[gimp-help] Add High-Pass filter

[Julien Hardlin <jhardlin src gnome org>]

commit 990a53c2e764a937b0de747982e1a33164dc0f07
Author: Julien Hardelin <jhardlin orange fr>
Date:   Sun Nov 25 08:58:07 2018 +0100

    Add High-Pass filter

 images/C/filters/enhance/high-pass-dialog.png      | Bin 0 -> 14222 bytes
 .../examples/enhance/high-pass-duplicate.png       | Bin 0 -> 16585 bytes
 .../C/filters/examples/enhance/high-pass-ex2.png   | Bin 0 -> 108432 bytes
 .../C/filters/examples/enhance/high-pass-mode.png  | Bin 0 -> 257288 bytes
 .../C/filters/examples/enhance/high-pass-open.png  | Bin 0 -> 151707 bytes
 .../filters/examples/enhance/high-pass-origin.png  | Bin 0 -> 174862 bytes
 .../filters/examples/enhance/high-pass-setting.png | Bin 0 -> 219858 bytes
 images/C/filters/examples/enhance/result.png       | Bin 0 -> 232131 bytes
 src/filters/enhance.xml                            |   1 +
 src/filters/enhance/high-pass.xml                  | 152 +++++++++++++++++++++
 10 files changed, 153 insertions(+)
---
diff --git a/images/C/filters/enhance/high-pass-dialog.png b/images/C/filters/enhance/high-pass-dialog.png
new file mode 100644
index 000000000..6f5bc303a
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diff --git a/images/C/filters/examples/enhance/high-pass-duplicate.png 
b/images/C/filters/examples/enhance/high-pass-duplicate.png
new file mode 100644
index 000000000..e6bebd848
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diff --git a/images/C/filters/examples/enhance/high-pass-ex2.png 
b/images/C/filters/examples/enhance/high-pass-ex2.png
new file mode 100644
index 000000000..715770c25
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diff --git a/images/C/filters/examples/enhance/high-pass-mode.png 
b/images/C/filters/examples/enhance/high-pass-mode.png
new file mode 100644
index 000000000..67b07f447
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diff --git a/images/C/filters/examples/enhance/high-pass-open.png 
b/images/C/filters/examples/enhance/high-pass-open.png
new file mode 100644
index 000000000..40b968051
Binary files /dev/null and b/images/C/filters/examples/enhance/high-pass-open.png differ
diff --git a/images/C/filters/examples/enhance/high-pass-origin.png 
b/images/C/filters/examples/enhance/high-pass-origin.png
new file mode 100644
index 000000000..c3a070bcc
Binary files /dev/null and b/images/C/filters/examples/enhance/high-pass-origin.png differ
diff --git a/images/C/filters/examples/enhance/high-pass-setting.png 
b/images/C/filters/examples/enhance/high-pass-setting.png
new file mode 100644
index 000000000..c87e80521
Binary files /dev/null and b/images/C/filters/examples/enhance/high-pass-setting.png differ
diff --git a/images/C/filters/examples/enhance/result.png b/images/C/filters/examples/enhance/result.png
new file mode 100644
index 000000000..c9ce0bf00
Binary files /dev/null and b/images/C/filters/examples/enhance/result.png differ
diff --git a/src/filters/enhance.xml b/src/filters/enhance.xml
index 3b73e4df5..0922e32c2 100644
--- a/src/filters/enhance.xml
+++ b/src/filters/enhance.xml
@@ -17,6 +17,7 @@
   <xi:include href="enhance/introduction.xml"/>
   <xi:include href="enhance/antialias.xml"/>
   <xi:include href="enhance/deinterlace.xml"/>
+  <xi:include href="enhance/high-pass.xml"/>
   <xi:include href="enhance/despeckle.xml"/>
   <xi:include href="enhance/destripe.xml"/>
   <xi:include href="enhance/NL_filter.xml"/>
diff --git a/src/filters/enhance/high-pass.xml b/src/filters/enhance/high-pass.xml
new file mode 100644
index 000000000..9227e46d0
--- /dev/null
+++ b/src/filters/enhance/high-pass.xml
@@ -0,0 +1,152 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE sect2 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+                       "http://www.docbook.org/xml/4.3/docbookx.dtd";>
+
+<!-- section history:
+  2018-11-15 j.h: Created
+-->
+
+<sect2 id="gimp-filter-high-pass">
+  <title>High Pass</title>
+
+  <indexterm>
+    <primary>Filters</primary>
+    <secondary>Enhance</secondary>
+    <tertiary>High Pass</tertiary>
+  </indexterm>
+  <indexterm>
+    <primary>High Pass</primary>
+  </indexterm>
+
+  <sect3>
+    <title>Overview</title>
+    <para>
+      In sound processing, a high-pass filter filters high frequencies above a threshold. In digital images, 
frequency refers to sudden changes in brightness or color in neighboring pixels. The High Pass filter filters 
high essential details, and larger scale gradients are removed. This result, combined with the original image 
and "Soft Light" or "Hard Light" merge mode, is used to sharpen images.
+    </para>
+  </sect3>
+
+  <sect3>
+    <title>Activating the filter</title>
+    <para>
+      You can find this filter through
+      <menuchoice>
+        <guimenu>Filters</guimenu>
+        <guisubmenu>Enhance</guisubmenu>
+        <guimenuitem>High Pass…</guimenuitem>
+      </menuchoice>.
+    </para>
+  </sect3>
+
+  <sect3>
+    <title>Options</title>
+    <figure>
+      <title><quote>High Pass</quote> filter options</title>
+      <mediaobject>
+        <imageobject>
+          <imagedata 
+            fileref="images/filters/enhance/high-pass-dialog.png"
+            format="PNG"/>
+        </imageobject>
+      </mediaobject>
+    </figure>
+    <variablelist>
+      <varlistentry>
+        <term><guilabel>Presets</guilabel>, <guilabel>Preview</guilabel>, 
+          <guilabel>Split view</guilabel></term>
+        <listitem>
+          <para>
+            These options are common to GEGL-based filters. Please refer to 
+            <xref linkend="gimp-filters-common"/>.
+          </para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><guilabel>Std. Dev.</guilabel></term>
+        <listitem>
+          <para>
+            Increasing this Standard Deviation lowers the filter threshold and more image details are taken 
in account for treatment.  
+          </para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><guilabel>Contrast</guilabel></term>
+        <listitem>
+          <para>
+            Increase/Decrease contrast of treated details.
+          </para>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </sect3>
+
+  <sect3>
+    <title>Using High Pass Filter</title>
+    <procedure>
+      <title>Sharpening</title>
+      <step>
+        <para>
+          Open your image:
+          <mediaobject>
+            <imageobject>
+              <imagedata 
+fileref="images/filters/examples/enhance/high-pass-origin.png"
+                format="PNG"/>
+            </imageobject>
+          </mediaobject>
+        </para>
+      </step>
+      <step>
+        <para>
+          Duplicate layer:
+          <mediaobject>
+            <imageobject>
+              <imagedata 
+fileref="images/filters/examples/enhance/high-pass-duplicate.png"
+                format="PNG"/>
+            </imageobject>
+          </mediaobject>
+          This duplicate layer becomes the active layer.
+        </para>
+      </step>
+      <step>
+        <para>
+          Open High Pass filter.
+          <mediaobject>
+            <imageobject>
+              <imagedata 
+fileref="images/filters/examples/enhance/high-pass-open.png"
+                format="PNG"/>
+            </imageobject>
+          </mediaobject>
+        </para>
+      </step>
+      <step>
+        <para>
+          Change mode to soft-light (try Hard-light also).
+          <mediaobject>
+            <imageobject>
+              <imagedata 
+fileref="images/filters/examples/enhance/high-pass-mode.png"
+                format="PNG"/>
+            </imageobject>
+          </mediaobject>
+        </para>
+      </step>
+      <step>
+        <para>
+          Settings and on-canvas view
+          <mediaobject>
+            <imageobject>
+              <imagedata 
+fileref="images/filters/examples/enhance/high-pass-setting.png"
+                format="PNG"/>
+            </imageobject>
+          </mediaobject>
+        </para>
+      </step>
+    </procedure>
+  </sect3>
+</sect2>
+