The masterclass regarding green-screen and composting helped me greatly with my post work as I already had some knowledge of composting and green-screen but over the time forgot the fundamental rules of green screen marking and also the reasons behind the traditional way of marking and composting because before this class I only knew what the standard distance and colour of markers are but never really knew the reason why they are there.
First of all for any green screen object to be tracked during the post work it needs to be perfectly marked and for that following factors are to be kept in mind. First is what color of the markers should be used. Steve told us that why it is always better to use black and white markers as the softwares that we use to track markers find it easier to find these colours due to the contrast but sometimes even this can get tricky as if we are using the black colour it might be hard to extract it when their are hair involved in a shot. Like in our exercise Steve put a marker right behind our actors hair which in a real world scenario you would try to avoid as it can be tedious and time consuming to extract the marker behind the hair due to the same colour but keeping that in mind color markers can also be a problem if the circumstances are not correct for example using a blue marker will require two keys which can be a problem for the wardrobe and props and also some cameras dont work well with such colour transitions and leave behind a visible difference in the keying of the shots.
Another key factor that I learnt was how many markers should be used for example in a moving shot Steve advised to have atleast 3 markers making a triangle reason behind this is that even if we move if one of the marker move out of the filming frame another is added and having a triangle shape or a rectangular one allows the camera tracker to trakc points horizontally and vertically.
Also while putting the markers make sure you have a good knowledge about the positioning cause in our case we were given a challenge to remove the markers from behind the gnome’s head which in an ideal situation shouldve been avoided because if you are putting a marker behind an object you will need to rotoscope it and mask it out step by step.
With markers being set the other key factors are the lighting, the camera that is being used and also the distance between the greenscreen and the object being filmed.
First we come to the lighting of the greenscreen for that we need to make sure that we use to lights to light the green screen at equal distances and get them centered so they can light the green screen evenly because if the light is not being emitted evenly on the green screen it will leave behind shadows which will appear in your backdrop making it difficult to key.
Its always a good idea to have some distance from the actor and the greenscreen preferably around 2 meters as this will help you avoid any shadow being cast by the actors and also assisting in easier access to setting the green screen lights.
The other important thing that needs to be considered while filming something on green screen is the camera. The camera that are being used should either film on 4k or ultra HD reason for this is that any camera that is having a codec that is compressing the footage will cause your green screen footage to have pixilated results which will be shown in the form of small boxes i.e pixels that will make your shot look unappealing to the eye another factor is that filming in 4k allows the post production process easy as they have more room to play with effects resizing and also framing repositioning after we track the camera.
After you have filmed the shot we take our footage in to the software to key out the greenscreen and mask out the markers and use our desired backdrop, but for that we need to have a proper understanding on which software can be used usually its one of the following
– Sony Vegas
– After Effects
In our case we used After Effects, now before we get in to the procedure on how to apply the backdrop and removing the green screen i’d like to address the problems that I faced while filming and working on post with this particular scene. First of all was the distance between the green screen and our set up was not sufficient which caused us some trouble while lighting the set up as it is always safe to have some distance which can help when it comes to the Z axis of the tracking and giving depth to your shot, but more importantly giving you enough room to light your shot.
Second was the challenge task set by Steve to have a marker right behind the gnomes head now it isnt a big problem in this case as the shot was fairly simple but having a complicated shot couldve made this task fairly difficult and time consuming as it takes time to extract a frame by masking out each frame. So going forward we were told to always make sure of where we position our markers.
On the minor difficulties was while filming the shot we had issues with the dolly which made the shot a bit shaky which going forward is something I would keep in mind as during post work it caused some issues when we applied the backdrop as it made it hard to track the shot and make the background more believable due to an unstable shot
Now when it comes to having your greenscreen removed we use a keying tool which is built in. In all the softwares that are mentioned above what that do is it extract the color that you choose from the shot and make it transparent. In our case its the colour green, We usually extract colour blue and green because these two colours are not find in our pigment and can be extracted completely.
Once you apply the keying plug in you have to play around with the whites and blacks on the shot with black showing the parts that are being shown in the color and white as the ones that have been extracted.