I’m trying to render a scaled image using the code:
new PdfToImageConverter
{
ScaleTo = 2200
}
.GenerateImage(
"sample.pdf",
1,
ImageFormat.Png,
"sample.pdf.png");
The code renders a good proportional image under Ubuntu, but a squared image under Windows.
The squared window has a white field:
Sample application:
https://github.com/sergei-voronkov/Test.NReco.ScaleTo
Also, the generated image is correct if I try to generate it using native poppler utility pdftoppm.exe under Windows:
pdftoppm.exe -png -aa yes -aaVector yes -f 1 -l 1 -singlefile -scale-to 2200 sample.pdf sample.pdf
The command line generates a proportional scaled image:
2
Answers
The problem has been fixed in the version 1.5.0.
The behaviour is different because ‘pdftoppm’ versions are different.
On Windows, NReco.PdfRenderer uses poppler tools binaries that are shipped in the nuget package — they are extracted on first use and there is no need to deploy them manually. The latest NReco.PdfRenderer includes poppler 21.03 release. In this version "-scale-to" parameter works differently, it always renders to square image; say, if ScaleTo=2000 then output always is 2000×2000. It seems this bug is already known and fixed: https://gitlab.freedesktop.org/poppler/poppler/-/issues/1062. I’ll check that, maybe it would be enough to prepare a new NReco.PdfRenderer release with the latest poppler tools binaries for Windows. As a temporary workaround, you may consider to use "Dpi" property to get better resolution for your output images.
On Linux you may choose what poppler tools version to install, and I guess in your case this version is older (like 0.68 or earlier), where "-scale-to" works correctly.