load_image_to_edit( string $attachment_id, string $mime_type, string $size = 'full' )

function load_image_to_edit( $attachment_id, $mime_type, $size = 'full' ) {
	$filepath = _load_image_to_edit_path( $attachment_id, $size );
	if ( empty( $filepath ) )
		return false;

	switch ( $mime_type ) {
		case 'image/jpeg':
			$image = imagecreatefromjpeg($filepath);
			break;
		case 'image/png':
			$image = imagecreatefrompng($filepath);
			break;
		case 'image/gif':
			$image = imagecreatefromgif($filepath);
			break;
		default:
			$image = false;
			break;
	}
	if ( is_resource($image) ) {
		/**
		 * Filters the current image being loaded for editing.
		 *
		 * @since WP-2.9.0
		 *
		 * @param resource $image         Current image.
		 * @param string   $attachment_id Attachment ID.
		 * @param string   $size          Image size.
		 */
		$image = apply_filters( 'load_image_to_edit', $image, $attachment_id, $size );
		if ( function_exists('imagealphablending') && function_exists('imagesavealpha') ) {
			imagealphablending($image, false);
			imagesavealpha($image, true);
		}
	}
	return $image;
}