Why did 3D TVs have to be specifically designed for the effect instead of the DVDs?


I remember magazines were printed with a specialized pattern (red and blue ink) that made them work with 3D glasses. What tech is used in the TVs that can’t just be used in the movies themselves?

In: Technology

Modern 3D TVs use a technology that displays alternating left and right images so that your left and right eye can see a slightly different perspective on the action. The glasses in this setup are a pair of lenses with embedded LCDs that are each able to fully block all light or display all light. The idea is that the right lens blocks all light when the left image is displayed, and the left lens blocks all light when the right image is displayed; and for this to happen so quickly, you brain perceives fluid motion. The TV in this setup needs to be aware that it’s displaying a 3D image because it’s gotta tell the glasses when to start alternating between blanking left and right eyes.

The TV also needs to accept different formats for 3D content, because, unfortunately, they couldn’t decide on a single format in the beginning. Three formats for 3D content include one where each frame of video (each image composing your video content) is composed of the left and right images side to side, top and bottom, or are just displayed every other frame. The first two formats are more for compatibility: A DVD had enough capacity for a regular 2D movie, so in order to display twice as much info, each frame just contained two half-quality images stacked or side by side and the TV figures out how to scale these stacked/side-by-side images up to full screen and display them one after the other in sync with the glasses. The every-other-frame format is possible on media with higher capacity, like a Bluray disc. There, the video content is just composed of alternating right-eye and left-eye images for each frame that the TV just displays after telling the glasses to start blanking.

Your two eyes view two slightly different angles of the same object. Your brain combines these two different perspectives into one image with depth perception. 3D images work by sending different images to your left and right eyes in order to give the illusion of depth. In order to give your left eye the left perspective, and your right eye the right perspective, the thing displaying the content must have some control over which eye sees which image.

With the old red and blue (or red and green) 3D, the two perspectives of the drawing were printed with two colours, and tinted glasses filtered specific colours to the correct eye where your brain would merge the drawing into one image with depth.

With Active 3D, which is what u/cttttt described, the TV would alternate displaying frames of the left and right perspectives, and would sync up with a set of powered LCD shutter glasses which would make sure each eye only saw the correct frames.

With Passive 3D, which later 3D TV models used and is also used in cinema, two different types of polarisation were used on the projected image, which the polarised glasses filtered for the correct eyes.

VR is more direct. The headset has separate screens for the left and right eye, and displays different perspectives for each eye.

The core concept of all of these is the same: specific images must be shown only to a specific eye. If the left eye views the right perspective or vice cersa, the depth illusion doesn’t work, it just looks like a blurry image. There’s no way to achieve this simply by changing the content (whether that be a downloaded video, a DVD, BluRay, projector etc). The output device must have some mechanism to display the different perspectives, and ensure the correct image is only seen by the correct eye. The content of course also needs to actually contain the two perspectives, and send them to the output device in a way the device understands.