The Green AdvantageAs a rule of thumb, when dealing with digital footage and non-linear editors and compositor, green is always the best choice. There are many advantages to using digital green over digital blue.
The primary reason we use green is because green is the color that is furthest away from human flesh tones. Also most cameras use a light capturing technology that “samples” colors and light. However, with the way color sampling works out, there is almost always a better sampling of green than its counter primary colors blue and red. This has always been a limiting factor for storage and transmission of color data.
Whenever possible, stick to Digital Green.
Color SamplingFor most professional cameras that output a single HD-SDI signal, the structure that color is transmitted is called 4:2:2 (Y Cb Cr). This means that the luminance (Y) is sampled 4 times, while its counter color difference components are samples twice.
Digital Green is noticeably brighter than Digital Blue and definitely brighter than Chroma Green. When talking about color sampling, what that means is that not only does the green in Digital Green get sampled as color difference (CbCr), but it also gets sampled with luminance (Y). This yields smoother edges between contrasting colors and, ultimately, yields a better key.
With that said, when using Previzion, avoid using cameras where the color sampling is 4:2:1 or 4:2:0 as it will prove a much tougher signal to key.
Chrome Blue and Chrome GreenChrome Blue and Chroma Green (as opposed to Digital Blue and Digital Green) refers to the color of Blue and Green designed for VFX shot using negative film. For photo-chemical processing of negative film, these two colors were made industry standard.
In general, these colors are very difficult to work with. As mentioned above, the sheer “lime green” brightness of Digital Green and the “smurf” blueness of Digital Blue allows for a better color sampling and easier lighting all around.
But you may be able to use chroma colors outdoors. Since there is so much light outdoors, sometimes the older chroma green and chroma blue screens can work well, but it is not recommended.
Shooting With BlueIf there are practical green foliage or a particular show has specific need for green props or characters, then using Digital Green is not an option. Digital Blue also has the added benefit of a a more natural looking spill than digital green.
Shooting on Blue Screen is not necessarily difficult, but it does require an extra bit of effort. Main differences from green:
- Blue is an inherently less bright color, because camera sensors, and human eyes are less attuned to it. Because of this blue keying requires almost a whole f-stop more light (twice as much light). Depending on the size of the your stage, this may be no small feat.
- The camera samples blue less than green. This means that when setting your key, there may be considerably more tweaks and adjustments for a smooth natural key.
- Keying darker haired people and wardrobe can prove more difficult with blue. However, with a Digital Blue Screen at the proper light levels, this is not as big of an issue.
- Blue can create a despill artifact that results in a hard magenta color. To add more separation from the background you may add blue gels to your screen lights (Lee 079 Just Blue) or blue fluorescent tubes (KinoFlo Blue Tubes).
When Blue and Green are not enoughIn exceedingly rare cases, where there are no human skin exposed, or an underwater type setup where green and blue may not work. Digital Red may be used, which poses similar challenges as blue.
Composite Color StandardsWhen we talk about Digital Green and Digital Blue we are referring to Composite Components Company’s (CCC) color materials. This will be the case for cloth, spandex, cycs, vynil and paint.
“Digital Green” and “Digital Blue” is trademark and/or registered under Composite Components Company, or CCC.
There are other alternative paints and materials, but it is important to make sure its sheen, pigment color and specs are up to par.