Channel Composite Processor

Overview

The Channel Composite processor assembles a new RGBA image by selecting and combining individual channels from one or more existing PNGs—loading all inputs as RGBA—or by using constant values. The resulting composite is always saved as an RGBA PNG.

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Example Usage

- processor:
    processor: "channel_composite"
    inputs:
      sky: "mem/sky_color.png" # full-color or single-channel image
      apple: "mem/apple_mask.png" # grayscale mask or color image
    params:
      r: "sky:R" # red channel from 'sky'
      g: "apple:A" # alpha channel from 'apple'
      b: "apple:RGB" # average of red, green, blue from 'apple'
      a: 255 # constant opaque alpha
    outputs:
      target: "mem/skyapple.png" # resulting RGBA composite

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Parameters

Key	Type	Req’d	Default	Description
r	str or int	No	0	Source for red channel. See options below.
g	str or int	No	0	Same options as r, but for green channel.
b	str or int	No	0	Same options as r, but for blue channel.
a	str or int	No	255	Same options as r, but for alpha channel. Default is fully opaque.

Options for r:

• An integer (0–255) constant (auto-clamped and cast to integer)
• An input key (e.g. sky → uses the key channel by default)
• "key:C" where C ∈ {R,G,B,A}, to extract one channel
• "key:RGB" to average R,G,B
• "key:RGBA" to average R,G,B and include alpha if present

If the given input key is missing, the processor will raise an error.

Exactly one specification must be provided for each channel; omitted channels use their defaults (R/G/B = 0, A = 255).

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Outputs

Key	Required	Description
target	Yes	Path to the resulting RGBA image composite

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Behavior

Define your channel mapping directly in YAML. Examples:

# use "sky" image's red channel, "apple" image's alpha, average blue/green, constant alpha
params:
  r: "sky" # sky:R implicit default for red
  g: "apple:A" # apple's alpha channel
  b: "apple:GR" # average of apple's green and red channels (order doesn't matter)
  a: "192" # constant alpha (0–255)