updated docs

docs/docs/imaging.xml

@@ -214,6 +214,7 @@
          <item>flip_image_dataset_left_right</item> 
          <item>rotate_image_dataset</item> 
          <item>extract_image_chips</item> 
+         <item>sub_image</item> 
       </section>
 
       <section>
@@ -1629,6 +1630,19 @@
          </description>
       </component>
 
+   <!-- ************************************************************************* -->
+
+      <component>
+         <name>sub_image</name>
+         <file>dlib/image_transforms.h</file>
+         <spec_file link="true">dlib/image_transforms/interpolation_abstract.h</spec_file>
+         <description>        
+            This function returns a lightweight sub-image of another image.  In particular,
+            the returned sub-image simply holds a pointer to the original image, meaning there
+            is no overhead for using or creating the sub-image.
+         </description>
+      </component>
+
    <!-- ************************************************************************* -->
 
       <component>

docs/docs/term_index.xml

@@ -1265,6 +1265,8 @@
          <term file="imaging.html" name="rotate_image"            include="dlib/image_transforms.h"/>
          <term file="imaging.html" name="resize_image"            include="dlib/image_transforms.h"/>
          <term file="imaging.html" name="extract_image_chips"     include="dlib/image_transforms.h"/>
+         <term file="imaging.html" name="sub_image"               include="dlib/image_transforms.h"/>
+         <term file="dlib/image_transforms/interpolation_abstract.h.html" name="sub_image_proxy"     include="dlib/image_transforms.h"/>
          <term file="dlib/image_transforms/interpolation_abstract.h.html" name="extract_image_chip"     include="dlib/image_transforms.h"/>
          <term file="dlib/image_transforms/interpolation_abstract.h.html" name="chip_details"           include="dlib/image_transforms.h"/>
          <term file="dlib/image_transforms/interpolation_abstract.h.html" name="get_face_chip_details"  include="dlib/image_transforms.h"/>