Image channel node

Converts rows and/or columns of pixels in an image to CHOP channels.

See also: Geometry, Particle, Shuffle

This CHOP converts rows and/or columns of pixels in an image to CHOP channels. It generates one CHOP channel per span of pixels in the image. Pixels, rows, columns or rectangular regions can be extracted from the image.

There is an optional input which supplies UV coordinates to sample the image. The input CHOP must contain two channels, one for U and one for V. The first channel is always assumed to be U. The channels produced (red, green, blue and alpha) will be exactly as long as the input channel’s length, with a value for each UV coordinate.

Parameters

Image

Source	Specify the COP Network, and the COP here as the source from which the image should be obtained.
Frame	The frame number from which to obtain the image.
Red, Green, Blue, Alpha	Creates a CHOP channel per scanline with the prefix specified here, starting at 0. For example, the default is “r” in the Red field. If the specified COP is a horizontal ramp that is 5 lines high, it creates five CHOP channels (r0 - r4) using the values of the red pixels in those scanlines.
RGBA Units	Scales the output to lie in the range `0-1`, `0-255` or `0-65535`.

Crop

Pixel (U.V)	Extracts a single pixel from the image.
Row (U)	Extracts a single row from the image. The V Start indicates the row to select, and the U Start and U End indicate the range to extract.
Column (V)	Extracts a single column from the image. The U Start indicates the column to select, and the V Start and V End indicate the range to extract.
Rows and Columns	Extracts an area from the image.
Full Image	Extracts the full image.

UV Units

Specifies the units for the following 4 parameters.

U Start

Starting point for sampling in U. Values outside the range of the image are determined by the image’s extend conditions, in the extend page.

U End

Ending point for sampling in U.

V Start

Starting point for sampling in V.

V End

Ending point for sampling in V.

Interpolate

Determines the interpolation method when UV sampling with an input CHOP is used.

Extend

Image Left

The image extend conditions when sampling the image with U less than 0.

Image Right

The image extend conditions for U greater than 1.

Image Bottom

The image extend conditions for V less than 0.

Image Top

The image extend conditions for V greater than 1. The extend conditions are:

Hold	Use the first or last pixel value.
Cycle	Loop back to the other side of the image.
Mirror	Zig-zap back into the image.
Default Color	Use a default color specified below.

Default Color

The color to use when outside the bounds of the image, and the Default Color extend condition is set.

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.

Usages in other examples

Example name	Example for