Green or Blue matte for vfx (3 replies)
hi roger & forum members,
some films use green matte, some films use blue matte for the VFX shots, is there any vast difference between those two while working in the post?
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.
Green channel is the least noisy and sometimes sharper, which makes for better keys. But blue screens are less bright and tend to spill less color onto objects. The main reason one would choose one or the other though is whether the subject in front as blue or green on them. Otherwise most would opt for green unless there was a compelling reason for blue.
Blue is storically better for film, be cause is simplier to build a black and white mask with chemical work from film.
Disney used yellow screen with a custom and segret souce with a sodium vapor lamp that allow them to build better mask then blue screen, try to see Mary Poppins or old Darby O Gill and you can see better mask than StarWars (before remaster, later they compose again in digital).
Today is often used a green screen be cause most of digital sensor are builded around bayer pattern, that mean green have full info, blu and red have half info; later with color compression you risk to loose more and more without green info.
Anyway, if you have a good camera, that shoot in a good format with low compression to keep the best of infos, you can key every colors.
The real pain when you do a chroma key are :
- poor signal / bad compression video
- bad chroma sampling (4:2:0) that cause to you strange things on keyed edge
- sharpening in camera that create halo and other problems on edge
- color reflection on people or elements surrounded from a too bright chroma key.
- too bad resolution to extract a good key of high freq dectails like hair
with modern tech and modern software yo can do a lots also with a bad shooting, but like ever, in post house there is an old said "garbage in - garbage out".
better shooting for green screen, better key for movie 😀