When I add a partially transparent image to a PDF, I'm getting 
grey/black edges along the mask border.  Am I missing something to help 
guide the calculations?  (Something document-level along the lines of 
PdfWriter.setRGBTransparency, but not that?)

In this example, I add a yellow oval as a raw image, and then add it to 
a white document.  The background of the image is transparent black, and 
I see gray or black (depending on scale) border in the resulting PDF. 
(I could change the background to transparent white in this case, but 
won't always be adding my images over a solid color.)

   // create image, transparent black
   BufferedImage bi = new BufferedImage(400, 400, 
BufferedImage.TYPE_INT_ARGB);

   // draw pale yellow oval
   Graphics2D g = bi.createGraphics();
   g.setColor(new Color(255, 255, 128, 255));
   g.fillOval(0, 0, 400, 400);
   g.dispose();

   // add to PDF
   Image i = Image.getInstance(bi, null);
   i.setAbsolutePosition(100, 400);
   writer.getDirectContent().addImage(i);

The resulting PDF shows the yellow oval with the mentioned border.  The 
data contains the RGB image and the grayscale smask:

1 0 obj
<</Type/XObject/ColorSpace/DeviceGray/Subtype/Image/BitsPerComponent 
8/Width 400/Length 1555/Height 400/Filter/FlateDecode>>stream

2 0 obj
<</Type/XObject/ColorSpace/DeviceRGB/SMask 1 0 
R/Subtype/Image/BitsPerComponent 8/Width 400/Length 2593/Height 
400/Filter/FlateDecode>>stream

I came across the following thread on implementing this feature:
 
http://www.mail-archive.com/[email protected]/msg42290.html
but it doesn't appear that these images are getting JPG compressed, so 
there shouldn't be any loss of alpha data?

Any pointers greatly appreciated.  Thanks,

Michael Brewer-Davis


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