Lookup channel node

Uses a channel in the first input to index into a lookup table in the second input, and output values from the lookup table.

All Parameters Example files

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.

A 0 to 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 input).

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.

Parameters

Lookup

Index Range

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.

Match By

Determines how index channels are matched with a lookup channel in 'One Lookup Table Channel' mode.

Channel Number

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.

Channel Name

An index channel is matched to a lookup table by name. Unmatched index channels are left “as is”.

Common

Some of these parameters may not be avaiable on all CHOP nodes.

Scope

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:

chan2

Matches a single channel name.

chan3 tx ty tz

Matches four channel names, separated by spaces.

chan*

Matches each channel that starts with chan.

*foot*

Matches each channel that has foot in it.

t?

The ? matches a single character. t? matches two-character channels starting with t.

r[xyz]

Matches channels rx, ry and rz.

blend[3-7:2]

Matches number ranges giving blend3, blend5, and blend7.

blend[2-3,5,13]

Matches channels blend2, blend3, blend5, blend13.

t[xyz]

[xyz]matches three characters, giving channels tx, ty and tz.

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.

Units

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).

Note

When you change the Units parameter, it does not convert the existing parameters to the new units.

Time Slice

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.

Unload

Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.

Export Prefix

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 /obj/geo1/tx.

Note

You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as obj:geo1:tx.

Graph Color

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.

Example files

Lookup

$HFS/houdini/help/examples/nodes/chop/lookup/LookupCHOPExample.otl

Load | Launch

This example demonstrates how to use the Lookup CHOP to play animation based on an event, or trigger.

Usages in other examples

Example name Example for