DesignWare Technical Bulletin Article

Propelled by HDMI, the First 3D Devices Hit the Shelves

Even though the concept of 3D images and movies was originally discovered in the early 1900s however, it is only recently that the first 3D digital home multimedia products have been made available for commercial purposes. A large credit for this goes to HDMI 1.4 for supporting most of the 3D formats and providing the necessary bandwidth to transfer the 3D content between the source and the sink devices. The TV industry has already gone through two major waves of change. The first is from black and white to color and the second is from Standard Definition to High Definition (HD). Some analysts are already comparing High Definition to 3D as the 3rd big wave. Though various segments of the market have different opinions on the success of 3D in digital homes, one obvious trend is the high number of system-on-chip (SoC) design starts, which enable the 3D content for next-generation systems.

Going from HD to 3D comes with special challenges on many fronts - recording, storing, transmitting, displaying and viewing of video. Essentially, the camera or camcorder has to simulate the human eye with two lenses that are separated by approximately 2.5 inches (the same distance as the human eyes) to capture a stereoscopic image. Once the image from each lens is presented to each eye separately through polarizing glasses, it creates the perception of depth or 3D vision for the human brain (same concept as binocular vision).

So how does stereoscopic image/binocular vision relate to HDMI? The bottom line is that the HDMI cable between the source and the sink device has to carry 2x the bandwidth required for 2D images (separate image for each eye, assuming no compression) and has to support 3D frame formats to display the content for each eye separately. There are eight 3D formats (ways to combine the image for the left and the right eye in the HDMI frame) that HDMI 1.4 can support:

  1. Full side-by-side
  2. Half side-by-side
  3. Frame alternative
  4. Field alternative
  5. Line alternative
  6. Line + Depth
  7. Line + Depth + Gfx + Gfx Depth
  8. Top and Bottom.
Figure 1 below shows how a typical HDMI frame looks with Video Data Period, Data Island Period, Command Period, blanking intervals, etc.

Figure 1: Typical HDMI frame with Video Data Period, Data Island Period, Command Period, blanking intervals, etc.

Some examples of the defined 3D modes are shown below:

Frame alternate (Figure 2): Each frame is presented alternatively to each eye. The bandwidth of this 3D mode is twice that of the comparable 2D mode. There is flicker because each eye gets to see the next frame after a longer period, hence not suitable for sports, fast moving games, etc.

Figure 2: Frame alternate signaling

Line alternative (Figure 3): The signals for the left and right eye are carried on alternative lines. The bandwidth is doubled compared to the 2D mode because each frame is twice as long (from top to bottom).

Figure 3: Line alternative signaling

Full side-by-side (Figure 4): The images for the left eye and the right eye are combined in a single horizontal line. Again the bandwidth is doubled because each frame is twice as wide (from left to right) as the comparable 2D mode.

Figure 4: Full side-by-side signaling

Half side-by-side (Figure 5): The images for the left eye and the right eye are combined in a single horizontal line, but this mode uses 50% compression to keep the width of the frame the same as the 2D frame. The 3D bandwidth remains the same as the 2D bandwidth because of horizontal compression.

Figure 5: Half side-by-side signaling

The overall content bandwidth of these signaling types = Resolution * Frame Rate * Color Depth * 8B/10B Encoding. For example, for frame alternative, line alternative or full side-by-side modes, a 1080p, 60 Hz, 8-bit, 3D signal would require 8.91 Gbps bandwidth. However, it would only require 4.455 Gbps of bandwidth in the half side-by-side mode of operation.

As 3D technology is beginning to get adopted by the main stream, we may see some volatility around the specification as various consumer electronics manufacturers, content providers and system operators work on coming up with the most optimized solution to deliver 3D content into the homes. Synopsys' DesignWare® HDMI 1.4 source (TX) and sink (RX) controllers support all of the 8 defined 3D modes. The DesignWare HDMI 1.4 TX and RX PHYs deliver a maximum bandwidth of 10.2 Gbps (3.4 Gbps on each lane) to support the maximum required bandwidth to transfer 3D content to cover all video timing formats as defined in the CEA-861-E specification.