Hi,
Am 26.10.2010 19:44, schrieb José Rodolfo Carrijo de Freitas:
Hi Andreas,
I read on session 8.4.2 of the pdf 1.7 spec (page 124) that:
-----------------------------
The stack is a LIFO (last in, first out) data structure in which the contents
of the graphics state may be saved and later restored using the following
operators:
•The q operator shall push a copy of the entire graphics state onto the stack.
•The Q operator shall restore the entire graphics state to its former value by
popping it from the stack.
NOTE: These operators can be used to encapsulate a graphical element so that it
can modify parameters of the graphics state and later restore them to their
previous values.
**Occurrences of the q and Q operators shall be balanced within a given content
stream** (or within the sequence of streams specified in a page dictionary’s
Contents array).
-----------------------------
Correct and I didn't say anything else.
I thought that ctm and others gs would be restored as stated in the second item
above.
But if it's not the case how can I restore The transformation matrix?
If the **Occurrences of the q and Q operators shall be balanced within a given
content stream** shouldn’t I extract them within the extracted image?
Imagine the following example:
original pdf:
=============
1 0 0 1 100 0 cm
....
q -> (put a copy of gs to the stack, the ctm is still the same 1 0 0 1 100 0)
1 0 0 1 100 0 cm
(the new ctm is concatenated to the ctm from the gs -> ctm = 1 0 0 1 200 0)
/Im0 Do (draw the image translated by 200)
Q -> restore the gs ctm = 1 0 0 1 100 0
....
1 0 0 1 200 0 cm
(the new ctm is concatenated to the ctm from the gs -> ctm = 1 0 0 1 300 0)
....
modified pdf as mentioned in your posted example:
=================================================
1 0 0 1 100 0 cm
....
q -> (put a copy of gs to the stack, the ctm is still the same 1 0 0 1 100 0)
1 0 0 1 100 0 cm
(the ctm from the gs and the new one are concatenated -> ctm = 1 0 0 1 200 0)
....
Q -> restore the gs ctm = 1 0 0 1 100 0
....
1 0 0 1 200 0 cm
(the new ctm is concatenated to the ctm from the gs -> ctm = 1 0 0 1 300 0)
....
q -> (put a copy of gs to the stack, the ctm is still the same 1 0 0 1 300 0)
1 0 0 1 100 0 cm
(the new ctm is concatenated to the ctm from the gs -> ctm = 1 0 0 1 400 0)
/Im0 Do (draw the image translated by 400 !!)
Q
Because of the concatenated ctms the image is drawn in the wrong place
(translated by 400 instead of 200).
BR
Andreas Lehmkühler
-----Mensagem original-----
De: Andreas Lehmkuehler [mailto:[email protected]]
Enviada em: terça-feira, 26 de outubro de 2010 15:23
Para: [email protected]
Assunto: Re: copy entire stream of a page ignoring images
Hi,
Am 26.10.2010 18:59, schrieb José Rodolfo Carrijo de Freitas:
Hi Andreas,
I guess that I couldn’t express me very well. when I said:
“I was wondering if the remaining operators which identifies image graphical
states would
affect fonts and texts operators.” I want to mean that if that set of graphical
state could affect another operators outside the q-Q stack.
I understand that ‘q’ saves the graphics state and ‘Q’ restore the gs saved by
q.
Correct.
So if a set of operators are between q and Q, it would not affect anything
outside this block.
Correct.
The thing is that I’m not removing any q/Q operators, and it seems to affect
other parts of the stream.
One thing I noticed is that when I redraw the image, it creates another stream,
a new one just to the new image.
At this case, I have 2 streams and my content stream is actually an array of
substreams as show in the figure:
Still correct.
http://b.imagehost.org/view/0482/comparing-pdfs-in-pdfdebugger
Is it possible that a gs of stream 1 affects an operator of stream 0 ?
The streams will be concatenated. So there is no difference between 2 single
streams and 1 stream combining two single streams.
But you are probably missing one detail. Saving a gs doesn't mean that
everything will be set to their initial value, especially the ctm will be still
the same after a "q" command. In your example the ctm may have another value at
the end of stream 0/the beginning of stream 1 than the value somewhere in
between the stream from where you copied the command sequence.
BR
Andreas Lehmkühler
