channel {EBImage} | R Documentation

## Color and image color mode conversions

### Description

`channel` allows to convert colors of images and color values given in vectors, arrays or matrices from one mode to another. The supported source and target modes are TrueColor (data of type: `integer`) and Grayscale (`numeric`) and X11 strings (`character`).

The mode of the argument is determined automatically from its type.

### Usage

      ## S4 methods for signatures 'x=Image,mode=character'
      ## and 'x=ANY,mode=character'
      channel(x, mode, ...)

      rgbImage(r, g, b)
      channelMix(r, g, b)

### Arguments

`x` | Either an object of `Image` or a vector of `numeric`, `integer` or `character`.
`mode` | A character value specifying the target mode for conversion. See 'Conversion Modes' below.
`...` | Reserved.
`r,g,b` | Objects of class `Image`.

### Details

Conversion modes:

`rgb`
  The result is a true color representation of the input. Its class is or includes `integer`, i.e. an integer array or a `TrueColor` integer-based image.
`gray`
  The result is a gray scale representation of the input. Its class is or includes `numeric`. Synonym: `grey`
`red, green, blue`
  The result is a gray scale representation of the input from only the red, the green or the blue channel was extracted, correspondingly. The result's class is `numeric`-based. As synonyms single letters `r, g, b` can be used correspondingly.
`asred, asgreen, asblue`
  The result is a true color with all the data in one channel only, the red, green or blue, correspondingly. The result's class is `integer`-based. As synonyms `2r, 2g, 2b` can be used.
`x11`
  The result is a `character`, which elements represent the input colors as X11 strings, i.e. RGB hex codes starting with a sharp sign.

Conversion modes are case insensitive!

If the input is a `character` vector, its values may contain color names instead of color hex codes, like `red, purple, white` etc. However, the result of the `X11` mode will always contain hex codes.

`channelMix` uses the following formula to calculate the mix: `mix = sqrt(r^2+g^+b^2)`. Any of the values can be missing.

### Value

For an argument of `Image` the function returns a new object of `Image` in all modes except `'X11'`. In case of `'X11'` it returns a `character` vector of the same length as the image.
For vectors the function returns a `vector` of the same size in the target mode.
`rgbImage` generated a TrueColor image using `r`, `g` and `b` as values for red, green and blue channels correspondingly.
`channelMix` generates a grayscale image as if the image was converted from a TrueColor one that was composed using `r`, `g` and `b`.

### Author(s)

Oleg Sklyar, osklyar@ebi.ac.uk

### See Also

`Image, readImage, writeImage`

### Examples

      cl <- channel("pink", "rgb")
      r <- channel( channel(cl, "red"), "asred")
      g <- channel( channel("pink", "green"), "asgreen")
      b <- channel( channel(cl, "blue"), "asblue")
      rgb <- r + g + b
      print( rgb == cl )
      clg <- channel(cl, "gray")
      print( channel(cl, "x11"))

      ## further example in 'paintObjects'

[Package EBImage version 2.4.0 Index]