ColorUtils.java

package spike.palette.paul.com.palettespike;

/*
 * Copyright 2014 Chris Banes
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.graphics.Color;

public class ColorUtils {

    public static int darken(final int color, float fraction) {
        return blendColors(Color.BLACK, color, fraction);
    }

    public static int lighten(final int color, float fraction) {
        return blendColors(Color.WHITE, color, fraction);
    }

    /**
     * @return luma value according to to YIQ color space.
     */
    public static final int calculateYiqLuma(int color) {
        return Math.round((299 * Color.red(color) + 587 * Color.green(color) + 114 * Color.blue(color)) / 1000f);
    }

    /**
     * Blend {@code color1} and {@code color2} using the given ratio.
     *
     * @param ratio of which to blend. 1.0 will return {@code color1}, 0.5 will give an even blend,
     *              0.0 will return {@code color2}.
     */
    public static int blendColors(int color1, int color2, float ratio) {
        final float inverseRatio = 1f - ratio;
        float r = (Color.red(color1) * ratio) + (Color.red(color2) * inverseRatio);
        float g = (Color.green(color1) * ratio) + (Color.green(color2) * inverseRatio);
        float b = (Color.blue(color1) * ratio) + (Color.blue(color2) * inverseRatio);
        return Color.rgb((int) r, (int) g, (int) b);
    }

    public static final int changeBrightness(final int color, float fraction) {
        return calculateYiqLuma(color) >= 128
                ? darken(color, fraction)
                : lighten(color, fraction);
    }

    public static final int calculateContrast(MedianCutQuantizer.ColorNode color1,
                                              MedianCutQuantizer.ColorNode color2) {
        return Math.abs(ColorUtils.calculateYiqLuma(color1.getRgb())
                - ColorUtils.calculateYiqLuma(color2.getRgb()));
    }

    public static final float calculateColorfulness(MedianCutQuantizer.ColorNode node) {
        float[] hsv = node.getHsv();
        return hsv[1] * hsv[2];
    }

}