Adobe Community : All Content - All Communities

Decompressing a cross reference stream with Params.

forums_noreply@adobe.com — Fri, 29 Aug 2014 04:14:21 GMT

I'm losing my mind trying to decompress this stream. I've asked everyone and am not having much luck with it. This is a cross reference stream with decode params.

I have used an external library for decompressing this and for some reason, the xref streams just cannot be decoded. I noticed that software designed to decompress pdf files such as Quick Pdf, VeryPdf etc will decompress all streams but these. So there must be something extra about the output of these that I don't understand.

A common error message would be that the stream cannot be displayed because it contains binary data. Very odd. Any clues.

25 0 obj

<</DecodeParms<</Columns 4/Predictor 12>>/Filter/FlateDecode/ID[<6647557224A6C102A60F6D82BB22C18D><AA383B5CF85B7F4BACB9D502B93 343E9>]/Index[10 20]/Info 9 0 R/Length 64/Prev 23381/Root 11 0 R/Size 30/Type/XRef/W[1 2 1]>>stream

hÞbbd ``b`Š ~@‚ñ `Ù $Øù€ W P°~.............compressed stream data.

endstream

endobj

Decompressing Xref Streams?

forums_noreply@adobe.com — Tue, 26 Aug 2014 14:50:21 GMT

I am having significant problems decompressing xref streams. Unfortunately the use of Params has complicated things a little.

I am using various open source libraries to do this but I just wanted to check if my understanding is right. The ISO3200 standard doesn't quiet put it in a way I can understand.

If I am returning a decompressed Xref stream to a buffer, can I output it as one long string (adhering to white space), or do I need to recognise the output another way. Such as Objects etc?

Are Xref streams and white space rules surrounding these streams the same as the rules for all other streams.

I have files written with Adobe 9 pdf printer, are the predictors in that version, relative to previous versions, different. I'm simply trying to decompress text streams and want the xref information to navigate the document.

If there is tips for decompressing these streams please add them as I could be here for the next two years trying to decompress a single

xref stream. Maybe that's the way it's supposed to be, I don't know.

Thanks

ISO 3200 - 7.5.8 Cross-Reference Streams

forums_noreply@adobe.com — Wed, 09 Jul 2014 08:32:18 GMT

I'm having trouble interpreting the Example 4 on page 48 of PDF 32000-1:2008, Specifically in relation to the blue bolded text below.

The first field of these entries is the entry type (2) ------What does the 2 represent?

number of the object stream (15) --------What does the 15 represent?

position within the sequence of objects in the object stream (0, 1, and 2)------What does this refer to?

It's just not clear what the 15 is if it's the second entry? Would somebody be able to explain where these numbers come from?

The following shows the same objects from the previous example stored in an object stream in a PDF 1.5 file, along with a cross-reference stream.

The cross-reference stream (see 7.5.8, "Cross-Reference Streams") contains entries for the fonts (objects 11 and 13) and the descriptor (object 12), which are compressed objects in an object stream. The first field of these entries is the entry type (2), the second field is the number of the object stream (15), and the third field is the position within the sequence of objects in the object stream (0, 1, and 2). The cross-reference stream also contains a type 1 entry for the object stream itself.

PDF File with Run Length Encoding?

forums_noreply@adobe.com — Thu, 13 Feb 2014 17:29:13 GMT

Would anyone have a PDF file containing text streams compressed in Run-Length Encoding? I need one to test a decompressor. I know they are probably rare and not used anymore which is why one is so difficult to find.

If you do have one could you attach it in a reply or refer me to it.

Thanks

Cropping PDF Files and printing?

forums_noreply@adobe.com — Tue, 25 Mar 2014 04:18:18 GMT

I'm having some problems with a PDF file. It is a document with a large margin (allot of space) befoer and after the writing on each page. I can crop the document so it removes this white space and it appears to work. The problem I'm having is this:

When I go to print the document (two pages per sheet), it doesn't seem to take into account that I have trimmed the white space from either side of each page. Obviously I want the writing to be as big as possible given that I have removed allot of the white space. But,,, despite removing this white space by cropping all the pages in the document (left, right, top, bottom margins) these broad white space margins still show up when I go to print the document. How can I get rid of this white space permenantly. Is it embedded somewhere else in the document? Maybe there's a setting I need to change in the document properties.

Thanks

PDF Stream Extent?

forums_noreply@adobe.com — Fri, 17 Jan 2014 03:52:02 GMT

Hello everyone.

I'm trying to interpret exacty what is and isn't included in a PDF stream and to date am still confused. I'll paste a section of the ISO3200 - 1 PDF reference below.

I'm not sure, but these statements appear to contradict each other.

So I have a stream which specifies a lenghth of 2215 bytes in its compressed form.

There is a carriage return and a line feed at the start and end of the stream data falling between the 'stream' and 'endstream' keywords.

So my data looks like this : stream CR LF Data Data Data CR LF endstream Keep in mind that CR = Carriage Return and LF = Line feed

Before I remove the CR and LF from each end of the data the total size of the stream is 2217 bytes (between the 'stream' and 'endstream' keywords. From the first paragraph below it appears that I am reading the data between the Carriage return and line feed characters at each end which brings the compressed size down to 2213 bytes (not 2215 as the stream 'Lenght' specifies.

If I follow the second paragraph from Table 5 in relation to Stream Lenghth, it appears that only the carriage return and line feed at the end of the stream are removed. So the stream to be decompressed would look like this: CR LF Data Data Data . This in fact adheres to the Stream Lenght specification for that stream which is 2215 bytes?

When decompressing a stream, what should and shouldn't be included? Cut the CR and LF from the start or the end ,,, or both? Note the red bolded section below: "lie between the end-of-line marker (I assume this means not inclusive). Like saying, stand between those two people (this doesn't mean stand on these two people and centre yourself). Yet... the green bolded area in the second section doesn't mention the initial white space?

Perhaps this is what it means. The first whitespace character after the 'stream' keyword and the whitespace character preceding the 'endstream' keyword are ignored so the stream looks like this:

Original Stream Data before removing whitespace: CR LF Data Data Data CR LF

Actual Stream data to be decompressed (whitespace removed): LF Data Data Data CR

That last option produces a stream of 2215 bytes as well.

Thanks

Under 'Stream Objects - General'

The keyword stream that follows the stream dictionary shall be followed by an end-of-line marker

consisting of either a CARRIAGE RETURN and a LINE FEED or just a LINE FEED, and not by a CARRIAGE RETURN alone. The sequence of bytes that make up a stream lie between the end-of-line marker following the stream keyword and the endstream keyword; the stream dictionary specifies the exact number of bytes. There should be an end-of-line marker after the data and before endstream; this marker shall not be included in the stream length.

AND

From table 5 in relation to the stream Length.

(Required) The number of bytes from the beginning of the line

following the keyword stream to the last byte just before the

keyword endstream. (There may be an additional EOL

marker, preceding endstream, that is not included in the count

and is not logically part of the stream data.) See 7.3.8.2,

"Stream Extent", for further discussion.

Reading a PDF stream for LZW decompression?

forums_noreply@adobe.com — Sun, 08 Dec 2013 11:45:31 GMT

Hello.. I'm really struggling here.

I am currently using the Rosetta Code implementation for LZW decompression (C++). This implementation requires numerical imput. That is.. the input in it's compressed state is in numerical form.. a series of numbers. My problem is this:

I want to read the compressed LZW stream (compressed only in LZW and notencoded in ASCII 85) into a buffer and that is then passed to the decompression algorithm for decompression. I open the pdf in binary mode, read each character and convert it to an int and load each integer into the buffer . Once the buffer (which is an int vector) is loaded, I pass this to the algorithm for decompression.

Unfortunately the data will not decompress. I seem to get the same output as I put into it in a character form. I have included white space (noskipws) and also tried the opposite. I have also tried (using bitwise shift operation) to create 12 bit chunks and then loading those into an int vector. This isn't working either. I'm thinking it has something to do with how I am reading the data in the first place. What do all these little glyphs represent (in the compressed stream)? How do I go about reading compressed data into a buffer if the algorithm I am using requires numberical input common to LZW compression?

Should I include white space? How should I read the compressed data?

Any clues would be greatly appreciated.

Thanks very much.

Reading a PDF stream for LZW decompression?

forums_noreply@adobe.com — Sun, 08 Dec 2013 10:42:14 GMT

Hello.. I'm really struggling here.

I want to read the compressed LZW stream (compressed only in LZW and not encoded in ASCII 85) into a buffer and that is then passed to the decompression algorithm for decompression. I open the pdf in binary mode, read each character and convert it to an int and load each integer into the buffer . Once the buffer (which is an int vector) is loaded, I pass this to the algorithm for decompression.

Should I include white space? How should I read the compressed data?

Any clues would be greatly appreciated.

Thanks very much.