PHP: create a cropped rectangle thumbnail

Question

I'm trying to resize and crop an image with @imagecopyresampled mantaining the original aspect ratio.

The idea is: 1) I fix a dimension of the thumbnail (f.e. 300x40) 2) Crop starting to the center of the height

I tried to read the documentation and a lot of other question on stackoverflow but without result. Anyone can help me?? My actual code is the following:

//$img_height, $img_width [original size of the image]

$thumb_width  = 300;
$thumb_height = 40;
$new_img = @imagecreatetruecolor($thumb_width, $thumb_height);
$middle = floor($img_height/2);

$src_x = 0;
$src_y = $middle-($thumb_width/2);

$src_w = $img_width;
$aspectRatio = $img_width/$thumb_width;

//$src_h = ?????

$imgCopyRes = @imagecopyresampled(
                  $new_img, $src_img,
                  0, 0, 
                  $src_x, $src_y, 
                  $thumb_width, $thumb_height, 
                  $src_w, $src_h);

---

EDIT :

Thank you so much @Joshua Burns , reading your class and editing your code I have found the solution without including the entire file.

Code:

$target_width  = 300;
$target_height = 40;
$new_img = @imagecreatetruecolor($target_width, $target_height);

$width_ratio  = $target_width  / $img_width;
$height_ratio = $target_height / $img_height;
if($width_ratio > $height_ratio) {
    $resized_width  = $target_width;
    $resized_height = $img_height * $width_ratio;
} else {
    $resized_height = $target_height;
    $resized_width  = $img_width * $height_ratio;
}
// Drop decimal values
$resized_width  = round($resized_width);
$resized_height = round($resized_height);

// Calculations for centering the image
$offset_width  = round(($target_width  - $resized_width) / 2);
$offset_height = round(($target_height - $resized_height) / 2);

$imgCopyRes = @imagecopyresampled(
                  $new_img, $src_img, 
                  $offset_width, $offset_height, 
                  0, 0, 
                  $resized_width, $resized_height, 
                  $img_width, $img_height);  

Answer 1

Alright, this is probably a little bloated for your needs, but it gets the job done and it gets it done well..

First off, include or paste this class into your PHP code: http://pastebin.com/dnmiUVmk

Then, use the class similarly to the following:

<?php
// Replace 'picture' w/ whatever the name of the file upload.
// Alternately, specify an absolute path to an image already on the server.
$upload_image_tmp_filename = $_FILES['picture']['tmp_name'];
$saveas_image_filename = 'my_resized_image.png';
$max_width = 300;
$max_height = 40;

// If there was a problem, an exception is thrown.
try {
    // Load the image
    $picture = New Image($upload_image_tmp_filename);
    // Save the image, resized.
    $picture->saveFile($saveas_image_filename, $max_width, $max_height, True);
} catch(Exception $e) {
    print $e->getMessage();
}