the_post_thumbnail( array() ) not working

Hello all,

just creating a theme now. I use function the_post_thumbnail() in index.php thus so:

<?php the_post_thumbnail( array(150,190) ); ?>

but the output is:

<img width="150" height="150" title="press1" alt="press1" class="attachment-150x190 wp-post-image" src="https://localhost/alfonstost/wp-content/uploads/2010/11/press1-150x150.jpg">

So the image outputs not at 150×190 but at 150×150 (WordPress default thumbnail size).
In the post, I have defined the Post Featured Image at “full size” (which is 190×150)

Any ideas why it’s not working?