Re: Flicker !!

Steve Roberts wrote:

> This assumes that your source images are already TV size (eg 720 x 576
> (PAL) or 720 x 480 (NTSC)), whereas I suspect that his are probably
> large and are being resized automatically.

Or 768x576 PAL with square pixels...

Okay Myles, yes resizing is bad for retaining your image resolution.
This is less relevant for tv than print, your TV resolution is
something like the figures above. Your printer probably uses 600 dots
per inch. If your TV used that the screen would be about an inch
square ! Luckily our eyes are not too sensitive to this, especially if
the image is moving.

Interlacing is a compromise between temporal(time) and spatial(space)
resolution. It was used to stop the screen looking flickery. A side
effect is that high resolution still images can have a sparkling
flickery effect. The only way to reduce this effect is to reduce the
vertical resolution.

Here are some samples, these are for PAL as I live in the UK.

http://www.zen54410.zen.co.uk/linkfiles/stills/PAL/

To make these I resized and cropped the image to 768x576. Cropping is
neccessary if the source image doesn't have a
4:3 aspect ratio.
Remember the edges of the image will be cut off on most TVs.
Now resize the image to 768x380, most software defaults to a good
quality resize(resample) which is what we want.
Now resize again to 720x576 and save for use in your project.

The change from 768 to 720 is because TV pixels are not square like
those on your PC.

380 is not a magic number, I just chose it as 66% of 576. Again, 66%
isn't a magic number either, just one I tested. Try increasing it to
80 or 90 percent, this may reduce the flicker enough and increase the
resolution _slightly_.

For NTSC, apparently you get your images to 720x531, and then resize to
720x480 to get the aspect ratio correct. This should have the
side-effect of reducing flicker too.
I don't have an NTSC monitor to try this out.

Alex

.

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