8-bit and 24-bit PNGs not supported

[brandonkelly]

I don’t believe it’s currently possible to create an 8-bit or 24-bit PNG with Imagine; all new PNGs created with Imagine currently end up as 32-bit (4-channel) PNGs. However if you re-save an existing 8/24-bit PNG, both GD and ImageMagick will preserve the file’s allocated colorspace, and save the new image as an 8/24-bit PNG like it should.

Both ImageMagick and GD do have ways to save out new 8/24-bit PNGs. With ImageMagick that's as simple as:

$im->writeImage('png8:filename.png');
$im->writeImage('png24:filename.png');

And here’s how to save an 8-bit PNG using GD: http://stackoverflow.com/a/8547087/1688568

Ideally, you would be able to set the type of PNG that will get saved from $options['format'] when calling Image::save():

$image->save('filename.png', array(
    // ...
    'format' => 'png8'
));