Resize an image to fit within a specified maximum width and height in PHP

Here is a PHP function that resizes an image to fit within a specified maximum width and height, preserving its aspect ratio. This can be useful if you’re working with WordPress or a similar PHP-based platform:

function resize_image($source_path, $destination_path, $max_width, $max_height) {
    // Get original image dimensions and type
    list($orig_width, $orig_height, $image_type) = getimagesize($source_path);
    
    // Calculate the aspect ratio
    $aspect_ratio = $orig_width / $orig_height;

    // Determine new dimensions based on max width and height while preserving aspect ratio
    if ($max_width / $max_height > $aspect_ratio) {
        $new_width = (int)($max_height * $aspect_ratio);
        $new_height = $max_height;
    } else {
        $new_width = $max_width;
        $new_height = (int)($max_width / $aspect_ratio);
    }

    // Create a new empty image with the calculated dimensions
    $new_image = imagecreatetruecolor($new_width, $new_height);

    // Load the source image based on its type
    switch ($image_type) {
        case IMAGETYPE_JPEG:
            $source_image = imagecreatefromjpeg($source_path);
            break;
        case IMAGETYPE_PNG:
            $source_image = imagecreatefrompng($source_path);
            // Preserve transparency for PNG images
            imagealphablending($new_image, false);
            imagesavealpha($new_image, true);
            break;
        case IMAGETYPE_GIF:
            $source_image = imagecreatefromgif($source_path);
            break;
        default:
            return false; // Unsupported image type
    }

    // Resize the original image into the new image
    imagecopyresampled($new_image, $source_image, 0, 0, 0, 0, $new_width, $new_height, $orig_width, $orig_height);

    // Save the new image based on its type
    switch ($image_type) {
        case IMAGETYPE_JPEG:
            imagejpeg($new_image, $destination_path);
            break;
        case IMAGETYPE_PNG:
            imagepng($new_image, $destination_path);
            break;
        case IMAGETYPE_GIF:
            imagegif($new_image, $destination_path);
            break;
    }

    // Free up memory
    imagedestroy($source_image);
    imagedestroy($new_image);

    return true;
}

Usage

$source_path = 'path/to/original/image.jpg';
$destination_path = 'path/to/resized/image.jpg';
$max_width = 800; // Max width in pixels
$max_height = 600; // Max height in pixels

resize_image($source_path, $destination_path, $max_width, $max_height);

Explanation

• Aspect Ratio: The function maintains the aspect ratio by checking whether width or height is the limiting factor based on the provided maximum dimensions.
• Transparency: Special handling is added for PNG images to preserve transparency.
• Supported Formats: This function supports JPEG, PNG, and GIF formats.