Nuke – Keylight

To key out the greenscreen I used Nukes Keylight-node. I found keying in Nuke quite different from keying in other software, such as fusion. Keylight seems to be more powerful and you can come up with some really good results even if youre doing a very simple key, although I have learnt that there is never a one-key solution.

I tried different techniques for the greenscreen, basically because it it a great way to learn the node, as well as try out which method works best for my shot.

I started with keying out the head and the body seperately using Beziers, creating an alpha for each part, and later merging these two alphas for a good result. This process was however quite time-consuming, alot of tweaking was needed on both keys to get a decent result.

So I tried another much simpler approach, but I thought the results were better. It becomes evident that a good lit greenscreen makes the keying-process much easier, and looking back, I am glad I took the time to carefully light the greenscreen before filming.

I connected the Keylights source input to the original footage, and used the color picker in Screen Color to sample an area close to his neck. This area took away most of the greenscreen around the actor. The clip black slider was then used to remove even more of the background. You can see the status of your keying by changing the view mode to “Status”. This gives you a grayscale image showing you the status of your key. The purpose is of course to get a solid black and white “alpha” image, the black being the greenscreen which you want to remove, the white being the mask of the actor, the part you want to keep. To find a balance between removing the greenscreen without cutting into the actual actor is quite tricky and requires some fine tuning.

The result was ok for a first key, so I added another Keylight node and changed the first keylights view mode to intermediate since I want to combine the two.
The same process was used for this keylight. To add the alpha created from keylight 1, I changed the source Alpha in the Inside Mask Tab to “Add to inside mask”, and changed the view mode to Composite. This gives you an overview of your current image. I still had some greenscreen parts left in the corner of the footage, and used a Bezier to create a quick garbage mask. The bezier was animated to never cut into the actor, but still cutting out the greenscreen parts in the corner. This Bezier was connected into the outM in the Keylight, and the OutM Component in “Crops” then needs to be changed to inverted alpha – which cuts out everything outside the mask.

To get a smoother edge around the actor I used an edgeblur connected to the keylight. This gives you a more natural result which hopefully blends in better with your background.

Be Sociable, Share!

Leave a Reply