PDF to PNG conversion

2023-04-07

It's been five years since I last put this together, so I asked GPT4 for recommendations.

It would be an error if the image was not embedded, as in the 2017 summary below.

$ pip install pdf2image

$ brew install poppler

code:python

from pdf2image import convert_from_path

images = convert_from_path(pdf_path)

for i, image in enumerate(tqdm(images)):

image.save(os.path.join(output_dir, f"{i+1}.png"), "PNG")

Example of output

https://gyazo.com/e475b087b9ff628e9d78baa62758e604

72dpi by default

2017-08-23

summary

pdftocairo -r 200 -f 0 -png mybook.pdf prefix

As for the cut scan PDF, the cleanest way is to extract the -r 300 equivalent image embedded in pdfimages.

The problem is that we need to decide if it is that kind of PDF or not.

The quality of pdftocairo is almost the same as pdfimages. But 48 times slower.

gs

$ time gs -q -dBATCH -dNOPAUSE -sDEVICE=png16m -r100 -sOutputFile=pages_%04d.png mybook.pdf

gs -q -dBATCH -dNOPAUSE -sDEVICE=png16m -r100 -sOutputFile=pages_%04d.png 219.36s user 5.22s system 95% cpu 3:54.68 total

552x823

Terrible jaggies.

pdftoppm

$ time pdftoppm -r 100 -png mybook.pdf mybook

pdftoppm -r 100 -png mybook.pdf mybook 464.95s user 6.77s system 96% cpu 8:07.62 total

552x823

much better

pdftoppm Output at twice the resolution

$ time pdftoppm -r 200 -png mybook.pdf mybook

pdftoppm -r 200 -png mybook.pdf mybook 1104.28s user 12.22s system 96% cpu 19:14.59 total

1104x1646

Has the atmosphere of the title changed a lot? (Thinner? Sharper impression)

After doubling the size, the thumbnail above is reduced to twice the size. Does the text become thinner in the process?

So what would happen if you put it out at twice the resolution on the gs?

$ time gs -q -dBATCH -dNOPAUSE -sDEVICE=png16m -r200 -sOutputFile=pages_%04d.png mybook.pdf

gs -q -dBATCH -dNOPAUSE -sDEVICE=png16m -r200 -sOutputFile=pages_%04d.png 619.65s user 13.83s system 93% cpu 11:14.36 total

dirty

Mincho font "Hen" horizontal strokes, etc. are missing.

Enlargement (left: gs, right: pdftoppm)

https://gyazo.com/7d3d0371af344c56ee8ce7ddfa66f05d

gs seems to sample only once per pixel. pdftoppm looks like a behavior of sampling and mixing several times.

ImageMagick(convert)

$ time convert -verbose -density 200 mybook.pdf pages_%04d.png

"gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r200x200" "-sOutputFile=/tmp/magick-le3ab9PT-%08d" "-f/tmp/magick-s7CciX7v" "-f/tmp/magick-6huEpaq8"

As you can see from the command line output, it is hitting gs internally. The image quality is also similar to gs.

pdfimages

$ time pdfimages -j mybook.pdf ./pages

pdfimages -j mybook.pdf ./pages 6.14s user 2.51s system 59% cpu 14.569 total

Extract image files in the target PDF

Since the experimental PDF is a cut scan of a paper book, the scan result is contained in an image file.

https://gyazo.com/112c27b96232c0d73b64c0c702265959

1656x2469

The -r option for gs and pdftoppm was 552x823 when the -r option was 100, so -r 300 equivalent.

Try to reduce it to the same resolution

$ convert -thumbnail 1104x1646 ex7/pages-002.jpg t.png

convert -thumbnail 1104x1646 ex7/pages-002.jpg t.png 3.86s user 0.09s system 98% cpu 4.002 total

Pretty, but choose PDF origin

pdftocairo

$ time pdftocairo -r 200 -f 0 -l 10 -png mybook.pdf pages

pdftocairo -r 200 -f 0 -l 10 -png mybook.pdf pages 27.02s user 0.29s system 79% cpu 34.260 total

Enlarge (top left gs, top right pdftoppm, bottom left pdfimages and shrink, bottom right pdftocairo)

https://gyazo.com/3c493d7126c0692c284717ff2c536c19

Output almost equivalent to reduced from pdfimages

Not equal, but close enough that you can see the difference when you cut out one line and look at them closely side by side.

It took 34 seconds for 10 pages, which is relatively slow (19 seconds to produce 270 pages with pdftoppm, so roughly 48 times slower).

2017-08-23

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