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drakaal | 11 years ago
The reflection off of the screen tends to bounce back almost as straight as it hit, where as a standard beam of light radiates more on the reflection.
My home theater which is about the same as a Movie theater with regard to the seat placement that is fine. You can't get to a spot in the room where you'd be at a 45 degree angle. But in many people's homes, or for outdoor projection in commercial settings it can be an issue.
Laser is also nice because you don't have to deal with focus. The Focus is fixed.
Where you do have issues with Lasers is color. Lasers are harder to get to match the Gamut, and harder still to manipulate to represent all the colors in 10 bit color, (10 bits x 4)
Lasers don't tend to burn out which is nice.
Laser projectors do have to be optimized for the size of the screen more than projection. With traditional projection the size of the pixel scales up. With Lasers the dot doesn't really get larger. This is fine if the projected dot is the right size, or some ratio of the right size.
Say a laser projects a dot, a pixel sort of, that is 1mm in size at a distance of 15 feet. at 1080p you would have no space between the dots if the projection was roughly 2 meters across.
Now you want to project something to the size of 4 meters across. With traditional projection you change the focal length or move the projector back and the dots get bigger. With a laser you have to put 4 dots (2x2) to do this.
If you want a dot that is only 1.4 times the size you have to use 4 dots and over lap them.
The better Laser Projectors due this. They use up to 9 dots (3x3) and to where each Dot may only be 4 bits, using 9 dots you can fake more colors (3 red, 3 green 3 blue). Cheaper projectors use a technique similar to sub pixels and may use a Line rather than a dot (more like a Dash) for Red, and will have 7 dots 1 Red that is 3x the size, 3 Green, 3 blue.
In any case you have to have enough control over the laser to do the adjustments or you end up with gaps in the dots which are noticeable far more than the space between pixels that show up in DLP and LCD projectors.
birschtl|11 years ago
>>There are some downsides though since you don't get the same viewing angle that you do with standard projection. The reflection off of the screen tends to bounce back almost as straight as it hit...
This isn't true at all. While Lasers do emit coherent light it doesn't cause laser to be reflected back straight reasonably more than standard light. The only issues with lasers is speckle which is caused by destructive and constructive interference of coherent light on rough surfaces. And as any projection surface is somewhat rough in respect to small wavelength, manufacturers have to take care of this issue by integrating laser over time inside the light engine. They do of course have trouble with green laser speckle due to the eyes higher sensitivity to green light but nevertheless they can reduce speckle by over 95 percent.
>>Laser is also nice because you don't have to deal with focus. The Focus is fixed.
This is also only true for MEMS based laser projectors from the 90s. Today's laser projectors are based on "standard" projection technology and therefore have changing focus over distance.
>>Where you do have issues with Lasers is color. Lasers are harder to get to match the Gamut, and harder still to manipulate to represent all the colors in 10 bit color, (10 bits x 4) Lasers don't tend to burn out which is nice.
Image reproduction is still based on RGB. As long as you choose primaries that lie well outside the standard color spaces (DCI P3, BTU 709) you can always map colors to fit any colorspace inside this gamut. Colordepth is absolutely unaffected of the Laser itself. Only color derivation technology reduces bit depth. For example time sequential light engines like OSRAMs "Phaser" (phosphor laser) do have the same issues like one chip DLPs. You can not fit enough inter color segmentation inside one frame to get enough bit depth. 3 Chip DLPs with one laser engine per color have 10bit and even more color depth.
>>Laser projectors do have to be optimized for the size of the screen more than projection. With traditional projection the size of the pixel scales up. With Lasers the dot doesn't really get larger. This is fine if the projected dot is the right size, or some ratio of the right size...
You do not shoot the laser "point" directly at the screen as with MEMS based laser projectors. Today's laser projectors replace lamps by laser light engines. You still use DLPs or LCos to reproduce the image.