--- a/PNGReader.st	Sat Oct 27 16:10:05 2018 +0200
+++ b/PNGReader.st	Sat Oct 27 17:40:05 2018 +0200
@@ -20,7 +20,7 @@
 		interlaceMode bytesPerScanline globalDataChunk thisScanline
 		prevScanline processTextChunks specialChunkHandlers
 		paletteAlphaEntries paletteIndexForMaskedPixels image forceRGB
-		depthImage specialChunks'
+		depthImage specialChunks extractSpecialChunksOnly'
 	classVariableNames:'ColorTypeGray ColorTypeGrayAlpha ColorTypePalette ColorTypeRGB
 		ColorTypeRGBAlpha Verbose'
 	poolDictionaries:''
@@ -172,6 +172,17 @@
 
 !PNGReader methodsFor:'accessing'!
 
+extractSpecialChunksOnly:aBoolean
+    "if set to true, only special chunks will be processed via
+     corresponding specialChunkHandlers.
+     No image will be extracted.
+     The default is (of course) false."
+     
+    extractSpecialChunksOnly := aBoolean.
+
+    "Modified (comment): / 27-10-2018 / 17:39:50 / Claus Gittinger"
+!
+
 makeImage
     image isNil ifTrue:[
         image := super makeImage.
@@ -260,6 +271,8 @@
 
     [self getChunk] whileTrue.
 
+    extractSpecialChunksOnly == true ifTrue:[^nil].
+    
     "/ kludge: if we get a grey image with alpha,
     "/ load as rgb+alpha
     forceRGB := false. 
@@ -328,7 +341,7 @@
     "
 
     "Modified: / 17-09-2017 / 15:30:45 / cg"
-    "Modified (format): / 02-06-2018 / 06:55:59 / Claus Gittinger"
+    "Modified: / 27-10-2018 / 17:29:21 / Claus Gittinger"
 ! !
 
 !PNGReader methodsFor:'reading-private'!
@@ -618,8 +631,22 @@
 !
 
 processChunk:type len:len
-    |chunk|
+    |chunk handler chunkData|
 
+    specialChunkHandlers notNil ifTrue:[
+        handler := specialChunkHandlers at:type ifAbsent:nil.
+        handler notNil ifTrue:[
+            chunkData := inStream nextBytes:len.
+            handler value:chunkData optionalArgument:self.
+            ^ true.
+        ].
+    ].
+
+    extractSpecialChunksOnly == true ifTrue:[
+        inStream skip:len.
+        ^ true.
+    ].
+    
     type = 'IDAT' ifTrue:[
         "---since the compressed data can span multiple
         chunks, stitch them all together first. later,
@@ -651,17 +678,6 @@
     type = 'hIST' ifTrue:[^ self processHISTChunkLen:len].
     type = 'spAL' ifTrue:[^ self processSPALChunkLen:len].
 
-    specialChunkHandlers notNil ifTrue:[
-        |handler chunkData|
-        
-        handler := specialChunkHandlers at:type ifAbsent:nil.
-        handler notNil ifTrue:[
-            chunkData := inStream nextBytes:len.
-            handler value:chunkData optionalArgument:self.
-            ^ true.
-        ].
-    ].
-
     type = 'niVI' ifTrue:[^ self processNIVIChunkLen:len].
     type = 'exEX' ifTrue:[^ self processEXEXChunkLen:len].
 
@@ -672,7 +688,7 @@
 
     "Created: / 21-06-1996 / 21:10:37 / cg"
     "Modified: / 11-04-2017 / 17:04:12 / cg"
-    "Modified: / 02-06-2018 / 06:43:03 / Claus Gittinger"
+    "Modified: / 27-10-2018 / 17:38:14 / Claus Gittinger"
 !
 
 processEXEXChunkLen:len