@Override
  public boolean equals(Object o) {
    return o instanceof BrightnessFilterTransformation &&
      ((BrightnessFilterTransformation) o).brightness == brightness;
  }
brightness value ranges from -1.0 to 1.0, with 0.0 as the normal level
transformations/src/main/java/jp/wasabeef/glide/transformations/gpu/BrightnessFilterTransformation.java