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Explanation of "vertical banding" on TV screen?


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#1 of 4 OFFLINE   Chris T. Kennedy

Chris T. Kennedy

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Posted November 09 2007 - 05:19 PM

Hello,

Could somebody explain to me what is wrong (technically) with a device when it outputs analog video with vertical "bars" such as those indicated by arrow #1 in this example:

vertical bars

These bars are static - they don't move when the image is on the screen. Doesn't look like typical interference (wavy lines, etc...). Coincidentally, the lines indicated by arrow #2 do move, but they can't be seen with a naked eye as easily as they could with the camera that took this picture.

The vertical bars really show up a lot on blues, but can be seen in other colors as well. They are thin and are present across the entire image.

Is the chroma signal not timed correctly? Too strong? Not enough? Help me out here.

Thanks!
CK

#2 of 4 OFFLINE   zeetal003

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Posted November 09 2007 - 09:14 PM

thank s ..................

#3 of 4 OFFLINE   Allan Jayne

Allan Jayne

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Posted November 10 2007 - 05:11 AM

A problem called vertical banding has been observed on LCD displays, notably on LCD projectors. I don't know the cause but the problem is known since most projectors nowadays have a menu tweak that usually reduces the problem.

The problem may be present on any or all of the three panels that provide the red, green, and blue subimages. Sometimes it is one bright line then three dim lines, sometimes it is five bright lines and then three dim lines, usually repeating in twosome, foursome, eightsome etc. groupings.

It's there no matter what the source is.

If you say you notice vertical banding only on some sources, I currently don't have an explanation.
.

#4 of 4 OFFLINE   ChrisWiggles

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Posted November 11 2007 - 04:15 AM

Vertical banding is usually used to describe specifically the vertical banding issues on LCD displays. It's caused by a difficulty in controlling the vertically controlled arrays of LCD pixels and keeping them all at the same voltages, etc. IT will vary from display to display, and is usually most visible on green, which causes itself to be seen on smooth images especially skies and the like.

Note that these will be vertical kinds of faint stripes in the image across the screen. OTher banding/contouring problems can appear on any display and in other directions because of bit-depth problems. Many LCDs have other contouring/banding problems besides VB.

Here is a picture of an AE700 vertical banding:
http://alphageek.pe.kr/archives/112

Notice the fixed vertical kind of texture, a sort of unevenness in brightness in vertical strips.

Here an ae900:
http://www.cine4home....TAE900/VB3.jpg

The image you provided in the original post does not show vertical banding problems, that shows god knows what, but not LCD VB.