optimizeimages: Add documentation for jpegoptim

docs/config.rst

@@ -683,8 +683,8 @@ Image options
         Using image optimizers will increase render times significantly.
 
     This option specifies which additional tools overviewer should use to
-    optimize the filesize of png tiles.
-    The tools used must be placed somewhere, where overviewer can find them, for
+    optimize the filesize of rendered tiles.
+    The tools used must be placed somewhere where overviewer can find them, for
     example the "PATH" environment variable or a directory like /usr/bin.
 
     The option is a list of Optimizer objects, which are then executed in
@@ -766,6 +766,34 @@ Image options
 
             **Default:** ``False``
 
+    ``jpegoptim``
+        jpegoptim can do both lossy and lossless JPEG optimisation. If no options are specified,
+        jpegoptim will only do lossless optimisations.
+        Available settings:
+
+        ``quality``
+            A number between 0 and 100 that corresponds to the jpeg quality level. If the input
+            image has a lower quality specified than the output image, jpegoptim will only do
+            lossless optimisations.
+            
+            If this option is specified and the above condition does not apply, jpegoptim will
+            do lossy optimisation.
+
+            **Default:** ``None`` *(= Unspecified)*
+
+        ``target_size``
+            Either a percentage of the original filesize (e.g. ``"50%"``) or a target filesize
+            in kilobytes (e.g. ``15``). jpegoptim will then try to reach this as its target size.
+
+            If specified, jpegoptim will do lossy optimisation.
+
+            .. warning::
+                This appears to have a greater performance impact than just setting ``quality``.
+                Unless predictable filesizes are a thing you need, you should probably use ``quality``
+                instead.
+
+            **Default:** ``None`` *(= Unspecified)*
+
     **Default:** ``[]``
 
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