What is Frame Compatible 3D?
With the increasing popularity of 3D TVs and 3D Content, many consumers have been left confused by the variety of different 3D formats and specifications that are currently out there. One of the terms floating around is the Frame Compatible 3D format. This article will explain everything you need to know about Frame Compatible 3D.
Both Frame Compatible 3D and Frame Packing 3D formats involve forming a single frame that contains “sub-frames” for the left and right eye. In both cases, the Sub-frames can be packaged together into a single frame via the Side-by-Side 3D format or the Top-and-Bottom 3D format. The key difference of a Frame Compatible signal is that each sub-frame for each eye is down sampled along one axis to lower the resolution of each sub-frame along one axis. As a result, the total dimension of a Frame Compatible Frame is the same as a regular 2D HD frame (since each sub-frame has half the resolution along either the horizontal or vertical dimension). This is the reason this format is called Frame Compatible.
Side-By-Side Frame Compatible 3D
In the case of the Side-by-Side, Frame Compatible 3D or what is also called Side-by-Side (Half) 3D, each frame has the same dimension as a regular 2D HD frame but each sub-frame is downsampled to reduce the horizontal resolution by half. As a result, in the case of 720p side-by-side 3D (ESPN uses 720p Side-by-Side 3D at 60fps for their 3D Channel), each sub-frame is downscaled from 1280×720 to 640×720 resolution (downscaled from 1920×1080 to 960×1080 in the case of 1080p content) and then the left and right eye sub-frames are combined to produce a single Frame Compatible Side-by-Side 3D frame.
Top-and-Bottom Frame Compatible 3D
Top-and-Bottom (or Over-Under) Frame Compatible 3D works in exactly the same way, except that the halving of resolution of each sub-frame is in the vertical dimension. So a 1080p video feed (1920×1080) formatted using Top-and-Bottom Frame Compatible 3D will consist of two vertically stacked sub-frames, each having a resolution of 1920×540 pixels.
When a 3D TV receives a Frame Compatible signal, it will take each Frame and split it to extract the sub-frames meant for each eye. Using upscaling algorithms, the 3D TV will then reconvert the sub-frame to a full frame at full HD resolution (although this doesn’t have full 1080p or 720p fidelity, since an upscaling algorithm is involved) and display these sub-frames in a frame sequential manner as shown in the image below.
The primary disadvantage of Frame Compatible 3D signals is that it results in a loss of “true HD” resolution images for each eye. Instead, you have to settle for a halving of the image resolution either along the vertical (Top-and-bottom, Frame Compatible 3D) or horizontal (Side-by-Side Frame Compatible 3D).
The main advantage of this format is that it is compatible within the HDMI 1.3 framework as the frames have the same dimension as regular 2D HD signals. Thus the required bandwidth for the video signal as well as the electronics on the hardware side remains the same. This is the fundamental reason why all cable providers have adopted Frame Compatible 3D formats such as Side-By-Side (Half) 3D, for their 3D Channels. It allows them to provide 3D to consumers without massive upgrades to their infrastructure and having to force consumers to buy a new 3D Capable cable box.
Ultimately, content providers will move towards the Full HD 3D format as consumer demand and infrastructure catches up, but in the mean time, Frame Compatible 3D formats provide a simple, if not ideal solution for providing 3D content to consumers.
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