--- a/Image.st	Fri Aug 25 12:38:12 2017 +0200
+++ b/Image.st	Fri Aug 25 12:38:44 2017 +0200
@@ -13675,14 +13675,16 @@
      of alpha bits i.e. (1 bitShift:bitsAlpha)-1.
      This has to be redefined by subclasses."
 
-    |redBits greenBits blueBits alphaBits|
+    |redBits greenBits blueBits alphaBits alphaMask|
 
     samplesPerPixel >= 4 ifTrue:[
+        alphaMask := (1 bitShift:alphaBits)-1.
+        
         photometric == #rgba ifTrue:[
             "/ alpha in low bits
             alphaBits := bitsPerSample at:4.
 
-            ^ pixel bitAnd:(1 bitShift:alphaBits)-1
+            ^ pixel bitAnd:alphaMask
         ].
         photometric == #argb ifTrue:[
             "/ alpha in high bits
@@ -13691,8 +13693,8 @@
             blueBits := bitsPerSample at:3.
             alphaBits := bitsPerSample at:4.
 
-            ^ (pixel bitShift:(redBits + greenBits + blueBits) negated)
-                bitAnd:(1 bitShift:alphaBits)-1
+            ^ (pixel rightShift:(redBits + greenBits + blueBits))
+                    bitAnd:alphaMask
         ].
         ^ 0
     ].
@@ -13700,7 +13702,7 @@
     self subclassResponsibility
 
     "Created: / 08-06-1996 / 09:44:51 / cg"
-    "Modified: / 22-08-2017 / 17:47:36 / cg"
+    "Modified: / 25-08-2017 / 12:24:21 / cg"
 !
 
 alphaMaskForPixelValue
@@ -13853,7 +13855,7 @@
         photometric == #rgba ifTrue:[
             "/ alpha in low bits
             alphaBits := self numAlphaBits.
-            ^ (pixel bitShift:alphaBits negated) bitAnd:blueMask
+            ^ (pixel rightShift:alphaBits) bitAnd:blueMask
         ].
         ^ pixel bitAnd:blueMask
     ].
@@ -13861,7 +13863,7 @@
     self subclassResponsibility
 
     "Created: / 08-06-1996 / 09:44:21 / cg"
-    "Modified: / 22-08-2017 / 18:12:00 / cg"
+    "Modified: / 25-08-2017 / 12:23:20 / cg"
 !
 
 blueComponentOf:pixel
@@ -14112,7 +14114,7 @@
     samplesPerPixel >= 3 ifTrue:[
         photometric == #rgba ifTrue:[
             alphaBits := self numAlphaBits.
-            (pixel bitShift:(blueBits + alphaBits) negated) bitAnd:greenMask.   
+            (pixel rightShift:(blueBits + alphaBits)) bitAnd:greenMask.   
         ].
         ^ (pixel bitShift:blueBits negated) bitAnd:greenMask
     ].
@@ -14120,7 +14122,7 @@
     self subclassResponsibility
 
     "Created: / 08-06-1996 / 09:44:37 / cg"
-    "Modified: / 22-08-2017 / 18:12:16 / cg"
+    "Modified: / 25-08-2017 / 12:23:29 / cg"
 !
 
 greenComponentOf:pixel
@@ -14141,13 +14143,13 @@
 
         s := (1 bitShift:greenBits) - 1.
 
-        ^ 100.0 / s * ((pixel bitShift:blueBits negated) bitAnd:(1 bitShift:greenBits)-1)
+        ^ 100.0 / s * ((pixel rightShift:blueBits) bitAnd:(1 bitShift:greenBits)-1)
     ].
 
     self subclassResponsibility
 
-    "Created: 8.6.1996 / 08:45:34 / cg"
-    "Modified: 10.6.1996 / 14:55:24 / cg"
+    "Created: / 08-06-1996 / 08:45:34 / cg"
+    "Modified: / 25-08-2017 / 12:24:33 / cg"
 !
 
 greenMaskForPixelValue
@@ -14424,7 +14426,7 @@
     samplesPerPixel >= 3 ifTrue:[
         photometric == #rgba ifTrue:[
             alphaBits := self numAlphaBits.
-            ^ (pixel bitShift:(greenBits+blueBits+alphaBits) negated) bitAnd:redMask.
+            ^ (pixel rightShift:(greenBits+blueBits+alphaBits)) bitAnd:redMask.
         ].
         ^ (pixel bitShift:(greenBits+blueBits) negated) bitAnd:redMask.
     ].
@@ -14432,7 +14434,7 @@
     self subclassResponsibility
 
     "Created: / 08-06-1996 / 09:44:51 / cg"
-    "Modified: / 22-08-2017 / 18:12:51 / cg"
+    "Modified: / 25-08-2017 / 12:24:40 / cg"
 !
 
 redComponentOf:pixel
@@ -14457,14 +14459,14 @@
         s := (1 bitShift:redBits) - 1.
 
         ^ 100.0 / s *
-          ((pixel bitShift:(greenBits + blueBits) negated)
+          ((pixel rightShift:(greenBits + blueBits))
            bitAnd:(1 bitShift:redBits)-1)
     ].
 
     self subclassResponsibility
 
-    "Created: 8.6.1996 / 08:45:30 / cg"
-    "Modified: 14.6.1996 / 17:34:00 / cg"
+    "Created: / 08-06-1996 / 08:45:30 / cg"
+    "Modified: / 25-08-2017 / 12:24:46 / cg"
 !
 
 redMaskForPixelValue