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<!DOCTYPE html>
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<title>dip::DFT class | DIPlib | a library for quantitative image analysis</title>
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<a href="https://diplib.org"><img src="DIPlib_logo.svg" alt="" />DIPlib</a><span class="m-breadcrumb">┃</span><a href="index.html" class="m-thin">a library for quantitative image analysis</a><span class="m-breadcrumb">┃</span><a href="https://github.com/DIPlib/diplib/releases/tag/3.5.2" class="m-thin">version 3.5.2</a> </span>
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<h1>
<div class="m-doc-include m-thin m-right-m m-text-right">
<a href="transform_lowlevel.html" class="m-doc">Low-level transform support</a> module<br/><span class="m-code m-thin">#include <a href="file--diplib--dft-h.html">"diplib/dft.h"</a></span> </div>
<div class="m-doc-template"><span class="m-doc-wrap-bumper">template<</span><span class="m-doc-wrap">typename T></span></div>
<span class="m-breadcrumb"><a href="dip.html">dip</a>::<wbr/></span>DFT <span class="m-thin">class</span> </h1>
<p>An object that encapsulates the Discrete Fourier Transform (DFT).</p>
<div class="m-block m-default">
<h3>Contents</h3>
<ul>
<li>
Reference
<ul>
<li><a href="#typeless-methods">Constructors, destructors, assignment and conversion operators</a></li>
<li><a href="#function-members">Functions</a></li>
</ul>
</li>
</ul>
</div>
<p>Usage:</p>
<div class="m-code"><pre><span></span><span class="n">DFT</span><span class="w"> </span><span class="nf">dft</span><span class="p">(</span><span class="w"> </span><span class="n">size</span><span class="p">,</span><span class="w"> </span><span class="n">inverse</span><span class="w"> </span><span class="p">);</span><span class="w"> </span><span class="c1">// creates the object with all the data ready to start running DFTs.</span>
<span class="n">dft</span><span class="p">.</span><span class="n">Apply</span><span class="p">(</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="p">);</span><span class="w"> </span><span class="c1">// computes a DFT, repeat as necessary</span>
<span class="n">dft</span><span class="p">.</span><span class="n">Initialize</span><span class="p">(</span><span class="w"> </span><span class="n">size2</span><span class="p">,</span><span class="w"> </span><span class="n">inverse</span><span class="w"> </span><span class="p">);</span><span class="w"> </span><span class="c1">// changes the options for the new size / direction</span>
<span class="n">dft</span><span class="p">.</span><span class="n">Apply</span><span class="p">(</span><span class="w"> </span><span class="n">in</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="p">);</span><span class="w"> </span><span class="c1">// computes a different DFT, repeat as necessary</span>
</pre></div>
<p>The template can be instantiated for <code>T = float</code> or <code>T = double</code>. Linker errors will result for other types.</p>
<aside class="m-note m-info">
<h4>Attention</h4>
<p>The object should not be created, copied or destroyed in multiple threads at the same time.</p>
</aside>
<p>The DFT is computed using either PocketFFT or FFTW, depending on compile-time configuration (see the
<code>DIP_ENABLE_FFTW</code> CMake configuration option).</p>
<p>When using FFTW, <a href="transform_lowlevel.html#dip-maximumDFTSize"><code>dip::maximumDFTSize</code></a> is the largest length of the transform. PocketFFT does not have this limit.</p>
<section id="typeless-methods">
<h2>Constructors, destructors, assignment and conversion operators</h2>
<dl class="m-doc">
<dt id="dip-DFT-T-DFT">
<span class="m-doc-wrap-bumper"><a href="#dip-DFT-T-DFT" class="m-doc-self">DFT</a>(</span><span class="m-doc-wrap">) <span class="m-label m-flat m-info">defaulted</span></span>
</dt>
<dd>A default-initialized <code>DFT</code> object is useless. Call <code>Initialize</code> to make it useful.</dd>
<dt id="dip-DFT-T-DFT-dip-uint--bool--Option-DFTOptions-">
<span class="m-doc-wrap-bumper"><a href="#dip-DFT-T-DFT-dip-uint--bool--Option-DFTOptions-" class="m-doc-self">DFT</a>(</span><span class="m-doc-wrap"><a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a> size,
bool inverse,
<a href="transform_lowlevel.html#dip-Option-DFTOptions" class="m-doc">dip::Option::DFTOptions</a> options = {})</span>
</dt>
<dd>Construct a <code>DFT</code> object, see <a href="dip-DFT-T.html#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-"><code>dip::DFT::Initialize</code></a> for the meaning of the parameters.
Note that this is not a trivial operation. Not thread safe.</dd>
</dl>
</section>
<section id="function-members">
<h2>Functions</h2>
<dl class="m-doc">
<dt>
<span class="m-doc-wrap-bumper">void <a href="#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-" class="m-doc">Initialize</a>(</span><span class="m-doc-wrap"><a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a> size,
bool inverse,
<a href="transform_lowlevel.html#dip-Option-DFTOptions" class="m-doc">dip::Option::DFTOptions</a> options = {})</span>
</dt>
<dd>Re-configure a <code>DFT</code> object to the given transform size and direction. <a href="#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-">more...</a></dd>
<dt>
<span class="m-doc-wrap-bumper">void <a href="#dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C" class="m-doc">Apply</a>(</span><span class="m-doc-wrap">std::complex<T>* source,
std::complex<T>* destination,
T scale) const</span>
</dt>
<dd>Apply the transform that the <code>DFT</code> object is configured for. <a href="#dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C">more...</a></dd>
<dt id="dip-DFT-T-IsInverse-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-DFT-T-IsInverse-C" class="m-doc-self">IsInverse</a>(</span><span class="m-doc-wrap">) const -> bool</span>
</dt>
<dd>Returns <code>true</code> if this represents an inverse transform, <code>false</code> for a forward transform.</dd>
<dt id="dip-DFT-T-IsInplace-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-DFT-T-IsInplace-C" class="m-doc-self">IsInplace</a>(</span><span class="m-doc-wrap">) const -> bool</span>
</dt>
<dd>Returns whether the transform is configured to work in place or not. Not meaningful when using PocketFFT.</dd>
<dt id="dip-DFT-T-IsAligned-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-DFT-T-IsAligned-C" class="m-doc-self">IsAligned</a>(</span><span class="m-doc-wrap">) const -> bool</span>
</dt>
<dd>Returns whether the transform is configured to work on aligned buffers or not. Not meaningful when using PocketFFT.</dd>
<dt id="dip-DFT-T-TransformSize-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-DFT-T-TransformSize-C" class="m-doc-self">TransformSize</a>(</span><span class="m-doc-wrap">) const -> <a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a></span>
</dt>
<dd>Returns the size that the transform is configured for.</dd>
<dt id="dip-DFT-T-BufferSize-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-DFT-T-BufferSize-C" class="m-doc-self">BufferSize</a>(</span><span class="m-doc-wrap">) const -> <a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a> <span class="m-label m-danger">deprecated</span></span>
</dt>
<dd>Returns the size of the buffer expected by <code>Apply</code>.</dd>
<dt id="dip-DFT-T-Destroy">
<span class="m-doc-wrap-bumper">void <a href="#dip-DFT-T-Destroy" class="m-doc-self">Destroy</a>(</span><span class="m-doc-wrap">) <span class="m-label m-flat m-danger">private</span></span>
</dt>
<dd>Frees memory</dd>
</dl>
</section>
<section>
<h2>Function documentation</h2>
<section class="m-doc-details" id="dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-"><div>
<h3>
<div class="m-doc-template">
template<typename T>
</div>
<span class="m-doc-wrap-bumper">void
</span><span class="m-doc-wrap"><span class="m-doc-wrap-bumper"><a href="#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-" class="m-doc-self">Initialize</a>(</span><span class="m-doc-wrap"><a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a> size,
bool inverse,
<a href="transform_lowlevel.html#dip-Option-DFTOptions" class="m-doc">dip::Option::DFTOptions</a> options = {})</span></span>
</h3>
<p>Re-configure a <code>DFT</code> object to the given transform size and direction.</p>
<p><code>size</code> is the size of the transform. The two pointers passed to <a href="dip-DFT-T.html#dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C"><code>dip::DFT::Apply</code></a> are expected to point at
buffers with this length. If <code>inverse</code> is <code>true</code>, an inverse transform will be computed.</p>
<p><code>options</code> determines some properties for the algorithm that will compute the DFT.</p>
<ul>
<li><a href="transform_lowlevel.html#dip-Option-DFTOption-InPlace"><code>dip::Option::DFTOption::InPlace</code></a> means the input and output pointers passed to <a href="dip-DFT-T.html#dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C"><code>dip::DFT::Apply</code></a> must be the same.</li>
<li><a href="transform_lowlevel.html#dip-Option-DFTOption-TrashInput"><code>dip::Option::DFTOption::TrashInput</code></a> means that the algorithm is free to overwrite the input array.
Ignored when working in place.</li>
<li><a href="transform_lowlevel.html#dip-Option-DFTOption-Aligned"><code>dip::Option::DFTOption::Aligned</code></a> means that the input and output buffers are aligned to 16-bit boundaries,
which can significantly improve the speed of the algorithm.</li>
</ul>
<p>When using PocketFFT, all these options are ignored.</p>
<p>Note that this is not a trivial operation, planning an FFT costs time.</p>
<p>This operation is not thread safe.</p>
</div></section>
<section class="m-doc-details" id="dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C"><div>
<h3>
<div class="m-doc-template">
template<typename T>
</div>
<span class="m-doc-wrap-bumper">void
</span><span class="m-doc-wrap"><span class="m-doc-wrap-bumper"><a href="#dip-DFT-T-Apply-std-complex<T>-P-std-complex<T>-P-T--C" class="m-doc-self">Apply</a>(</span><span class="m-doc-wrap">std::complex<T>* source,
std::complex<T>* destination,
T scale) const</span></span>
</h3>
<p>Apply the transform that the <code>DFT</code> object is configured for.</p>
<p><code>source</code> and <code>destination</code> are pointers to contiguous buffers with <a href="dip-DFT-T.html#dip-DFT-T-TransformSize-C"><code>dip::DFT::TransformSize</code></a> elements.
This is the value of the <code>size</code> parameter of the constructor or <a href="dip-DFT-T.html#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-"><code>dip::DFT::Initialize</code></a>. These two pointers
can point to the same address for in-place operation; otherwise they must point to non-overlapping
regions of memory. When using FFTW, the <code>inplace</code> parameter to the constructor or <a href="dip-DFT-T.html#dip-DFT-T-Initialize-dip-uint--bool--Option-DFTOptions-"><code>dip::DFT::Initialize</code></a>
must be <code>true</code> if the two pointers here are the same, or <code>false</code> if they are different.</p>
<p>The input array is not marked <code>const</code>. If <a href="transform_lowlevel.html#dip-Option-DFTOption-TrashInput"><code>dip::Option::DFTOption::TrashInput</code></a> is given when planning,
the input array can be overwritten with intermediate data, but otherwise will be left intact.</p>
<p><code>scale</code> is a real scalar that the output values are multiplied by. It is typically set to <code>1/size</code> for
the inverse transform, and 1 for the forward transform.</p>
</div></section>
</section>
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