Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Miscellaneous Techniques › Under/Overscanning question
- This topic has 1 reply, 1 voice, and was last updated 12 years, 9 months ago by Anonymous.
May 28, 2008 at 10:30 AM #37275AnonymousInactive
IfI burn my footage to dvd is the full image (including the extra border beyond the action-safe area)onthe dvdor is justthe cropped version (starting at the action-safe area and going inward)on the dvd? Or is this an NLE dependent optionwhich canbe set to either? (I use Avid Xpress Pro)
In your opinion do most modern tvs fully overscan? Or now, do most show the whole image – or at least close to it?
Thanks for any and all help.
May 28, 2008 at 3:38 PM #165061AnonymousInactive
Unless you reduce the image size (or zoom-in) you will ALWAYS have the full video image at ever point in the post process.
I have no idea what you mean when you ask if “moden tvs fully overscan?” I’ve never heard of a TV that can display anything less than the full signal that is being sent (ie the full video image.) TV’s are stupid devices. They expect a rather particular & precise signal. If you send them a proper signal, it will display according to the TV’s settings and the type of display. If you don’t send a proper signal, it will still attempt to display it as if it were a proper signal. Now on to “overscanning” of video images.
Each & every cathode ray tube has an electron gun at the back that is shooting electrons at the display screen. Although hard to believe, these electron streams are being aimed by the gun to hit particular points on the screen. Provided the guns have been “sighted in” correctly, the electrons will strike the display tube in the same relative location on every TV set displaying the same image. Now we have to add another variable, which is the aging process of cathode ray tubes. Modern TV’s have added electronics to correct for much of the aging process. But essentially what is going on is a drifting of the display center & edges. Aging tubes change the electric field they generate, which then changes the TV picture. The old “tube TV’s” would require periodic adjustments of the aiming of the electron gun to account for those changes.
Now if we all watched TV’s with underscanned images, that wouldn’t matter nearly as much. There would be black (unused) area around the video image and as the tubes aged, the image would gradually drift about the screen. The factory could aim the guns and the images would always be fully visible. However, manufacturers knew consumers wouldn’t like getting a new 15″ TV and only have a 14″ picture displayed on it. The picture had to cover the entire screen. In order to do that, the easiest way was to generate a picture just a bit larger than the TV screen. But if the TV image was composed so elements were along the edges, like movies shots are composed, differentt TV’s would be cutting off parts of those scene elements. This wouldn’t be too bad, except when you were adding titles or text to the image. There would be real problems with people being able to read stuff if parts of the letters aren’t even displayed.
So in order to insure that all the viewers would be able to see all the important elements of the TV picture, the “safe zone” was created. The safe area was defined as roughly 85% of the actual video image, or 15% of the edge portion was considered as a buffer for all the variations between TV’s in the homes of viewers. This buffer space or safe zone continues to be necessary for TV’s using a cathode ray tube for display. And that constitutes the vast majority of TV’s in the nation.
Now the new flat panel TV’s (LCD or plasma) display a digital image (decoded from the analog broadcast signal.) So if they want to, I see no reason a digital TV couldn’t display the entire video image (except for the data bars at the top & bottom of the video signal.) From what I’ve seen in stores, most flat panel TV’s display practically all of the image (while eliminating the data bars.) But TV’s with picture tubes will continue cropping the image to greater & lesser degrees. So the video safe area will continue well into the digital age. (As proof, check out a computer with cathode ray tube display. The monitor’s menu will have adjustments for image size (horz. & vert.) and position on screen (horz. & vert.) and a couple of other aiming adjustments.)
So to wrap up, every video display cuts off certain parts of the image you would see on a professional monitor set to underscan. But that entire image is required for proper display so it is always recorded. The display device is responsible for the apparent cropping of the image. So long as there are people viewing TV on cathode ray tubes, the safe zone will be required. (Although with modern TV’s that safe zone is a bit larger, only 10% of the picture is liable to be cut off.) And keep in mind, most of the homes that have a nice flat panel TV for viewing will also have other TV’s that are not flat panels, like the TV’s in bedrooms.
And by the way, the opposite of underscanning in not overscanning. It is a full scan or an underscan, unless you are some sort of electrical engineer. In which case you wouldn’t have had the question to begin with.
So good luck and keep framing in the safe zone.
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