HDMI is a newer digital audio/video interface developed and promoted by the consumer electronics industry. DVI and HDMI have the same electrical specifications for their TMDS and VESA/DDC links. However, HDMI and DVI differ in several key ways:
HDMI lacks VGA compatibility. The necessary analog contacts are absent in HDMI connectors.
DVI is limited to the RGB color range (0-255). HDMI supports RGB, but also supports YCbCr 4:4:4 and YCbCr 4:2:2. These ranges are widely used outside of (beyond) computer graphics, color rendering.
HDMI supports the transport of packets, needed for digital audio, in addition to digital video. An HDMI source differentiates between a legacy DVI display and an HDMI-capable display by reading the display's EDID block.
To promote interoperability between DVI-D and HDMI devices, HDMI source components and displays support DVI-D signalling. For example, a 1080p HDMI display can be driven by a single-link DVI-D source - since HDMI and DVI-D both define an overlapping minimum set of supported resolutions and frame buffer formats. So, DVI-D devices output HDMI signals, many including audio, (examples: ATI 3000-series and NVIDIA GTX 200-series video cards), and some multimedia displays input that HDMI signal, including audio, by using a DVI to HDMI adapter. Exact capabilities vary by video card specifications.
In the reverse scenario, a DVI monitor that lacks optional support for HDCP might be unable to display protected content, even though it is otherwise compatible with the HDMI source. And, features specific to HDMI, such as: remote-control, audio transport, xvYCC, and deep-color, are not usable in devices that support only DVI signals. Effectively, HDCP compatibility between source and destination devices is completely subject to the manufacturer's specifications for each, respective HDMI capable device.
HDMI is backward compatible with single-link Digital Visual Interface digital video (DVI-D or DVI-I, but not DVI-A). No signal conversion is required when an adapter or asymmetric cable is used, so there is no loss of video quality.
From a user's perspective, an HDMI display can be driven by a single-link DVI-D source, since HDMI and DVI-D define an overlapping minimum set of supported resolutions and framebuffer formats to ensure a basic level of interoperability. In the reverse case a DVI-D monitor would have the same level of basic interoperability unless there are content protection issues with High-bandwidth Digital Content Protection (HDCP) or the HDMI color encoding is in component color space YCbCr which is not supported by DVI, instead of RGB. An HDMI source such as a Blu-ray player may demand HDCP-compliance of the display, and refuse to output HDCP-protected content to a non-compliant display. A further complication is that there is a small amount of display equipment, such as some high-end home theater projectors, designed with HDMI inputs but not HDCP-compliant.
Any DVI-to-HDMI adapter can function as an HDMI-to-DVI adapter (and vice-versa). Typically, the only limitation is the gender of the adapter's connectors and the gender of the cables and sockets it is used with.
Features specific to HDMI, such as remote-control and audio transport, are not available in devices that use legacy DVI-D signalling. However, many devices output HDMI over a DVI connector (e.g. ATI 3000-series and NVIDIA GTX 200-series video cards), and some multimedia displays may accept HDMI (including audio) over a DVI input. Exact capabilities beyond basic compatibility vary from product to product. Adapters are generally bi-directional.