Thursday, July 21, 2011

The Next Generation 3D Digital Video Test

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Testing 3D video requires a thorough understanding of the HDMI specification packaging techniques for 3D content. Both the source (Blu-ray Disc player or set top box) and the sink (HDTV) must be 3D capable and support a common 3D packaging technique. Engineers must test that a device will package and transmit or receive and unpackage content correctly.

The common 3D content packaging techniques are frame packaging, field alternative, line alternative, side by side, and L+Depth or L+Depth+Graphics.
The most important aspect to test is the timing of the horizontal blanking interval and vertical blanking interval. If the timing of these two signals meets the HDMI specification, the 3D content will be transmitted correctly, however testing the quality of that content requires a second set of tests.

Testing the timing parameters of 3D video is challenging because more than two times as much data must be transmitted for a given frame rate. This means that a 1080p/24 Hz video signal, which traditionally required a 59.4 MHz clock rate for 2D video (24 frames/sec*2,200 pixels/line*1,125 lines/frame), would require a 148.5 MHz clock rate for 3D content using the frame packaging technique.

Testing the quality of 3D content requires the active picture region of the left and right images, including the color levels to see if they meet the CEA-861-D colorimetry or IEC 61966-2-x extended color standard. If the color levels meet the specifications for 8, 10, or 12 bit color levels, then the video source packaged and transmitted the 3D content correctly. A response time test will show whether errors occur in fast changing environments, such as an action scene, or whether any stuck bits are causing poor color translation in scenes with rapidly changing or smooth color levels.

The same timing, level, and linearity measurements made on 2D video signals can evaluate the structure and content quality of 3D content. As 3D video test matures, engineers will see the introduction of new video measurements that characterize the relationship between the left and right images of a frame or sequential frames in a video sequence.

Because 3D video is only one of several new features in HDMI 1.4, the new specification will likely cause manufacturers around the world to reconsider their test strategies to prepare for next generation multimedia device test.

To view a webcast series on testing multimedia devices, visit National Instrument and input code nsi0206.

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