[gimp-help] Add Image Gradient filter

[Julien Hardlin <jhardlin src gnome org>]

commit e04f6a99488aa8bc5dd87a66bb135b54c11dacd9
Author: Julien Hardelin <jhardlin orange fr>
Date:   Sat Jan 4 07:48:59 2020 +0100

    Add Image Gradient filter

 .../filters/edge-detect/image_gradient-dialog.png  | Bin 0 -> 19616 bytes
 .../edge-detect/image_gradient-direction.jpg       | Bin 0 -> 75668 bytes
 .../examples/edge-detect/image_gradient-ex0.jpg    | Bin 0 -> 2497 bytes
 .../examples/edge-detect/image_gradient-ex1.jpg    | Bin 0 -> 3075 bytes
 .../examples/edge-detect/image_gradient-ex2.jpg    | Bin 0 -> 2773 bytes
 .../examples/edge-detect/image_gradient.jpg        | Bin 0 -> 42963 bytes
 src/filters/edge-detect.xml                        |   1 +
 src/filters/edge-detect/image_gradient.xml         | 143 +++++++++++++++++++++
 8 files changed, 144 insertions(+)
---
diff --git a/images/C/filters/edge-detect/image_gradient-dialog.png 
b/images/C/filters/edge-detect/image_gradient-dialog.png
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diff --git a/images/C/filters/examples/edge-detect/image_gradient-direction.jpg 
b/images/C/filters/examples/edge-detect/image_gradient-direction.jpg
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index 000000000..865efbcea
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diff --git a/images/C/filters/examples/edge-detect/image_gradient-ex0.jpg 
b/images/C/filters/examples/edge-detect/image_gradient-ex0.jpg
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diff --git a/images/C/filters/examples/edge-detect/image_gradient-ex1.jpg 
b/images/C/filters/examples/edge-detect/image_gradient-ex1.jpg
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diff --git a/images/C/filters/examples/edge-detect/image_gradient-ex2.jpg 
b/images/C/filters/examples/edge-detect/image_gradient-ex2.jpg
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index 000000000..ed599b455
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diff --git a/images/C/filters/examples/edge-detect/image_gradient.jpg 
b/images/C/filters/examples/edge-detect/image_gradient.jpg
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diff --git a/src/filters/edge-detect.xml b/src/filters/edge-detect.xml
index 88a586e75..a66fce746 100644
--- a/src/filters/edge-detect.xml
+++ b/src/filters/edge-detect.xml
@@ -15,4 +15,5 @@
   <xi:include href="edge-detect/laplace.xml"/>
   <xi:include href="edge-detect/neon.xml"/>
   <xi:include href="edge-detect/sobel.xml"/>
+  <xi:include href="edge-detect/image_gradient.xml"/>
 </sect1>
diff --git a/src/filters/edge-detect/image_gradient.xml b/src/filters/edge-detect/image_gradient.xml
new file mode 100644
index 000000000..ea01335f6
--- /dev/null
+++ b/src/filters/edge-detect/image_gradient.xml
@@ -0,0 +1,143 @@
+<?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:
+  2020-01-02 j.h: initial version
+-->
+<sect2 xmlns:xi="http://www.w3.org/2001/XInclude"; 
+        id="gimp-filter-image-gradient">
+  <title>Image Gradient</title>
+
+  <indexterm>
+    <primary>Filters</primary>
+    <secondary>Edge Detect</secondary>
+    <tertiary>Image Gradient</tertiary>
+  </indexterm>
+  <indexterm>
+    <primary>Image Gradient</primary>
+  </indexterm>
+  
+  <sect3>
+    <title>Overview</title>
+    <figure>
+      <title>Applying example for the Image Gradient filter</title>
+      <mediaobject>
+        <imageobject>
+          <imagedata format="JPG"
+            fileref="images/filters/examples/taj_orig.jpg"/>
+        </imageobject>
+        <caption>
+          <para>Original image</para>
+        </caption>
+      </mediaobject>
+      <mediaobject>
+        <imageobject>
+          <imagedata format="JPG"
+          fileref="images/filters/examples/edge-detect/image_gradient.jpg"/>
+        </imageobject>
+        <caption>
+          <para>
+            Filter <quote>Image Gradient</quote> applied with default options.
+          </para>
+        </caption>
+      </mediaobject>
+    </figure>
+    <mediaobject>
+      <imageobject>
+        <imagedata format="JPG"
+fileref="images/filters/examples/edge-detect/image_gradient-direction.jpg"/>
+      </imageobject>
+      <caption>
+        <para>
+          Filter <quote>Image Gradient</quote> applied with Direction option.
+        </para>
+      </caption>
+    </mediaobject>
+    <para>
+      This filter detects edges in one or two gradient directions.
+    </para>
+  </sect3>
+  <sect3>
+    <title>Activating the filter</title>
+    <para>
+      You can find this filter through
+      <menuchoice>
+        <guimenu>Filters</guimenu>
+        <guisubmenu>Edge-Detect</guisubmenu>
+        <guimenuitem>Image Gradient…</guimenuitem>
+      </menuchoice>.
+    </para>
+  </sect3>
+  
+  <sect3>
+    <title>Options</title>
+    <figure>
+      <title>Image Gradient filter options</title>
+      <mediaobject>
+        <imageobject>
+          <imagedata format="PNG"
+            fileref="images/filters/edge-detect/image_gradient-dialog.png"/>
+        </imageobject>
+      </mediaobject>
+    </figure>
+    <variablelist>
+      <varlistentry>
+        <term>Presets, Preview, Split view</term>
+        <listitem>
+          <xi:include href="../about-common-features.xml"/>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Output mode</term>
+        <listitem>
+          <para>
+            <guilabel>Magnitude</guilabel> is default: it combines both 
+            directions. <guilabel>Direction</guilabel>: only one direction is 
+            used. <guilabel>Both</guilabel> is like Magnitude.
+          </para>
+          <figure>
+            <title>Output mode examples</title>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="JPG"
+       fileref="images/filters/examples/edge-detect/image_gradient-ex0.jpg"/>
+              </imageobject>
+              <caption>
+                <para>Original image, with abrupt luminosity change</para>
+              </caption>
+            </mediaobject>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="JPG"
+       fileref="images/filters/examples/edge-detect/image_gradient-ex1.jpg"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Option Magnitude is selected
+                </para>
+              </caption>
+            </mediaobject>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="JPG"
+       fileref="images/filters/examples/edge-detect/image_gradient-ex2.jpg"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Option Direction is selected. In result, black is 
+                  no edge detected, white is edge detected.
+                </para>
+              </caption>
+            </mediaobject>
+          </figure>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Clipping</term>
+        <listitem>
+          <xi:include href="../clipping-feature.xml"/>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </sect3>
+</sect2>
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