On Fri, 28 Jun 2002, Erik Mooney wrote:
> Actually, IIRC from Video Demystified, it's VSYNC that's "blacker than
> black", a signal at much lower voltage than regular black. VBLANK
> shows up on a TV the same as writing 0 to COLUBK and urning off
> any objects/playfield. (Try it in the middle of a frame.)
The blanking level is suppposed to be "blacker than black". And the sync
level is even blacker. It's "blacker than blacker-than-black". If I were
to draw a "proper" greyscale stair step on a given scanline, starting with
black, jumping to white and stepping back down to black, the brightness
would look like:
---
| ---
| ---
| ---
| ---
| ---
| ---
______ ______--- ---______ ______
| | | |
|__| |__|
| |
h h h | b w g g g g g g b | h h h
b s b | l h r r r r r r l | b s b
l y l | a i a a a a a a a | l y l
a n a | c t y y y y y y c | a n a
n c n | k e k | n c n
k k | | k k
| visible line |
+---------------------------+
Notice that black is actually above the blanking level. This is in the
original NTSC spec. And it is implemented on some 2600 motherboards, by
using the /BLANK pin. On other motherboards, this pin is left out of the
circuit, so black is the same as blank. In all cases, sync is far below
blanking level.
-Chris
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