I have looked all over for how to correctly manage alpha when I\'m resizing a png. I\'ve managed to get it to keep transparency, but only for pixels that are completely tran
"They have not worked at all and I'm not sure why."
Well you must have been doing something wrong. The code from the linked duplicate with a couple of lines added to load and save the image:
$im = imagecreatefrompng(PATH_TO_ROOT."var/tmp/7Nsft.png");
$srcWidth = imagesx($im);
$srcHeight = imagesy($im);
$nWidth = intval($srcWidth / 4);
$nHeight = intval($srcHeight /4);
$newImg = imagecreatetruecolor($nWidth, $nHeight);
imagealphablending($newImg, false);
imagesavealpha($newImg,true);
$transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
imagefilledrectangle($newImg, 0, 0, $nWidth, $nHeight, $transparent);
imagecopyresampled($newImg, $im, 0, 0, 0, 0, $nWidth, $nHeight,
$srcWidth, $srcHeight);
imagepng($newImg, PATH_TO_ROOT."var/tmp/newTest.png");
Produces the image:

i.e. this question (and answer) are a complete duplicate.