chromatism/src/operations/contrast.js

A simple set of utility functions for colours.

import makeColourObject from './convert'
import convert from '../helpers/convert-to-type'

export default function contrast (shift, colourRef) {
  var colour = convert('rgb', colourRef)

  colour.r = (((((colour.r / 255.0) - 0.5) * shift) + 0.5) * 255.0)
  if (colour.r < 0) {
    colour.r = 0
  } else if (colour.r > 255) {
    colour.r = 255
  }

  colour.g = (((((colour.g / 255.0) - 0.5) * shift) + 0.5) * 255.0)
  if (colour.g < 0) {
    colour.g = 0
  } else if (colour.g > 255) {
    colour.g = 255
  }

  colour.b = (((((colour.b / 255.0) - 0.5) * shift) + 0.5) * 255.0)
  if (colour.b < 0) {
    colour.b = 0
  } else if (colour.b > 255) {
    colour.b = 255
  }

  return makeColourObject(colour)
}