Why does Imagick turn the switch backgroundcolor? - php

Question

I'm trying to convert an pdf to a jpeg, trim the whitespaces around the content and resize it to 300x600
In PHP using ImageMagick 6.7.7-10
here's my code:
$im = new \Imagick();
$im->setBackgroundColor("white");
$im->readimage($url);
$im->setImageFormat("jpeg");
$im->trimImage(0);
$im->resizeImage(300, 600, Imagick::FILTER_LANCZOS, 0.9);
$im->writeImage($tmpFilePath);
$im->clear();
$im->destroy();
here is the PDF
http://cs1.fuman.de/file.php/1AOrL6-PzT71Z-dk0000-CsjquC
and here the resulting JPG
http://cs1.fuman.de/file.php/1AOrL0-kWAl8P-ml0000-xAhOiw
Does anyone know, what's going wrong here?
Thanks in advance
JD

Answer 1

I don't know why the background color is being ignored. I think it's to do with JPEG not having a concept of a 'background' colour, and so when the image is converted from having alpha to not having alpha, bad things happen.
I suggest using this code:
$imagick = new \Imagick();
// Make the image be large when read from PDF so have decent quality later
$imagick->setResolution(92, 92);
// only use the first page of the PDF
$imagick->readimage("./orig.pdf[0]");
// Make a white background imge
$canvas = new Imagick();
$canvas->newPseudoImage(
$imagick->getImageWidth(),
$imagick->getImageHeight(),
'canvas:white'
);
// Need to use png format to keep alpha channge
$imagick->setImageFormat('png');
// Composite our image, into the white background
$canvas->compositeImage($imagick, \Imagick::COMPOSITE_ATOP, 0, 0);
$canvas->resizeImage(300, 600, Imagick::FILTER_LANCZOS, 1);
$canvas->setImageFormat('png');
$canvas->writeImage("output.png");