--- a/ImageReader.st	Tue Jan 16 16:21:26 2018 +0100
+++ b/ImageReader.st	Tue Jan 16 16:24:03 2018 +0100
@@ -1,3 +1,5 @@
+"{ Encoding: utf8 }"
+
 "
  COPYRIGHT (c) 1991 by Claus Gittinger
 	      All Rights Reserved
@@ -24,6 +26,13 @@
 	category:'Graphics-Images-Readers'
 !
 
+Query subclass:#EnforcedImageTypeQuery
+	instanceVariableNames:''
+	classVariableNames:''
+	poolDictionaries:''
+	privateIn:ImageReader
+!
+
 !ImageReader primitiveDefinitions!
 %{
 
@@ -2373,6 +2382,22 @@
     ^ self == ImageReader.
 ! !
 
+!ImageReader class methodsFor:'signal constants'!
+
+enforcedImageTypeQuery
+    "the query signal which can be used to override the default type
+     of image as returned by a reader.
+     Currently, only PNGReader supports.
+     Usage:
+        ImageReader enforcedImageTypeQuery answer:#rgb
+            do:[
+                Image fromFile:anRGBAFile
+            ]
+    "
+
+    ^ EnforcedImageTypeQuery
+! !
+
 !ImageReader class methodsFor:'testing'!
 
 canRepresent:anImage
@@ -2885,6 +2910,38 @@
     ].
 ! !
 
+!ImageReader::EnforcedImageTypeQuery class methodsFor:'documentation'!
+
+documentation
+"
+    consider this a hack (but a not too bad one):
+
+    with pngReader (and maybe others), we may want to read an image file,
+    but ignore the alpha channel.
+    I.e. read it as an rgb image although the image file is actually rgba formatted.
+    This is useful, if the image contains invalid alpha information anyway,
+    as when asking appium for a screen shot 
+    (there are no transparent pixels on the screen - at least not until we get glass-plate displays...)
+
+    Instead of passing this information down through all the possible image and image reader interfaces,
+    this query is asked by some readers (currently only pngReader) and
+    can be answered high above by a caller to answer #rgb.
+
+    The default answer (nil) leads to the old behavior in that the file itself determines the format.
+    Please take a look at the concrete image reader documentation for which answers are valid and useful.
+
+    [author:]
+        cg
+
+    [instance variables:]
+
+    [class variables:]
+
+    [see also:]
+
+"
+! !
+
 !ImageReader class methodsFor:'documentation'!
 
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