svn commit: r603243 - /xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java

[je...@apache.org]

Author: jeremias
Date: Tue Dec 11 05:49:04 2007
New Revision: 603243

URL: http://svn.apache.org/viewvc?rev=603243&view=rev
Log:
Convenience method to retrieve just the alpha channel from a bitmap.

Modified:
    xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java

Modified: xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java
URL: http://svn.apache.org/viewvc/xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java?rev=603243&r1=603242&r2=603243&view=diff
==============================================================================
--- xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java (original)
+++ xmlgraphics/commons/trunk/src/java/org/apache/xmlgraphics/image/GraphicsUtil.java Tue Dec 11 05:49:04 2007
@@ -1084,4 +1084,28 @@
             }
 */
 
+    /**
+     * Extracts an alpha raster from a RenderedImage. The method tries to avoid copying data
+     * unnecessarily by checking if the RenderedImage is a BufferedImage which offers suitable
+     * direct methods.
+     * @param image the image
+     * @return the alpha raster
+     */
+    public static Raster getAlphaRaster(RenderedImage image) {
+        ColorModel cm = image.getColorModel();
+        if (!cm.hasAlpha() || cm.getTransparency() != ColorModel.TRANSLUCENT) {
+            throw new IllegalStateException("Image doesn't have an alpha channel");
+        }
+        Raster alpha;
+        if (image instanceof BufferedImage) {
+            //Optimization possible with BufferedImage (No copying)
+            alpha = ((BufferedImage)image).getAlphaRaster();
+        } else {
+            WritableRaster wraster = GraphicsUtil.makeRasterWritable(image.getData());
+            alpha = image.getColorModel().getAlphaRaster(wraster);
+        }
+        return alpha;
+    }
+    
+    
 }



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