[Dr Force]

I see Overscan in my PJ menu.

Can someone explain what it means in laymans terms, how it works and how it would affect PQ with regards to films and gaming (XB360 component).

i am not sure that i have the best picture at 1080 for my xbox and I wonder if its anything to do with this (HC6000)

Thanks

Dave

[Jeff]

I'm sure it has to do with old CRT technology, as with most things legacy requirements tend to effect future decisions. Ideally you don't want to use overscan, the problem is many sources expect it, so if you don't use overscan you can end up with crap or blank bits round the edges. With HD sources overscan tends to be less needed.

[nwgarratt]

It has nothing to do with picture quality in terms of bad/good picture. Back in CRT TV days the picture would be clipped at the edges and lose around 3.5% of the picture at the sides.

PJ's often have overscan adjustment so no overscan can be used. I find on my setup that analogue siganals automatically get overscanned and digital signals do not. This may be different for someone else.

Because of overscan, 1.85:1 aspect ratio will not have borders top and bottom on a 16:9 display and fill the screen. With no overscan, there will be small borders. Only 1.78:1 aspect ratio will fill a 16:9 display when no overscan is used.

With overscan you are always losing part of the picture.

A couple of pics I did ages ago (2.35:1 AR).

Automatic Overscan (Component)

Automatic No overscan (HDMI)

[Dr Force]

Thanks Jeff & NW

I do sem to have some missing bits when it comes to the text in particular when feeding a component (set at 1080i) to the PJ via the 360.HD films and SD is lovely.

When I had a demo of the gaming on the PJ (it was a PS3 though) it all seemed very sharp and clear.

I think I'll turn it off as I only play games and watch films, will it not effect my films though??

[dovercat]

Overscan is due to broadcast standards being setup for CRTs which might not be completely flat and might not display with constant geometry (varies with brightness luminance). Analogue recording methods also might not record the whole image perfectly centered.

If you do not overscan you might display noise around the picture, usually at the top. White lines - dots above the image are time code information used in editing.

Overscan should not be needed with digital sources including DVDs & Blu-rays. The whole of the image resolution available can be used for picture information.

Overscan does reduce picture quality if source and display have the same native resolution. Scaling up the picture reduces - blurs some very fine details as they are spread across more than one pixel, this can be seen on calibration discs as bluring of lines when displaying maximum resolution 1pixel wide white 1pixel wide black lines. Because with overscan the image is magnified so some of the lines are no longer 1 pixel wide and some are. A calibration disc will also enable you to check the display-source is displaying the image properly centered, so no image is lost off the top, bottom or sides.

Overscan may improve picture quaity if source is standard definition PAL and display is 1080HD. The PAL image 575 vertical lines maybe overscanned to make it 540 then upscaled to 1080 vertical lines, so 1pixel high becomes 2 pixels high across the whole image rather than varying as with 575 upscaled to 1080. (Some PAL CRTs only display 540 lines see bottom of explanation.)

The amount of overscan should be adjustable on a digital display. It should have the option of no overscan for best-sharpest picture with sources which have the same native resolution as the display, enabling pixel to pixel mapping. If noise is present above, below, left or right of the image then blanking-shutters or what ever the display calls them should be used to remove - blackout the noise.

Overscan Amounts

Action safe = Area viewer expected to see, a good display should not lose more of the picture than this, poor displays may overscan upto the title safe area. Nothing important should happen outside the action safe area of the image as some viewers may not be able to see it. The title safe area is the area used for subtitles and text.

4:3 image displayed on 4:3 screen: vertical 3.5%action 5% title safe, horizontal 3.3% action 6.7% title safe

16:9 image displayed on 16:9 screen: vertical 3.5% action 5% title safe, horizontal 3.5% action 10% title safe

14:9 image displayed on 16:9 screen: vertical 3.5% action 5% title safe, 14:9 on 16:9 horizontal 10% action 15% title safe

4:3 image displayed on 16:9 screen: vertical 3.5% action 5% title safe, 4:3 on 16:9 horizontal 15% action 17.5% title safe

PAL DVD Maximum Image Resolution
4:3 720x576
16:9 720 anamorphic stretched to 1024 x576
2.35:1 720 anamorphic stretched to 1024 x (576-140 black bars) 436

PAL Analogue may be recorded in 720 which due to sideways shift may be displayed as 702

PAL CRT may display PAL 720x576 cropped to 658x540, then scaled to 720x540 4:3 or 960x540 16:9 (The 540 lines of resolution that enables 1080 High Definition to claim twice the vertical lines four times the resolution of standard definition PAL)