I have about 20 large pdfs which I have split by pages for easier access. When I split it by pages using qpdf I am observing an inflation of 10x in total size, meaning that I have some redundant data in all per-page pdfs. It is very likely stored fonts that are cause of the bloat. Is there a way to externalize these fonts (like the user can install those fonts beforehand on their devices)? My goal is that once I split the pdfs by page the total size should be within 1x-2x of original so that I can host it on my website.
Here is the sample pdf from repository
https://www.mea.gov.in/Images/CPV/Volume17_Part_III.pdf
Any help regarding pdf splitting is welcomed
Thanks!
I split the file into files of one page each and then tried to squeeze them. There is no un-needed data:
$ cpdf -squeeze 641.pdf -o out.pdf
Initial file size is 947307 bytes
Beginning squeeze: 2178 objects
Squeezing... Down to 1519 objects
Squeezing page data and xobjects
Recompressing document
Final file size is 945176 bytes, 99.78% of original.
So no luck there. About 4/5 of the size of each file is the (uncompressed) XML metadata from the main file. You may well not need this. If so, you can run:
cpdf -remove-metadata in.pdf -o small.pdf
on each output file. This reduces the size of each file by about 5 times. Obviously if you're splitting into groups of more than one page, the effect will not be as large.
Related
I have no experience of programming.
My PDFs won't display images on the iPad in PDFExpert or GoodNotes as the images are in JPEG2000, from what I could find on the internet.
These are large PDFs, upto 1500-2000 pages with images. One of these was an 80MB or so file. I tried printing it with Foxit to convert the images to JPG from JPEG2000 but the file size jumped to 800MB...plus it's taking too long.
I stumbled upon Ghostscript, but I have NO clue how to use the command line interface.
I am very short on time. Pretty much need a step by step guide for a small script that converts all my PDFs in one go.
Very sorry about my inexperience and helplessness. Can someone spoon-feed me the steps for this?
EDIT: I want to switch the JPEG2000 to any other format that produces less of an increase in file size and causes a minimal loss in quality (within reason). I have no clue how to use Ghostscript. I basically want to change the compression on the images to something that will display correctly on the iPad while maintaining the quality of the rest of the text, as well as the embedded bookmarks.
I'll repeat that I have NO experience with command line...I don't even know how to point GS to the folder my PDFs are in...
You haven't really said what it is you want. 'Convert' PDFs how exactly ?
Note that switching from JPX (JPEG2000) to JPEG will result in a quality loss, because the image data will be quantised (with a different quantisation scheme to JPX) by the JPEG encoder. You can use a lossless compression scheme instead, but then you won't get the same kind of compression. You won't get the same compression ratio as JPX anyway no matter what you use, the result will be larger.
A simple Ghostscript command would be:
gs -sDEVICE=pdfwrite -o out.pdf in.pdf
Because JPEG2000 encoding is (or at least, was) patent encumbered, the pdfwrite device doesn't write images as JPX< by default it will write them several times with different compression schemes, and then use the one that gives the best compression (practically always JPEG).
Getting better results will require more a complex command line, but you'll also have to be more explicit about what exactly you want to achieve, and what the perceived problem with the simplistic command line is.
[EDIT]
Well, giving help on executing a command line is a bit off-topic for Stack Overflow, this is supposed to be a site for software developers :-)
Without knowing what operating system you are using its hard to give you detailed instructions, I also have no idea what an iPad uses, I don't generally use Apple devices and my only experience is with Macs.
Presumably you know where (the directory) you installed Ghostscript. Either open a command shell there and type the command ./gs or execute the command by giving the full path, such as :
/usr/bin/gs
I thought the arguments on the command line were self-explanatory, but....
The -sDEVICE=pdfwrite switch tells Ghostscript to use the pdfwrite device, as you might guess from the name, that device writes PDF files as its output.
The -o switch is the name (and full path if required) of the output file.
The final argument is the name (and again, full path if its not in the current directory) of the input file.
So a command might look like:
/usr/bin/gs -sDEVICE=pdfwrite -o /home/me/output.pdf /home/me/input.pdf
Or if Ghostscript and the input file are in the same directory:
./gs -sDEVICE=pdfwrite -o out.pdf input.pdf
Whenever I try to compress a PDF file to a lower possible size, by either using ghostscript or pdftk or pdfopt, I end up having a file near to half the size of original. But lately, I am getting files of size in 1000 MB range, which are compressing to say a few hundreds. Can we further reduce them?
The pdf is made from jpg images which are of higher resolutions, cant we reduce the size of those images and further bring in some more reduction in size?
As far I know, without degrading jpeg streams and loosing quality, you can try the special feature offered by
Multivalent
https://rg.to/file/c6bd7f31bf8885bcaa69b50ffab7e355/Multivalent20060102.jar.html
java -cp path/to.../multivalent.jar tool.pdf.Compress -compact file.pdf
resulting output will be compressed in a special way. the resulting file needs Multivalent browser to be read again
it is unpredictable how much space you can save (many times you cannot save any further space)
So there are some threads here on PDF compression saying that there is some, but not a lot of, gain in compressing PDFs as PDFs are already compressed.
My question is: Is this true for all PDFs including older version of the format?
Also I'm sure its possible for someone (an idiot maybe) to place bitmaps into the PDF rather than JPEG etc. Our company has a lot of PDFs in its DBs (some older formats maybe). We are considering using gzip to compress during transmission but don't know if its worth the hassle
PDFs in general use internal compression for the objects they contain. But this compression is by no means compulsory according to the file format specifications. All (or some) objects may appear completely uncompressed, and they would still make a valid PDF.
There are commandline tools out there which are able to decompress most (if not all) of the internal object streams (even of the most modern versions of PDFs) -- and the new, uncompressed version of the file will render exactly the same on screen or on paper (if printed).
So to answer your question: No, you cannot assume that a gzip compression is adding only hassle and no benefit. You have to test it with a representative sample set of your files. Just gzip them and take note of the time used and of the space saved.
It also depends on the type of PDF producing software which was used...
Instead of applying gzip compression, you would get much better gain by using PDF utilities to apply compression to the contents within the format as well as remove things like unneeded embedded fonts. Such utilities can downsample images and apply the proper image compression, which would be far more effective than gzip. JBIG2 can be applied to bilevel images and is remarkably effective, and JPEG can be applied to natural images with the quality level selected to suit your needs. In Acrobat Pro, you can use Advanced -> PDF Optimizer to see where space is used and selectively attack those consumers. There is also a generic Document -> Reduce File Size to automatically apply these reductions.
Update:
Ika's answer has a link to a PDF optimization utility that can be used from Java. You can look at their sample Java code there. That code lists exactly the things I mentioned:
Remove duplicated fonts, images, ICC profiles, and any other data stream.
Optionally convert high-quality or print-ready PDF files to small, efficient and web-ready PDF.
Optionally down-sample large images to a given resolution.
Optionally compress or recompress PDF images using JBIG2 and JPEG2000 compression formats.
Compress uncompressed streams and remove unused PDF objects.
I was able to use Ned Batchelder's python code, which I converted to C++, to extract jpgs from pdf files. I'm wondering if the same technique can be used to extract tiff files and if so, does anyone know the appropriate offsets and markers to find them?
Thanks,
David
PDF files may contain different image data (not surprisingly).
Most common cases are:
Fax data (CCITT Group 3 and 4)
raw raster data with decoding parameters and optional palette all compressed with Deflate or LZW compression
JPEG data
Recently, I (as developer of a PDF library) start noticing more and more PDFs with JBIG2 image data. Also, JPEG2000 sometimes can be put into a PDF.
I should say, that you probably can extract JPEG/JBIG2/JPEG2000 data into corresponding *.jpeg / *.jp2 / *.jpx files without external libraries but be prepared for all kinds of weird PDFs emitted by broken generators. Also, PDFs quite often use object streams so you'll need to implement sophisticated parser for PDF.
Fax data (i.e. what you probably call TIFF) should be at least packed into a valid TIFF. You can borrow some code for that from open source libtiff for example.
And then comes raw raster data. I don't think that it makes sense to try to extract such data without help of a library. You could do that, of course, but it will take months of work.
So, if you are trying to extract only specific kind of image data from a set of PDFs all created with the same generator, then your task is probably feasible. In all other cases I would recommend to save time, money and hair and use a library for the task.
PDF files store Jpegs as actual JPEGS (DCT and JPX encoding) so in most cases you can rip the data out. With Tiffs, you are looking for CCITT data (but you will need to add a header to the data to make it a Tiff). I wrote 2 blog articles on images in PDF files at http://www.jpedal.org/PDFblog/2010/09/understanding-the-pdf-file-format-images/ and http://www.jpedal.org/PDFblog/2011/07/extract-raw-jpeg-images-from-a-pdf-file/ which might help.
I have an input PDF file (usually, but not always generated by pdfTeX), which I want to convert to an output PDF, which is visually equivalent (no matter the resolution), it has the same metadata (Unicode text info, hyperlinks, outlines etc.), but the file size is as small as possible.
I know about the following methods:
java -cp Multivalent.jar tool.pdf.Compress input.pdf (from http://multivalent.sourceforge.net/). This recompresses all streams, removes unused objects, unifies equivalent objects, compresses whitespace, removes default values, compresses the cross-reference table.
Recompressing suitable images with jbig2 and PNGOUT.
Re-encoding Type1 fonts as CFF fonts.
Unifying equivalent images.
Unifying subsets of the same font to a bigger subset.
Remove fillable forms.
When distilling or otherwise converting (e.g. gs -sDEVICE=pdfwrite), make sure it doesn't degrade image quality, and doesn't increase (!) the image sizes.
I know about the following techniques, but they don't apply in my case, since I already have a PDF:
Use smaller and/or less fonts.
Use vector images instead bitmap images.
Do you have any other ideas how to optimize PDF?
Optimize PDF Files
Avoid Refried Graphics
For graphics that must be inserted as bitmaps, prepare them for maximum compressibility and minimum dimensions. Use the best quality images that you can at the output resolution of the PDF. Inserting compressed JPEGs into PDFs and Distilling them may recompress JPEGs, which can create noticeable artifacts. Use black and white images and text instead of color images to allow the use of the newer JBIG2 standard that excels in monochromatic compression. Be sure to turn off thumbnails when saving PDFs for the Web.
Use Vector Graphics
Use vector-based graphics wherever possible for images that would normally be made into GIFs. Vector images scale perfectly, look marvelous, and their mathematical formulas usually take up less space than bitmapped graphics that describe every pixel (although there are some cases where bitmap graphics are actually smaller than vector graphics). You can also compress vector image data using ZIP compression, which is built into the PDF format. Acrobat Reader version 5 and 6 also support the SVG standard.
Minimize Fonts
How you use fonts, especially in smaller PDFs, can have a significant impact on file size. Minimize the number of fonts you use in your documents to minimize their impact on file size. Each additional fully embedded font can easily take 40K in file size, which is why most authors create "subsetted" fonts that only include the glyphs actually used.
Flatten Fat Forms
Acrobat forms can take up a lot of space in your PDFs. New in Acrobat 8 Pro you can flatten form fields in the Advanced -> PDF Optimizer -> Discard Objects dialog. Flattening forms makes form fields unusable and form data is merged with the page. You can also use PDF Enhancer from Apago to reduce forms by 50% by removing information present in the file but never actually used. You can also combine a refried PDF with the old form pages to create a hybrid PDF in Acrobat (see "Refried PDF" section below).
see article
From PDF specification version 1.5 there are two new methods of compression, object streams and cross reference streams.
You mention that the Multivalent.jar compress tool compresses the cross reference table. This usually means the cross reference table is converted into a stream and then compressed.
The format of this cross reference stream is not fixed. You can change the bit size of the three "columns" of data. It's also possible to pre-process the stream data using a predictor function which will improve the compression level of the data. If you look inside the PDF with a text editor you might be able to find the /Predictor entry in the cross reference stream dictionary to check whether the tool you're using is taking advantage of this feature.
Using a predictor on the compression might be handy for images too.
The second type of compression offered is the use of object streams.
Often in a PDF you have many similar objects. These can now be combined into a single object and then compressed. The documentation for the Multivalent Compress tool mentions that object streams are used but doesn't have many details on the actual choice of which objects to group together. The compression will be better if you group similar objects together into an object stream.