How to flatten images in PDF files with transparency?
convert PDF to PS (postscript)
pdftops input.pdf output.pdf.ps
If a PDF file contains eg. PNG files with alpha channel (transparency) the PDF is rendered/rasterized to an image and that is not a solution because then you lose the plain text in the file
Is there a tool (linux command line) to flatten images in PDF files with transparency?
Its not clear why you want to do this. If you want PostScript then Ghostscript can produce PostScript for you from a PDF file (use the ps2write device). Obviously transparency will have to be rendered to an image, in which case the resolution is important. The default is 720 dpi which is probably higher than you might need.
Note that a PDF file can't contain a PNG, that's not a possible image type in PDF. A PNG would have to be stored as an image with a separate alpha.
Related
I tried to convert Python Tkinter canvas to pdf. For that I used Ghostscript. Here is the code part,
canvas.postscript(file="tmp.ps",colormode='color')
somecommand = "gswin64c -o output.pdf -sDEVICE=pdfwrite -g57750x62070 - dPDFFitPage tmp.ps"
call(somecommand, shell=True)
The output pdf with large size but the pdf shows canvas GUI cropped and it is in bottom left corner of the pdf.
I want to show complete canvas on pdf.
You've specified -dPDFFitPage, but your input file appears to be PostScript (judging by the '.ps' extension and your question title). PDFFitPage works with PDF input. Even using -dPSFitPage of the simpler -dFitPage will only work if the input PostScript program requests a media size. If it doesn't then the interpreter can't tell what its bounding box is, and so cannot scale it to fit the media.
You've also specified a media size in pixels (-g57750x62070) which is entirely inappropriate when the input and output are vector formats. For what it's worth, you are specifying a fixed media size of (approximately) 80 inches by 86 inches, using the default resolution of 720 dpi.
If all you want to do is turn a PostScript file into a PDF file then the simpler:
gs -sDEVICE=pdfwrite -o out.pdf input.ps
is sufficient.
I have a base64 image data which I want to save a png file. But When I save it as file, it does not retain the transparent portions but becomes fully black.
Is there a way to retain transparency while writing png file in Nodejs?
Background
I am using Tesseract-OCR 3.04 on a Linux setup to batch OCR process for a bunch of non-searchable PDFs.
My process is such that I take the PDF, convert it to a tiff format, then using Tesseract, I convert that tiff into a searchable pdf format.
The issue
The output from the Tesseract 3.04 tiff to pdf conversion always produces a pdf with a blue background. I have checked and the tiff file has a white background.
Here is the output I am getting. Obviously mostly-censored for privacy.
What I have tried
I have created by own "untouched" tiff file with a white background and ran it through Tesseract to a pdf output and the blue background persists. I did this by typing paragraphs of text into my text editor, screenshotting it, and converting it to tiff.
I have had absolutely no results in google searching my issue.
--
I do not know what the issue is within the Tesseract process, does anyone have any information that could help?
Thanks!
I have tried nearly every library to convert pdf to svg, Following are the results of them
gs or ghostscript and imagemagick: The size gets multiplied by 100
pdf2svg and inkscape: The image on the top of the pdf is not at all accurate here are the links to the pdf and the svg.
PDF: https://drive.google.com/open?id=0BxyQR1owWa_pcnhhSk5wQWJGMVk
SVG: https://drive.google.com/open?id=0BxyQR1owWa_pVnhoLVlob1U2d1k
Please suggest me if I am missing something that needs to be done.
The Ghostscript SVG output device is seriously deprecated and no longer supported (or indeed built into the standard Ghostscript binary).
In any event, you need to be aware that PDF is a very rich graphics model, and it is simply not possible to reproduce every possible nuance of a PDF using the SVG graphics model, in particular fonts are a problem, but so is almost any kind of transparency. When that occurs Ghostscript will render the PDF to an image, and insert that into an SVG file. Almost certainly that's why you are seeing the SVG file being considerably larger than the PDF file. You should be able to use the -r switch to control the resolution of the rendering, allowing you to trade off quality for size.
Even if the whole file isn't converted to a bitmap, its possible that large portions of it are, or that the bitmap compression in SVG is less good than for PDF (or GS isn't taking advantage of all the possibilities). FWIW the PDF file uncompressed runs to > 4MB.
I have a PDF file containing some tabular data.
http://dl.dropbox.com/u/44235928/sample_rotate-0.pdf
I have to extract the tabular data from it. I have tried following with no success :
Select the text and paste it to notepad/excel-sheet. (I am getting junk characters)
Used save as text from Acrobat Reader. It is also giving junk characters and not the actual text.
Tried ApachePDFBox command line utility to extract text from PDF. It is also giving junk characters instead of real texts.
Finally I am trying a OCR solution. I am converting the pdf file into .tif images using ImageMagick and getting those images processed by tesseract OCR.
The OCR solution is not very accurate though( about 80% words matched ).
I tried changing density and geometry of the image created from PDF to get better results from tesseract OCR.
convert -rotate 90 -geometry 10000 -depth 8 -density 800 sample.pdf img_800_10000.tif;
tesseract img_800_10000.tif img_800_10000.tif nobatch letters;
I am not sure for what kind of image( density, geometry, monochromatic, sharpen boundary etc) would be best suited for the OCR.
Please suggest what could be the best possible parameters(density,geometry,depth etc) for generating images from a PDF file, so that the tesseract accuracy will increase.
I am open to other( non-ocr ) solutions as well.
In this case I recommend to NOT use ImageMagick for the PDF -> TIFF conversion. Instead, use Ghostscript. Two reasons:
Using Ghostscript directly will give you more control over individual parameters of the conversion.
ImageMagick cannot do that particular conversion itself -- it will call Ghostscript as its 'delegate' anyway, but will not allow you to give all the same fine-grained control that your own Ghostscript command will give you.
Most of the text in the table of your sample PDF is extremely small (I guess, only 4 or 5 pt high). This makes it rather difficult to run a successful OCR unless you increase the resolution considerably.
Ghostscript uses -r72 by default for image format output (such as TIFF). Tesseract works best with r=300 or r=400 -- but only for a font size from 10-12 pt or higher. Therefor, to compensate for the small text size you should make Ghostscript using a resolution of at least 1200 DPI when it renders the PDF to the image.
Also, you'll have to rotate the image so the text displays in the normal reading direction (not bottom -> top).
This is the command which I would try first:
gs \
-o sample.tif \
-sDEVICE=tiffg4 \
-r1200 \
-dAutoRotatePages=/PageByPage \
sample_rotate-0.pdf
You may need to play with variations of the -r1200 parameter (higher or lower) for best results.
Since a comment asked "How to define the geometry of an image when using Ghostscript as we do in convert?", here is an answer:
It does not make sense to define geometry (that is image dimensions) and resolution for a raster image created by Ghostscript at the same time.
Once you convert a vector based page of a given dimension (such as PDF) into a raster image (such as the TIFF G4 format) giving a desired resolution (as done in the other answer), you already indirectly and implicitly also did set the dimension:
The original PDF dimension of your sample file sample_rotate-0.pdf is 1008x612 points.
At a resolution of 72 DPI (the default Ghostscript uses if not given directly, or -r72 in the Ghostscript command if given directly) the image dimensions will be 1008x612 pixels.
At a resolution of 720 DPI (-r720 in the Ghostscript command) the image dimensions will be 10080x6120 pixels.
At a resolution of 1440 DPI (-r1440 in the Ghostscript command of my other answer) the image dimensions will be 20160x12240 pixels.
At a resolution of 1200 DPI (-r1200 in the Ghostscript command) the image dimensions will be 16800x10200 pixels.
At resolution of 1000 DPI (-r1000 in the Ghostscript command) the image dimensions will be 14000x8500 pixels.
At a resolution of 120 DPI (-r120 in the Ghostscript command) the image dimensions will be 1680x1020 pixels.
At resolution of 100 DPI (-r100 in the Ghostscript command) the image dimensions will be 1400x850 pixels.
If you absolutely insist to specify the dimension/geometry for the output image on the Ghostscript commandline (rather than the resolution), you can do so by adding -gNNNNxMMMM -dPDFFitPage to the commandline.
There you can find decoded content of your file: https://docs.google.com/open?id=0B1YEM-11PerqSHpnb1RQcnJ4cFk
A absolutely sure the OCR is the best way to read pdf file, but you can try REGEX-ing the native content. It going to be be the hard and long way.