How to use the Clean Plate input on Delta Keyer?

Hi there. The manual doesn't say anything about how to use the Clean Plate input on the Delta Keyer. Neither does the fusion e-book. When I create a clean plate (background image with no subject in foreground) out of a green screen image, and connect it to the clean-plate input on the Delta Keyer, it seems to do a really good job of keying out the green screen, but leaves in non-green colors that appear in both images. My clean plate is clean and the camera didn't move.

Just curious how it works and why it's deciding to automatically key on the green screen without me doing anything? Is there any documentation on this input and how to use it with the Delta Keyer?

Thanks.

Mark.

The manual has an entry for both the CleanPlate node and the CleanPlate input on the Delta Keyer. The CleanPlate node allows you to select the green that you want to key out in the DeltaKeyer. You connect the output of the CleanPlate node into the CleanPlate input on the DeltaKeyer.

Just curious how it works and why it's deciding to automatically key on the green screen without me doing anything?

You are doing something, connecting the cleanplate that is.
It is not a difference keyer in the direct sense, so not-green objects are not keyed out, keyer still bases its logic on having a chroma key background.

In simple terms, the clean plate is like a position specific keying colour. It uses the clean plate as input for the Delta keyer to say this is the colour to key from so variations in the green screen are effectively accounted for. If you have shot a clean plate (no foreground elements) and the foreground elements when in shot aren't casting shadows or bouncing any light onto the screen you can use this. Otherwise you can use the footage and threshold out the non greenscreen elements and 'grow' the edges of the green screen into the semi transparent/edge areas. At least that is how I think it works, as you said the doc is not the best.

I have found it very useful as it often means I don't have to do a number of different keys to compensate for greenscreen variations.

Thank you!