The fundamentals to producing good chroma key are choice of background colour and flat lighting. You will save time and effort at edit if you spend an extra 10 minutes on this before a shoot. I often bounce light of a wall or flag the lights so as not to produce harsh changes in colour, I then monitor the colour through the camera display to ensure I produce a flat and even blue or green.

I shall talk about the controls I use in Adobe Premiere Pro as it is my current edit suite environment but controls the the video effects are much the same in Final Cut. For greater detail I would use Adobe After Effects to produce perfect results.

If you have produced an even background and once you get used to the controls you will be able to knock out the background in seconds. Apart from the Key Color / Eye Dropper used to select the colour you wish to remove, the three main controls are Color Tolerance, Edge Thin and Edge Feather. Select the tone roughly in the middle of the range of colour you wish to remove, I have often placed my new background in the video timeline under my clip so as I can see what I am doing. Adjust the Color Tolerance until the majority of the chroma has been removed. There will usually be a thin line left around the subject. Use the Edge Thin to remove most of this by increasing the value. The line is still pretty harsh so now tidy the effect up using the feather tool again by increasing the value, this will soften the change in color.

If you didn’t manage to achieve an even flat light you can use the Colour Key effect more than once in order to remove the rest of the colour but be sure to keep an eye on the shades on the subject to make sure nothing is removed. If you have chosen the background colour wisely this shouldn’t be a problem.

For Chroma Key in more detail using Adobe After Effects see this tutorial, very simple but great results.