--- a/PNGReader.st	Mon Apr 10 03:48:41 2017 +0000
+++ b/PNGReader.st	Tue Apr 11 12:42:12 2017 +0200
@@ -1404,11 +1404,7 @@
     
     image mask notNil ifTrue:[
         ((photometric ~~ #rgb) and:[(photometric ~~ #rgba)]) ifTrue: [
-            image maskedPixelsAre0 ifTrue:[
-                paletteIndexForMaskedPixels := 0
-            ] ifFalse:[
-                self determinePaletteIndexForMaskedPixels
-            ]
+            self determinePaletteIndexForMaskedPixels
         ] ifFalse:[
             photometric := #rgba.
         ].    
@@ -1420,7 +1416,7 @@
     self writeImageDataChunk.
     self writeEndChunk
 
-    "Modified: / 22-02-2017 / 11:00:26 / cg"
+    "Modified: / 11-04-2017 / 12:35:19 / cg"
 ! !
 
 !PNGReader methodsFor:'writing-private'!
@@ -1467,6 +1463,29 @@
 
 !PNGReader methodsFor:'writing-private chunks'!
 
+determineColorTypeAndHasMask
+    ((photometric == #whiteIs0) or:[ (photometric == #blackIs0)]) ifTrue:[
+        colorType := ColorTypeGray.
+        ^ (samplesPerPixel > 1)
+    ].
+    (photometric == #rgb) ifTrue:[
+        colorType := ColorTypeRGB.
+        ^ (samplesPerPixel > 3)
+    ].
+    (photometric == #rgba) ifTrue:[
+        colorType := ColorTypeRGBAlpha.
+        ^ (samplesPerPixel > 3)
+    ].
+    (photometric == #palette) ifTrue:[
+        colorType := ColorTypePalette.
+        ^ (samplesPerPixel > 1)
+    ].
+    self error:'unhandled photometric: ',photometric asString.
+    ^ false.
+
+    "Created: / 11-04-2017 / 12:39:30 / cg"
+!
+
 writeChunk:chunkTypeChars size:len with:aBlock
     |crc realOutStream chunkBytes|
 
@@ -1496,31 +1515,7 @@
 writeIHDRChunk
     |hasMask|
 
-    hasMask := 0.
-    
-    ((photometric == #whiteIs0) or:[ (photometric == #blackIs0)]) ifTrue:[
-        colorType := ColorTypeGray.
-        hasMask := (samplesPerPixel > 1)
-    ].
-    (photometric == #rgb) ifTrue:[
-        colorType := ColorTypeRGB.
-        hasMask := (samplesPerPixel > 3)
-    ].
-    (photometric == #rgba) ifTrue:[
-        colorType := ColorTypeRGBAlpha.
-        hasMask := (samplesPerPixel > 3)
-    ].
-    (photometric == #palette) ifTrue:[
-        colorType := ColorTypePalette.
-        hasMask := (samplesPerPixel > 1)
-    ].
-    colorType isNil ifTrue:[
-        self error:'unhandled photometric'
-    ].
-
-    mask notNil ifTrue:[
-        hasMask := true.
-    ].
+    hasMask := self determineColorTypeAndHasMask.
     hasMask ifTrue:[
         "/ make it grayAlpha / rgba
         ((colorType == ColorTypeGray) or:[colorType == ColorTypeGray]) ifTrue:[
@@ -1530,7 +1525,7 @@
     
     self 
         writeChunk: 'IHDR'
-        size: 13
+        size: (4+4+5)
         with:[ 
             self writeLong:width.
             self writeLong:height.
@@ -1541,7 +1536,7 @@
             outStream nextPut: 0   "Non-interlaced"
         ]
 
-    "Modified (format): / 16-02-2017 / 21:24:22 / cg"
+    "Modified: / 11-04-2017 / 12:40:53 / cg"
 !
 
 writeImageDataChunk
@@ -1556,8 +1551,6 @@
 
     (mask notNil and:[photometric ~~ #palette]) ifTrue:[
         (depth == 32) ifTrue:[
-            "/ on-the-fly put mask into the alpha channel.
-            
             bytesPerPixel := 4
         ] ifFalse:[
             "/ for now - only support depth24 + mask
@@ -1566,7 +1559,6 @@
         ].
         
         "/ on-the-fly place mask into the alpha channel.
-
         row32 := ByteArray new:(4 * width).
         self assert:(bytesPerScanline == (bytesPerPixel * width)).
 
@@ -1613,6 +1605,7 @@
         ]
 
     "Modified: / 25-02-2017 / 14:27:34 / cg"
+    "Modified (format): / 11-04-2017 / 12:41:22 / cg"
 !
 
 writePaletteChunk