PHP+Imagick - PNG Compression

Question

How do I efficiently compress a PNG? In my case, the images are small grayscale images with transparency.

Currently I\'m playing with this:

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Answer 1

I'm definitely not sure if it is correct way to save PNG, but my way is:

$im->setImageCompression(\Imagick::COMPRESSION_UNDEFINED);
$im->setImageCompressionQuality(0);

This gives me perfect quality of the image and file size very similar to PS6 saved 'Save for Web'. Sometimes even smaller sizes!