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<div class="refentry">
<a name="libvips-histogram"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="libvips-histogram.top_of_page"></a>histogram</span></h2>
<p>histogram — find, manipulate and apply histograms and lookup tables</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="libvips-histogram.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-histogram.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-histogram.html#vips-maplut" title="vips_maplut ()">vips_maplut</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-histogram.html#vips-percent" title="vips_percent ()">vips_percent</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-histogram.html#vips-stdif" title="vips_stdif ()">vips_stdif</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-histogram.html#vips-hist-cum" title="vips_hist_cum ()">vips_hist_cum</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-histogram.html#vips-hist-norm" title="vips_hist_norm ()">vips_hist_norm</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-histogram.html#vips-hist-equal" title="vips_hist_equal ()">vips_hist_equal</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-histogram.html#vips-hist-plot" title="vips_hist_plot ()">vips_hist_plot</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-histogram.html#vips-hist-match" title="vips_hist_match ()">vips_hist_match</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-histogram.html#vips-hist-local" title="vips_hist_local ()">vips_hist_local</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-histogram.html#vips-hist-ismonotonic" title="vips_hist_ismonotonic ()">vips_hist_ismonotonic</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-histogram.html#vips-hist-entropy" title="vips_hist_entropy ()">vips_hist_entropy</a> <span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="libvips-histogram.includes"></a><h2>Includes</h2>
<pre class="synopsis">#include <vips/vips.h>
</pre>
</div>
<div class="refsect1">
<a name="libvips-histogram.description"></a><h2>Description</h2>
<p>Histograms and look-up tables are 1xn or nx1 images, where n is less than
256 or less than 65536, corresponding to 8- and 16-bit unsigned int images.
They are tagged with a <a class="link" href="libvips-VipsImage.html#VipsInterpretation" title="enum VipsInterpretation"><span class="type">VipsInterpretation</span></a> of
<a class="link" href="libvips-VipsImage.html#VIPS-INTERPRETATION-HISTOGRAM:CAPS"><span class="type">VIPS_INTERPRETATION_HISTOGRAM</span></a> and usually displayed by user-interfaces
such as nip2 as plots rather than images.</p>
<p>These functions can be broadly grouped as things to find or build
histograms (<a class="link" href="libvips-arithmetic.html#vips-hist-find" title="vips_hist_find ()"><code class="function">vips_hist_find()</code></a>, <a class="link" href="libvips-create.html#vips-buildlut" title="vips_buildlut ()"><code class="function">vips_buildlut()</code></a>, <a class="link" href="libvips-create.html#vips-identity" title="vips_identity ()"><code class="function">vips_identity()</code></a>),
operations that
manipulate histograms in some way (<a class="link" href="libvips-histogram.html#vips-hist-cum" title="vips_hist_cum ()"><code class="function">vips_hist_cum()</code></a>, <a class="link" href="libvips-histogram.html#vips-hist-norm" title="vips_hist_norm ()"><code class="function">vips_hist_norm()</code></a>),
operations to apply histograms (<a class="link" href="libvips-histogram.html#vips-maplut" title="vips_maplut ()"><code class="function">vips_maplut()</code></a>), and a variety of utility
operations.</p>
<p>A final group of operations build tone curves. These are useful in
pre-press work for adjusting the appearance of images. They are designed
for CIELAB images, but might be useful elsewhere.</p>
</div>
<div class="refsect1">
<a name="libvips-histogram.functions_details"></a><h2>Functions</h2>
<div class="refsect2">
<a name="vips-maplut"></a><h3>vips_maplut ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_maplut (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> *lut</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Optional arguments:</p>
<p><em class="parameter"><code>band</code></em>
: apply one-band <em class="parameter"><code>lut</code></em>
to this band of <em class="parameter"><code>in</code></em>
</p>
<p>Map an image through another image acting as a LUT (Look Up Table).
The lut may have any type and the output image will be that type.</p>
<p>The input image will be cast to one of the unsigned integer types, that is,
VIPS_FORMAT_UCHAR, VIPS_FORMAT_USHORT or VIPS_FORMAT_UINT.</p>
<p>If <em class="parameter"><code>lut</code></em>
is too small for the input type (for example, if <em class="parameter"><code>in</code></em>
is
VIPS_FORMAT_UCHAR but <em class="parameter"><code>lut</code></em>
only has 100 elements), the lut is padded out
by copying the last element. Overflows are reported at the end of
computation.
If <em class="parameter"><code>lut</code></em>
is too large, extra values are ignored. </p>
<p>If <em class="parameter"><code>lut</code></em>
has one band and <em class="parameter"><code>band</code></em>
is -1 (the default), then all bands of <em class="parameter"><code>in</code></em>
pass through <em class="parameter"><code>lut</code></em>
. If <em class="parameter"><code>band</code></em>
is >= 0, then just that band of <em class="parameter"><code>in</code></em>
passes
through <em class="parameter"><code>lut</code></em>
and other bands are just copied. </p>
<p>If <em class="parameter"><code>lut</code></em>
has same number of bands as <em class="parameter"><code>in</code></em>
, then each band is mapped
separately. If <em class="parameter"><code>in</code></em>
has one band, then <em class="parameter"><code>lut</code></em>
may have many bands and
the output will have the same number of bands as <em class="parameter"><code>lut</code></em>
.</p>
<p>See also: <a class="link" href="libvips-arithmetic.html#vips-hist-find" title="vips_hist_find ()"><code class="function">vips_hist_find()</code></a>, <a class="link" href="libvips-create.html#vips-identity" title="vips_identity ()"><code class="function">vips_identity()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.2.12"></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>lut</p></td>
<td class="parameter_description"><p>look-up table</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="id-1.4.8.7.2.13"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-percent"></a><h3>vips_percent ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_percent (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">double</span> percent</code></em>,
<em class="parameter"><code><span class="type">int</span> *threshold</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>vips_percent() returns (through the <em class="parameter"><code>threshold</code></em>
parameter) the threshold
above which there are <em class="parameter"><code>percent</code></em>
values of <em class="parameter"><code>in</code></em>
. If for example percent=10, the
number of pels of the input image with values greater than <em class="parameter"><code>threshold</code></em>
will correspond to 10% of all pels of the image.</p>
<p>The function works for uchar and ushort images only. It can be used
to threshold the scaled result of a filtering operation.</p>
<p>See also: <a class="link" href="libvips-arithmetic.html#vips-hist-find" title="vips_hist_find ()"><code class="function">vips_hist_find()</code></a>, <a class="link" href="libvips-arithmetic.html#vips-profile" title="vips_profile ()"><code class="function">vips_profile()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.3.7"></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>percent</p></td>
<td class="parameter_description"><p>threshold percentage</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>threshold</p></td>
<td class="parameter_description"><p>output threshold value</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="id-1.4.8.7.3.8"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-stdif"></a><h3>vips_stdif ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_stdif (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code><span class="type">int</span> width</code></em>,
<em class="parameter"><code><span class="type">int</span> height</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Optional arguments:</p>
<p><em class="parameter"><code>a</code></em>
: weight of new mean
<em class="parameter"><code>m0</code></em>
: target mean
<em class="parameter"><code>b</code></em>
: weight of new deviation
<em class="parameter"><code>s0</code></em>
: target deviation</p>
<p>vips_stdif() preforms statistical differencing according to the formula
given in page 45 of the book "An Introduction to Digital Image
Processing" by Wayne Niblack. This transformation emphasises the way in
which a pel differs statistically from its neighbours. It is useful for
enhancing low-contrast images with lots of detail, such as X-ray plates.</p>
<p>At point (i,j) the output is given by the equation:</p>
<div class="informalexample"><pre class="programlisting">
vout(i,j) = @a * @m0 + (1 - @a) * meanv +
(vin(i,j) - meanv) * (@b * @s0) / (@s0 + @b * stdv)
</pre></div>
<p></p>
<p>Values <em class="parameter"><code>a</code></em>
, <em class="parameter"><code>m0</code></em>
, <em class="parameter"><code>b</code></em>
and <em class="parameter"><code>s0</code></em>
are entered, while meanv and stdv are the values
calculated over a moving window of size <em class="parameter"><code>width</code></em>
, <em class="parameter"><code>height</code></em>
centred on pixel
(i,j). <em class="parameter"><code>m0</code></em>
is the new mean, <em class="parameter"><code>a</code></em>
is the weight given to it. <em class="parameter"><code>s0</code></em>
is the new
standard deviation, <em class="parameter"><code>b</code></em>
is the weight given to it. </p>
<p>Try:</p>
<div class="informalexample"><pre class="programlisting">
vips stdif $VIPSHOME/pics/huysum.v fred.v 0.5 128 0.5 50 11 11
</pre></div>
<p></p>
<p>The operation works on one-band uchar images only, and writes a one-band
uchar image as its result. The output image has the same size as the
input.</p>
<p>See also: <a class="link" href="libvips-histogram.html#vips-hist-local" title="vips_hist_local ()"><code class="function">vips_hist_local()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.4.16"></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>width</p></td>
<td class="parameter_description"><p>width of region</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>height</p></td>
<td class="parameter_description"><p>height of region</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="id-1.4.8.7.4.17"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-cum"></a><h3>vips_hist_cum ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_cum (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Form cumulative histogram. </p>
<p>See also: <a class="link" href="libvips-histogram.html#vips-hist-norm" title="vips_hist_norm ()"><code class="function">vips_hist_norm()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.5.6"></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="id-1.4.8.7.5.7"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-norm"></a><h3>vips_hist_norm ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_norm (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Normalise histogram ... normalise range to make it square (ie. max ==
number of elements). Normalise each band separately.</p>
<p>See also: <a class="link" href="libvips-histogram.html#vips-hist-cum" title="vips_hist_cum ()"><code class="function">vips_hist_cum()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.6.6"></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="id-1.4.8.7.6.7"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-equal"></a><h3>vips_hist_equal ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_equal (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Optional arguments:</p>
<p><em class="parameter"><code>band</code></em>
: band to equalise</p>
<p>Histogram-equalise <em class="parameter"><code>in</code></em>
. Equalise using band <em class="parameter"><code>bandno</code></em>
, or if <em class="parameter"><code>bandno</code></em>
is -1,
equalise bands independently.</p>
<p>See also:</p>
<div class="refsect3">
<a name="id-1.4.8.7.7.8"></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="id-1.4.8.7.7.9"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-plot"></a><h3>vips_hist_plot ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_plot (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Plot a 1 by any or any by 1 image file as a max by any or
any by max image using these rules:</p>
<p><span class="emphasis"><em>unsigned char</em></span> max is always 256 </p>
<p><span class="emphasis"><em>other unsigned integer types</em></span> output 0 - maxium
value of <em class="parameter"><code>in</code></em>
.</p>
<p><span class="emphasis"><em>signed int types</em></span> min moved to 0, max moved to max + min.</p>
<p><span class="emphasis"><em>float types</em></span> min moved to 0, max moved to any
(square output)</p>
<div class="refsect3">
<a name="id-1.4.8.7.8.9"></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="id-1.4.8.7.8.10"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-match"></a><h3>vips_hist_match ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_match (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> *ref</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Adjust <em class="parameter"><code>in</code></em>
to match <em class="parameter"><code>ref</code></em>
. If <em class="parameter"><code>in</code></em>
and <em class="parameter"><code>ref</code></em>
are normalised
cumulative histograms, <em class="parameter"><code>out</code></em>
will be a LUT that adjusts the PDF of the image
from which <em class="parameter"><code>in</code></em>
was made to match the PDF of <em class="parameter"><code>ref</code></em>
's image. </p>
<p>See also: <a class="link" href="libvips-histogram.html#vips-maplut" title="vips_maplut ()"><code class="function">vips_maplut()</code></a>, <a class="link" href="libvips-arithmetic.html#vips-hist-find" title="vips_hist_find ()"><code class="function">vips_hist_find()</code></a>, <a class="link" href="libvips-histogram.html#vips-hist-norm" title="vips_hist_norm ()"><code class="function">vips_hist_norm()</code></a>,
<a class="link" href="libvips-histogram.html#vips-hist-cum" title="vips_hist_cum ()"><code class="function">vips_hist_cum()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.9.6"></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 histogram</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>ref</p></td>
<td class="parameter_description"><p>reference histogram </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>output histogram</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="id-1.4.8.7.9.7"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-local"></a><h3>vips_hist_local ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_local (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">VipsImage</span> **out</code></em>,
<em class="parameter"><code><span class="type">int</span> width</code></em>,
<em class="parameter"><code><span class="type">int</span> height</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Performs local histogram equalisation on <em class="parameter"><code>in</code></em>
using a
window of size <em class="parameter"><code>xwin</code></em>
by <em class="parameter"><code>ywin</code></em>
centered on the input pixel. </p>
<p>The output image is the same size as the input image. The edge pixels are
created by copy edge pixels of the input image outwards.</p>
<p>See also: <a class="link" href="libvips-histogram.html#vips-hist-equal" title="vips_hist_equal ()"><code class="function">vips_hist_equal()</code></a>.</p>
<div class="refsect3">
<a name="id-1.4.8.7.10.7"></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>width</p></td>
<td class="parameter_description"><p>width of region</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>height</p></td>
<td class="parameter_description"><p>height of region</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="id-1.4.8.7.10.8"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-ismonotonic"></a><h3>vips_hist_ismonotonic ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_ismonotonic (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">gboolean</span> *out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Test <em class="parameter"><code>in</code></em>
for monotonicity. <em class="parameter"><code>out</code></em>
is set non-zero if <em class="parameter"><code>in</code></em>
is monotonic.</p>
<div class="refsect3">
<a name="id-1.4.8.7.11.5"></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>lookup-table to test</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>set non-zero if <em class="parameter"><code>in</code></em>
is monotonic </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="id-1.4.8.7.11.6"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="vips-hist-entropy"></a><h3>vips_hist_entropy ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span>
vips_hist_entropy (<em class="parameter"><code><span class="type">VipsImage</span> *in</code></em>,
<em class="parameter"><code><span class="type">double</span> *out</code></em>,
<em class="parameter"><code>...</code></em>);</pre>
<p>Estimate image entropy from a histogram. Entropy is calculated as:</p>
<div class="informalexample"><pre class="programlisting">
-sum( p * log2( p ) )
</pre></div>
<p></p>
<p>where p is histogram-value / sum-of-histogram-values.</p>
<div class="refsect3">
<a name="id-1.4.8.7.12.8"></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 histogram </p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>out</p></td>
<td class="parameter_description"><p>image entropy</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="id-1.4.8.7.12.9"></a><h4>Returns</h4>
<p> 0 on success, -1 on error</p>
</div>
</div>
</div>
<div class="refsect1">
<a name="libvips-histogram.other_details"></a><h2>Types and Values</h2>
</div>
<div class="refsect1">
<a name="libvips-histogram.see-also"></a><h2>See Also</h2>
image<a class="link" href="libvips-arithmetic.html" title="arithmetic">arithmetic</a><a class="link" href="libvips-create.html" title="create">create</a>
</div>
</div>
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