The `COLOR_OPACITY` doesn't exist if you are using ImageMagick lib 7 or newer version!Here is the c source code:#if MagickLibVersion < 0x700 IMAGICK_REGISTER_CONST_LONG("COLOR_OPACITY", PHP_IMAGICK_COLOR_OPACITY);#endifThere isn't any information about it anywhere (or I didn't find it)! So, if you want to use it, use the 6 version of lib! You can see the current installed version of lib with this command:$ identify -version