Chroma shooting (Blue Chroma or Green Chroma) is one of the oldest and most trusted VFX techniques of film making. But, to chroma or not to chroma always depends on the expertise of the VFX supervisor.
Chroma shooting was at its inception stage in the era of 1930s. By that time, it was known as Travelling Matte. All major actors has faced this green and blue monster aka Chroma Cloth, to do act with. Gradually it has gone through a tremendous scientific and technical up-gradation and development. It today’s fully digital world, it has become much cheaper and robust tool of the entire VFX pipeline. On a standard note, we use only two colors as Chroma cloth or Chroma paint – Blue or Green. Currently, we are at very advanced level of digital film making process with top notch algorithms and various macro/gizmo that it can also remove purple backdrop. But, generally they are avoided.
In the Post Production Compositing process, the green screen or blue screen is removed and the output is integrated with required 3D renders and other backplates of live action shooting. The technique is known as Chroma keying (also known as Chromakey). There are various options to do chroma shooting. Some of them are supported with tension rod and clips for better control. :
- Backdrops as green and blue Cloth or Fabric (green screen / blue screen)
- Green and blue screen Paper
- Green and blue wall Paint material
- Spray of green and blue key
- Collapsible chroma screens
Following are the Benefits and Drawbacks of Chroma Keying. It will give an idea regarding to chroma or not to chroma during live action shooting.
The benefits of Chroma shooting:
- The first and foremost positive point – It is one of the best cost cutting techniques at various levels of production .
- It is very much cheap compare to on-location shooting. There are huge numbers of things to look forward when you choose any outdoor shooting – transportation, accommodation, food expenses, proper care of digital equipments and so on. The worst is weather condition; you cannot control the natural changes. If it changes against you during the shooting, you just can’t help but wait for it to get settled.
- Reduces the work of Rotoscoping, Characters and props can be easily keyed out if they have shooted properly with greenscreen or bluescreen. Otherwise, it has to go through laborious roto or masking process.
- Ideal for background replacement. Once the digital artist removes chroma, it can be replaced with other live action shooting plate or 3D renders passes. Creative ideas can be used for the back plate. Light wrap is essential for convincing post production output. It helps to ensure faster post production process.
- Reusable material as the colors are standard for any shooting condition.
- Convenient and easy carrying as they are only cloth material. It also becomes light weighted if folded properly. Make sure, it is always shipped with necessary supporting rods and clips.
- Double side chroma key flexi is widely popular as it is multipurpose for various lighting modes and conditions. At one side it is green screen and on the other it is blue screen.
- It simplifies the post production process in digital body doubles shooting.
- The chroma shooting video gives you fully controlled environment for Compositing.
The drawbacks of Chroma shooting:
Everything has its flip side as well. Check out the minus points of using chroma in visual effects shooting.
- Perfect lighting condition (natural or studio based) is must for easy keying. If it is not achieved on the set, the keying process can be difficult and time consuming.
- Production time and money is wasted if the shooting is not done professionally. It is better to hire an experienced visual effects supervisor for perfect video shooting. No any chroma key software or tool can help to generate proper alpha mattes if shooting is not done as per the standards.
- Chroma shooting sometimes leaves green or blue spill on the edges of character and prop. The chroma colour remains around hair and other fine details if there is less distance between chroma cloth and character. It is knows as ‘Spill’. Wrong lighting setup can also cause this problem.
- The worst thing is to shoot with the chroma key material having wrinkles, folds, creases or larger color variation. By this time, hard edge (articulate) rotoscoping is the only solution.
- The situation can be bad when actor’s clothes and accessories matches with the chroma key colour. The most common scenario – actor wears blue jeans against blue screen shooting. The VFX supervisor must take care of this thing.
The chroma shooting done on 3200 fps of Quicksilver slow motion shot is one of the best examples of perfect green screen shooting.
Chroma key is a double sided sword. It can be boon or bane, depending how well you do video shooting with green screen or blue screen. Till now, we just had scratched the surface of this chroma key technology. All the major movies are heavily relied on this computer generated visual effects technique. It greatly helps to narrate the screenplay as per the vision of the director. So, it is going to stay forever. The only matter is to think carefully when to chroma or not to chroma as per the shot.
Check out some of the best visual effects before and after chroma shootings.