Size

Controls how the image needs to be resized. You can use both &w= and &h= parameters or only one of them: the other dimension is automatically updated.

Width &w=

Sets the width of the image, in pixels.

Height &h=

Sets the height of the image, in pixels.

Device pixel ratio &dpr=

The device pixel ratio is used to easily convert between CSS pixels and device pixels. This makes it possible to display images at the correct pixel density on a variety of devices such as Apple devices with Retina Displays and Android devices. You must specify either a width, a height, or both for this parameter to work. Use values between 1 and 8.

More info: Issue #115 - DPI support(opens new window).