why does the computer screen looks shaky when viewed in a video?

Question

like for instance when in news they show some slide where the computer screen is at the back,the screen keeps shaking

Answer 1

That's because the refresh rate on the monitor is faster then the frames per second the video camera is capturing the event. The video camera is slowing down the monitor screen, showing the refresh rate, thus producing the shakes on the screen.

Answer 2

This is called "aliasing". The TV screen image is repainted 30 times per second for example, which is the same rate at which the video camera is capturing frames itself, but the timing is not perfectly synchronized between the camera and the TV screen being recorded. This causes the flicker you see in the video. It's the same phenomenon you see when a rotating spoked bicycle wheel or car rim hits a certain speed and appears to spin backwards.

Now the same thing happens with computer monitor screen, but there it appears to be a more drifting/random effect because the refresh rates of monitors tend to be faster than 60 times per second, 75 for eample... so you might actually spot the horizontal retrace lines, like a little horizontal bar of static slowly drifting down the screen and then reappearing at the top after it slides off the bottom.

Answer 3

you are viewing typically, 30 frames per second. The tv in the background is refreshing at 60 frames per second.

Your eye is seeing the blank interleave, but, the sustenance period of the optical receptors in your brain piece together all the fragments to create the optical illusion that there are pictures there constantly, while really, over half the time, all the screens, or selected portions thereof, are black!

Google "interleave" and "sychronization" and "TV picture flyback"

Sometimes, before digital the analog circuits would make a black band move at a slow pace up the screen of any tv in the background, unless a synchronization signal was coordinated between all the cameras and TVs... Yeah there is some simple math to figure out the timing...

Answer 4

From what I understand, a computer, or a tv screen works, not by showing one continual lit image, but by flashing (very very quickly, so you don't notice it) a series of images (this is why some epileptics have problems with tv).

When you have a tv recording a tv, or a computer, that flashing in not always in sync, so the image is often messed up.

If you have a camera phone, or even a digital camera, try looking through it at your computer, and you will see it goes all 'wrong'.

Answer 5

Ten years, this could be a hard one, and it does be counted on how lots you shoot. a expert who could shoot 5000 photos each and each month in some godforsaken place will positioned on out the mechanicals of a digicam particularly at as quickly as, in decrease than 3 years. If that's annoying use which you're undertaking your digicam to, then you somewhat ought to get a tank of a digicam Nikon D3/3S/3X and Canon 1DmkIV and 1DsMkIII may be the style of digicam you go with for. you would be wanting a climate sealed lens to flow with it. Even then that's not going to be indestructible. once you're somewhat keen to splash then a Leica M9 device is additionally an decision, the Leica is a greater spartan digicam meaning much less to flow incorrect. once you are going to apply it in severe circumstances, then you somewhat ought to look at organic mechanical cameras, and taking photos action picture, perhaps a Leica M3, which has no electronics to interrupt. once you are going to toddler your digicam, and in basic terms take it out whilst the sunlight is shining, and the climate is heat then i could think of the present Canon 550D (or the different get right of entry to point SLR) and equipment lens could in all likelihood do the interest. of direction it is going devoid of asserting that between the 550D and the 1D there are multiple cameras which could stand up to various quantity of abuse, so it somewhat relies upon on the form you go with for to apply the digicam.

Answer 6

The speed in which a video is shown on any screen is slower than the speed in which a camera would record it, making the "shaking" look when you're trying to record a t.v. show with a camera.
Kind of like playing a PAL (european) movie/game in a NTSC (USA/Canada) VCR/Video game system. you'll get the same thing because of different speeds.

Answer 7

The 'refresh rate' on TVs and computer monitors is different. Each new frame on TV sees a slightly different frame on the computer monitor, so it seems to shake or roll.

Answer 8

Just because it doesn't have that much capacity too load motion pictures normally this apperas in LCD monitors,you might be using LCD one sure it's good but it's only defect is while playing motion pictures..... smoothness can't be seen, In CRT monitors rarely this problem occurs.

Answer 9

The refresh rate that your eye doesn't see is at a different rate of refresh from your camera, which your eye can't see either