ee42963164
Implements the proposal detailed at #112 (comment) This is a limited implementation of JBIG2, which can be extended to support multiple pages, symbol tables, and other features of the format in the future. To test, I included a test fixture. You can also download 042.bmp (the same one as @josch already downloaded in #112 (comment) from https://git.ghostscript.com/?p=tests.git;a=blob_plain;f=jbig2/042.bmp;hb=HEAD and run the following command: jbig2 042.bmp | img2pdf > 042.pdf This results in a small PDF, just as @josch originally found in the comment mentioned above. This is my first contribution to this repository so let me know if something else is needed. Thanks for a great library!
323 lines
12 KiB
Markdown
323 lines
12 KiB
Markdown
[](https://app.travis-ci.com/josch/img2pdf)
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[](https://ci.appveyor.com/project/josch/img2pdf/branch/main)
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img2pdf
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=======
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Lossless conversion of raster images to PDF. You should use img2pdf if your
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priorities are (in this order):
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1. **always lossless**: the image embedded in the PDF will always have the
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exact same color information for every pixel as the input
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2. **small**: if possible, the difference in filesize between the input image
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and the output PDF will only be the overhead of the PDF container itself
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3. **fast**: if possible, the input image is just pasted into the PDF document
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as-is without any CPU hungry re-encoding of the pixel data
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Conventional conversion software (like ImageMagick) would either:
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1. not be lossless because lossy re-encoding to JPEG
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2. not be small because using wasteful flate encoding of raw pixel data
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3. not be fast because input data gets re-encoded
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Another advantage of not having to re-encode the input (in most common
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situations) is, that img2pdf is able to handle much larger input than other
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software, because the raw pixel data never has to be loaded into memory.
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The following table shows how img2pdf handles different input depending on the
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input file format and image color space.
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| Format | Colorspace | Result |
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| ------------------------------------- | ------------------------------ | ------------- |
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| JPEG | any | direct |
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| JPEG2000 | any | direct |
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| PNG (non-interlaced, no transparency) | any | direct |
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| TIFF (CCITT Group 4) | monochrome | direct |
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| JBIG2 (single-page generic coding) | bi-level | direct |
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| any | any except CMYK and monochrome | PNG Paeth |
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| any | monochrome | CCITT Group 4 |
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| any | CMYK | flate |
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For JPEG, JPEG2000, non-interlaced PNG, TIFF images with CCITT Group 4
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encoded data, and JBIG2 with single-page generic coding (e.g. using `jbig2enc`),
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img2pdf directly embeds the image data into the PDF without
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re-encoding it. It thus treats the PDF format merely as a container format for
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the image data. In these cases, img2pdf only increases the filesize by the size
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of the PDF container (typically around 500 to 700 bytes). Since data is only
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copied and not re-encoded, img2pdf is also typically faster than other
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solutions for these input formats.
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For all other input types, img2pdf first has to transform the pixel data to
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make it compatible with PDF. In most cases, the PNG Paeth filter is applied to
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the pixel data. For monochrome input, CCITT Group 4 is used instead. Only for
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CMYK input no filter is applied before finally applying flate compression.
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Usage
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-----
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The images must be provided as files because img2pdf needs to seek in the file
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descriptor.
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If no output file is specified with the `-o`/`--output` option, output will be
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done to stdout. A typical invocation is:
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$ img2pdf img1.png img2.jpg -o out.pdf
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The detailed documentation can be accessed by running:
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$ img2pdf --help
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Bugs
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----
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- If you find a JPEG, JPEG2000, PNG or CCITT Group 4 encoded TIFF file that,
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when embedded into the PDF cannot be read by the Adobe Acrobat Reader,
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please contact me.
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- An error is produced if the input image is broken. This commonly happens if
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the input image has an invalid EXIF Orientation value of zero. Even though
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only nine different values from 1 to 9 are permitted, Anroid phones and
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Canon DSLR cameras produce JPEG images with the invalid value of zero.
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Either fix your input images with `exiftool` or similar software before
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passing the JPEG to `img2pdf` or run `img2pdf` with `--rotation=ifvalid`
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(if you run img2pdf from the commandline) or by passing
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`rotation=img2pdf.Rotation.ifvalid` as an argument to `convert()` when using
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img2pdf as a library.
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- img2pdf uses PIL (or Pillow) to obtain image meta data and to convert the
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input if necessary. To prevent decompression bomb denial of service attacks,
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Pillow limits the maximum number of pixels an input image is allowed to
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have. If you are sure that you know what you are doing, then you can disable
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this safeguard by passing the `--pillow-limit-break` option to img2pdf. This
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allows one to process even very large input images.
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Installation
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------------
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On a Debian- and Ubuntu-based systems, img2pdf can be installed from the
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official repositories:
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$ apt install img2pdf
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If you want to install it using pip, you can run:
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$ pip3 install img2pdf
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If you prefer to install from source code use:
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$ cd img2pdf/
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$ pip3 install .
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To test the console script without installing the package on your system,
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use virtualenv:
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$ cd img2pdf/
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$ virtualenv ve
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$ ve/bin/pip3 install .
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You can then test the converter using:
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$ ve/bin/img2pdf -o test.pdf src/tests/test.jpg
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If you don't want to setup Python on Windows, then head to the
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[releases](/josch/img2pdf/releases) section and download the latest
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`img2pdf.exe`.
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GUI
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---
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There exists an experimental GUI with all settings currently disabled. You can
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directly convert images to PDF but you cannot set any options via the GUI yet.
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If you are interested in adding more features to the PDF, please submit a merge
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request. The GUI is based on tkinter and works on Linux, Windows and MacOS.
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Library
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-------
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The package can also be used as a library:
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import img2pdf
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# opening from filename
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert('test.jpg'))
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# opening from file handle
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with open("name.pdf","wb") as f1, open("test.jpg") as f2:
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f1.write(img2pdf.convert(f2))
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# opening using pathlib
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(pathlib.Path('test.jpg')))
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# using in-memory image data
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert("\x89PNG...")
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# multiple inputs (variant 1)
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert("test1.jpg", "test2.png"))
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# multiple inputs (variant 2)
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(["test1.jpg", "test2.png"]))
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# convert all files ending in .jpg inside a directory
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dirname = "/path/to/images"
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imgs = []
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for fname in os.listdir(dirname):
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if not fname.endswith(".jpg"):
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continue
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path = os.path.join(dirname, fname)
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if os.path.isdir(path):
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continue
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imgs.append(path)
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(imgs))
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# convert all files ending in .jpg in a directory and its subdirectories
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dirname = "/path/to/images"
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imgs = []
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for r, _, f in os.walk(dirname):
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for fname in f:
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if not fname.endswith(".jpg"):
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continue
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imgs.append(os.path.join(r, fname))
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(imgs))
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# convert all files matching a glob
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import glob
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(glob.glob("/path/to/*.jpg")))
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# convert all files matching a glob using pathlib.Path
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from pathlib import Path
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert(*Path("/path").glob("**/*.jpg")))
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# ignore invalid rotation values in the input images
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert('test.jpg'), rotation=img2pdf.Rotation.ifvalid)
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# writing to file descriptor
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with open("name.pdf","wb") as f1, open("test.jpg") as f2:
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img2pdf.convert(f2, outputstream=f1)
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# specify paper size (A4)
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a4inpt = (img2pdf.mm_to_pt(210),img2pdf.mm_to_pt(297))
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layout_fun = img2pdf.get_layout_fun(a4inpt)
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert('test.jpg', layout_fun=layout_fun))
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# use a fixed dpi of 300 instead of reading it from the image
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dpix = dpiy = 300
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layout_fun = img2pdf.get_fixed_dpi_layout_fun((dpix, dpiy))
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert('test.jpg', layout_fun=layout_fun))
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# create a PDF/A-1b compliant document by passing an ICC profile
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with open("name.pdf","wb") as f:
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f.write(img2pdf.convert('test.jpg', pdfa="/usr/share/color/icc/sRGB.icc"))
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Comparison to ImageMagick
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-------------------------
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Create a large test image:
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$ convert logo: -resize 8000x original.jpg
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Convert it into PDF using ImageMagick and img2pdf:
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$ time img2pdf original.jpg -o img2pdf.pdf
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$ time convert original.jpg imagemagick.pdf
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Notice how ImageMagick took an order of magnitude longer to do the conversion
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than img2pdf. It also used twice the memory.
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Now extract the image data from both PDF documents and compare it to the
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original:
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$ pdfimages -all img2pdf.pdf tmp
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$ compare -metric AE original.jpg tmp-000.jpg null:
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0
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$ pdfimages -all imagemagick.pdf tmp
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$ compare -metric AE original.jpg tmp-000.jpg null:
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118716
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To get lossless output with ImageMagick we can use Zip compression but that
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unnecessarily increases the size of the output:
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$ convert original.jpg -compress Zip imagemagick.pdf
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$ pdfimages -all imagemagick.pdf tmp
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$ compare -metric AE original.jpg tmp-000.png null:
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0
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$ stat --format="%s %n" original.jpg img2pdf.pdf imagemagick.pdf
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1535837 original.jpg
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1536683 img2pdf.pdf
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9397809 imagemagick.pdf
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Comparison to pdfLaTeX
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----------------------
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pdfLaTeX performs a lossless conversion from included images to PDF by default.
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If the input is a JPEG, then it simply embeds the JPEG into the PDF in the same
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way as img2pdf does it. But for other image formats it uses flate compression
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of the plain pixel data and thus needlessly increases the output file size:
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$ convert logo: -resize 8000x original.png
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$ cat << END > pdflatex.tex
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\documentclass{article}
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\usepackage{graphicx}
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\begin{document}
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\includegraphics{original.png}
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\end{document}
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END
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$ pdflatex pdflatex.tex
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$ stat --format="%s %n" original.png pdflatex.pdf
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4500182 original.png
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9318120 pdflatex.pdf
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Comparison to podofoimg2pdf
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---------------------------
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Like pdfLaTeX, podofoimg2pdf is able to perform a lossless conversion from JPEG
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to PDF by plainly embedding the JPEG data into the pdf container. But just like
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pdfLaTeX it uses flate compression for all other file formats, thus sometimes
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resulting in larger files than necessary.
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$ convert logo: -resize 8000x original.png
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$ podofoimg2pdf out.pdf original.png
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stat --format="%s %n" original.png out.pdf
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4500181 original.png
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9335629 out.pdf
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It also only supports JPEG, PNG and TIF as input and lacks many of the
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convenience features of img2pdf like page sizes, borders, rotation and
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metadata.
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Comparison to Tesseract OCR
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---------------------------
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Tesseract OCR comes closest to the functionality img2pdf provides. It is able
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to convert JPEG and PNG input to PDF without needlessly increasing the filesize
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and is at the same time lossless. So if your input is JPEG and PNG images, then
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you should safely be able to use Tesseract instead of img2pdf. For other input,
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Tesseract might not do a lossless conversion. For example it converts CMYK
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input to RGB and removes the alpha channel from images with transparency. For
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multipage TIFF or animated GIF, it will only convert the first frame.
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Comparison to econvert from ExactImage
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--------------------------------------
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Like pdflatex and podofoimg2pf, econvert is able to embed JPEG images into PDF
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directly without re-encoding but when given other file formats, it stores them
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just using flate compressen, which unnecessarily increases the filesize.
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Furthermore, it throws an error with CMYK TIF input. It also doesn't store CMYK
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jpeg files as CMYK but converts them to RGB, so it's not lossless. When trying
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to feed it 16bit files, it errors out with Unhandled bps/spp combination. It
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also seems to choose JPEG encoding when using it on some file types (like
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palette images) making it again not lossless for that input as well.
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