Convert pdf to png, size issue

Question

I have a pdf file created from an impress presentation. I want to convert the pdf to png images to add them to create a video using them. I am using pdftoppm to convert the pdf to png, but the exported images are getting a size of 1654x931 px. I need 1920x1080, as my video is going to be in that resolution.

The command I am using is the following:

pdftoppm -png report.pdf report

In Impress I haven't found any setting the set the size of the exported pdf, and I haven't been able to find anything to set the size of the png conversion.

Is there anyway to adjust the size of the generated pngs?

Answer 1

pdftoppm appears to provide the following scaling options:

   -scale-to number
          Scales  the  long  side of each page (width for landscape pages,
          height for portrait pages) to fit in scale-to pixels.  The  size
          of  the short side will be determined by the aspect ratio of the
          page.

   -scale-to-x number
          Scales each page horizontally to fit in  scale-to-x  pixels.  If
          scale-to-y  is  set  to -1, the vertical size will determined by
          the aspect ratio of the page.

   -scale-to-y number
          Scales each page vertically to  fit  in  scale-to-y  pixels.  If
          scale-to-x  is set to -1, the horizontal size will determined by
          the aspect ratio of the page.

Since 1654x931 and 1920x1080 have essentially the same aspect 16:9 ratio, it may be sufficient to use -scale-to to set the long edge to 1920 pixels:

pdftoppm -png -scale-to 1920 report.pdf report

Otherwise, you can set the x and y dimensions explicitly

pdftoppm -png -scale-to-x 1920 -scale-to-y 1080 report.pdf report

Answer 2

I'm not very familiar with *.cbr / *.cbz, but it seems you'll have to combine two steps:

Convert PDF to Images

Compress them into a ZIP / RAR archive.

Regarding step 1, you could use ImageMagick's convert command. You can feed convert with a PDf comprising multiple pages, and convert will return each page as single graphics file. I've tested it with a text scanned at 400 dpi, and the following command resulted in nice single JPGEs:

$ convert -verbose -colorspace RGB -interlace none -density 400 -quality 100 yourPdfFile.pdf 00%d.jpeg

(credits regarding the -quality option: this forum entry)

As a result, you get 000.jpeg, 001.jpeg and so on. Just zip them into a .cbz file, and you're done.

You could even combine both steps by "concatenating" them:

*$ convert -verbose -colorspace RGB -interlace none -density 400 -quality 100 yourPdfFile.pdf 00%d.jpg && zip -vm comic.cbz .jpg

(make sure that there aren't any other JPEGs in your current working directory, since using the code above, zip will move all JPEGs into the cbz file)