[WordPress] Resizing Images Programmatically in WordPress

00-filename.php

<?php

$filename = '/Users/tommcfarlin/Projects/acme/wp-content/uploads/2018/06/original-image.jpg';
if (!file_exists($filename)) {
  return;
}

01-get-editor.php

<?php

// Grab the editor for the filename of the image. 
$filename = '/Users/tommcfarlin/Projects/acme/wp-content/uploads/2018/06/original-image.jpg';
if (!file_exists($filename)) {
  return;
}

$editor = wp_get_image_editor( $filename, array() );

02-check-for-errors.php

<?php

// Grab the editor for the file and the size of the original image.
$filename = '/Users/tommcfarlin/Projects/acme/wp-content/uploads/2018/06/original-image.jpg';
if (!file_exists($filename)) {
  return;
}

$editor = wp_get_image_editor( $filename, array() );
if (is_wp_error($editor)) {
   // handle the problem however you deem necessary.
}

03-sizing-the-image.php

<?php

// Grab the editor for the file and the size of the original image.
$filename = '/Users/tommcfarlin/Projects/acme/wp-content/uploads/2018/06/original-image.jpg';
if (!file_exists($filename)) {
  return;
}

$editor = wp_get_image_editor( $filename, array() );
if (is_wp_error($editor)) {
   // Handle the problem however you deem necessary.
}

// Get the dimensions for the size of the current image.
$dimensions = $editor->get_size();
$width = $dimensions['width'];
$height = $dimensions['height'];

// Calculate the new dimensions for the image.
$newWidth = 0.4 * $width;
$newHeight = 0.3 * $height;

// Resize the image.
$result = $editor->resize($newWidth, $newHeight, true);

04-saving-the-image.php

<?php

// Grab the editor for the file and the size of the original image.
$filename = '/Users/tommcfarlin/Projects/acme/wp-content/uploads/2018/06/original-image.jpg';
if (!file_exists($filename)) {
  return;
}

$editor = wp_get_image_editor( $filename, array() );
if (is_wp_error($editor)) {
   // handle the problem however you deem necessary.
}

// Get the dimensions for the size of the current image.
$dimensions = $editor->get_size();
$width = $dimensions['width'];
$height = $dimensions['height'];

// Calculate the new dimensions for the image.
$newWidth = 0.4 * $width;
$newHeight = 0.3 * $height;

// Resize the image.
$result = $editor->resize($newWidth, $newHeight, true);

// If there's no problem, save it; otherwise, print the problem.
if (!is_wp_error($result)) {
  $editor->save($editor->generate_filename());
} else {
   // Handle the problem however you deem necessary.
}