Lookupfile – Apple Shake 4 User Manual
Page 653
Chapter 23
Color Correction
653
LookupFile
Use the LookupFile node to apply a lookup table to any image by reading a text file. The
file should consist of an arbitrary number of rows, and each row can have three or four
entries, corresponding to red, green, blue, and possibly alpha. Shake determines the
range of the lookup to apply based on the number of rows in the file—with “black”
always mapping to 0 and “white” mapping to (n-1), where n is the number of lines in
the file. Therefore, if your file contains 256 rows, Shake assumes that your entries are all
normalized to be in the range of 0 (black) to 255 (white). If you have 1024 lines in your
file, then “white” is considered to be a value of 1023. Interpolation between entries is
linear, so lookups with only a few entries may show undesirable artifacts. For example,
the following simple five-line lookup file produces the following lookup curve:
0 0 0 0
.3 .3 .3 .3
1 1 1 1
2 2 2 2
4 4 4 4
Because of this linear interpolation, you may want to instead use the standard Lookup
node with lookups that do not have a large number of points.
Function
Spline Lookup
Linear Lookup
Lookup Expression
CSplineV(x,0,
0@0,
1@1
)
LinearV(x,0,
0@0,
1@1
)
Graph (white is result,
gray is input)