HDMI Part 2 - "I Want My Version X.Z"

Over the past few years, I have maintained technical discussions and exchanged ideas with Silicon Image and the related organizations on a regular basis since DVI was implemented, but more specially during the life of HDMI, as versions evolved, and as the industry adopted the digital connectivity standard for uncompressed HD video (and multichannel audio). The following presentation from Silicon Image highlights the efforts of this company to meet the increasing demand for digital connectivity solutions from a world that is moving to an "everything digital" model: http://www.siliconimage.com/presentations/hdmi/index.html I anticipate that some of our readers would be interested in my notes and analysis from those exchanges. The material is complex and is long; as I mentioned in Part 1, I am covering the subject in 10 parts. The material is the product of many exchanges between Paul Wolf (Chief of Engineering HDMI Licensing, LLC), Joseph Lee (Director of Marketing for Simplay Labs, LLC), Leslie Chard (President, HDMI Licensing LLC), and me; it was intended to cover all the angles, and was summarized here to single statements to facilitate reading. In other words, is a teamwork brainstorming of a variety of technical issues, an exclusive of HDTV Magazine. Enjoy the ride.

8-bits per Component?

In the words of Silicon Image, "There is virtually no digital content that is mastered at more than 8 bits per component. Most of the relevant digital standards (DVD, ATSC, etc.) do not even have support for more than 8 bits/component. Therefore, up until now, HDMI's 24-bit/pixel limitation was not too much of a limitation." HDMI 1.0 can carry up to 8 bits/component in RGB 4:4:4 and YCbCr 4:4:4 but can actually carry up to 12-bits/component in YCbCr 4:2:2 so even in 1.0, there was some support for greater color depth, but at the expense of horizontal chroma bandwidth/resolution. Versions 1.0, 1.1, 1.2 are all identical with respect to video. Regarding the use of the term 8 bit per sub-pixel (24 for the 3 sub-pixels, on a pack of 30, where 6 are control, etc), Silicon Image prefers to use the term "components" rather than sub-pixels since that is a physical spot on a panel and in some cases (and I quote) "we're referring to YCbCr which has no direct physical representation." One can think of the 30-bits on the HDMI link when considering the TMDS encoding step but it's best just to think in terms of 8-bits per clock per channel, for a total of 24 bits. In other words, versions 1.0, 1.1, 1.2 all support 24-bit pixels. For RGB and YCbCr 4:4:4 this means 8-bits per component, but for YCbCr 4:2:2 this means up to 12-bits per component.

HDMI enables intelligence

CEC (Consumer Electronics Control) allows one touch control over the entire system, Leslie Chard, President of HDMI Licensing commented, and I quote: "This is very interesting and is coming now. Panasonic is currently running a huge advertising campaign in Japan touting this functionality under the name HDAVI (EZ-Sync). CEC works across devices from all manufacturers and eliminates the need for buying one of those complex programmable remotes." Additionally, HDMI facilitates automatic configuration where a sink device can tell the source it's preferred audio/video formats - eliminating the need for consumers to manually configure. More detail on this subject is mentioned in Part 5 - Audio in HDMI Versions.

This is Good Already, why Another Version?

So, why would we need 1.3 coming along? Why would we need more bandwidth, more bits per pixel, etc.? PS3, game machines in general, PCs, and other source devices that actually create the content on the fly (rather than playing it back from a pre-recorded stream) can all take advantage of the expanded color depth of HDMI 1.3. In addition, several of the newer digital media standards are looking to support deeper colors in the future. Version 1.3 adds the capability of 30-bit, 36-bit, and 48-bit pixels, which in 4:4:4 (the primarily target) means 10-bit, 12-bit, and 16-bit per component. These and many more features, make HDMI 1.3 with a foundation to support the future of CE, not seen on earlier versions. The next article explores that subject. Stay tuned for Part 3 "Version 1.3, Digital Connectivity at its Best"