Daniel Kristjansson wrote:
On Wed, 2005-05-04 at 16:15 -0700, Bruce Markey wrote:
Daniel Kristjansson wrote:
The one anomaly was the TVout from a "GeForce4 MX 420" was correct
for all negative values and positive values up to 3%. At four
percent or higher, the fields were off by one scan line causing
doubled horizontal edges. This was not the case for TVout from
a 5200 or monitor output so I believe this was an anomaly of
that card/driver rather than a miscalculation.
Hmmm, I'm using a GeForce 4 MX. I just added a fix for this
that does overscan compensation when the overscan is greater
than or equal to 5%. It does get one scan line off, but then
never gets worse (like it did before). But if this is a
GeForce 4 MX problem only then we should detect this and only
do this compensation in this one case.
For me, the cutoff is at 4%. 3% doesn't have this problem.
Do people generally use an overscan >= 5%?
Good question and in theory, the answer should be no. The TV image
is supposed to extend beyond the edge of the screen. The 'action
safe' area is 5% in from the edge and anything the viewer needs
see see to understand what's going on should fall inside those
bounds. The 'title safe' area is 10% in from the edge for text
that needs to be read.
If the X display area is set to fit the edges of the screen exactly,
the image should not have to be overscanned by more than 5% to cut
off the ragged edges and the empty space below a crawl for example
and to look normal. More than 5% would start to cutoff parts of the
image that need to be seen.
I used 6% for the test case to be sure the uncentered image would
be obvious but 2% or 3% would be more typical values.
-- bjm
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