diff --git a/libgimp/gimpimage.c b/libgimp/gimpimage.c
index 0152f10783..a319b0dc4a 100644
--- a/libgimp/gimpimage.c
+++ b/libgimp/gimpimage.c
@@ -326,7 +326,7 @@ gimp_image_list_vectors (GimpImage *image)
 /**
  * gimp_image_get_colormap:
  * @image:      The image.
- * @num_colors: Returns the number of colors in the colormap array.
+ * @num_colors: (out): Returns the number of colors in the colormap array.
  *
  * Returns the image's colormap
  *
@@ -334,7 +334,7 @@ gimp_image_list_vectors (GimpImage *image)
  * well as the number of colors contained in the colormap. If the image
  * is not of base type INDEXED, this pointer will be NULL.
  *
- * Returns: The image's colormap.
+ * Returns: (array): The image's colormap.
  */
 guchar *
 gimp_image_get_colormap (GimpImage *image,
@@ -354,7 +354,7 @@ gimp_image_get_colormap (GimpImage *image,
 /**
  * gimp_image_set_colormap:
  * @image:      The image.
- * @colormap:   The new colormap values.
+ * @colormap: (array): The new colormap values.
  * @num_colors: Number of colors in the colormap array.
  *
  * Sets the entries in the image's colormap.
diff --git a/libgimpcolor/gimpcmyk.c b/libgimpcolor/gimpcmyk.c
index def52dddd0..be85f1d269 100644
--- a/libgimpcolor/gimpcmyk.c
+++ b/libgimpcolor/gimpcmyk.c
@@ -109,10 +109,10 @@ gimp_cmyk_set_uchar (GimpCMYK *cmyk,
 /**
  * gimp_cmyk_get_uchar:
  * @cmyk:    A #GimpCMYK structure which will hold the specified CMYK value.
- * @cyan:    The Cyan channel of the CMYK value
- * @magenta: The Magenta channel
- * @yellow:  The Yellow channel
- * @black:   The blacK channel
+ * @cyan:    (out) (optional): The Cyan channel of the CMYK value
+ * @magenta: (out) (optional): The Magenta channel
+ * @yellow:  (out) (optional): The Yellow channel
+ * @black:   (out) (optional): The blacK channel
  *
  * Retrieve individual channel values from a #GimpCMYK structure. Channel
  * values are pointers to unsigned chars in the range 0 to 255.
@@ -192,14 +192,15 @@ gimp_cmyka_set_uchar (GimpCMYK *cmyka,
   cmyka->k = (gdouble) black   / 255.0;
   cmyka->a = (gdouble) alpha   / 255.0;
 }
+
 /**
  * gimp_cmyka_get_uchar:
  * @cmyka:   A #GimpCMYK structure which will hold the specified CMYKA value.
- * @cyan:    The Cyan channel of the CMYK value
- * @magenta: The Magenta channel
- * @yellow:  The Yellow channel
- * @black:   The blacK channel
- * @alpha:   The Alpha channel
+ * @cyan:    (out) (optional): The Cyan channel of the CMYK value
+ * @magenta: (out) (optional): The Magenta channel
+ * @yellow:  (out) (optional): The Yellow channel
+ * @black:   (out) (optional): The blacK channel
+ * @alpha:   (out) (optional): The Alpha channel
  *
  * Retrieve individual channel values from a #GimpCMYK structure.
  * Channel values are pointers to unsigned chars in the range 0 to 255.
diff --git a/libgimpcolor/gimpcolormanaged.c b/libgimpcolor/gimpcolormanaged.c
index 17cf733b38..dca1fdbae8 100644
--- a/libgimpcolor/gimpcolormanaged.c
+++ b/libgimpcolor/gimpcolormanaged.c
@@ -75,13 +75,13 @@ gimp_color_managed_default_init (GimpColorManagedInterface *iface)
 /**
  * gimp_color_managed_get_icc_profile:
  * @managed: an object the implements the #GimpColorManaged interface
- * @len:     return location for the number of bytes in the profile data
+ * @len: (out): return location for the number of bytes in the profile data
  *
- * Returns: A pointer to a blob of data that represents an ICC
- *               color profile.
+ * Returns: (array length=len): A blob of data that represents an ICC color
+ *                              profile.
  *
  * Since: 2.4
- **/
+ */
 const guint8 *
 gimp_color_managed_get_icc_profile (GimpColorManaged *managed,
                                     gsize            *len)
diff --git a/libgimpcolor/gimpcolormanaged.h b/libgimpcolor/gimpcolormanaged.h
index 8b45f46eb2..b6a473b509 100644
--- a/libgimpcolor/gimpcolormanaged.h
+++ b/libgimpcolor/gimpcolormanaged.h
@@ -48,7 +48,16 @@ struct _GimpColorManagedInterface
 {
   GTypeInterface  base_iface;
 
-  /*  virtual functions  */
+  /**
+   * GimpColorManagedInterface::get_icc_profile:
+   * @managed: an object the implements the #GimpColorManaged interface
+   * @len: (out): return location for the number of bytes in the profile data
+   *
+   * Returns: (array length=len): A blob of data that represents an ICC color
+   *                              profile.
+   *
+   * Since: 2.4
+   */
   const guint8     * (* get_icc_profile)   (GimpColorManaged *managed,
                                             gsize            *len);
 
diff --git a/libgimpcolor/gimpcolorprofile.c b/libgimpcolor/gimpcolorprofile.c
index 7f7d092410..006277b32f 100644
--- a/libgimpcolor/gimpcolorprofile.c
+++ b/libgimpcolor/gimpcolorprofile.c
@@ -265,7 +265,7 @@ gimp_color_profile_new_from_file (GFile   *file,
 
 /**
  * gimp_color_profile_new_from_icc_profile:
- * @data:   pointer to memory containing an ICC profile
+ * @data: (array length=length): The memory containing an ICC profile
  * @length: length of the profile in memory, in bytes
  * @error:  return location for #GError
  *
@@ -397,12 +397,12 @@ gimp_color_profile_save_to_file (GimpColorProfile  *profile,
 /**
  * gimp_color_profile_get_icc_profile:
  * @profile: a #GimpColorProfile
- * @length:  return location for the number of bytes
+ * @length: (out): return location for the number of bytes
  *
  * This function returns @profile as ICC profile data. The returned
  * memory belongs to @profile and must not be modified or freed.
  *
- * Returns: a pointer to the IIC profile data.
+ * Returns: (array length=length): a pointer to the IIC profile data.
  *
  * Since: 2.10
  **/
diff --git a/libgimpcolor/gimppixbuf.c b/libgimpcolor/gimppixbuf.c
index d2c3ae3dc7..afe270b7e2 100644
--- a/libgimpcolor/gimppixbuf.c
+++ b/libgimpcolor/gimppixbuf.c
@@ -118,12 +118,12 @@ gimp_pixbuf_create_buffer (GdkPixbuf *pixbuf)
 /**
  * gimp_pixbuf_get_icc_profile:
  * @pixbuf: a #GdkPixbuf
- * @length: return location for the ICC profile's length
+ * @length: (out): return location for the ICC profile's length
  *
  * Returns the ICC profile attached to the @pixbuf, or %NULL if there
  * is none.
  *
- * Returns: (nullable): The ICC profile data, or %NULL.
+ * Returns: (array length=length) (nullable): The ICC profile data, or %NULL.
  *          The value should be freed with g_free().
  *
  * Since: 2.10
diff --git a/libgimpconfig/gimpconfig-register.c b/libgimpconfig/gimpconfig-register.c
index d74540de58..f783a60149 100644
--- a/libgimpconfig/gimpconfig-register.c
+++ b/libgimpconfig/gimpconfig-register.c
@@ -54,7 +54,7 @@ static void     gimp_config_value_free   (GValue        *value);
  * gimp_config_type_register:
  * @parent_type: type from which this type will be derived
  * @type_name:   string used as the name of the new type
- * @pspecs:      array of #GParamSpec to install as properties on the new type
+ * @pspecs: (array length=n_pspecs): array of #GParamSpec to install as properties on the new type
  * @n_pspecs:    the number of param specs in @pspecs
  *
  * This function is a fancy wrapper around g_type_register_static().
diff --git a/libgimpmath/gimpmatrix.c b/libgimpmath/gimpmatrix.c
index 95bf384ca0..99f7d143ea 100644
--- a/libgimpmath/gimpmatrix.c
+++ b/libgimpmath/gimpmatrix.c
@@ -292,8 +292,8 @@ gimp_matrix2_invert (GimpMatrix2 *matrix)
  * @matrix: The transformation matrix.
  * @x: The source X coordinate.
  * @y: The source Y coordinate.
- * @newx: The transformed X coordinate.
- * @newy: The transformed Y coordinate.
+ * @newx: (out): The transformed X coordinate.
+ * @newy: (out): The transformed Y coordinate.
  *
  * Transforms a point in 2D as specified by the transformation matrix.
  *
@@ -971,10 +971,9 @@ gimp_matrix4_mult (const GimpMatrix4 *matrix1,
 /**
  * gimp_matrix4_to_deg:
  * @matrix:
- * @a:
- * @b:
- * @c:
- *
+ * @a: (out):
+ * @b: (out):
+ * @c: (out):
  *
  **/
 void
@@ -994,9 +993,9 @@ gimp_matrix4_to_deg (const GimpMatrix4 *matrix,
  * @x: The source X coordinate.
  * @y: The source Y coordinate.
  * @z: The source Z coordinate.
- * @newx: The transformed X coordinate.
- * @newy: The transformed Y coordinate.
- * @newz: The transformed Z coordinate.
+ * @newx: (out): The transformed X coordinate.
+ * @newy: (out): The transformed Y coordinate.
+ * @newz: (out): The transformed Z coordinate.
  *
  * Transforms a point in 3D as specified by the transformation matrix.
  *
diff --git a/libgimpwidgets/gimppreviewarea.c b/libgimpwidgets/gimppreviewarea.c
index a2ef669de1..3f49effaee 100644
--- a/libgimpwidgets/gimppreviewarea.c
+++ b/libgimpwidgets/gimppreviewarea.c
@@ -1752,7 +1752,7 @@ gimp_preview_area_set_offsets (GimpPreviewArea *area,
 /**
  * gimp_preview_area_set_colormap:
  * @area:       a #GimpPreviewArea
- * @colormap:   a #guchar buffer that contains the colormap
+ * @colormap: (array): a #guchar buffer that contains the colormap
  * @num_colors: the number of colors in the colormap
  *
  * Sets the colormap for the #GimpPreviewArea widget. You need to