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Xavier.d@adobe.con
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How to find decoder name from decoded stream?

Sep 23, 2013 6:08 AM

Hey,

 

177 0 obj^M<</Length 110 /Filter /FlateDecode >>^Mstream^M

x<9c>3´Ô30P0^@^Q<86> B^WÂ4^C<91>Fæ 2ÅP¡^P"^@Q^G#Á²^P]0¡ä\^E'O^Eýp r^E}^O

^E}§^@g^EC^E}O_<85><92>¢ÒT^E}^W<85>hC^E<83>X^O^W^E^F>Âð^A^X~à+<90>©°±ÿ !ÿ<81>ÿ<80>«§B ^@ßÆ"Ø^Mendstream^Mendobj

 

I have decoded the above stream by using the FlateDecode and I can get the below result.

 

19.00 0.00 1.00 -0.00 16.00 27.00 d1 q 16.000 0.000 0.000 27.000 1.000 0.000 cm BI /W 16 /H 27 /BPC 1 /IM true /D [1 0]

ID                   ¢ ¢ ¢ ￰ p x<?￸ ￰ ￀EI Q

 

Still the Image Data [ID] is encoded.  I have to decode this Image data by using the corresponding decoder to get the exact value.

But I'm confused, how to find the decoder name? Which decoder needs to be used for decode this ID [Image Data]?

Can someone help me to find the decoder for Image Data [ID].

 

Thanks,

Xavier

 
Replies
  • Currently Being Moderated
    Sep 23, 2013 6:14 AM   in reply to Xavier.d@adobe.con

    What makes you assume it is encoded? It is just bits, as you are dealing with an imagemask and htis with a bit depth of 1. Also, based on the D entry you know when bits are filled and when not.

     

    Olaf

     
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  • Currently Being Moderated
    Sep 23, 2013 7:01 AM   in reply to Xavier.d@adobe.con

    Youy are mixing up encoding of a Typ3 font (howe to go from character names to gyph defintions) with encoding for an image stream (or more generically,  a filtered stream). Your image data is noit compressed, no encoding applies. Your Type3 font's encoding has nothing to do with the image encoding. A character name in a Type3 font simply points to an object that defines the appearance of the respecive glyph. Your glyph seems to contain a mask - not uncommon for bitmap fonts. None of the font types that can be used in a PDF support bitmap fonts, except Type3 fonts.

     

    Aaah - and ID does not stand for "identity" but rather for "image data". Please read the inline image section in the PDF standard some more....

     

    Olaf

     
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  • Currently Being Moderated
    Sep 23, 2013 7:29 AM   in reply to Xavier.d@adobe.con

    If there is no filter entry, then no filter has been applied - you have raw data for the inline image.

     

    For small bitmap inline images it often does not make a lot of sense to apply compression to the inline image data  (especially when the content or appearance stream is compressed anyway, albeittypically just with Flate).

     

     

    Olaf

     
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