svoid test_BWImage() {
  assertEqualsVerbose(127.0, BWImage(2, 2, 0.5f).averageBrightness());
  assertEqualsVerbose(63.0, BWImage(2, 2, 0.25f).averageBrightness());
  assertEqualsVerbose(191.25, BWImage(2, 2, new float[] {0, 1, 1, 1}).averageBrightness());
}