How to insert transparent PNG in PDF?

Question

I am able to insert JPG image into a PDF document with DCTDecode filter. I think the all parameters should be the same for PNG image too, except the filter which should be FlateDecode. However, when I try to insert PNG with the same parameters, the PNG image is not visible in he PDF document.

UPDATE: I came to conclusion that the PDF file should include

1 0 obj <<
/Type /XObject
/Subtype /Image
/Width 512
/Height 512
/BitsPerComponent 8
/ColorSpace /DeviceRGB
/SMask 9 0 R
/Length 134753    
/Filter /FlateDecode
>>
stream
PNG_RAW DATA
endstream
endobj
9 0 obj <<
/Type /XObject
/Subtype /Image
/Width 512
/Height 512
/BitsPerComponent 8
/ColorSpace /DeviceGray
/Length 12087     
/Filter /FlateDecode
>>
stream
ALPHA_PIXELS
endstream
endobj

BUT how can I separate the PNG raw data and the alpha pixels via ImageMagick? In other words, what ImageMagick command can produce PDF_RAW_DATA and ALPHA_PIXELS for insertion into the pdf file.

Answer 1

@Bobrovsky

Here is an example: http://pd4ml.com/i/pd4ml18130.pdf

To be more accurate: you cannot embed a PNG absolutely with no manipulations with it. You would need to split a PNG to sections: IDAT (image data) goes to PDF as byte stream unchanged, PLTE (palette) - to colorspace definition, iCCP optionally goes to color profile object.

An object dictionary may look like that:

<<
/Filter /FlateDecode
/Type /XObject
/Subtype /Image
/BitsPerComponent 8
/Length 1277
/Height 250
/Width 250
/DecodeParms <<
    /BitsPerComponent 8
    /Predictor 15
    /Columns 250
    /Colors 1
>>
/ColorSpace [/Indexed /DeviceRGB 1 <1989d1ffffff>]
>>
stream
... IDAT bytes ...

Answer 2

Most probably you didn't decode PNG images.

PNGs are not directly supported in PDF. I mean they are not supported in way JPEGs are supported.

You have to produce raw uncompressed raster bytes from PNGs before embedding them into PDF. You may encode the raster bytes with Flate or LZW encoder if you wish.