Unable to load mimetype within cache function

[scottybo]

If I try to get the mime of the image within the cache function (code below) I get the following error:

"call_user_func_array() expects parameter 1 to be a valid callback, class 'Intervention\Image\ImageManager' does not have a method 'mime'"

            // pass calls to image cache
            $img = Image::cache(function($image) use ($imageUrl, $width, $height) {
                $mime = $image->mime();
                if (!empty($width) && !empty($height)) {
                    $image->make($imageUrl)->fit($width, $height)->encode();
                } else {
                    $image->make($imageUrl)->encode();
                }
            },525600);

It works fine if I use Image:: within the function, but then I'm loading the image again which defeats the purpose of the cache.

I want to be able to detect the mimetype and change the encoding if it's (For example) a bmp or tiff, but leave all other images in the same type (eg png)