TobyEggitt wrote:And success! Thank you again for your pointers. I was a bit confused by the manual, but it seems like the downstream key works in linear mode (though there's something in the menu about pre-multiplied which seemed to affect it.) Anyway, I selected a fixed color for the fill, a video input for the key, set the computer generating that video to a black background with a larger than normal white mouse, and hit the "On Air" button in the DSK group. So easy when someone nudges you in the right direction. Thanks again.
I'd suggest you read up a bit on keying.
Keys have both a key and a fill signal - the key cuts the hole in the background video (*) and the fill source fills that hole (*). You can self-key (where the luminance or chrominance of the source video both cuts the whole in the background AND provides the video to fill the hole), but you can also replace the video fill with either a colour matte (as you are) or a different input source (a 'split key' rather than a 'self key').
With a split-key you can use linear keying where black will be 100% background, and white will be 100% foreground, and mid-grey will be a mix of 50% background and 50% foreground. Alternatively you can do a hard clip where you just switch hard between foreground and background (this level of softness is controlled by the gain of the keyer, the level at which the switch happens is controlled by the clip)
(*) With linear keying you have two choices for how the key signal processes the foreground that is filling the hole the key signal has made in the background.
If you use the key signal to also process the foreground (i.e. to cut the foreground out in the reverse to the way the background has been cut out) then this is called un-shaped, multiplicative, or linear keying. This is what you do with a matte fill or if you are filling with another camera etc.
However it is sometimes possible that the foreground has already been processed so that it can just be added to the background with the hole cut out in the background only by the key signal, and the key will do nothing to the foreground, which is just added to the background with the hole cut in it. This is called pre-matted, shaped, additive, or clean keying.
If you get the key setting wrong you'll often see graphics burn through black as they fade themselves in and out, or they will appear to have black edges that aren't expected (both the result of pre-matted or shaped keys being treated as if they are not pre-matted or are unshaped).
Or you'll see graphics overlaid parts of the picture you're not expecting etc. when the foreground is being treated as pre-matted, additive or shaped, when it isn't. (Colour matte fills will never be shaped for example)
Sat Feb 15, 2025 8:16 pm
