[Mono-bugs] [Bug 80323][Nor] Changed - Incorrect ColorMatrix alpha processing

bugzilla-daemon at bugzilla.ximian.com bugzilla-daemon at bugzilla.ximian.com
Wed Dec 20 11:34:18 EST 2006

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Changed by sebastien at ximian.com.


--- shadow/80323	2006-12-20 09:34:01.000000000 -0500
+++ shadow/80323.tmp.10962	2006-12-20 11:34:18.000000000 -0500
@@ -1,12 +1,12 @@
 Bug#: 80323
 Product: Mono: Class Libraries
 Version: 1.2
 OS: other
 OS Details: SUSE 10.1
-Status: NEW   
+Status: ASSIGNED   
 Severity: Unknown
 Priority: Normal
 Component: libgdiplus
 AssignedTo: sebastien at ximian.com                            
 ReportedBy: josecoig at cae.net               
@@ -52,6 +52,28 @@
 Created an attachment (id=18351)
 ColorMatrix bug test case - binary and source
 ------- Additional Comments From robertj at gmx.net  2006-12-20 06:23 -------
 --> Windows.Forms
+------- Additional Comments From sebastien at ximian.com  2006-12-20 11:34 -------
+The problem seems to be that the (current) code works on ARGB while
+the bitmap itself isn't (really) using alpha (i.e. the original color
+100,255,0,0 is transformed into 255,255,155,155 on both Mono and MS).
+Bitmap.GetPixel (50,50) = Color [A=255, R=255, G=155, B=155]
+Bitmap.GetPixel (150,50) = Color [A=255, R=255, G=255, B=255]
+Bitmap.GetPixel (50,50) = Color [A=255, R=255, G=155, B=155]
+Bitmap.GetPixel (150,50) = Color [A=255, R=255, G=205, B=205]
+Applying the (current) calculation on the original (100,255,0,0) color
+looks good (i.e. the algo doesn't match the data).
+For the blue background I suspect the calculations (including
+float/int conversions) are introducing small variations that gets
+amplified at each iteration.

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