On Sun, 30 Jun 2002, Billy Eno wrote:
> Interesting background on how TV's actually work. I certainly was unaware.
> It would be pretty easy to write a demo to see if it worked (I think), and I
> may try. But, if a TV interlaces two succesive Atari 2600 "frames" to
> create an image, how would you (or the TV)know if the first frame was an
> "odd" (to the TV) or an "even" (to the TV). If the you didn't start with
> the correct frame, likely the graphics wouldn't look right.
The 2 fields should properly look like this:
******************** xxxxxxxxxx
******************** xxxxxxxxxxxxxxxxxxxx
******************** xxxxxxxxxxxxxxxxxxxx
******************** xxxxxxxxxxxxxxxxxxxx
******************** xxxxxxxxxxxxxxxxxxxx
******************** xxxxxxxxxxxxxxxxxxxx
********** xxxxxxxxxxxxxxxxxxxx
field 0 field 1
Notice that field 1 starts in midline, just where field 0 left off. And
field 0 starts at the beginning of the line, where field 1 left off.
If you draw these 2 fields sequentially, you see how the lines get
interlaced. Remember that the lines are actually drawn diagonally,
because the electron beam moves downward at a constant rate. It's hard
to draw in text, but I'll try. Heres a display with 2.5 lines per field,
or 5 lines per frame: (again, "*" represents field 0 and "x" represents
field 1)
* x
* x
* x
x *
x *
x *
* x
* x
* x
x *
x *
x *
* x
* x
* x
-Chris
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