3D: active vs. passive

Maybe this is a bit off-topic for this blog, but it holds my interest and I have done some testing myself lately with these different type of screens. First time I saw 3D in the cinema (Dolby 3D) I thought it worked very well, so I was pretty disappointed when the first active screens arrived at the home. The active shutter glasses have poor contrast, therefor also lots of crosstalk (ghosting) and they are inconvenient because of the batteries, not to mention the flickering.

So I had high hopes for the passive polarized system. Ofcourse the fans of the active system point out that passive has only half of the resolution, while the active system is full HD. But LG promised a new firmware that would fix this and I even found a site that proclaimed that our brain would combine the left and right half HD images to a single full HD image (sorry, could not find the link anymore), so the passive system would have no downsides at all.

Now back to reality when I got my LG 3D monitor. First the good things. Contrast is way better with the passive glasses than the active ones. This can also be easily seen when comparing the screen with and without the glasses. With the passive glasses the image only gets a bit darker, while with the active ones it is like night falls. Because of this also the colors are much better with the passive glasses and there is virtually no crosstalk.

Unfortunately there are also disadvantages, which were so bad for me that I returned the monitor. The biggest problem is that there is no such thing as magic de-interlacing by the brain as proclaimed by that site. At least my brain does not have this capability, nor some other people I showed it to. When you think of it, it is also ridiculous. The brain gets a left and right image consisting of alternating colored and black lines, so the most logical match is to overlay the black lines on top of each other. And this is also what happens, which is pretty clear from the fact that any text is illegible and the screen looks like when you look through blinds (luxaflex).

And this would not even be the worst part. The image is still in full HD mode, so the overlapping left and right lines do not match with each other! Now depending on your dominant eye, you will see the left or the right line, with depth info taken from the other line. So in reality half of the resolution is thrown away after all. And this is one of the worst ways of down converting an image. It will result in all kinds of artifacts, most notably jagged lines (stair-casing) and aliasing.


Passive 3D system indeed have only half the resolution of active systems. And by denying this fact the resulting image quality is less than optimal. The solution is to down-convert the image using a proper filter before putting it on the display, which would at least avoid the above mentioned artifacts. Unfortunately there is no solution for the blinds problem, except for doubling the distance to your screen.

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