On Sat, 19 Mar 2005, Dik Takken wrote:
> I was wondering what experience you have with putting static images in DVD
> movies (like creating a slide show of digital photographs and text
> slides) and displaying them on a TV screen.
My experience has been to use no lines thinner than 4 pixels, preferably
6 pixel and to use a bold or semi-bold sans serif font.
> The problem is that when the odd and even fields differ a lot (white
> serif fonts on black background) the image flickers really bad. When you
If you're dealing with an interlaced display thin lines/stripes will
cause problems.
The same issue has to be dealt with when creating DVD menus. Using a
bolder sans serif font and a minimum line height of 4 to 6 pixels
is the work-around.
A line 1 pixel tall can only be in 1 field or the other and will
thus appear/disappear every other field - a very bad flicker. Increase
to 2 pixels and you'll see the line "jiggle" up/down slightly as each
field is displayed. By the time you get to 4 pixels the situation is
better since now you have 2 lines present at all times.
> My question: How can I have the best of both solutions: decent detail and
> image stability? My guess is that the flicker will no longer be visible
You want to 'have your cake and eat it too' as the saying over here goes
> when the fields are sufficiently similar. Maybe I can scale each slide to,
> say, 3/4 vertical resolution and then scale them back to full res?
Scaling up/down just blurs/softens the image but in the end you will
still have problems with line lines (such as the serif fonts use)
on interlaced displays.
> Is the flicker problem the same on all types of television (small CRT,
> large CRT, LCD, Plasma, etc) ?
If the video is interlaced the type of TV doesn't matter - thin lines
will still be a problem.
The only thing that might help is to have a progressive scan TV, a
progressive scan DVD player (which almost every unit today can do) and
create a progressive/film DVD (as has been discussed on this mailing
list). That might give a more steady picture without the flickering -
the temporal resolution goes down of course (from 60 fields/sec to
30 frams/sec for NTSC, 50 to 25 for PAL) but if there's not a lot of
fast pans/motion (slides/photos do not have motion so you should be
ok in this regard).
Cheers,
Steven Schultz
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