Controls the output density of your image, so you can serve images at the correct density for every user's device from a single master image.
ImgIX documentation for PixelDensity
The PixelDensity type
Device pixel ratio (DPR) is an easy way to convert between device-independent pixels and device pixels (also called "CSS pixels"), so that high-DPR images are only delivered to devices that can support them. This makes images faster and saves bandwidth for users with lower-DPR devices, while delivering the expected crispness of high-DPR imagery to those devices.
dpr : Basics.Int -> PixelDensity
The density of the output image.
toQueryParameters : List PixelDensity -> List Url.Builder.QueryParameter
Takes a list of pixel density operations and turns it in to a list of query parameters that ImgIX understands