Legacy ImageMagick Discussions Archive

Using Imagick, how can I detect if a gif is transparent or not?

I tried the following using getImageChannelDepth(imagick::ALPHA_CHANNEL), but did not work for me:

if (result is zero or null) // API doc only says "TRUE on success" which I think should be the number of bits for that channel and API does not say the return value if that channel does not exist
{
this is NOT a transparent gif
}
else
{
this is a transparent gif //has 1 bit alpha channel
}

However, I tried this on a transparent and a non-transparent gif. Both return 1 bit depth for alpha_channel (both return types are int using is_int to check). Using the command line identify, only the transparent gif has alpha channel info that shows 1 bit though. Could this be a bug with Imagick?

But anyways, I just need to know how to detect the transparent gif. I am using Imagick 2.2.2RC1 and ImageMagick 6.2.9 12/17/07 Q16

Just went through the API doc again and found this function called getImageChannelStatistics, seems like I can use it to do the trick:

$stats = $im->getImageChannelStatistics();
$alphastat = $stats[imagick::CHANNEL_ALPHA];
if($alphastat['mean'] == 0)
{
non-transparent;
}
else
{
transparent;
}

I tested with transparent and non-transparent gifs, seems like working. I also noticed that for all gifs, the depth value for alpha channel stat is always 1. This is probably why getImageChannelDepth(imagick::CHANNEL_ALPHA) always returns 1, even for jpg images.

If there are other better ways, please let me know. Thanks!