jit.chromakey Reference

Key images based on chromatic distance

jit.chromakey

Description

Produces an chromakey effect based on a reference color. Tolerance and fade settings allow for control over the resulting combined image. An alternate mode outputs a matrix with the keying values, which can be used by other Jitter objects.

Examples

Discussion

The jit.chromakey object measures the chromatic distance of each of the left input's cells (pixels) with a reference color (a.k.a "green screening"). The total chromatic distance is calculated by summing the absolute value of each color channel's distance from the reference color's corresponding color channel.

If the distance is less than or equal to a tolerated distance (tol) value, the right input cell is multiplied by a maximum keying (maxkey) value.

If the distance is greater than the tolerated distance but less than the sum of the tolerated value and a set fade value (fade) an interpolated value between the some value between minkey and maxkey values is applied.

For values whose distance is greater than the sum of the tolerated and fade values, the right input cell is multiplied by the minkey value.

The left input is always multiplied by the additive inverse of the left input's multiplicand.

The jit.chromakey object has two modes of output; the first keys between the two input sources, and the second mode will output the keying values (i.e., the left input multiplicands) rather than applying the keying -- the left input is ignored. This is useful for outputting keying information for use with other Jitter objects. Keying can be inverted by swapping the minkey and maxkey values.

Matrix Operator

matrix inputs:2, matrix outputs:1
Name IOProc Planelink Typelink Dimlink Plane Dim Type
in2 resamp 1 1 1 1 1 char long float32 float64
out n/a 1 1 1 1 1 char long float32 float64

More about Matrix Operators

The Jitter MOP

MOP Arguments

MOP Attributes

MOP Messages

Attributes

alphaignore [int]

Ignore alpha channel flag (default = 1)
0 = use alpha channel (plane 0) when calculating chromatic distance
1 = ignore alpha channel (plane 0) when calculating chromatic distance

color [32 floats]

The reference color to be used for keying (default = all 0.)

fade [float]

The amount of fade (default = 0.)

maxkey [float]

The maximum keying value (default = 1.)

minkey [float]

Minimum keying value

mode [int]

Output mode (default = 0)
0 = perform keying and output matrix
1 = output the key map for use elsewhere
2 = alpha contains key map, other planes are from left input

Possible values:

0 = 'Composite'
1 = 'Key Map in All Channels'
2 = 'Key Map in Alpha'

tol [float]

The tolerated distance -- the range of variance from which an input cell's absolute value can diverge when calculating keying (default = 0.)

Common Box Attributes

See Also

Name Description
Working with Video in Jitter Working with Video in Jitter
jit.alphablend
jit.keyscreen
jit.lumakey
jit.op
Tutorial 10: Chromakeying Tutorial 10: Chromakeying