Re: Anti flicker filter
- From: "Roger Hamlett" <rogerspamignored@xxxxxxxxxxxxxxxxxxx>
- Date: Wed, 05 Apr 2006 10:36:44 GMT
"Matthias Melcher" <mm@xxxxxxxxxxxxx> wrote in message
news:e10025$kef$01$1@xxxxxxxxxxxxxxxxxxxx
npavankumar@xxxxxxxxx wrote:The key difference, is 'interlace'.
Hello Experts
I am lookng forward for implementation of a Anti-flicker filter for my
NTSC Display.
There is absolutely no flicker when the same image is displayed on a
VGA monitor .
can any body tell me what is the simplest and best algorithm for
removing flicker on NTSC TV
A TV image, updates _half_ it's lines every 1/60th of a second (actually
59.97Hz). So if you look at the even lines down the tube, these are being
updated only every 1/30th second. If you have a horizontal line on the
tube, that sits on two of the horizontal scan lines, then the top half
will be drawn, and 1/60th of a second latter, the bottom half will be
drawn. 1/60th second latter, the top half is drawn again. This leads to
such lines 'flickering' up and down.
Now this was done, simply to save bandwidth. Sending the full frame every
1/60th second, required an unacceptable amount of broadcast bandwidth.
Your VGA image, may well only still update at 60Hz, but updates the whole
frame. This requires a monitor, and link with a much higher bandwidth (a
good VGA monitor, capable of displaying 1600*1200*75Hz, will require at
least 144MHz bandwidth - this compares with a TV broadcast bandwidth of
just 6MHz for the channel - only just under 3.5MHz ued for the actual
picture data...). Even a standard 'VGA' image at 640*480*60, uses over
18MHz.
Now there are a number of ways of improving what it seen, depending on how
far you want to go. The standard method used on modern '120Hz' sets
(really a misnomer...), is to store both half frames, and refresh the
whole image at 60Hz. These sets then need a display with twice the
bandwidth of a normal TV tube. There are some real '120Hz' sets (a few of
the latest HDTV sets, put the whole frame out twice for each half frame
interval). You cannot do this into a standard TV, since the display itself
is not capable of outputting the higher frequencies required.
The alternative (unfortunately), is to degrade the image, so that the
shimmer is less noticeable. Deliberately applying a blur between adjacent
lines on the display, makes the shimmer much less noticeable, without
degrading the image too much, but does require a significant amount of
processing (storing two frames, blurring these vertically, and outputting
the result.
The cheapest/best way, is to buy a television able to output the higher
bandwidth required by the frame doubling process. These will already have
the frame store to get rid of the shimmer, and will cost less than
building such a store...
Best Wishes
.
- References:
- Anti flicker filter
- From: npavankumar@xxxxxxxxx
- Re: Anti flicker filter
- From: Matthias Melcher
- Anti flicker filter
- Prev by Date: Re: Anti flicker filter
- Next by Date: Re: Anti flicker filter
- Previous by thread: Re: Anti flicker filter
- Next by thread: Re: Anti flicker filter
- Index(es):
Relevant Pages
|
