Scaling images with alpha blending properly with PHP gd

I had some code trying to scale an image in gd using the imagescale function, that looked something like this:

/* makes a copy of the image, instead of modifying in place */
$target = imagescale($image, $width, $height);

However, the images it created were heavily distorted when using bilinear filtering, and didn’t quite look right with neared neighbour either. For example, with bilinear filtering…

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