I'm trying to get all new thumbnails to conform to a MAX 150px width.
I have found references to this line of code:
$max_side = apply_filters( 'wp_thumbnail_max_side_length', 128, $attachment_id, $file );
...but the problem is that it's setting the Y -- vertical -- axis of the image to max out at 150px, when it's only the X axis that needs the limitation.
In short, how do you make thumbnails with a max width of 150px, and not care about the height?