Scale an image with Imagick without deforming the original

Question

One have an application in which the user can upload an image, do Crop and "work" the image, adding props etc... My problem is with Crop because the max size of Crop is always different depending on the resolution of the images, to combat this I thought of putting all the images with the same resolution that also works but I need to specify the width and height image, any way to define only one of them (other solutions are welcome) in a way that never deforms the image that was 'uploaded' by the user? I got this code, it works fine:

$thumb = new Imagick();
$thumb->readImage('imgTest.jpg');
$thumb->resizeImage(300,3000,Imagick::FILTER_LANCZOS,1);
$thumb->writeImage('imgTest.jpg');
$thumb->clear();
$thumb->destroy();