>
<p>
The value of <em class="parameter"><code>flag</code></em> sets the type pf mask created, and extra parameters set
the exact mask shape. All extra parameters are doubles. This table
summarises the possible values:
</p>
<p>
</p>
<div class="table">
<a name="idp9872192"></a><p class="title"><b>Table 6. Parameters for <a class="link" href="libvips-freq-filt.html#im-create-fmask" title="im_create_fmask ()"><code class="function">im_create_fmask()</code></a></b></p>
<div class="table-contents"><table summary="Parameters for im_create_fmask()" border="1">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th align="left"><a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType"><span class="type">VipsMaskType</span></a></th>
<th align="left">nargs</th>
<th align="left">Parameters (all double)</th>
</tr></thead>
<tbody>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_HIGHPASS</span></td>
<td align="left">1</td>
<td align="left">frequency_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_LOWPASS</span></td>
<td align="left">1</td>
<td align="left">frequency_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_HIGHPASS</span></td>
<td align="left">3</td>
<td align="left">order, frequency_cutoff, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_LOWPASS</span></td>
<td align="left">3</td>
<td align="left">order, frequency_cutoff, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_HIGHPASS</span></td>
<td align="left">2</td>
<td align="left">frequency_cutoff, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_LOWPASS</span></td>
<td align="left">2</td>
<td align="left">frequency_cutoff, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_RINGPASS</span></td>
<td align="left">2</td>
<td align="left">frequency_cutoff, width</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_RINGREJECT</span></td>
<td align="left">2</td>
<td align="left">frequency_cutoff, width</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_RINGPASS</span></td>
<td align="left">4</td>
<td align="left">order, frequency_cutoff, width, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_RINGREJECT</span></td>
<td align="left">4</td>
<td align="left">order, frequency_cutoff, width, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_RINGPASS</span></td>
<td align="left">3</td>
<td align="left">frequency_cutoff, width, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_RINGREJECT</span></td>
<td align="left">3</td>
<td align="left">frequency_cutoff, width, amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_BANDPASS</span></td>
<td align="left">3</td>
<td align="left">frequency_cutoffx, frequency_cutoffy, radius</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_IDEAL_BANDREJECT</span></td>
<td align="left">3</td>
<td align="left">frequency_cutoffx, frequency_cutoffy, radius</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_BANDPASS</span></td>
<td align="left">5</td>
<td align="left">order, frequency_cutoffx, frequency_cutoffy, radius,
amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_BUTTERWORTH_BANDREJECT</span></td>
<td align="left">5</td>
<td align="left">order, frequency_cutoffx, frequency_cutoffy, radius,
amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_BANDPASS</span></td>
<td align="left">4</td>
<td align="left">frequency_cutoffx, frequency_cutoffy, radius,
amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_GAUSS_BANDREJECT</span></td>
<td align="left">4</td>
<td align="left">frequency_cutoffx, frequency_cutoffy, radius,
amplitude_cutoff</td>
</tr>
<tr>
<td align="left"><span class="type">VIPS_MASK_FRACTAL_FLT</span></td>
<td align="left">1</td>
<td align="left">fractal_dimension</td>
</tr>
</tbody>
</table></div>
</div>
<p><br class="table-break">
</p>
<p>
Unless noted below, all parameters are expressed as percentages, scaled to
[0, 1].
</p>
<p>
<span class="emphasis"><em>High-pass, low-pass masks:</em></span> A high pass filter
mask filters the low frequencies while allowing the high frequencies to
get through. The reverse happens with a low pass filter mask.
</p>
<p>
<span class="emphasis"><em>Ring-pass, ring-reject masks:</em></span> A ring filter passes or
rejects a range of frequencies. The range is specified by the
<em class="parameter"><code>frequency_cutoff</code></em> and the <em class="parameter"><code>width</code></em>.
</p>
<p>
<span class="emphasis"><em>Band-pass, band-reject masks:</em></span> These masks are used to
pass or remove spatial frequencies around a given frequency. The position
of the frequency to pass or remove is given by <em class="parameter"><code>frequency_cutoffx</code></em> and
<em class="parameter"><code>frequency_cutoffy</code></em>. The size of the region around the point is given by
<em class="parameter"><code>radius</code></em>.
</p>
<p>
<span class="emphasis"><em>Ideal filters:</em></span> These filters pass or reject
frequencies with a sharp cutoff at the transition.
</p>
<p>
<span class="emphasis"><em>Butterworth filters:</em></span> These filters use a Butterworth
function to separate the frequencies (see Gonzalez and Wintz, Digital
Image Processing, 1987). The shape of the curve is controlled by <em class="parameter"><code>order</code></em>:
higher values give a sharper transition.
</p>
<p>
<span class="emphasis"><em>Gaussian filters:</em></span> These filters have a smooth Gaussian
shape, controlled by <em class="parameter"><code>amplitude_cutoff</code></em>.
</p>
<p>
<span class="emphasis"><em>VIPS_MASK_FRACTAL_FLT:</em></span> This mask is handy for
filtering images of gaussian noise in order to create surfaces of a given
fractal dimension. <em class="parameter"><code>fractal_dimension</code></em> should be between 2 and 3.
</p>
<p>
See also: <a class="link" href="libvips-freq-filt.html#im-flt-image-freq" title="im_flt_image_freq ()"><code class="function">im_flt_image_freq()</code></a>, <a class="link" href="libvips-freq-filt.html#im-rotquad" title="im_rotquad ()"><code class="function">im_rotquad()</code></a>,
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>out</code></em> :</span></p></td>
<td>image to write to</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>xsize</code></em> :</span></p></td>
<td>image size</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>ysize</code></em> :</span></p></td>
<td>image size</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>flag</code></em> :</span></p></td>
<td>mask type</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>Varargs</code></em> :</span></p></td>
<td>mask parameters</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="im-disp-ps"></a><h3>im_disp_ps ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_disp_ps (<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>);</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#im-scaleps" title="im_scaleps ()"><code class="function">im_scaleps()</code></a>, and <a class="link" href="libvips-freq-filt.html#im-rotquad" title="im_rotquad ()"><code class="function">im_rotquad()</code></a>.
</p>
<p>
See also: <a class="link" href="libvips-conversion.html#im-scaleps" title="im_scaleps ()"><code class="function">im_scaleps()</code></a>, <a class="link" href="libvips-freq-filt.html#im-rotquad" title="im_rotquad ()"><code class="function">im_rotquad()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-flt-image-freq"></a><h3>im_flt_image_freq ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_flt_image_freq (<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><a class="link" href="libvips-freq-filt.html#VipsMaskType" title="enum VipsMaskType"><span class="type">VipsMaskType</span></a> flag</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>
Creates a mask (see <a class="link" href="libvips-freq-filt.html#im-create-fmask" title="im_create_fmask ()"><code class="function">im_create_fmask()</code></a>) and filters an image with it (see
<a class="link" href="libvips-freq-filt.html#im-freqflt" title="im_freqflt ()"><code class="function">im_freqflt()</code></a>).
</p>
<p>
See also: <a class="link" href="libvips-freq-filt.html#im-create-fmask" title="im_create_fmask ()"><code class="function">im_create_fmask()</code></a>, <a class="link" href="libvips-freq-filt.html#im-freqflt" title="im_freqflt ()"><code class="function">im_freqflt()</code></a>,
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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>flag</code></em> :</span></p></td>
<td>mask type</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>Varargs</code></em> :</span></p></td>
<td>mask parameters</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="im-fractsurf"></a><h3>im_fractsurf ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_fractsurf (<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><span class="type">int</span> size</code></em>,
<em class="parameter"><code><span class="type">double</span> frd</code></em>);</pre>
<p>
Generate an image of size <em class="parameter"><code>size</code></em> and fractal dimension <em class="parameter"><code>frd</code></em>. The dimension
should be between 2 and 3.
</p>
<p>
See also: <a class="link" href="libvips-conversion.html#im-gaussnoise" title="im_gaussnoise ()"><code class="function">im_gaussnoise()</code></a>, <a class="link" href="libvips-freq-filt.html#im-flt-image-freq" title="im_flt_image_freq ()"><code class="function">im_flt_image_freq()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<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>size</code></em> :</span></p></td>
<td>size of image to generate</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>frd</code></em> :</span></p></td>
<td>fractal dimension</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="im-freqflt"></a><h3>im_freqflt ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_freqflt (<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>);</pre>
<p>
Filter an image in Fourier space.
</p>
<p>
<em class="parameter"><code>in</code></em> is transformed to Fourier space, multipled with the mask image, 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-freq-filt.html#im-invfftr" title="im_invfftr ()"><code class="function">im_invfftr()</code></a>, <a class="link" href="libvips-freq-filt.html#im-create-fmask" title="im_create_fmask ()"><code class="function">im_create_fmask()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-fwfft"></a><h3>im_fwfft ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_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>);</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-freq-filt.html#im-invfft" title="im_invfft ()"><code class="function">im_invfft()</code></a>, <a class="link" href="libvips-freq-filt.html#im-disp-ps" title="im_disp_ps ()"><code class="function">im_disp_ps()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-invfft"></a><h3>im_invfft ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_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>);</pre>
<p>
Transform an image from Fourier space to real space. The result is complex.
If you are OK with a real result, use <a class="link" href="libvips-freq-filt.html#im-invfftr" title="im_invfftr ()"><code class="function">im_invfftr()</code></a> instead, it's quicker.
</p>
<p>
VIPS uses the fftw3 or fftw2 Fourier transform libraries if possible. If
they were not available when VIPS was built, it falls back to it's own
FFT functions which are slow and only work for square images whose sides
are a power of two.
</p>
<p>
See also: <a class="link" href="libvips-freq-filt.html#im-invfftr" title="im_invfftr ()"><code class="function">im_invfftr()</code></a>, <a class="link" href="libvips-freq-filt.html#im-fwfft" title="im_fwfft ()"><code class="function">im_fwfft()</code></a>, <a class="link" href="libvips-freq-filt.html#im-disp-ps" title="im_disp_ps ()"><code class="function">im_disp_ps()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-invfftr"></a><h3>im_invfftr ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_invfftr (<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>);</pre>
<p>
Transform an image from Fourier space to real space, giving a real result.
This is faster than <a class="link" href="libvips-freq-filt.html#im-invfft" title="im_invfft ()"><code class="function">im_invfft()</code></a>, which gives a complex result.
</p>
<p>
VIPS uses the fftw3 or fftw2 Fourier transform libraries if possible. If
they were not available when VIPS was built, it falls back to it's own
FFT functions which are slow and only work for square images whose sides
are a power of two.
</p>
<p>
See also: <a class="link" href="libvips-freq-filt.html#im-invfft" title="im_invfft ()"><code class="function">im_invfft()</code></a>, <a class="link" href="libvips-freq-filt.html#im-fwfft" title="im_fwfft ()"><code class="function">im_fwfft()</code></a>, <a class="link" href="libvips-freq-filt.html#im-disp-ps" title="im_disp_ps ()"><code class="function">im_disp_ps()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-phasecor-fft"></a><h3>im_phasecor_fft ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_phasecor_fft (<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>);</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-freq-filt.html#im-fwfft" title="im_fwfft ()"><code class="function">im_fwfft()</code></a>, <a class="link" href="libvips-arithmetic.html#im-cross-phase" title="im_cross_phase ()"><code class="function">im_cross_phase()</code></a>,
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><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="im-rotquad"></a><h3>im_rotquad ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> im_rotquad (<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>);</pre>
<p>
Rotate the quadrants of the image so that the point that was at the
top-left is now in the centre. Handy for moving Fourier images to optical
space.
</p>
<p>
See also: <a class="link" href="libvips-conversion.html#im-wrap" title="im_wrap ()"><code class="function">im_wrap()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<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"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, -1 on error</td>
</tr>
</tbody>
</table></div>
</div>
</div>
<div class="refsect1">
<a name="libvips-freq-filt.see-also"></a><h2>See Also</h2>
image
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