On this page |
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 ¶
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 available on all CHOP nodes.
Scope
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in 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.
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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the 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 of the time parameters.
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, the existing parameters are not converted to the new units.
Time Slice
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the 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 to it for display in the graph, but you can override the color with the 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.
See also |