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Posted to users@pdfbox.apache.org by "christopher.begley@outlook.com" <ch...@outlook.com> on 2016/11/01 14:58:16 UTC
Re: cosDocument.getXrefTable() returns negative offsets
On 2016-10-31 12:44 (-0400), Andreas Lehmkuehler <an...@lehmi.de> wrote:
> Am 31.10.2016 um 16:10 schrieb christopher.begley@outlook.com:
> >
> >>> OBJ_NUMBER , OFFSET
> >>> 49,12769
> >>> 50,25217
> >>> 51,25502
> >>> 52,26034
> >>> 53,116
> >>> 54,-36
> >>> 55,-36
> >>> 56,-36
> >
> >> A negative offset indicates that the given object is part of a compressed object
> >> stream. In your case that stream is object 36 0.
> >>
> >>> Thanks in advance for your time.
> >>
> >> BR
> >> Andreas
> >
> > Thanks Andreas. Where can I find more documentation on compressed objects with respect to negative offsets?
> PDF spec, chapter "7.5.7 Object Streams"
>
> BR
> Andreas
>
> Thanks. I read that section. I also read about cross-reference streams. Nowhere in the entire PDF Spec does it mention negative offsets. I'm relatively new to pdf parsing and where I'm stumped is I don't know exactly how to handle these negative offsets.
> >>> OBJ_NUMBER , OFFSET
> >>> 49,12769
> >>> 50,25217
> >>> 51,25502
> >>> 52,26034
> >>> 53,116
> >>> 54,-36
> >>> 55,-36
> >>> 56,-36
Let's take Object Number 54 for example. In your answer you stated that this would be Object [36,0] and that it is compressed. How did you know it's object 36,0? Where did you find this information?How - using the PDFBox API, would I retrieve this object and decode it? I wish I could find documentation (somewhere) on how to handle this scenario - maybe I'm missing something or not searching for the right keywords.
I appreciate your patience in helping me out. I'm more than willing to read/research anything necessary, but I just got through reading 3 sections of the PDF Reference and while it discussed at length the structure of objects, object streams, cross reference streams , it did not help me in dealing with how to handle/ locate / parse objects with a negative offset.
>
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Re: cosDocument.getXrefTable() returns negative offsets
Posted by Andreas Lehmkuehler <an...@lehmi.de>.
Am 01.11.2016 um 15:58 schrieb christopher.begley@outlook.com:
>
> On 2016-10-31 12:44 (-0400), Andreas Lehmkuehler <an...@lehmi.de> wrote:
>> Am 31.10.2016 um 16:10 schrieb christopher.begley@outlook.com:
>>>
>>>>> OBJ_NUMBER , OFFSET
>>>>> 49,12769
>>>>> 50,25217
>>>>> 51,25502
>>>>> 52,26034
>>>>> 53,116
>>>>> 54,-36
>>>>> 55,-36
>>>>> 56,-36
>>>
>>>> A negative offset indicates that the given object is part of a compressed object
>>>> stream. In your case that stream is object 36 0.
>>>>
>>>>> Thanks in advance for your time.
>>>>
>>>> BR
>>>> Andreas
>>>
>>> Thanks Andreas. Where can I find more documentation on compressed objects with respect to negative offsets?
>> PDF spec, chapter "7.5.7 Object Streams"
>>
>> BR
>> Andreas
>>
>> Thanks. I read that section. I also read about cross-reference streams. Nowhere in the entire PDF Spec does it mention negative offsets. I'm relatively new to pdf parsing and where I'm stumped is I don't know exactly how to handle these negative offsets.
>
>>>>> OBJ_NUMBER , OFFSET
>>>>> 49,12769
>>>>> 50,25217
>>>>> 51,25502
>>>>> 52,26034
>>>>> 53,116
>>>>> 54,-36
>>>>> 55,-36
>>>>> 56,-36
>
> Let's take Object Number 54 for example. In your answer you stated that this would be Object [36,0] and that it is compressed. How did you know it's object 36,0? Where did you find this information?How - using the PDFBox API, would I retrieve this object and decode it? I wish I could find documentation (somewhere) on how to handle this scenario - maybe I'm missing something or not searching for the right keywords.
>
> I appreciate your patience in helping me out. I'm more than willing to read/research anything necessary, but I just got through reading 3 sections of the PDF Reference and while it discussed at length the structure of objects, object streams, cross reference streams , it did not help me in dealing with how to handle/ locate / parse objects with a negative offset.
OK, I understand your confusion. There is no negative offset within the spec. We
are using negative values to distinguish "direct" xref entries from those which
point to a compressed object stream.
Have a look at COSParser#parseObjectStream to see how PDFBox handles those
object streams.
BR
Andreas
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