Implement made "Thumbnail upscale & correct crop in WordPress"

Many thanks for help…

Download modified and replace files – https://maciej.kuzniczysko.pl/files/manual-image-crop.zip
Or modify it by your own:

wp-content\plugins\manual-image-crop\lib\ManualImageCrop.php

//prepares coordinates that will be passed to cropping function
		$dst_x = 0;
		$dst_y = 0;
		$src_x = max(0, $_POST['select']['x']) * $_POST['previewScale'];
		$src_y = max(0, $_POST['select']['y']) * $_POST['previewScale'];
		$src_w = max(0, $_POST['select']['w']) * $_POST['previewScale'];
		$src_h = max(0, $_POST['select']['h']) * $_POST['previewScale'];

		//saves the selected area
		$imageMetadata = wp_get_attachment_metadata($_POST['attachmentId']);
		$imageMetadata['micSelectedArea'][$_POST['editedSize']] = array(
																	'x' => $_POST['select']['x'],
																	'y' => $_POST['select']['y'],
																	'w' => $_POST['select']['w'],
																	'h' => $_POST['select']['h'],

->

//prepares coordinates that will be passed to cropping function
		$dst_x = 0;
		$dst_y = 0;
		$src_x = max(0, $_POST['select']['x']) * $_POST['previewScale'];
		$src_y = max(0, $_POST['select']['y']) * $_POST['previewScale'];
		$src_w = max(0, $_POST['select']['w']) * $_POST['previewScale'];
		$src_h = max(0, $_POST['select']['h']) * $_POST['previewScale'];

		$is_higher = ( $dst_h > wp_get_image_editor( $src_file )->get_size()["height"] );
		$is_wider = ( $dst_w > wp_get_image_editor( $src_file )->get_size()["width"] );

		if ( $is_higher || $is_wider ) :
			if ( $is_higher )
				$scale = $src_h / wp_get_image_editor( $src_file )->get_size()["height"];
			else
				$scale = $src_w / wp_get_image_editor( $src_file )->get_size()["width"];	

			$src_w = $src_w / $scale;
			$src_h = $src_h / $scale;
			$src_x = $src_x / $scale;
			$src_y = $src_y / $scale;
		endif;	

		//saves the selected area
		$imageMetadata = wp_get_attachment_metadata($_POST['attachmentId']);
		$imageMetadata['micSelectedArea'][$_POST['editedSize']] = array(
																	'x' => $_POST['select']['x'],
																	'y' => $_POST['select']['y'],
																	'w' => $_POST['select']['w'],
																	'h' => $_POST['select']['h'],

wp-content\plugins\manual-image-crop\lib\ManualImageCropEditorWindow.php

$src_file_url = wp_get_attachment_image_src($_GET['postId'], 'full');
				if (!$src_file_url) {
					echo json_encode (array('status' => 'error', 'message' => 'wrong attachement' ) );
					exit;
				}
				$src_file = str_replace($uploadsDir['baseurl'], $uploadsDir['basedir'], $src_file_url[0]);
				$sizes = getimagesize($src_file);

				$previewWidth = min($sizes[0], 500);
				$previewHeight = min($sizes[1], 350);
				$previewRatio = 1;

->

$src_file_url = wp_get_attachment_image_src($_GET['postId'], 'full');
				if (!$src_file_url) {
					echo json_encode (array('status' => 'error', 'message' => 'wrong attachement' ) );
					exit;
				}
				$src_file = str_replace($uploadsDir['baseurl'], $uploadsDir['basedir'], $src_file_url[0]);
				$sizes = getimagesize($src_file);

				$original[0] = $sizes[0];
				$original[1] = $sizes[1];

				if ($width > $sizes[0]) {
					$sizes[1] = ( $sizes[1] * ($width / $sizes[0]) );
					$height = ceil($height);
					$sizes[0] = $width;
				}

				$previewWidth = min($sizes[0], 500);
				$previewHeight = min($sizes[1], 350);
				$previewRatio = 1;

and

<?php _e('Original picture dimensions:','microp') ?> <strong><?php echo $sizes[0]; ?> x <?php echo $sizes[1]; ?> px</strong><br />

->

<?php _e('Original picture dimensions:','microp') ?> <strong><?php echo $original[0]; ?> x <?php echo $original[1]; ?> px</strong><br />