mirror of
https://github.com/TheAnachronism/docspell.git
synced 2025-04-04 10:29:34 +00:00
More research on how to create pdfs from other files
This commit is contained in:
Eike Kettner
parent
3deba44282
commit
919381be1e
@ -119,7 +119,16 @@ office documents, common images, plain text (i.e. markdown) and html
|
|||||||
should be supported. In terms of file extensions: `doc`, `docx`,
|
should be supported. In terms of file extensions: `doc`, `docx`,
|
||||||
`xls`, `xlsx`, `odt`, `md`, `html`, `txt`, `jpg`, `png`, `tif`.
|
`xls`, `xlsx`, `odt`, `md`, `html`, `txt`, `jpg`, `png`, `tif`.
|
||||||
|
|
||||||
|
There is always the preference to use jvm internal libraries in order
|
||||||
|
to be more platform independent and to reduce external dependencies.
|
||||||
|
But this is not always possible (like doing OCR).
|
||||||
|
|
||||||
|
- Office documents (`doc`, `docx`, `xls`, `xlsx`, `odt`, `ods`):
|
||||||
|
unoconv (see [ADR 9](0009_convert_office_docs))
|
||||||
|
- HTML (`html`): wkhtmltopdf (see [ADR 7](0007_convert_html_files))
|
||||||
|
- Text/Markdown (`txt`, `md`): Java-Lib flexmark + wkhtmltopdf
|
||||||
|
- Images (`jpg`, `png`, `tif`): Tesseract (see [ADR
|
||||||
|
10](0010_convert_image_files))
|
||||||
|
|
||||||
## Links
|
## Links
|
||||||
|
|
||||||
|
|||||||
@ -9,8 +9,184 @@ title: Convert Image Files
|
|||||||
|
|
||||||
How to convert image files properly to pdf?
|
How to convert image files properly to pdf?
|
||||||
|
|
||||||
|
Since there are thousands of different image formats, there will never
|
||||||
|
be support for all. The most common containers should be supported,
|
||||||
|
though:
|
||||||
|
|
||||||
|
- jpeg (jfif, exif)
|
||||||
|
- png
|
||||||
|
- tiff (baseline, single page)
|
||||||
|
|
||||||
|
The focus is on document images, maybe from digital cameras or
|
||||||
|
scanners.
|
||||||
|
|
||||||
## Considered Options
|
## Considered Options
|
||||||
|
|
||||||
* [pdfbox]() library
|
* [pdfbox]() library
|
||||||
* [pandoc](https://pandoc.org/) external command
|
* [imagemagick](https://www.imagemagick.org/) external command
|
||||||
|
* [img2pdf](https://github.com/josch/img2pdf) external command
|
||||||
|
* [tesseract](https://github.com/tesseract-ocr/tesseract) external command
|
||||||
|
|
||||||
|
There are no screenshots here, because it doesn't make sense since
|
||||||
|
they all look the same on the screen. Instead we look at the files
|
||||||
|
properties.
|
||||||
|
|
||||||
|
**Input File**
|
||||||
|
|
||||||
|
The input files are:
|
||||||
|
|
||||||
|
```
|
||||||
|
$ identify input/*
|
||||||
|
input/jfif.jpg JPEG 2480x3514 2480x3514+0+0 8-bit sRGB 240229B 0.000u 0:00.000
|
||||||
|
input/letter-en.jpg JPEG 1695x2378 1695x2378+0+0 8-bit Gray 256c 467341B 0.000u 0:00.000
|
||||||
|
input/letter-en.png PNG 1695x2378 1695x2378+0+0 8-bit Gray 256c 191571B 0.000u 0:00.000
|
||||||
|
input/letter-en.tiff TIFF 1695x2378 1695x2378+0+0 8-bit Grayscale Gray 4030880B 0.000u 0:00.000
|
||||||
|
```
|
||||||
|
|
||||||
|
Size:
|
||||||
|
- jfif.jpg 240k
|
||||||
|
- letter-en.jpg 467k
|
||||||
|
- letter-en.png 191k
|
||||||
|
- letter-en.tiff 4.0M
|
||||||
|
|
||||||
|
### pdfbox
|
||||||
|
|
||||||
|
Using a java library is preferred, if the quality is good enough.
|
||||||
|
There is an
|
||||||
|
[example](https://github.com/apache/pdfbox/blob/2cea31cc63623fd6ece149c60d5f0cc05a696ea7/examples/src/main/java/org/apache/pdfbox/examples/pdmodel/ImageToPDF.java)
|
||||||
|
for this exact use case.
|
||||||
|
|
||||||
|
This is the sample code:
|
||||||
|
|
||||||
|
``` scala
|
||||||
|
def imgtopdf(file: String): ExitCode = {
|
||||||
|
val jpg = Paths.get(file).toAbsolutePath
|
||||||
|
if (!Files.exists(jpg)) {
|
||||||
|
sys.error(s"file doesn't exist: $jpg")
|
||||||
|
}
|
||||||
|
val pd = new PDDocument()
|
||||||
|
val page = new PDPage(PDRectangle.A4)
|
||||||
|
pd.addPage(page)
|
||||||
|
val bimg = ImageIO.read(jpg.toFile)
|
||||||
|
|
||||||
|
val img = LosslessFactory.createFromImage(pd, bimg)
|
||||||
|
|
||||||
|
val stream = new PDPageContentStream(pd, page)
|
||||||
|
stream.drawImage(img, 0, 0, PDRectangle.A4.getWidth, PDRectangle.A4.getHeight)
|
||||||
|
stream.close()
|
||||||
|
|
||||||
|
pd.save("test.pdf")
|
||||||
|
pd.close()
|
||||||
|
|
||||||
|
ExitCode.Success
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
Using pdfbox 2.0.18 and twelvemonkeys 3.5. Running time: `1384ms`
|
||||||
|
|
||||||
|
```
|
||||||
|
$ identify *.pdf
|
||||||
|
jfif.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 129660B 0.000u 0:00.000
|
||||||
|
letter-en.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
|
||||||
|
letter-en.png.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
|
||||||
|
letter-en.tiff.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49118B 0.000u 0:00.000
|
||||||
|
```
|
||||||
|
|
||||||
|
Size:
|
||||||
|
- jfif.jpg 1.1M
|
||||||
|
- letter-en.jpg 142k
|
||||||
|
- letter-en.png 142k
|
||||||
|
- letter-en.tiff 142k
|
||||||
|
|
||||||
|
### img2pdf
|
||||||
|
|
||||||
|
This is a python tool that adds the image into the pdf without
|
||||||
|
reencoding.
|
||||||
|
|
||||||
|
Using version 0.3.1. Running time: `323ms`.
|
||||||
|
|
||||||
|
```
|
||||||
|
$ identify *.pdf
|
||||||
|
jfif.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 129708B 0.000u 0:00.000
|
||||||
|
letter-en.jpg.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
|
||||||
|
letter-en.png.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
|
||||||
|
letter-en.tiff.pdf PDF 595x842 595x842+0+0 16-bit sRGB 49864B 0.000u 0:00.000
|
||||||
|
```
|
||||||
|
|
||||||
|
Size:
|
||||||
|
- jfif.jpg 241k
|
||||||
|
- letter-en.jpg 468k
|
||||||
|
- letter-en.png 191k
|
||||||
|
- letter-en.tiff 192k
|
||||||
|
|
||||||
|
### ImageMagick
|
||||||
|
|
||||||
|
The well known imagemagick tool can convert images to pdfs, too.
|
||||||
|
|
||||||
|
Using version 6.9.10-71. Running time: `881ms`.
|
||||||
|
|
||||||
|
```
|
||||||
|
$ identify *.pdf
|
||||||
|
jfif.jpg.pdf PDF 595x843 595x843+0+0 16-bit sRGB 134873B 0.000u 0:00.000
|
||||||
|
letter-en.jpg.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 360100B 0.000u 0:00.000
|
||||||
|
letter-en.png.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 322418B 0.000u 0:00.000
|
||||||
|
letter-en.tiff.pdf PDF 1695x2378 1695x2378+0+0 16-bit sRGB 322418B 0.000u 0:00.000
|
||||||
|
```
|
||||||
|
|
||||||
|
Size:
|
||||||
|
- jfif.jpg 300k
|
||||||
|
- letter-en.jpg 390k
|
||||||
|
- letter-en.png 180k
|
||||||
|
- letter-en.tiff 5.1M
|
||||||
|
|
||||||
|
|
||||||
|
### Tesseract
|
||||||
|
|
||||||
|
Docspell already relies on tesseract for doing OCR. And in contrast to
|
||||||
|
all other candidates, it can create PDFs that are searchable. Of
|
||||||
|
course, this yields in much longer running time, that cannot be
|
||||||
|
compared to the times of the other options.
|
||||||
|
|
||||||
|
```
|
||||||
|
tesseract doc3.jpg out -l deu pdf
|
||||||
|
```
|
||||||
|
|
||||||
|
It can also create both outputs in one go:
|
||||||
|
|
||||||
|
```
|
||||||
|
tesseract doc3.jpg out -l deu pdf txt
|
||||||
|
```
|
||||||
|
|
||||||
|
Using tesseract 4. Running time: `6661ms`
|
||||||
|
|
||||||
|
```
|
||||||
|
$ identify *.pdf
|
||||||
|
tesseract/jfif.jpg.pdf PDF 595x843 595x843+0+0 16-bit sRGB 130535B 0.000u 0:00.000
|
||||||
|
tesseract/letter-en.jpg.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
|
||||||
|
tesseract/letter-en.png.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
|
||||||
|
tesseract/letter-en.tiff.pdf PDF 1743x2446 1743x2446+0+0 16-bit sRGB 328716B 0.000u 0:00.000
|
||||||
|
```
|
||||||
|
|
||||||
|
Size:
|
||||||
|
- jfif.jpg 246k
|
||||||
|
- letter-en.jpg 473k
|
||||||
|
- letter-en.png 183k
|
||||||
|
- letter-en.tiff 183k
|
||||||
|
|
||||||
|
|
||||||
|
## Decision
|
||||||
|
|
||||||
|
Tesseract.
|
||||||
|
|
||||||
|
To not use more external tools, imagemagick and img2pdf are not
|
||||||
|
chosen, even though img2pdf shows the best results and is fastest.
|
||||||
|
|
||||||
|
Pdfbox library would be the favorite, because results are good and
|
||||||
|
with the [twelvemonkeys](https://github.com/haraldk/TwelveMonkeys)
|
||||||
|
library there is support for many images. The priority is to avoid
|
||||||
|
more external commands if possible.
|
||||||
|
|
||||||
|
But since there already is a dependency to tesseract and it can create
|
||||||
|
searchable pdfs, the decision is to use tesseract for this. Then PDFs
|
||||||
|
with images can be converted to searchable PDFs with images. And text
|
||||||
|
extraction is required anyways.
|
||||||
|
|||||||
Loading…
x
Reference in New Issue
Block a user