Catalogue images, scrolls and theme sizes
Check product list, detail gallery and zoom separately. A theme adjustment can load the original instead of the intended image size.
Check the role of the image in the product as well as the size requested by the theme. A correct original can still be loaded too large or distorted by incorrect thumbnail selection or inappropriate gallery output.
Where to check the setting in Magento
Under Images and Videos, check the scrolls of the product and the output in the active theme. Compare the file loaded in the browser with the intended role and size. Variants and Store Views may use other media or captions.
Example of this specific finding
Illustrative control case: A product tile with 360 CSS pixels wide loads the 4,000 pixels wide original. What matters is the variant loaded in the network protocol, not the file name in the CMS.
follow-up audit in Magento
Test product listing, main image and zoom separately. After a variation or image change, also check the actually used cache/media URLs.
For multiple screen widths, check the selected image URL, file size and sharpness. On high-resolution displays, higher natural resolution may make sense.
Derogations and scope
A detailed view with Zoom may require larger files than a preview list. Balancing quality and transmission effort against actual use.
Reference: Magento Open Source or Adobe Commerce with classic storefront. Consider store views and extensions; other storefront architectures have their own configurations.
Classify the general error
Definition, system-independent causes and further correction examples: Check image weight, output size and subject together