Content-DPR header

Deprecated

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Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Non-standard: This feature is not standardized. We do not recommend using non-standard features in production, as they have limited browser support, and may change or be removed. However, they can be a suitable alternative in specific cases where no standard option exists.

The HTTP Content-DPR response header is used to confirm the image device to pixel ratio (DPR) in requests where the screen DPR client hint was used to select an image resource.

Note: The Content-DPR header was removed from the client hints specification in draft-ietf-httpbis-client-hints-07. The Responsive Image Client Hints specification proposes to replace this header by specifying intrinsic resolution/dimensions in EXIF metadata.

If the DPR client hint is used to select an image, the server must specify Content-DPR in the response. If the value in Content-DPR is different from the DPR value in the request (i.e., image DPR is not the same as screen DPR), the client must use the Content-DPR for determining intrinsic image size and scaling the image.

If the Content-DPR header appears more than once in a message, the last occurrence is used.

Header type	Response header, Client hint
Forbidden request header	No
CORS-safelisted response header	No

Syntax

http

Content-DPR: <number>

Directives

<number>: The image device pixel ratio, calculated according to the following formula: Content-DPR = Selected image resource size / (Width / DPR)