How to convert PDF to low-resolution (but good quality) JPEG?
When I use the following ghostscript command to generate jpg thumbnails from PDFs, the image quality is often very poor:
gs -q -dNOPAUSE -dBATCH -sDEVICE=jpeggray -g465x600 -dUseCropBox -dPDFFitPage -sOutputFile=pdf_to_lowres.jpg test.pdf
By contrast, if I use ghostscript to generate a high-resolution png, and then use mogrify to convert the high-res png to a low-res jpg, I get pretty good results.
gs -q -dNOPAUSE -dBATCH -sDEVICE=pnggray -g2550x3300 -dUseCropBox -dPDFFitPage -sOutputFile=pdf_to_highres.png 开发者_如何转开发test.pdf
mogrify -thumbnail 465x600 -format jpg -write pdf_to_highres_to_lowres.jpg pdf_to_highres.png
Is there any way to achieve good results while bypassing the intermediate pdf -> high-res png step? I need to do this for a large number of pdfs, so I'm trying to minimize the compute time.
Here are links to the images referenced above:
- test.pdf
- pdf_to_lowres.jpg
- pdf_to_highres.png
- pdf_to_highres_to_lowres.jpg
One option that seems to improve the output a lot: -dDOINTERPOLATE
. Here's what I got by running the same command as you but with the -dDOINTERPOLATE
option:
I'm not sure what interpolation method this uses but it seems pretty good, especially in comparison to the results without it.
P.S. Consider outputting PNG images (-sDEVICE=pnggray
) instead of JPEG. For most PDF documents (which tend to have just a few solid colors) it's a more appropriate choice.
Your PDF looks like it is just a wrapper around a jpeg already.
Try using the pdfimages program from xpdf to extract the actual image rather than rendering to a file.
精彩评论