The same algorithm that scales down can also scale up. This is untested code, and it is only designed to scale down, but if you remove the "scale down" tests it might do the trick for you.
<?php // RAY_image_resize_and_crop.php
error_reporting(E_ALL);
// RESIZE AN IMAGE PROPORTIONALLY AND CROP TO THE CENTER
function resize_and_crop($original_image_url, $thumb_image_url, $thumb_w, $thumb_h, $quality=75)
{
// ACQUIRE THE ORIGINAL IMAGE: http://php.net/manual/en/function.imagecreatefromjpeg.php
$original = imagecreatefromjpeg($original_image_url);
if (!$original) return FALSE;
// GET ORIGINAL IMAGE DIMENSIONS
list($original_w, $original_h) = getimagesize($original_image_url);
// RESIZE IMAGE AND PRESERVE PROPORTIONS
$thumb_w_resize = $thumb_w;
$thumb_h_resize = $thumb_h;
if ($original_w > $original_h)
{
$thumb_h_ratio = $thumb_h / $original_h;
$thumb_w_resize = (int)round($original_w * $thumb_h_ratio);
}
else
{
$thumb_w_ratio = $thumb_w / $original_w;
$thumb_h_resize = (int)round($original_h * $thumb_w_ratio);
}
if ($thumb_w_resize < $thumb_w)
{
$thumb_h_ratio = $thumb_w / $thumb_w_resize;
$thumb_h_resize = (int)round($thumb_h * $thumb_h_ratio);
$thumb_w_resize = $thumb_w;
}
// CREATE THE PROPORTIONAL IMAGE RESOURCE
$thumb = imagecreatetruecolor($thumb_w_resize, $thumb_h_resize);
if (!imagecopyresampled($thumb, $original, 0,0,0,0, $thumb_w_resize, $thumb_h_resize, $original_w, $original_h)) return FALSE;
// ACTIVATE THIS TO STORE THE INTERMEDIATE IMAGE
// imagejpeg($thumb, 'RAY_temp_' . $thumb_w_resize . 'x' . $thumb_h_resize . '.jpg', 100);
// CREATE THE CENTERED CROPPED IMAGE TO THE SPECIFIED DIMENSIONS
$final = imagecreatetruecolor($thumb_w, $thumb_h);
$thumb_w_offset = 0;
$thumb_h_offset = 0;
if ($thumb_w < $thumb_w_resize)
{
$thumb_w_offset = (int)round(($thumb_w_resize - $thumb_w) / 2);
}
else
{
$thumb_h_offset = (int)round(($thumb_h_resize - $thumb_h) / 2);
}
if (!imagecopy($final, $thumb, 0,0, $thumb_w_offset, $thumb_h_offset, $thumb_w_resize, $thumb_h_resize)) return FALSE;
// STORE THE FINAL IMAGE - WILL OVERWRITE $thumb_image_url
if (!imagejpeg($final, $thumb_image_url, $quality)) return FALSE;
return TRUE;
}
// USE CASE
echo '<a target="_blank" href="RAY_orig_600x374.jpg">Original 600x374</a><br/>';
resize_and_crop('RAY_orig_600x374.jpg', 'RAY_temp_100x100.jpg', 100, 100);
echo '<a target="_blank" href="RAY_temp_100x100.jpg">100x100</a><br/>';
resize_and_crop('RAY_orig_600x374.jpg', 'RAY_temp_200x100.jpg', 200, 100);
echo '<a target="_blank" href="RAY_temp_200x100.jpg">200x100</a><br/>';
resize_and_crop('RAY_orig_600x374.jpg', 'RAY_temp_200x300.jpg', 200, 300);
echo '<a target="_blank" href="RAY_temp_200x300.jpg">200x300</a><br/>';