Currently Firefox requests images from our image cache as jpeg with quality=60, which can result in jpeg artifacts. Image parameters are set client-side such that it can request the right resolution, because only the client knows the container size that the image will be shown in.

Proposal:

1. The Proxy Server formats the image cache url and preserves png image types.
2. The client parses image_src and changes the image size to 2x the container size. It only changes the resolution, not the image type.
3. Ad-ops / design are responsible for saving the image as jpeg or png.

Result:

• Firefox continues to choose the image resolution based on the container size.
• The server can preserve the PNG image type.

We will more likely adjust the JPEG compression level than allow PNGs due to them often being misused (eg: photographic content encoded as a PNG24 resulting in unnecessary weight) which can be a significant perf hit. Current JPEG compression level was vetted by multiple designers.