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This CHOP uses a channel in the first input to index into a lookup table in the second input, and output values from the lookup table. The first input is the Index input, and should contain a single channel to use as an index reference. The second input is the Lookup Table, and can contain any number of channels.
1 in the Index range means that a
0 in the Index (first) input
maps to the beginning (left) of the lookup table, and
1 in the Index
(first) input maps to the end (right) of the lookup table (second
The output CHOP is the same length as the Index input. It is the same number of channels as the Lookup Table input, and has the same channel names as the Lookup Table input. The output is filled with the data extracted from the lookup tables. Indexes that fall between two lookup table samples are interpolated. The lookup table can be sampled outside its range. The Extend Conditions are used in this case.
The sample rate of the output is the sample rate of the Index input.
The Lookup CHOP can be used to fetch values from a color lookup table, where a single index produces red, green and blue channels. It can also be used for rolloff or decay tables, where it specifies how much a parameter drops with distance.
The index range maps the index channel’s values to the lookup table’s start and end.
The first parameter represents the start of the lookup table. When the index channel has this value, it will index the start of the lookup table.
The second parameter represents the end of the lookup table and behaves in the same way.
Per Index Channel
Determines how index channels are mapped to lookup tables.
One Lookup Table Channel
An index channels is matched to only one lookup table.
All Lookup Table Channels
Each index channel is matched with every lookup table.
Determines how index channels are matched with a lookup channel in One Lookup Table Channel mode.
An index channel is matched to a lookup table by its index within the clip. Lookup tables are cycled if there are few of them than index channels.
An index channel is matched to a lookup table by name. Unmatched index channels are left "as is".
It is sometimes desirable to produce a warning or an error when channels in the first input fail to be correctly matched to channels in the other inputs. A failure may occur when matching by Channel Number if the index input has more channels than the lookup table input, or when matching by Channel Name if a channel name in the index input cannot be found in the lookup table input.
Some of these parameters may not be available on all CHOP nodes.
To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example
* (match all), and
? (match single character).
The following are examples of possible channel name matching options:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
Sample Rate Match
The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.
Resample At First Input’s Rate
Use rate of first input to resample others.
Resample At Maximum Rate
Resample to highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
The units for which time parameters are specified.
For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).
When you change the Units parameter, it does not convert the existing parameters to the new units.
Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
The Export prefix is prepended to CHOP channel names to determine where to export to.
For example, if the CHOP channel was named
geo1:tx, and the prefix was
/obj, the channel would be exported to
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.
Graph Color Step
When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.
This example demonstrates how to use the Lookup CHOP to play animation based on an event, or trigger.
The following examples include this node.