Code for "How to resize a logo to specific dimensions keeping its aspect ratio using PHP" tutorial published at http://burnmind.com/tutorials/resize-logo-keeping-aspect-ratio

composer.json

{
    "require": {
        "intervention/image": "~2.1"
    },
    "autoload": {
        "psr-0": {
            "LogoResizer": "src/"
        }
    }
}

logo-resize.php

<?php
require_once('vendor/autoload.php');

use LogoResizer\LogoResizer;

function get_resized_logo($logo) {
    $resizer = new LogoResizer(300, 200);
    $resizer->set_source_logo($logo);

    if(!$resizer->is_source_logo_valid()) {
        return false;
    }

    $logo_resized = $resizer->resize_logo();

    if(!$logo_resized) {
        return false;
    }

    return $resizer->get_resized_logo();
}

if(isset($_FILES['logo'])) {
    $resized_logo = get_resized_logo($_FILES['logo']);

    if($resized_logo === false) {
        //show error
    } else {
        echo $resized_logo->response('jpg', 70);
        die();
    }
}
?>

<form method="POST" action="" enctype="multipart/form-data">
    <input type="file" name="logo" />
    <input type="submit" value="Upload logo" />
</form>

LogoResizer.php

<?php
namespace LogoResizer;

use Intervention\Image\ImageManagerStatic as Image;

class LogoResizer {

    private $desired_width;
    private $desired_height;
    private $desired_aspect_ratio;
    private $source_logo;
    private $resized_logo;

    public function __construct($desired_width = 300, $desired_height = 200) {
        $this->desired_width = $desired_width;
        $this->desired_height = $desired_height;
        $this->desired_aspect_ratio = $this->get_aspect_ratio($desired_width, $desired_height);
    }

    public function set_source_logo($source_image) {
        $this->source_logo = $source_image;
    }

    public function is_source_logo_valid() {
        $details = getimagesize($this->source_logo['tmp_name']);

        if($details === false) {
            return false;
        }

        return true;
    }

    public function get_resized_logo() {
        return $this->resized_logo;
    }

    public function resize_logo() {
        try {
            $logo = Image::make($this->source_logo['tmp_name']);

            if($logo->width() === $this->desired_width && $logo->height() === $this->desired_height) {
                $this->resized_logo = $logo;
                return true;
            }

            $logo_aspect_ratio = $this->get_aspect_ratio($logo->width(), $logo->height());

            if($this->desired_aspect_ratio === $logo_aspect_ratio) {
                $logo = $this->resize($logo, $this->desired_width, $this->desired_height);
                $this->resized_logo = $logo;
                return true;
            }

            $background_colour = $logo->pickColor(0, 0, 'hex');

            if($this->desired_aspect_ratio > $logo_aspect_ratio) {
                $logo = $this->resize($logo, null, $this->desired_height);
            } else {
                $logo = $this->resize($logo, $this->desired_width, null);
            }

            $logo->resizeCanvas($this->desired_width, $this->desired_height, 'center', false, $background_colour);

            $this->resized_logo = $logo;
            return true;

        } catch (Exception $e) {
            return false;
        }
    }

    private function get_aspect_ratio($width, $height) {
        return $width / $height;
    }

    private function resize($logo, $width, $height) {
        $logo->resize($width, $height, function ($constraint) {
            $constraint->aspectRatio();
        });

        return $logo;
    }
}