ColorUtils.java

import android.graphics.Color;

public final class ColorUtils {
  public static boolean useLightOnPrimaryColor(int color) {
    return computeContrastBetweenColors(color, Color.WHITE) > 3f;
  }

  /**
   * Copyright (C) 2014 The Android Open Source Project
   * Calculates the contrast between two colors, using the algorithm provided by the WCAG v2.
   */
  private static float computeContrastBetweenColors(int bg, int fg) {
    float bgR = Color.red(bg) / 255f;
    float bgG = Color.green(bg) / 255f;
    float bgB = Color.blue(bg) / 255f;
    bgR = (bgR < 0.03928f) ? bgR / 12.92f : (float) Math.pow((bgR + 0.055f) / 1.055f, 2.4f);
    bgG = (bgG < 0.03928f) ? bgG / 12.92f : (float) Math.pow((bgG + 0.055f) / 1.055f, 2.4f);
    bgB = (bgB < 0.03928f) ? bgB / 12.92f : (float) Math.pow((bgB + 0.055f) / 1.055f, 2.4f);
    float bgL = 0.2126f * bgR + 0.7152f * bgG + 0.0722f * bgB;

    float fgR = Color.red(fg) / 255f;
    float fgG = Color.green(fg) / 255f;
    float fgB = Color.blue(fg) / 255f;
    fgR = (fgR < 0.03928f) ? fgR / 12.92f : (float) Math.pow((fgR + 0.055f) / 1.055f, 2.4f);
    fgG = (fgG < 0.03928f) ? fgG / 12.92f : (float) Math.pow((fgG + 0.055f) / 1.055f, 2.4f);
    fgB = (fgB < 0.03928f) ? fgB / 12.92f : (float) Math.pow((fgB + 0.055f) / 1.055f, 2.4f);
    float fgL = 0.2126f * fgR + 0.7152f * fgG + 0.0722f * fgB;

    return Math.abs((fgL + 0.05f) / (bgL + 0.05f));
  }

  private ColorUtils() {
    throw new AssertionError("No instances.");
  }
}