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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.
Specify the COP Network, and the COP here as the source from which the image should be obtained.
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.
Scales the output to lie in the range
Extracts a single pixel from the image.
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.
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.
Extracts the full image.
Specifies the units for the following 4 parameters.
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.
Ending point for sampling in U.
Starting point for sampling in V.
Ending point for sampling in V.
Determines the interpolation method when UV sampling with an input CHOP is used.
The image extend conditions when sampling the image with U less than 0.
The image extend conditions for U greater than 1.
The image extend conditions for V greater than 1. The extend conditions are:
Use the first or last pixel value.
Loop back to the other side of the image.
Zig-zap back into the image.
Use a default color specified below.
The color to use when outside the bounds of the image, and the Default Color extend condition is set.
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.