Resizing Images

In order to use images with custom dimensions, you can use a built-in Magento re-sizer function to generate image URLs with the correct dimensions and you will need to amend the product model.

Start by reading how to extend Nosto module and how to alter Nosto product data.

Note: In case you want a square image, only the first parameter is required.

File app/code/My/Nosto/Observer/Product/Load.php

<?php

namespace My\Nosto\Observer\Product;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Catalog\Api\ProductRepositoryInterface;

class Load implements ObserverInterface
{
    protected $imageHelper;
    protected $productRepository;

    public function __construct(
        \Magento\Catalog\Helper\Image $imageHelper,
        ProductRepositoryInterface $productRepository
    ) {
        $this->imageHelper = $imageHelper;
        $this->productRepository = $productRepository;
    }

    /**
     * Observer for "nosto_product_load_after" event
     *
     * @param Observer $observer
     * @return void
     * @throws \Magento\Framework\Exception\NoSuchEntityException
     */
    public function execute(Observer $observer)
    {
        /** @var $product \NostoProduct */
        $product = $observer->getProduct();

        $width = 200;
        $height = 300;

        $magentoProduct = $this->productRepository->getById($product->getProductId());
        $resizedImageUrl = $this->imageHelper
            ->init($magentoProduct, 'product_base_image')
            ->constrainOnly(true) // Optional
            ->keepAspectRatio(true) // Optional
            ->keepTransparency(true) // Optional
            ->keepFrame(false) // Optional
            ->resize($width, $height)
            ->getUrl();

        $product->setImageUrl($resizedImageUrl);
    }
}