One of the techniques used in Post-production is the composition of images to add special effects (VFX) the decorated.
Technique “Chroma” consists of overlapping portions of different images, eliminating a color of one of them and making transparent.
This technique allows you to shoot in a studio and eliminate homogeneous background of a landscape or other location.
From version 2.64 the Blender, Available in August 2012, it incorporates a complete node, on node editor, that lets you do this almost automatically.
The chroma, insertion or chroma key color (del ingles Chrome key) audiovisual technique is widely used in film and television and photography, which involves removing a color from the image (usually green or blue) and replace that color area occupied by another image, with the help of specialized equipment or computer. (W)
A very illuminating example can be seen in this short video.
Nodo Chroma Key
For example, we superimpose a figure like this, with green background:
with a background as:
Entering the node editor, we can add the new node “Chroma” from the menu:
Add -> Matte -> Keying
The new node has two main entrances:
- The image with a uniform background color
- The color will become transparent
The filter produces three possible outputs:
- Image: Filtered image with transparent background
- Matte: A mask
- Edge: Image with contours or silhouetted
The mask image is composed of black and white pixels that indicate what is the image and what is transparent.
The output “Edge” finesse serves to control the transition zone, outline of the image, between the transparent area will occupy the bottom and the main reason.
The use of the filter scheme is as follows.
- Scale images are first “Chroma” and thoroughly and properly positioned to compose the shot.
- Filtering the background (green) to become transparent
- The two images are composed by a node “Alfa over”, to which is indicated by the mask (Matte) the transparent area of the image “Chroma” is replaced with the background.