Extracting Images using pdfimages: Getting 3 Images Per Page: .jp2, .png, .jb2e

Question

Using pdfimages -all on a .pdf file, each page of which is text, I'm getting 3 images for each page in the pdf:

Foo-001-000.jp2
Foo-001-002.png
Foo-001-002.jb2e

The first file is mostly blank, but contains some ghostly background plus an occasional piece of text. The second file is black and white and appears to be some kind of mask, perhaps identifying where the text in the third file is located (?) The third file I am not able to view in Ubuntu's image viewer or gimp.

If I use -png I similarly get three images, but all are .png's. Most (almost all) of the pdf's text in in the third image.

pdfimages -list looks like this:

page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
   1     0 image     829  1254  rgb     3   8  jpx    yes     3659  0   150   150 76.2K 2.5%
   1     1 image     829  1254  rgb     3   8  image  yes     3663  0   150   150 5250B 0.2%
   1     2 mask     1658  2508  -       1   1  image  yes     3663  0   300   300 5250B 1.0%
   2     3 image     934  1254  rgb     3   8  jpx    yes       11  0   150   150 85.6K 2.5%
   2     4 image     934  1254  rgb     3   8  image  yes       15  0   150   150 14.1K 0.4%
   2     5 mask     1868  2508  -       1   1  image  yes       15  0   300   300 14.1K 2.5%
   3     6 image     858  1243  rgb     3   8  jpx    yes       47  0   150   150 78.0K 2.5%
   3     7 image     858  1243  rgb     3   8  image  yes       51  0   150   150 7681B 0.2%

Could someone help me understand what I've got here, and how I might combine these three images to get a single images for each page. Or equivalently, just extract single images per page. They key issue for me is to keep as much information as is available in these images. I want to avoid degradation in quality.

Answer 1

I guess, you think you have a single image as a page and are surprised it's actually composited. This is a widespread method for archiving magazines as these are graphically more complex than a simple book with some images. It preserves the quality and gives a very small pdf file in the end - but unusably slow to render.

Now for the solution. You don't actually want to extract anything from the pdf. You want to render it the same way your pdf reader does. I would suggest using Ghostscript. Something like this will work:

gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=png16m -r600 -dGraphicsAlphaBits=4 -sOutputFile=./img/img-%03d.png "$pdffilename"

Adjust as needed.