--- a/PNGReader.st	Thu Oct 25 12:49:12 2018 +0200
+++ b/PNGReader.st	Sat Oct 27 12:15:41 2018 +0200
@@ -1,3 +1,5 @@
+"{ Encoding: utf8 }"
+
 "
  COPYRIGHT (c) 1996 by Claus Gittinger
               All Rights Reserved
@@ -18,7 +20,7 @@
 		interlaceMode bytesPerScanline globalDataChunk thisScanline
 		prevScanline processTextChunks specialChunkHandlers
 		paletteAlphaEntries paletteIndexForMaskedPixels image forceRGB
-		depthImage'
+		depthImage specialChunks'
 	classVariableNames:'ColorTypeGray ColorTypeGrayAlpha ColorTypePalette ColorTypeRGB
 		ColorTypeRGBAlpha Verbose'
 	poolDictionaries:''
@@ -58,6 +60,13 @@
         if #rgb is returned AND the image is rgba, then the alpha channel is ignored
         and an rgb (Depth24Image) is returned instead.
 
+        Proprietary chunks can be extracted by defining a specialChunkHandler,
+        which is invoked (indexed by chunkType) with the chunk data when such a
+        chunk is encountered. This allows for private data to be extracted.
+        (labview does this, and expecco can do this)
+        Proprietary chunks can be written by setting the specialChunks collection
+        before writing.
+        
     [See also:]
         Image Form Icon
         BlitImageReader FaceReader GIFReader JPEGReader MacOSXIconReader
@@ -1674,10 +1683,12 @@
     photometric == #palette ifTrue: [self writePaletteChunk].
     paletteIndexForMaskedPixels notNil ifTrue: [self writeTRNSChunk].
     self writeImageDataChunk.
+    specialChunks notNil ifTrue:[self writeSpecialChunks].
     self writeEndChunk
 
     "Modified: / 23-08-2017 / 16:25:00 / cg"
     "Modified (format): / 31-08-2017 / 17:26:28 / cg"
+    "Modified: / 27-10-2018 / 12:13:03 / Claus Gittinger"
 ! !
 
 !PNGReader methodsFor:'writing-private'!
@@ -1902,6 +1913,19 @@
         ]
 !
 
+writeSpecialChunks
+    specialChunks keysAndValuesDo:[:chunkType :chunkData |        
+        self 
+            writeChunk:chunkType
+            size:chunkData size
+            with:[
+                outStream nextPutBytes:chunkData
+            ]
+    ].
+
+    "Created: / 27-10-2018 / 12:14:02 / Claus Gittinger"
+!
+
 writeTRNSChunk
     self 
         writeChunk: 'tRNS'