Everytime I watch a news broadcast with computers, the monitor appears to be flickering. Why does this happen? Tv operates at 30 Hz, and monitors at 60 Hz. Since tv is at a lower frequency, shouldn't we not be able to see the monitor refreshing?
Why do monitors flicker when seen on tv?
- Thread starter MastaTam
- Start date
- Nov 27, 1999
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UnatcoAgent
Diamond Member
- Oct 25, 1999
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It's a visual artifact caused by interference between the scan lines of the CRT in the picture and the frame rate of the camera. It's the same effect you get when you look at a window screen through another window screen. A difference of 30Hz isn't that much, and you'll still see the interference. Read about moire patterns for more info.
you will notice in movies or certain programs like CNN news when computers are shown they don't flicker. they are synched with the tv cameras.
When a TV crew takes the time to do it "right," they use video cards that have an input called "genlock". They can then sync up the refresh of all of the monitors by chaining the genlock inputs of all of the video cards to the output of the (high-end) camera. Genlock is most commonly found on high-end SGI and Sun workstations; not terribly common for PCs (so if they use a PC, odds are that it's in conjunction with an LCD monitor - no v-refresh, no flicker). You can get some PC video cards with genlock on them, but they tend to be the super-high-end overpriced cards like Intergraph Wildcat3D ($$$$).
Zeeky Boogy Doog
Platinum Member
- Mar 31, 2004
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Since we seem to have this one figured out can someone explain this? When my video camera is hooked to the tv and I use the tv remote I can see a blinking light on the remote. Why?
neutralizer
Lifer
- Oct 4, 2001
- 11,552
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Because (most) digital cameras and camcorders, unlike people, can see the infrared spectrum just fine.
I just used my Camcorder (new Sony HC20) to look at my computer screen and then a TV. The computer screen flickers a heck of a lot more than the TV. I'm guessing this is due to the refresh rate.
Originally posted by: Eli
Because (most) digital cameras and camcorders, unlike people, can see the infrared spectrum just fine.
Why then can I see it on the tv?
Originally posted by: fredtam
Originally posted by: Eli
Because (most) digital cameras and camcorders, unlike people, can see the infrared spectrum just fine.
Why then can I see it on the tv?
I'd like to know that too.. Why do cameras interpret infrared as bluish-white light?
Originally posted by: WinkOsmosis
Originally posted by: fredtam
Originally posted by: Eli
Because (most) digital cameras and camcorders, unlike people, can see the infrared spectrum just fine.
Why then can I see it on the tv?
I'd like to know that too.. Why do cameras interpret infrared as bluish-white light?
I have googled it but the keywords needed provide me with useless results.
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