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Metadata formats for display devices

Extended Display Identification Data (EDID) and Enhanced EDID (E EDID) are metadata formats for display devices to describe their capabilities to a video source (e. g., graphics card or set top box). The data format is defined by a standard published by the Video Electronics Standards Association (VESA). The EDID data structure includes manufacturer name and serial number, product type, phosphor or filter type (as chromaticity data), timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data. DisplayID is a VESA standard targeted to replace EDID and E EDID extensions with a uniform format suited for both PC monitor and consumer electronics devices.

EDID structure (base block) versions range from v1.0 to v1.4; all these define upwards compatible 128 byte structures. Version 2.0 defined a new 256 byte structure but it has been deprecated and replaced by E EDID which supports multiple extension blocks. HDMI versions 1.0–1.3c use E EDID v1.3. Before Display Data Channel (DDC) and EDID were defined, there was no standard way for a graphics card to know what kind of display device it was connected to. Some VGA connectors in personal computers provided a basic form of identification by connecting one, two or three pins to ground, but this coding was not standardized. This problem is solved by EDID and DDC, as it enables the display to send information to the graphics card it is connected to. The transmission of EDID information usually uses the Display Data Channel protocol, specifically DDC2B, which is based on I²C bus (DDC1 used a different serial format which never gained popularity). The data is transmitted via the cable connecting the display and the graphics card; VGA, DVI, DisplayPort and HDMI are supported. The EDID is often stored in the monitor in the firmware chip called serial EEPROM (electrically erasable programmable read only memory) and is accessible via the I²C bus at address The EDID PROM can often be read by the host PC even if the display itself is turned off. Many software packages can read and display the EDID information, such as read edid for Linux and DOS, PowerStrip for Microsoft Windows and the X. Org Server for Linux and BSD unix. Mac OS X natively reads EDID information and programs such as SwitchResX or DisplayConfigX can display the information as well as use it to define custom resolutions. E EDID was introduced at the same time as E DDC, which supports multiple extensions blocks and deprecated EDID version 2.0 structure (it can be incorporated in E EDID as an optional extension block). Data fields for preferred timing, range limits, and monitor name are required in E EDID. E EDID also adds support for the Dual GTF curve concept and partially changed the encoding of aspect ratio within the standard timings. With the use of extensions, E EDID structure can be extended up to 32 KiB, because the E DDC added the capability to address multiple (up to 128) 256 byte segments.

August 1994, DDC standard version 1 – introduce EDID v1.0. April 1996, EDID standard version 2 – introduce EDID v1.1. November 1997, EDID standard version 3 – introduce EDID v1.2 and EDID v2.0. September 1999, E EDID Standard Release A – introduce EDID v1.3 and E EDID v1.0, which supports multiple extensions blocks. February 2000, E EDID Standard Release A introduce E EDID v1.3 (used in HDMI), based on EDID v1.3. EDID v2.0 deprecated. September 2006, E EDID Standard Release A – introduce E EDID v1.4, based on EDID v1.4.

Some graphics card drivers have historically coped poorly with the EDID, using only its standard timing descriptors rather than its Detailed Timing Descriptors (DTDs). Even in cases where the DTDs were read, the drivers are/were still often limited by the standard timing descriptor limitation that the horizontal/vertical resolutions must be evenly divisible by 8. This means that many graphics cards cannot express the native resolutions of the most common wide screen flat panel displays and liquid crystal display televisions. The number of vertical pixels is calculated from the horizontal resolution and the selected aspect ratio. To be fully expressible, the size of wide screen display must thus be a multiple of 16×9 pixels. For 1366×768 pixel Wide XGA panels the nearest resolution expressible in the EDID standard timing descriptor syntax is 1360×765 pixels, typically leading to 3 pixel thin black bars. Specifying 1368 pixels as the screen width would yield an unnatural screen height of 769.5 pixels. Many Wide XGA panels do not advertise their native resolution in the standard timing descriptors, instead offering only a resolution of 1280×768. Some panels advertise a resolution only slightly smaller than the native, such as 1360×765. For these panels to be able to show a pixel perfect image, the EDID data must be ignored by the display driver or the driver must correctly interpret the DTD and be able to resolve resolutions whose size is not divisible by 8. Special programs are available to override the standard timing descriptors from EDID data. Even this is not always possible, as some vendors' graphics drivers (notably those of Intel) require specific registry hacks to implement custom resolutions, which can make it very difficult to use the screen's native resolution.

Version 1 of the extension block (as defined in CEA−861) allowed the specification of video timings only through the use of 18 byte Detailed Timing Descriptors (DTD) (as detailed in EDID 1.3 data format above). DTD timings are listed in order of preference in the CEA EDID Timing Extension. Version 2 (as defined in 861 A) added the capability to designate a number of DTDs as "native" (i. e., matching the resolution of the display) and also included some "basic discovery" functionality for whether the display device contains support for "basic audio", YCBCR pixel formats, and underscan. Version 3 (from the 861 B spec onward) allows two different ways to specify digital video timing formats: As in Version 1 & 2 by the use of 18 byte DTDs, or by the use of the Short Video Descriptor (SVD) (see below). HDMI 1.0–1.3c uses this version. Version 3 also defines a format for a collection of data blocks, which in turn can contain a number of individual descriptors. This Data Block Collection (DBC) initially had four types of Data Blocks (DBs): Video Data Blocks containing the aforementioned Short Video Descriptor (SVD), Audio Data Blocks containing Short Audio Descriptors (SAD), Speaker Allocation Data Blocks containing information about the speaker configuration of the display device, and Vendor Specific Data Blocks which can contain information specific to a given vendor's use. Subsequent versions of CTA 861 defined additional data blocks.