Have a site that was recently upgraded to ImageMagick 7. Using pThumb with Resizer enabled, every page on the site returned a 500 error due to:
PHP Fatal error: Uncaught Error: Undefined class constant 'COLOR_OPACITY' in /components/resizer/model/vendor/sepiariver/reductionist/src/Reductionist/Imagick/RImagine.php:36
Seems 'COLOR_OPACITY' doesn't exist in v7: https://www.php.net/manual/en/imagick.constants.php#122744. Disabling Resizer resolved the error