Our vision, as well as 3D technology rely on perception. The basic principle of 3D is that each eye captures a different image from its perspective and the brain puts the pictures together to create the third dimension. There are active and passive 3D TVs and while the passive option is very popular because the glasses are more affordable, active 3D TVs have a superior resolution. Before comparing passive and active 3D TVs, let’s take a look at the way 3D works, starting with the way we see things in real life.
The way we see things
In real life, we can see an object in three dimensions because each eye captures it from a different perspective. When we see something, both eyes focus on the object and create two individual visual images, which are then combined into a single, defined three dimensional perception. The left eye captures more accurately the left side of an object, while the right eye sees more of the right side. The brain puts these two images together, aligns them and creates the 3D model based on them.
Also known as Active Shutter, Active 3D works by alternating images displayed on the screen with great speed. This technology requires battery powered glasses that control which of the two pictures on the screen is seen. It does it by moving back and forth between opaque and transparent. The reason why this kind of 3D technology is known as active is that the battery-powered glasses have active control of the image that is captured by each eye.
Since the glasses have to be in synch with the TV screen, they require higher technology and can cost up to $100 USD, making Active 3D technology more expensive than passive 3D. Another thing that may put off some people from active 3D TVs is that the constant alternating between images can cause dizziness and headaches. Many TV sets have a refresh rate of 120Hz, but the latest LED TVs feature television panels with a refresh rate of 240Hz. At this rate, the TV flashes so fast that it would go practically unnoticed by the brain. Some of the best 3D TVs with active technology are the Samsung H6400 (available from $820) and the Samsung H7150, which starts at around $1,400.
Passive 3D TVs work in a similar way as the 3D technology used in movie theatres and the same glasses can be used in both cases. Passive 3D TVs display two images at the same time, but while one appears with horizontal light polarization, the other one has vertical light polarization. The glasses don’t require batteries to work and they are considerably cheaper than the ones used for active shutter technology. They have different filters on each side, designed to cut horizontal light for one eye and vertical for the other.
The difference between the 3D method used in movie theatres and the one implemented in passive 3D TVs is that while in cinemas, two projectors with different filter are used, in TV screens pixels are divided by half to display each image. Half of them are used for the right picture and the other half for the left one. The screen changes between the lines of the image and each line has a set polarization that matches the glasses. The main disadvantage of passive 3D is that it offers reduced resolution, but it is still the preferred option for many users and here are great quality TVs in this category such as Sony’s W950B, which can be yours for less than $1,200.
Frequent Issues with 3D TVs
Some of the problems that you may experience with 3D TVs include flickering (active 3D), reduced brightness and ghosting. We will go through the most common issues associated with 3D TVs.
As we previously mentioned, the constant alternation or flickering of images is one of the downsides of active 3D systems as it can lead to dizziness. However, the flashing on the screen is not as noticeable in advanced TVs that have refresh rate of 240Hz, instead of the 120Hz used by less sophisticated models.
Once you put your glasses on, the brightness of the screen is affected and in general a reduction of 50% can be expected. This happens with both passive and active 3D TVs. However, in most cases, manufacturers address the issue by making sure that the TV sets automatically increase the brightness when 3D content is displayed.
Ghosting or crosstalk is when two images appear superposed, making certain sections of the picture blurry. If you take off your 3D glasses while you are watching a movie in the cinema, the whole picture would appear with crosstalk, but in some TVs, the issue appears (although in a lower scale) even while you have your glasses on. Active 3D TVs (particularly the cheaper models) are more affected by crosstalk than passive 3D TVs and while the issue is only noticed in some parts of the picture, it still impacts your viewing experience.
Crosstalk may appear when the movie itself was not originally filmed in 3D and was only released in this format after remasterization. Another cause could be that the glasses are not perfectly synchronized with the TV screen so the images that each eye is supposed to see, are not correctly displayed. Ghosting or crosstalk may still be a problem for older active 3D TVs, but the latest active 3D models don’t seem to be affected by it.
Passive 3D TVs dominate the market thanks to the fact that the glasses are not as expensive as those required for active 3D TVs. Furthermore, they are not impacted by flickering issues and have less crosstalk. Active 3D TVs offer a better vertical resolution, but overall, passive 3D TVs are more convenient.