Popular IT channel Linus Tech Tip on 3D

[revgen]

Originally Posted by Just_Discovered_3D

When Linus says that the LCD is not fast enough to stop ghosting, is he referring to the LCD in the glasses, or to the LCD of the PlayStation 3D TV?

Frankly, 120-144 Hz glasses are too slow for active 3D (this goes for theatrical RealD as well). Linus is right that the 3D makers price gouged back in the day, as today's DLP glasses are more convenient and $15 a piece. DLP projection removes many of the downsides of active 3D that they mentioned, and turn them into assets...perhaps active 3D should have been for projectors or dark room viewing only?

This article explains why DLP projectors don't suffer from crosstalk.

Most consumer level DLP projectors use a single DMD imaging chip and a motor driven rotating “Color Wheel”. With this arrangement the color wheel sequentially displays as a minimum, the primary colors (red, blue and green) while the DMD chip displays only the elements of the image that corresponds to the wheel color currently in the light path. Thus the image on the screen is rapidly showing a sequence of single color images and the human eye/brain puts these together to form the desired full color image.

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High-end DLP projectors (typically costing over $15K) frequently use 3 DMD chips with one for each of the 3 primary colors (the 3 chip arrangement is similar to the configuration used with all LCoS and LCD projectors). Frequently these 3 chip DLP projectors project a brighter (i.e., higher lumens) image and do not suffer from the rainbow effect of the single chip/colorwheel models.

On the positive side such single DMD chip DLP projectors do not suffer from misconvergence of the primary colors (i.e., misconvergence is a slight misalignment of the red, blue and green primary colors that make up the projected image) as is frequently the case with projectors that use individual imaging chips for each of the 3 primary colors.

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The DLP Advantage for 3D

One of the most frequent complaints when viewing 3D, either in a commercial movie theater or in a home theater environment, is 3D Crosstalk (or 3D Ghosting). This occurs when one eye sees some elements from the image intended for the other eye. Some experiments indicate that if the brightest elements of the alternative image (the unwanted image intended for the other eye) are more than 0.1% as bright as the desired image then some viewers will be able to detect crosstalk on certain scenes. However, most viewers will find 3D displays that are capable of suppressing the alternative images to levels on the order of 0.5% to be reasonably good with 3D crosstalk only occasionally being noticed. With active 3D projection systems crosstalk will generally originate from any of the following 3 sources (assuming the source 3D device provides a crosstalk-free signal into the projector).

1. The display chip within the projector is not able to fully replace all elements of the previous image with the new (i.e., next) image fast enough, thus allowing some traces of the previous image to remain on the display when only the new image should be displayed.

2. The synchronization of the timing between the projector and the 3D active shutter glasses must be very precise otherwise a lens of the glasses may become transparent too early or opaque too late and as a result briefly allow the previous or the next image (i.e., intended for the other eye) to be seen. This timing is complicated as a result of the lenses being used in the active shutter glasses are made from liquid crystals that themselves take some time to fully transition between opaque and transparent states. This transition time typically will be between 0.5 millisecond and 2 millisecond depending on the specific 3D active shutter glasses being used.

3. If the lenses of the 3D active shutter glasses do not become adequately opaque to fully block all visible light that is intended to only be seen by the other eye, then there will be visible 3D crosstalk.

While projectors using LCoS or LCD technology may suffer from 3D crosstalk due to any of the three above sources, DLP projectors inherently do not suffer from item 1 above as the DMDs used with DLP projectors are able to fully transition from one image to the next without the possibility of the any remaining traces from the previous image. Thus if you do see 3D crosstalk with a DLP projector the cause originates from item 2 and/or 3 above (or is present in the source 3D signal).

https://www.projectorreviews.com/hom...on-technology/

The best way to avoid issue #2 on DLP projectors is to use RF glasses instead of DLP-Link.