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Old June 6th, 2007, 06:46 PM   #1
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Overscan/Underscan Dofus

That's me, I'm talking about. For years I have understood the definitions of "Underscan" and "Overscan" to mean just to opposite of what they actually do mean. I was recently having an IM chat with a buddy and he referred to an underscan field monitor and I "corrected" him. Then we both became confused.

Read this to see why I believe I was wrong all this time. But if you ask me, I still think the terms are used bass-ackward. Completely counter-intuitive.

Underscan & Overscan

The Underscan mode displays the full video frame, which reveals content on the edges that is recorded but not shown in the camera's flip-out LCD. In Overscan, the Field Monitor zooms in to the area that would be visible on most televisions. Set the Field Monitor to Underscan if your video will be viewed on a computer monitor or shown with a projector and also to look for light stands, microphones, and other unwanted objects on the edges of your shot. Set it to Overscan to see how the video will look on a television.

To switch between these two views, click the U. Scan button on the Field Monitor or press ALT+U.

A Little Background on "Underscan:" Back in the early days of television, the image on their little screens shrunk as TV sets got older because the electron gun that created the picture didn't move as well as it aged. As a result, a black border would appear around the edges of the picture. The electron gun could be recalibrated to fill the whole screen, but that was time consuming and costly. The solution that the TV industry settled upon was to "crank up" the electron guns of new picture tubes to paint the image beyond the borders of the picture tube. Then, as a TV set aged, more of the image would become visible rather than black bands appearing.

While this remedy worked, it created two problems. First, the broadcast industry coined the terms underscan and overscan and gave them counterintuitive meanings: "overscan" is the central part of the image that you can see on standard TV, whereas "underscan" is the full frame, which is visible only a production monitor. So the underscan actually shows more more of the picture than the overscan.

Second, the underscan solution has frustrated videographers and graphic designers to this day because they cannot be sure just how much of the frame will be visible on any given TV set. So they have to make sure that everything essential to scene is visible within the "Safe Area" while also taking care that nothing extraneous creeps into the overscan margin.
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Old June 6th, 2007, 07:44 PM   #2
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If it's any comfort, you aren't the first. I agree that it does seem counterintuitive. However, it might help if you think of 'overscan' as 'overshoot' where the beam goes too far and doesn't stop in time when it gets to the edge of the screen.

So Underscan shows the full frame, while Overscan goes too far and slides the end of the frame behind the edge of the screen.

Kind of weird, I know.

-gb-
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Old June 6th, 2007, 10:15 PM   #3
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Wait! It seems like you're saying the same thing I believed all those years. Now I'm really confused. I guess I'm not quite sure what you mean by "the beam".

Let's say you did screen grabs of an underscan and an overscan, of a shot of a picket fence. Which image would have the most pickets?
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Old June 6th, 2007, 11:46 PM   #4
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Quote:
Originally Posted by Jack Barker View Post
Wait! It seems like you're saying the same thing I believed all those years. Now I'm really confused. I guess I'm not quite sure what you mean by "the beam".

Let's say you did screen grabs of an underscan and an overscan, of a shot of a picket fence. Which image would have the most pickets?
The underscan image would show the entire image, while the overscan would show about 90%. The 'beam' I'm referring to is the electron beam that sweeps back and forth, top to bottom in a CRT, hitting and illuminating phosphor dots to create a picture.

As CRT's go away, the overscan issue will fade as well. Although the flip out LCD on my camera only shows the 90% (overscan), edges cropped off, however you want to say it, while the CRT viewfinder shows the full image being recorded by the sensor which makes it underscan.

Overscan...you don't see all of the picture.
Underscan....you see all of the picture.

-gb-
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