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More research on how to create pdfs from other files
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Eike Kettner
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@ -119,7 +119,16 @@ office documents, common images, plain text (i.e. markdown) and html
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should be supported. In terms of file extensions: `doc`, `docx`,
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`xls`, `xlsx`, `odt`, `md`, `html`, `txt`, `jpg`, `png`, `tif`.
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There is always the preference to use jvm internal libraries in order
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to be more platform independent and to reduce external dependencies.
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But this is not always possible (like doing OCR).
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- Office documents (`doc`, `docx`, `xls`, `xlsx`, `odt`, `ods`):
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unoconv (see [ADR 9](0009_convert_office_docs))
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- HTML (`html`): wkhtmltopdf (see [ADR 7](0007_convert_html_files))
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- Text/Markdown (`txt`, `md`): Java-Lib flexmark + wkhtmltopdf
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- Images (`jpg`, `png`, `tif`): Tesseract (see [ADR
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10](0010_convert_image_files))
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## Links
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@ -9,8 +9,184 @@ title: Convert Image Files
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How to convert image files properly to pdf?
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Since there are thousands of different image formats, there will never
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be support for all. The most common containers should be supported,
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though:
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- jpeg (jfif, exif)
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- png
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- tiff (baseline, single page)
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The focus is on document images, maybe from digital cameras or
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scanners.
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## Considered Options
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* [pdfbox]() library
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* [pandoc](https://pandoc.org/) external command
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* [imagemagick](https://www.imagemagick.org/) external command
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* [img2pdf](https://github.com/josch/img2pdf) external command
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* [tesseract](https://github.com/tesseract-ocr/tesseract) external command
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There are no screenshots here, because it doesn't make sense since
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they all look the same on the screen. Instead we look at the files
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properties.
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**Input File**
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The input files are:
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```
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$ identify input/*
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input/jfif.jpg JPEG 2480x3514 2480x3514+0+0 8-bit sRGB 240229B 0.000u 0:00.000
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input/letter-en.jpg JPEG 1695x2378 1695x2378+0+0 8-bit Gray 256c 467341B 0.000u 0:00.000
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input/letter-en.png PNG 1695x2378 1695x2378+0+0 8-bit Gray 256c 191571B 0.000u 0:00.000
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input/letter-en.tiff TIFF 1695x2378 1695x2378+0+0 8-bit Grayscale Gray 4030880B 0.000u 0:00.000
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```
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Size:
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- jfif.jpg 240k
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- letter-en.jpg 467k
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- letter-en.png 191k
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- letter-en.tiff 4.0M
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### pdfbox
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Using a java library is preferred, if the quality is good enough.
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There is an
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[example](https://github.com/apache/pdfbox/blob/2cea31cc63623fd6ece149c60d5f0cc05a696ea7/examples/src/main/java/org/apache/pdfbox/examples/pdmodel/ImageToPDF.java)
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for this exact use case.
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This is the sample code:
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``` scala
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def imgtopdf(file: String): ExitCode = {
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val jpg = Paths.get(file).toAbsolutePath
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if (!Files.exists(jpg)) {
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sys.error(s"file doesn't exist: $jpg")
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}
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val pd = new PDDocument()
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val page = new PDPage(PDRectangle.A4)
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pd.addPage(page)
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val bimg = ImageIO.read(jpg.toFile)
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val img = LosslessFactory.createFromImage(pd, bimg)
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val stream = new PDPageContentStream(pd, page)
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stream.drawImage(img, 0, 0, PDRectangle.A4.getWidth, PDRectangle.A4.getHeight)
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stream.close()
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pd.save("test.pdf")
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pd.close()
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ExitCode.Success
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}
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```
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Using pdfbox 2.0.18 and twelvemonkeys 3.5. Running time: `1384ms`
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```
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$ identify *.pdf
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jfif.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 129660B 0.000u 0:00.000
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letter-en.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
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letter-en.png.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
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letter-en.tiff.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
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```
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Size:
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- jfif.jpg 1.1M
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- letter-en.jpg 142k
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- letter-en.png 142k
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- letter-en.tiff 142k
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### img2pdf
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This is a python tool that adds the image into the pdf without
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reencoding.
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Using version 0.3.1. Running time: `323ms`.
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```
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$ identify *.pdf
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jfif.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 129708B 0.000u 0:00.000
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letter-en.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
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letter-en.png.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
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letter-en.tiff.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
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```
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Size:
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- jfif.jpg 241k
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- letter-en.jpg 468k
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- letter-en.png 191k
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- letter-en.tiff 192k
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### ImageMagick
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The well known imagemagick tool can convert images to pdfs, too.
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Using version 6.9.10-71. Running time: `881ms`.
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```
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$ identify *.pdf
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jfif.jpg.pdf PDF 595x843 595x843+0+0 16-bit sRGB 134873B 0.000u 0:00.000
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letter-en.jpg.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 360100B 0.000u 0:00.000
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letter-en.png.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 322418B 0.000u 0:00.000
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letter-en.tiff.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 322418B 0.000u 0:00.000
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```
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Size:
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- jfif.jpg 300k
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- letter-en.jpg 390k
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- letter-en.png 180k
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- letter-en.tiff 5.1M
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### Tesseract
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Docspell already relies on tesseract for doing OCR. And in contrast to
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all other candidates, it can create PDFs that are searchable. Of
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course, this yields in much longer running time, that cannot be
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compared to the times of the other options.
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```
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tesseract doc3.jpg out -l deu pdf
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```
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It can also create both outputs in one go:
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```
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tesseract doc3.jpg out -l deu pdf txt
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```
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Using tesseract 4. Running time: `6661ms`
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```
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$ identify *.pdf
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tesseract/jfif.jpg.pdf PDF 595x843 595x843+0+0 16-bit sRGB 130535B 0.000u 0:00.000
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tesseract/letter-en.jpg.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
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tesseract/letter-en.png.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
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tesseract/letter-en.tiff.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
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```
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Size:
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- jfif.jpg 246k
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- letter-en.jpg 473k
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- letter-en.png 183k
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- letter-en.tiff 183k
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## Decision
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Tesseract.
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To not use more external tools, imagemagick and img2pdf are not
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chosen, even though img2pdf shows the best results and is fastest.
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Pdfbox library would be the favorite, because results are good and
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with the [twelvemonkeys](https://github.com/haraldk/TwelveMonkeys)
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library there is support for many images. The priority is to avoid
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more external commands if possible.
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But since there already is a dependency to tesseract and it can create
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searchable pdfs, the decision is to use tesseract for this. Then PDFs
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with images can be converted to searchable PDFs with images. And text
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extraction is required anyways.
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