I am using Imagick::resizeImage to create a thumbnail PNG image of each page of a pdf file. However, the image I am getting back is really blurry. How can I make it a little sharper? Any pointers would be really appreciated.
I have tried adjusting the 'blur' paramter of Imagick::resizeImage between 0.1 - 1, without success.
$pdfPage = '1Mpublic.pdf[0]';
$im = new imagick($pdfPage);
$im->setImageFormat('png');
// Resize thumbnail image
$imgHeight = $im -> getImageHeight();
$imgWidth = $im -> getImageWidth();
$desiredWidth = 200;
$desiredHeight = resizedImageHeight($imgWidth, $imgHeight, $desiredWidth);
$im -> setResolution(1500, 1500);
$im -> resizeImage($desiredWidth, $desiredHeight, imagick::STYLE_NORMAL, 0.1);
/* Resize image */
function resizedImageHeight($imgWidth, $imgHeight, $desiredImgWidth){
$quoient = $imgWidth/$imgHeight;
$height = $desiredImgWidth/$quoient;
return $height;
}
original pdf link:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4905263/pdf/ksgt-06-04-1091539.pdf
Unfortunately, I do not know Imagick that well. But in Imagemagick command line, I would do what is sometimes called supersampling. That is use a large density to read the PDF, then resize down by the inverse scale factor.
For example, nominal density is 72 dpi. I would read the input PDF at 4*72=288 dpi. Then after rasterizing, I would resize by 1/4=25% or for a larger result by something larger than 25%, say 50%. Here is your first page done both ways:
In Imagick, the key is something like:
Rather than rendering and then resizing the raster, it might be better to render the PDF to the right number of pixels in the first place. It'll be faster, and you can be sure that the amount of sharpness is correct for the content.
For example:
Makes:
The
-density 50
makes a page about the same number of pixels across as your sample, 425.In imagick you could do it like this (as @fmw42's excellent answer already says):
Doing both the ping and the read is a little slow in imagick, unfortunately:
It's not imagick, but
vipsthumbnail
can do the ping and read in one operation:It might be worth considering if speed is important. libvips has a php binding so you can call it directly, but if you do that you'll run into awful licensing problems because it uses the GPL library poppler for PDF rendering, sigh. ImageMagick uses GhostScript and shells out to that for the same reason.