I used Adobe Acrobat Pro to do a pre-press on the PDF. The images which
print too big are specified to be at 75 DPI, the ones that print right
are about 120~126 DPI. In all cases the numbers are not exact, and vary
slightly from image to image.
So what is happening is that the PDF specified how many pixels wide, and
this interacts with DPI to determine how large it will be on the paper.
Lower DPI, larger on paper.
Editing the PDF with vi, the PDF contains a line that specifies the
width and height in pixels, but not the DPI. That must be encoded with
the image somehow.
I expect that the larger images were captured with a different process,
for example a different PC with a different screen resolution, or on a
PC where the X-Windows DPI was set different/incorrectly.
Another possibility is that one or the other was edited with an
application, for example to crop. Some applications I have run into
strip all of the tags out of the file and put their own. Or if there is
no resolution, put one in that they like.
There are two ways to go from here:
[1] Fix the capture files with an application that edits the tags, or
capture new images.
[2] Change the PDF coding to specify a bounding box of the image so that
the PDF renderer will make it the desired size regardless of the number
of pixels and resolution. This would be the preferred method.
Googleing for PDF Referend brings me to:
ww w.adobe.com/devnet/pdf/pdf_reference.ht ml
Document management - Portable document format - Part1: PDF 1.7, First
Edition (July,2008)
Section 8.9, Images
Specifically section 8.9.5, Image Dictionaries
Specifically section 8.9.1 on page 209, example showing translation and
scaling of an Xobject Image with the cm operator, and encapsulating it
within q and Q to save and restore the graphics state, so as to not goof
up the larger context into which the image is placed.
Reading around a little bit confirms through implication that images are
sized based on the number of pixels and the resolution. The example
also reinforces this, as it is necessary to perform a transformation for
the image to be a different size.
ww w.adobe.com/devnet/pdf/pdf_reference_archive.ht ml contains older
versions.
Hope this helps. Hope this works!
--Ray
Derek Atkins wrote:
Tom,
Tom Browder <tom.brow...@gmail.com> writes:
Derek, I'll be happy to take a look and see if I can fix at least a
couple of the bad figures to see what kind of effort is involved. I
don't know much docbook, but I'm sure there are various ways to
manipulate a figure without having to import or make a new image file
(and it shouldn't affect the same figure in other products--just pdf).
I have done similar things to lots of figures with LaTeX and ConTeXt.
That would be most excellent! Thank you.
If "make pdf" is all that's needed, I can set that up as part of
the daily doc build on 'code'.
Regards,
-Tom
Tom Browder
Niceville, Florida
USA
-derek
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