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API endpoint -
Optimise - optimises images using lossy compression automatically.
dppx (optional) - Number of dots per pixel defines the ratio between device and CSS pixels. The query parameter is a hint that enables extra optimisations for high density screens. The format is a float number in the same format as window.devicePixelRatio.
dppx=2- sending a hint to the API that screen has DPI=2
You can see URL of the examples by "right-click -> Copy Image address"