WICG/responsive-image-client-hints

Question: Content-DPR - this is gone?

hamishwillee opened this issue · 3 comments

hamishwillee commented

Content-DPR appears to be gone from the old spec and not present in the new one. It's gone for good?

eeeps commented

The removal was intentional; Content-DPR was shelved in favor of specifying intrinsic resolution/dimensions in EXIF metadata.

WebKit objected to Content-DPR, on the grounds that "image resolution is not a transport level feature."

WebKit were, however, amenable to the idea of reading/applying resolution metadata contained in EXIF, as long as it could be done in a web-compatible way. So, we figured out how to do that, in order to meet this and other use cases for giving servers (and image authoring tools!) control over intrinsic dimensions/density. EXIF-based intrinsic sizing is now shipping in Chrome and Safari, and should ship in Firefox 90.

Specifying this metadata in the response body (in different ways, for different image formats) makes things significantly more complex for servers who want to modify resolution metadata as part of their delivery flow, and reduces caching opportunities. OTOH, the embedded, portable, permanence of EXIF vs. Content-DPR is better for the EXIF-Resolution use cases that involve a static intrinsic resolution (like low-quality image placeholders, or sharing high-dpi screenshots) rather than a dynamic one (like Client Hints).

Ultimately, though, Content-DPR was shelved because it lacked consensus.

hamishwillee commented

Thanks very much! Makes sense.

  1. Re "EXIF-based intrinsic sizing is now shipping in Chrome and Safari, and should ship in Firefox 90.". Do you happen to know what issue? I ask because I'm part of the team documenting FF90 and this is not on the roadmap and I can't find the issue on bugzilla search.