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"Colour bars" flashing in vision when watching projected TV show?


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Old 23-04-2013, 10:48
Inkblot
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Went to a screening of a TV show where the picture was projected on to a screen, about the size of a medium cinema screen (so not huge but not small). Picture was very sharp but if I blinked or looked quickly from left to right (or vice versa) I saw flashes of colour, a bit like colour bars, momentarily across the screen. What causes this, and why doesn't it happen with digital TV or cinemas?
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Old 23-04-2013, 12:33
fastest finger
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Possibly "rainbow effect" caused by the use of a spinning colour wheel in some DLP projectors. Not everybody is affected by it though.

Doesn't happen with other types of projectors, such as LCD or a triple chip DLP.

You can google "rainbow effect" or "RBE" for a full explanation.
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Old 23-04-2013, 13:18
Inkblot
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Possibly "rainbow effect" caused by the use of a spinning colour wheel in some DLP projectors. Not everybody is affected by it though.

Doesn't happen with other types of projectors, such as LCD or a triple chip DLP.

You can google "rainbow effect" or "RBE" for a full explanation.
Thanks. It was definitely when I shifted my gaze rapidly from one side of the screen to the other, so "rainbow effect" sounds like the correct explanation. Strange that not everyone sees this - wonder why?
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Old 23-04-2013, 14:11
Chris Frost
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Not everyone affected because they:

1) are less sensitive to (or just don't notice) colour as much as others

2) see it but ignore the effect

3) focus on the central part of the image so they don't scan their eyes across the picture to provoke RBE

4) are more tolerant of lower frequency refresh rate. They don't see florescent lights flickering and never noticed 50Hz CRT picture refresh flickering
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Old 23-04-2013, 14:56
Nigel Goodwin
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never noticed 50Hz CRT picture refresh flickering
To be fair, hardly anyone noticed 50Hz sets 'flickering' - it was really quite rare.
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Old 23-04-2013, 16:34
Chris Frost
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CRT flicker: Well, not until the mags pointed out how they could provoke the effect using peripheral vision.

It's much the same now with DLP RBE. Faster spin speeds mean it's no longer a major issue for a lot of people when viewing normally using a home cinema single chipper. However, it can be provoked.
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Old 25-04-2013, 12:05
Inkblot
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CRT flicker: Well, not until the mags pointed out how they could provoke the effect using peripheral vision.

It's much the same now with DLP RBE. Faster spin speeds mean it's no longer a major issue for a lot of people when viewing normally using a home cinema single chipper. However, it can be provoked.
Where I found it distracting was a theatre with the screen on the stage and the projector at the back. The picture quality was good but maybe the viewing angle made the RBE more noticeable. Obviously in a home cinema you would not choose to sit at an angle to the action but in a theatre that's not considered unusual..
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