Media Features for Display, Print, and Fax
Extracted elements (13)
Additional media type values beyond the seven defined for 'ua-media' were not included because their utility was deemed relative; the selected values cover the most practically useful distinctions between display and print media.
The 'dpi' feature only encompasses uniform resolution and does not account for devices where pixels are non-square (different resolution in different directions), a known limitation noted in the specification.
The 'dpi' feature uses Rational values rather than integers to accommodate devices with SI-based resolution specifications, allowing precise representation of non-integer dots-per-inch values such as 77 dots per centimeter.
The 'paper-size' feature is provided in addition to (not as a replacement for) absolute resolution and pixel sizes because some applications find paper size tokens more convenient, even though absolute dimensions are more precise and predictable.
This specification was originally motivated by the requirements from web browsers to send display characteristics to web servers, enabling servers to choose an appropriate representation variant (e.g., higher or lower resolution images) for the recipient device.
Interoperability with the Internet Print Protocol (IPP) may require registration of additional 'ua-media' feature values beyond those defined in this specification.
The 'color' feature tag indicates the gross level of color capability using a token with equality relationship. Defined values are: binary (black-and-white), grey (multi-level intensity), limited (small number of colors), mapped (palette-mapped color space), and full (continuous tone color).
The 'dpi' feature tag indicates the resolution that the recipient can display or print without loss, measured in pixels per inch. Values are Rational to accommodate SI-based devices (e.g., dpi=19558/100 represents 77 dots per centimeter).
The 'paper-size' feature tag describes the paper size for stationery using a token with equality relationship. Defined values include: letter (8.5x11.0 inches), a4 (210x297 mm), b4 (250x353 mm), a3 (297x420 mm), and legal (8.5x14 inches).
The 'pix-x' and 'pix-y' feature tags indicate the display size of the recipient for display or print, measured in pixels; pix-x is the horizontal dimension and pix-y is the vertical dimension. Values are Signed Integer.
The 'ua-media' feature tag indicates the recipient's device media type using a simple token with equality relationship. Defined values include: screen, screen-paged, stationery, transparency, envelope, envelope-plain, and continuous.
This document registers six feature tags with IANA per [REG]: pix-x, pix-y, dpi, ua-media, paper-size, and color. ASN.1 identifiers 1.3.6.1.8.1.1 through 1.3.6.1.8.1.6 are assigned to these tags respectively.
Inaccurate media feature information ascribed to a recipient might cause a sender to send content the recipient cannot actually process, thus causing a denial of service.