My last film I filmed against a greenscreen, and then composited my actors and my creatures onto a background. I will talk more about that later, but one thing that took a little work was to keep the scales or the sizes consistent through out the film. I had three different characters that I manipulated to appear larger or smaller for the film, and had several shots where a 7′ orc, a 5′ tall human, a 4′ tall dwarf, and a 3′ tall goblin would interact with each other. And they are all the same actor. So, how do you keep the sizes consistent from shot to shot?
This is the basic shot setup. You film your actor on greenscreen.
Now film your creature on greenscreen.
Now bring both of them onto a background image or video.
So, how do we figure out what size to make them? Well, let’s assume that the hero is 5 feet tall, and the creature is 8 feet tall. Figure out these measurements before you start. Don’t just eyeball them together. Once you know their heights you can add them into any scene and just adjust them accordingly. Use something in the scene to determine the scale, then adjust your greenscreen footage. I often find that it helps to put the hero in first, make sure he is the right size, then add the creature. You can base the creature’s size off the measurements of the hero. Once you get the creature the right size you can even remove the hero if you want.
So, we place the hero on the background plate and adjust so it is the correct size. How do you then size the creature? Well, in my example the 5 feet tall hero measures 3 inches tall on my screen. The creature if real, would be 8 feet tall. So, how many inches on my screen should the video be?
Well, if 3/5 then x/8. Simple ratio. 3*8=5x, 24=5x, 4.8=x
So, now I know that when I put the creature video in on the background, it has to be 4.8 inches tall on my screen. Even if I remove the hero, the creature will always be the correct height.
Another tip, measure stuff in the scene to figure out your scale. If you are shooting on site, you could have an actor walk out so you can film what size a human really is on site to show scale. I also had my actors hold up a ruler at times so I would know what a foot looked like for scale purposes later.
So, know your measurements before you begin to composite your footage. Use the measurements, and don’t just eyeball it. Place a human in first to establish the scale. Measure other things in the scene to figure out your scale. Use simple ratios to determine how large imported video should be.
Go ahead, make a mess, have some fun.