In your Shift4Shop Online Store Manager, you can set the default sizing for product images that your store will use. This helps in making your image files conform to a specific parameter and give you some uniformity as to how your products are displayed. To set these parameters, go to Settings > General > Store Settings and click on the Products Display tab. Within the "Products" section of that page, you will have the following parameters available:
Thumbnail image size
The size confinements for your store's small thumbnail images when they are created by the store.
Thumbnail images usually appear in category pages, as related/upsell items, or on the home page.
(The default for Thumbnail is 150 pixels by 150 pixels.)
Product page image size
The size confinements for your store's main product images shown on the product listing page.
(Default is 300 pixels by 300 pixels.)
Large image size
The size confinements for your store's zoomed images and also the size that large images will be compressed to when assigning them to products.
(Default is 450 pixels by 450 pixels.)
The size confinements will resize and confine your images to be within your specified parameters. Therefore it will resize the largest side of your image so that the overall image falls within the set parameter ranges. In other words, if your main image parameter is set to use the default 300x300 resolution but your image is wider than it is tall - for example; 600px width x 400px height - the parameters will resize the image so that its width falls within the 300 pixel range. (i.e. 300x200).
Alternately, if the image is taller than it is wide (400x600), the parameters will resize it so that its height is confined to the 300 pixel range and make it 200x300.