How to add a PNG to a PDF?

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PDF

image

PNG

Hi,

My MFC application generates PDF's and now I'm trying to add support to PNG files with transparency.

I'm starting with just using the entry /Mask to mask one color.

What I have tried:

I extracted the IDAT chunk of the PNG and added to the object stream and used the "transparent color" (which I obtained with FreeImage) in the /Mask entry.

My PDF image object:

6 0 obj
<<
/Type /XObject
/Subtype /Image
/Name /Im1
/Width 60
/Height 23
/BitsPerComponent 8
/Length 484
/ColorSpace /DeviceRGB
/Filter /FlateDecode
/Mask [0 0 0 0 0 0]
>>
stream
    % IDAT CHUNK %
endstream
endobj


I also tried adding the tRNS chunk to the stream of a XObject and using SMask but that didn't work.

I'm starting with the "color key mask" because I believe it's the easiest one. I know this is a very broad question but any hint or direction will be very appreciated.

This is my PDF and I'm using this image to test.

Thanks!