Index: tip/529.md
==================================================================
--- tip/529.md
+++ tip/529.md
@@ -83,10 +83,57 @@
 The write file commands uses any dict keys it knows.
 Any unknown dict keys are ignored.
 
 ## C interface
 
+The current C interface for drivers and other programs is not sufficient to support the metadata dict.
+
+A new extensible interface is envisaged with:
+
+   *   a pair of functions to get or set all options of the image.
+   *   a new driver interface to basically only pass the command.
+   *   and a compatibility layer to the current driver interface
+
+There are currently functions to access the raster data (Tk_PhotoGetImage, Tk_PhotoPutBlock).
+The other properties (-file, -data, -format, -gamma) are not exposed.
+
+A new interface may also be used for other image formats like svg where the image data consists of the rastered image, the image data and metadata.
+In this case, an image save operation might even not use the raster data but only metadata and image data.
+
+### image property get and set functions
+
+Two new stub table functions are added:
+
+    Tcl_Obj * Tk_PhotoGetOption(Tk_PhotoHandle handle, char *OptionName)
+
+    void Tk_PhotoSetOption(Tk_PhotoHandle handle, char *OptionName, Tcl_Obj *optionValue)
+
+### Revised image driver commands
+
+The new command interface only passes the image handle. Any required data may be accquired by the get/set functions. Also, access to the raster data is done by the raster access functions.
+
+The current registration function is
+    Tk_CreatePhotoImageFormat()
+
+...
+
+
+# Implementation
+
+The current implementation is only a sketch in my brain.
+I hope, that an image handler can set the options after reading and a binary extension of the image handlers is not necessary.
+Nevertheless, I don't know jet.
+
+Any help and comments are appreciated.
+I am realy a novice here.
+
+Implementation may start soon with the tag tip-529-image-metadata.
+
+# Rejected alternatives
+
+## C interface: only use metadata dict get and set functions
+
 Two new stub table functions are added:
 
     Tcl_Obj * Tk_PhotoGetMetadata(Tk_PhotoHandle handle)
 
     void Tk_PhotoSetMetadata(Tk_PhotoHandle handle, Tcl_Obj *metadata)
@@ -100,24 +147,9 @@
             WriteBytesFunc *writeProc,
             Tcl_Obj *format,
             Tk_PhotoImageBlock *blockPtr);
 
 In consequence, the write function should be extended by the metadata object pointer.
-
-# Implementation
-
-The current implementation is only a sketch in my brain.
-I hope, that an image handler can set the options after reading and a binary extension of the image handlers is not necessary.
-Nevertheless, I don't know jet.
-
-Any help and comments are appreciated.
-I am realy a novice here.
-
-Implementation may start soon with the tag tip-529-image-metadata.
-
-# Rejected alternatives
-
-
 
 # Copyright
 
 This document has been placed in the public domain.