You can use Magento default image resize command.
To resize image please follow the steps below.
Assume You are using a custom them name "Conpany_MyTheme"
step 1: create the xml file view.xml under MAGENTOROOT/app/design/frontend/Company/MyTheme/etc
FIle: view.xml
<?xml version="1.0"?>
<!--
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
-->
<view xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/view.xsd">
<media>
<images module="Magento_Catalog">
<image id="bundled_product_customization_page" type="thumbnail">
<width>140</width>
<height>140</height>
</image>
<image id="cart_cross_sell_products" type="small_image">
<width>240</width>
<height>300</height>
</image>
<image id="cart_page_product_thumbnail" type="small_image">
<width>165</width>
<height>165</height>
</image>
<image id="category_page_grid" type="small_image">
<width>800</width>
<height>800</height>
</image>
<image id="category_page_grid-1" type="small_image">
<width>800</width>
<height>800</height>
</image>
<image id="category_page_list" type="small_image">
<width>800</width>
<height>800</height>
</image>
<image id="customer_account_my_tags_tag_view" type="small_image">
<width>100</width>
<height>100</height>
</image>
<image id="customer_account_product_review_page" type="image">
<width>285</width>
<height>285</height>
</image>
<image id="customer_shared_wishlist" type="small_image">
<width>113</width>
<height>113</height>
</image>
<image id="gift_messages_checkout_small_image" type="small_image">
<width>75</width>
<height>75</height>
</image>
<image id="gift_messages_checkout_thumbnail" type="thumbnail">
<width>100</width>
<height>100</height>
</image>
<image id="mini_cart_product_thumbnail" type="thumbnail">
<width>75</width>
<height>75</height>
</image>
<image id="new_products_content_widget_grid" type="small_image">
<width>240</width>
<height>300</height>
</image>
<image id="new_products_content_widget_list" type="small_image">
<width>270</width>
<height>340</height>
</image>
<image id="new_products_images_only_widget" type="small_image">
<width>78</width>
<height>78</height>
</image>
<image id="product_base_image" type="image">
<width>265</width>
<height>265</height>
</image>
<image id="product_comparison_list" type="small_image">
<width>140</width>
<height>140</height>
</image>
<image id="product_page_image_large" type="image"/>
<image id="product_page_image_large_no_frame" type="image">
<frame>false</frame>
</image>
<image id="product_page_image_medium" type="image">
<width>700</width>
<height>560</height>
</image>
<image id="product_page_image_medium_no_frame" type="image">
<width>1500</width>
<height>1500</height>
<frame>false</frame>
</image>
<image id="product_page_image_small" type="thumbnail">
<width>88</width>
<height>110</height>
</image>
<image id="product_page_main_image" type="image">
<width>700</width>
<height>560</height>
</image>
<image id="product_page_main_image_default" type="image">
<width>700</width>
<height>560</height>
</image>
<image id="product_page_more_views" type="thumbnail">
<width>88</width>
<height>110</height>
</image>
<image id="product_stock_alert_email_product_image" type="small_image">
<width>76</width>
<height>76</height>
</image>
<image id="product_small_image" type="small_image">
<width>135</width>
<height>135</height>
</image>
<image id="product_thumbnail_image" type="thumbnail">
<width>75</width>
<height>75</height>
</image>
<image id="recently_compared_products_grid_content_widget" type="small_image">
<width>240</width>
<height>300</height>
</image>
<image id="recently_compared_products_images_names_widget" type="thumbnail">
<width>75</width>
<height>90</height>
</image>
<image id="recently_compared_products_images_only_widget" type="thumbnail">
<width>76</width>
<height>76</height>
</image>
<image id="recently_compared_products_list_content_widget" type="small_image">
<width>270</width>
<height>340</height>
</image>
<image id="recently_viewed_products_grid_content_widget" type="small_image">
<width>240</width>
<height>300</height>
</image>
<image id="recently_viewed_products_images_names_widget" type="small_image">
<width>75</width>
<height>90</height>
</image>
<image id="recently_viewed_products_images_only_widget" type="small_image">
<width>76</width>
<height>76</height>
</image>
<image id="recently_viewed_products_list_content_widget" type="small_image">
<width>270</width>
<height>340</height>
</image>
<image id="related_products_list" type="small_image">
<width>152</width>
<height>190</height>
</image>
<image id="hotpicks_products_list" type="small_image">
<width>400</width>
<height>400</height>
</image>
<image id="review_page_product_image" type="small_image">
<width>285</width>
<height>285</height>
</image>
<image id="rss_thumbnail" type="thumbnail">
<width>75</width>
<height>75</height>
</image>
<image id="sendfriend_small_image" type="small_image">
<width>75</width>
<height>75</height>
</image>
<image id="shared_wishlist_email" type="small_image">
<width>135</width>
<height>135</height>
</image>
<image id="side_column_widget_product_thumbnail" type="thumbnail">
<width>75</width>
<height>90</height>
</image>
<image id="upsell_products_list" type="small_image">
<width>600</width>
<height>600</height>
</image>
<image id="wishlist_sidebar_block" type="thumbnail">
<width>75</width>
<height>90</height>
</image>
<image id="wishlist_small_image" type="small_image">
<width>113</width>
<height>113</height>
</image>
<image id="wishlist_thumbnail" type="small_image">
<width>240</width>
<height>300</height>
</image>
</images>
</media>
</view>
You can mention image sizes with their XML entity name in the view.xml file
product_page_main_image
product_page_main_image_default
product_page_more_views
step 2: Run the CLI command from the Magento root.
sudo php bin/magneto catalog:images:resize
Note: Depending on your requirement you can delete other media XML entity like bundled_product_customization_page, cart_cross_sell_products etc
