xref: /frameworks/base/core/java/com/android/internal/graphics/ColorUtils.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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
 */

package com.android.internal.graphics;

import android.annotation.ColorInt;
import android.annotation.FloatRange;
import android.annotation.IntRange;
import android.annotation.NonNull;
import android.graphics.Color;

/**
 * Copied from: frameworks/support/core-utils/java/android/support/v4/graphics/ColorUtils.java
 *
 * A set of color-related utility methods, building upon those available in {@code Color}.
 */
public final class ColorUtils {

    private static final double XYZ_WHITE_REFERENCE_X = 95.047;
    private static final double XYZ_WHITE_REFERENCE_Y = 100;
    private static final double XYZ_WHITE_REFERENCE_Z = 108.883;
    private static final double XYZ_EPSILON = 0.008856;
    private static final double XYZ_KAPPA = 903.3;

    private static final int MIN_ALPHA_SEARCH_MAX_ITERATIONS = 10;
    private static final int MIN_ALPHA_SEARCH_PRECISION = 1;

    private static final ThreadLocal<double[]> TEMP_ARRAY = new ThreadLocal<>();

    private ColorUtils() {}

    /**
     * Composite two potentially translucent colors over each other and returns the result.
     */
    public static int compositeColors(@ColorInt int foreground, @ColorInt int background) {
        int bgAlpha = Color.alpha(background);
        int fgAlpha = Color.alpha(foreground);
        int a = compositeAlpha(fgAlpha, bgAlpha);

        int r = compositeComponent(Color.red(foreground), fgAlpha,
                Color.red(background), bgAlpha, a);
        int g = compositeComponent(Color.green(foreground), fgAlpha,
                Color.green(background), bgAlpha, a);
        int b = compositeComponent(Color.blue(foreground), fgAlpha,
                Color.blue(background), bgAlpha, a);

        return Color.argb(a, r, g, b);
    }

    private static int compositeAlpha(int foregroundAlpha, int backgroundAlpha) {
        return 0xFF - (((0xFF - backgroundAlpha) * (0xFF - foregroundAlpha)) / 0xFF);
    }

    private static int compositeComponent(int fgC, int fgA, int bgC, int bgA, int a) {
        if (a == 0) return 0;
        return ((0xFF * fgC * fgA) + (bgC * bgA * (0xFF - fgA))) / (a * 0xFF);
    }

    /**
     * Returns the luminance of a color as a float between {@code 0.0} and {@code 1.0}.
     * <p>Defined as the Y component in the XYZ representation of {@code color}.</p>
     */
    @FloatRange(from = 0.0, to = 1.0)
    public static double calculateLuminance(@ColorInt int color) {
        final double[] result = getTempDouble3Array();
        colorToXYZ(color, result);
        // Luminance is the Y component
        return result[1] / 100;
    }

    /**
     * Returns the contrast ratio between {@code foreground} and {@code background}.
     * {@code background} must be opaque.
     * <p>
     * Formula defined
     * <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef">here</a>.
     */
    public static double calculateContrast(@ColorInt int foreground, @ColorInt int background) {
        if (Color.alpha(background) != 255) {
            throw new IllegalArgumentException("background can not be translucent: #"
                    + Integer.toHexString(background));
        }
        if (Color.alpha(foreground) < 255) {
            // If the foreground is translucent, composite the foreground over the background
            foreground = compositeColors(foreground, background);
        }

        final double luminance1 = calculateLuminance(foreground) + 0.05;
        final double luminance2 = calculateLuminance(background) + 0.05;

        // Now return the lighter luminance divided by the darker luminance
        return Math.max(luminance1, luminance2) / Math.min(luminance1, luminance2);
    }

    /**
     * Calculates the minimum alpha value which can be applied to {@code background} so that would
     * have a contrast value of at least {@code minContrastRatio} when alpha blended to
     * {@code foreground}.
     *
     * @param foreground       the foreground color
     * @param background       the background color, opacity will be ignored
     * @param minContrastRatio the minimum contrast ratio
     * @return the alpha value in the range 0-255, or -1 if no value could be calculated
     */
    public static int calculateMinimumBackgroundAlpha(@ColorInt int foreground,
            @ColorInt int background, float minContrastRatio) {
        // Ignore initial alpha that the background might have since this is
        // what we're trying to calculate.
        background = setAlphaComponent(background, 255);
        final int leastContrastyColor = setAlphaComponent(foreground, 255);
        return binaryAlphaSearch(foreground, background, minContrastRatio, (fg, bg, alpha) -> {
            int testBackground = blendARGB(leastContrastyColor, bg, alpha/255f);
            // Float rounding might set this alpha to something other that 255,
            // raising an exception in calculateContrast.
            testBackground = setAlphaComponent(testBackground, 255);
            return calculateContrast(fg, testBackground);
        });
    }

    /**
     * Calculates the minimum alpha value which can be applied to {@code foreground} so that would
     * have a contrast value of at least {@code minContrastRatio} when compared to
     * {@code background}.
     *
     * @param foreground       the foreground color
     * @param background       the opaque background color
     * @param minContrastRatio the minimum contrast ratio
     * @return the alpha value in the range 0-255, or -1 if no value could be calculated
     */
    public static int calculateMinimumAlpha(@ColorInt int foreground, @ColorInt int background,
            float minContrastRatio) {
        if (Color.alpha(background) != 255) {
            throw new IllegalArgumentException("background can not be translucent: #"
                    + Integer.toHexString(background));
        }

        ContrastCalculator contrastCalculator = (fg, bg, alpha) -> {
            int testForeground = setAlphaComponent(fg, alpha);
            return calculateContrast(testForeground, bg);
        };

        // First lets check that a fully opaque foreground has sufficient contrast
        double testRatio = contrastCalculator.calculateContrast(foreground, background, 255);
        if (testRatio < minContrastRatio) {
            // Fully opaque foreground does not have sufficient contrast, return error
            return -1;
        }
        foreground = setAlphaComponent(foreground, 255);
        return binaryAlphaSearch(foreground, background, minContrastRatio, contrastCalculator);
    }

    /**
     * Calculates the alpha value using binary search based on a given contrast evaluation function
     * and target contrast that needs to be satisfied.
     *
     * @param foreground         the foreground color
     * @param background         the opaque background color
     * @param minContrastRatio   the minimum contrast ratio
     * @param calculator function that calculates contrast
     * @return the alpha value in the range 0-255, or -1 if no value could be calculated
     */
    private static int binaryAlphaSearch(@ColorInt int foreground, @ColorInt int background,
            float minContrastRatio, ContrastCalculator calculator) {
        // Binary search to find a value with the minimum value which provides sufficient contrast
        int numIterations = 0;
        int minAlpha = 0;
        int maxAlpha = 255;

        while (numIterations <= MIN_ALPHA_SEARCH_MAX_ITERATIONS &&
                (maxAlpha - minAlpha) > MIN_ALPHA_SEARCH_PRECISION) {
            final int testAlpha = (minAlpha + maxAlpha) / 2;

            final double testRatio = calculator.calculateContrast(foreground, background,
                    testAlpha);
            if (testRatio < minContrastRatio) {
                minAlpha = testAlpha;
            } else {
                maxAlpha = testAlpha;
            }

            numIterations++;
        }

        // Conservatively return the max of the range of possible alphas, which is known to pass.
        return maxAlpha;
    }

    /**
     * Convert RGB components to HSL (hue-saturation-lightness).
     * <ul>
     * <li>outHsl[0] is Hue [0 .. 360)</li>
     * <li>outHsl[1] is Saturation [0...1]</li>
     * <li>outHsl[2] is Lightness [0...1]</li>
     * </ul>
     *
     * @param r      red component value [0..255]
     * @param g      green component value [0..255]
     * @param b      blue component value [0..255]
     * @param outHsl 3-element array which holds the resulting HSL components
     */
    public static void RGBToHSL(@IntRange(from = 0x0, to = 0xFF) int r,
            @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b,
            @NonNull float[] outHsl) {
        final float rf = r / 255f;
        final float gf = g / 255f;
        final float bf = b / 255f;

        final float max = Math.max(rf, Math.max(gf, bf));
        final float min = Math.min(rf, Math.min(gf, bf));
        final float deltaMaxMin = max - min;

        float h, s;
        float l = (max + min) / 2f;

        if (max == min) {
            // Monochromatic
            h = s = 0f;
        } else {
            if (max == rf) {
                h = ((gf - bf) / deltaMaxMin) % 6f;
            } else if (max == gf) {
                h = ((bf - rf) / deltaMaxMin) + 2f;
            } else {
                h = ((rf - gf) / deltaMaxMin) + 4f;
            }

            s = deltaMaxMin / (1f - Math.abs(2f * l - 1f));
        }

        h = (h * 60f) % 360f;
        if (h < 0) {
            h += 360f;
        }

        outHsl[0] = constrain(h, 0f, 360f);
        outHsl[1] = constrain(s, 0f, 1f);
        outHsl[2] = constrain(l, 0f, 1f);
    }

    /**
     * Convert the ARGB color to its HSL (hue-saturation-lightness) components.
     * <ul>
     * <li>outHsl[0] is Hue [0 .. 360)</li>
     * <li>outHsl[1] is Saturation [0...1]</li>
     * <li>outHsl[2] is Lightness [0...1]</li>
     * </ul>
     *
     * @param color  the ARGB color to convert. The alpha component is ignored
     * @param outHsl 3-element array which holds the resulting HSL components
     */
    public static void colorToHSL(@ColorInt int color, @NonNull float[] outHsl) {
        RGBToHSL(Color.red(color), Color.green(color), Color.blue(color), outHsl);
    }

    /**
     * Convert HSL (hue-saturation-lightness) components to a RGB color.
     * <ul>
     * <li>hsl[0] is Hue [0 .. 360)</li>
     * <li>hsl[1] is Saturation [0...1]</li>
     * <li>hsl[2] is Lightness [0...1]</li>
     * </ul>
     * If hsv values are out of range, they are pinned.
     *
     * @param hsl 3-element array which holds the input HSL components
     * @return the resulting RGB color
     */
    @ColorInt
    public static int HSLToColor(@NonNull float[] hsl) {
        final float h = hsl[0];
        final float s = hsl[1];
        final float l = hsl[2];

        final float c = (1f - Math.abs(2 * l - 1f)) * s;
        final float m = l - 0.5f * c;
        final float x = c * (1f - Math.abs((h / 60f % 2f) - 1f));

        final int hueSegment = (int) h / 60;

        int r = 0, g = 0, b = 0;

        switch (hueSegment) {
            case 0:
                r = Math.round(255 * (c + m));
                g = Math.round(255 * (x + m));
                b = Math.round(255 * m);
                break;
            case 1:
                r = Math.round(255 * (x + m));
                g = Math.round(255 * (c + m));
                b = Math.round(255 * m);
                break;
            case 2:
                r = Math.round(255 * m);
                g = Math.round(255 * (c + m));
                b = Math.round(255 * (x + m));
                break;
            case 3:
                r = Math.round(255 * m);
                g = Math.round(255 * (x + m));
                b = Math.round(255 * (c + m));
                break;
            case 4:
                r = Math.round(255 * (x + m));
                g = Math.round(255 * m);
                b = Math.round(255 * (c + m));
                break;
            case 5:
            case 6:
                r = Math.round(255 * (c + m));
                g = Math.round(255 * m);
                b = Math.round(255 * (x + m));
                break;
        }

        r = constrain(r, 0, 255);
        g = constrain(g, 0, 255);
        b = constrain(b, 0, 255);

        return Color.rgb(r, g, b);
    }

    /**
     * Set the alpha component of {@code color} to be {@code alpha}.
     */
    @ColorInt
    public static int setAlphaComponent(@ColorInt int color,
            @IntRange(from = 0x0, to = 0xFF) int alpha) {
        if (alpha < 0 || alpha > 255) {
            throw new IllegalArgumentException("alpha must be between 0 and 255.");
        }
        return (color & 0x00ffffff) | (alpha << 24);
    }

    /**
     * Convert the ARGB color to its CIE Lab representative components.
     *
     * @param color  the ARGB color to convert. The alpha component is ignored
     * @param outLab 3-element array which holds the resulting LAB components
     */
    public static void colorToLAB(@ColorInt int color, @NonNull double[] outLab) {
        RGBToLAB(Color.red(color), Color.green(color), Color.blue(color), outLab);
    }

    /**
     * Convert RGB components to its CIE Lab representative components.
     *
     * <ul>
     * <li>outLab[0] is L [0 ...1)</li>
     * <li>outLab[1] is a [-128...127)</li>
     * <li>outLab[2] is b [-128...127)</li>
     * </ul>
     *
     * @param r      red component value [0..255]
     * @param g      green component value [0..255]
     * @param b      blue component value [0..255]
     * @param outLab 3-element array which holds the resulting LAB components
     */
    public static void RGBToLAB(@IntRange(from = 0x0, to = 0xFF) int r,
            @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b,
            @NonNull double[] outLab) {
        // First we convert RGB to XYZ
        RGBToXYZ(r, g, b, outLab);
        // outLab now contains XYZ
        XYZToLAB(outLab[0], outLab[1], outLab[2], outLab);
        // outLab now contains LAB representation
    }

    /**
     * Convert the ARGB color to its CIE XYZ representative components.
     *
     * <p>The resulting XYZ representation will use the D65 illuminant and the CIE
     * 2° Standard Observer (1931).</p>
     *
     * <ul>
     * <li>outXyz[0] is X [0 ...95.047)</li>
     * <li>outXyz[1] is Y [0...100)</li>
     * <li>outXyz[2] is Z [0...108.883)</li>
     * </ul>
     *
     * @param color  the ARGB color to convert. The alpha component is ignored
     * @param outXyz 3-element array which holds the resulting LAB components
     */
    public static void colorToXYZ(@ColorInt int color, @NonNull double[] outXyz) {
        RGBToXYZ(Color.red(color), Color.green(color), Color.blue(color), outXyz);
    }

    /**
     * Convert RGB components to its CIE XYZ representative components.
     *
     * <p>The resulting XYZ representation will use the D65 illuminant and the CIE
     * 2° Standard Observer (1931).</p>
     *
     * <ul>
     * <li>outXyz[0] is X [0 ...95.047)</li>
     * <li>outXyz[1] is Y [0...100)</li>
     * <li>outXyz[2] is Z [0...108.883)</li>
     * </ul>
     *
     * @param r      red component value [0..255]
     * @param g      green component value [0..255]
     * @param b      blue component value [0..255]
     * @param outXyz 3-element array which holds the resulting XYZ components
     */
    public static void RGBToXYZ(@IntRange(from = 0x0, to = 0xFF) int r,
            @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b,
            @NonNull double[] outXyz) {
        if (outXyz.length != 3) {
            throw new IllegalArgumentException("outXyz must have a length of 3.");
        }

        double sr = r / 255.0;
        sr = sr < 0.04045 ? sr / 12.92 : Math.pow((sr + 0.055) / 1.055, 2.4);
        double sg = g / 255.0;
        sg = sg < 0.04045 ? sg / 12.92 : Math.pow((sg + 0.055) / 1.055, 2.4);
        double sb = b / 255.0;
        sb = sb < 0.04045 ? sb / 12.92 : Math.pow((sb + 0.055) / 1.055, 2.4);

        outXyz[0] = 100 * (sr * 0.4124 + sg * 0.3576 + sb * 0.1805);
        outXyz[1] = 100 * (sr * 0.2126 + sg * 0.7152 + sb * 0.0722);
        outXyz[2] = 100 * (sr * 0.0193 + sg * 0.1192 + sb * 0.9505);
    }

    /**
     * Converts a color from CIE XYZ to CIE Lab representation.
     *
     * <p>This method expects the XYZ representation to use the D65 illuminant and the CIE
     * 2° Standard Observer (1931).</p>
     *
     * <ul>
     * <li>outLab[0] is L [0 ...1)</li>
     * <li>outLab[1] is a [-128...127)</li>
     * <li>outLab[2] is b [-128...127)</li>
     * </ul>
     *
     * @param x      X component value [0...95.047)
     * @param y      Y component value [0...100)
     * @param z      Z component value [0...108.883)
     * @param outLab 3-element array which holds the resulting Lab components
     */
    public static void XYZToLAB(@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_X) double x,
            @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Y) double y,
            @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Z) double z,
            @NonNull double[] outLab) {
        if (outLab.length != 3) {
            throw new IllegalArgumentException("outLab must have a length of 3.");
        }
        x = pivotXyzComponent(x / XYZ_WHITE_REFERENCE_X);
        y = pivotXyzComponent(y / XYZ_WHITE_REFERENCE_Y);
        z = pivotXyzComponent(z / XYZ_WHITE_REFERENCE_Z);
        outLab[0] = Math.max(0, 116 * y - 16);
        outLab[1] = 500 * (x - y);
        outLab[2] = 200 * (y - z);
    }

    /**
     * Converts a color from CIE Lab to CIE XYZ representation.
     *
     * <p>The resulting XYZ representation will use the D65 illuminant and the CIE
     * 2° Standard Observer (1931).</p>
     *
     * <ul>
     * <li>outXyz[0] is X [0 ...95.047)</li>
     * <li>outXyz[1] is Y [0...100)</li>
     * <li>outXyz[2] is Z [0...108.883)</li>
     * </ul>
     *
     * @param l      L component value [0...100)
     * @param a      A component value [-128...127)
     * @param b      B component value [-128...127)
     * @param outXyz 3-element array which holds the resulting XYZ components
     */
    public static void LABToXYZ(@FloatRange(from = 0f, to = 100) final double l,
            @FloatRange(from = -128, to = 127) final double a,
            @FloatRange(from = -128, to = 127) final double b,
            @NonNull double[] outXyz) {
        final double fy = (l + 16) / 116;
        final double fx = a / 500 + fy;
        final double fz = fy - b / 200;

        double tmp = Math.pow(fx, 3);
        final double xr = tmp > XYZ_EPSILON ? tmp : (116 * fx - 16) / XYZ_KAPPA;
        final double yr = l > XYZ_KAPPA * XYZ_EPSILON ? Math.pow(fy, 3) : l / XYZ_KAPPA;

        tmp = Math.pow(fz, 3);
        final double zr = tmp > XYZ_EPSILON ? tmp : (116 * fz - 16) / XYZ_KAPPA;

        outXyz[0] = xr * XYZ_WHITE_REFERENCE_X;
        outXyz[1] = yr * XYZ_WHITE_REFERENCE_Y;
        outXyz[2] = zr * XYZ_WHITE_REFERENCE_Z;
    }

    /**
     * Converts a color from CIE XYZ to its RGB representation.
     *
     * <p>This method expects the XYZ representation to use the D65 illuminant and the CIE
     * 2° Standard Observer (1931).</p>
     *
     * @param x X component value [0...95.047)
     * @param y Y component value [0...100)
     * @param z Z component value [0...108.883)
     * @return int containing the RGB representation
     */
    @ColorInt
    public static int XYZToColor(@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_X) double x,
            @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Y) double y,
            @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Z) double z) {
        double r = (x * 3.2406 + y * -1.5372 + z * -0.4986) / 100;
        double g = (x * -0.9689 + y * 1.8758 + z * 0.0415) / 100;
        double b = (x * 0.0557 + y * -0.2040 + z * 1.0570) / 100;

        r = r > 0.0031308 ? 1.055 * Math.pow(r, 1 / 2.4) - 0.055 : 12.92 * r;
        g = g > 0.0031308 ? 1.055 * Math.pow(g, 1 / 2.4) - 0.055 : 12.92 * g;
        b = b > 0.0031308 ? 1.055 * Math.pow(b, 1 / 2.4) - 0.055 : 12.92 * b;

        return Color.rgb(
                constrain((int) Math.round(r * 255), 0, 255),
                constrain((int) Math.round(g * 255), 0, 255),
                constrain((int) Math.round(b * 255), 0, 255));
    }

    /**
     * Converts a color from CIE Lab to its RGB representation.
     *
     * @param l L component value [0...100]
     * @param a A component value [-128...127]
     * @param b B component value [-128...127]
     * @return int containing the RGB representation
     */
    @ColorInt
    public static int LABToColor(@FloatRange(from = 0f, to = 100) final double l,
            @FloatRange(from = -128, to = 127) final double a,
            @FloatRange(from = -128, to = 127) final double b) {
        final double[] result = getTempDouble3Array();
        LABToXYZ(l, a, b, result);
        return XYZToColor(result[0], result[1], result[2]);
    }

    /**
     * Returns the euclidean distance between two LAB colors.
     */
    public static double distanceEuclidean(@NonNull double[] labX, @NonNull double[] labY) {
        return Math.sqrt(Math.pow(labX[0] - labY[0], 2)
                + Math.pow(labX[1] - labY[1], 2)
                + Math.pow(labX[2] - labY[2], 2));
    }

    private static float constrain(float amount, float low, float high) {
        return amount < low ? low : (amount > high ? high : amount);
    }

    private static int constrain(int amount, int low, int high) {
        return amount < low ? low : (amount > high ? high : amount);
    }

    private static double pivotXyzComponent(double component) {
        return component > XYZ_EPSILON
                ? Math.pow(component, 1 / 3.0)
                : (XYZ_KAPPA * component + 16) / 116;
    }

    /**
     * Blend between two ARGB colors using the given ratio.
     *
     * <p>A blend ratio of 0.0 will result in {@code color1}, 0.5 will give an even blend,
     * 1.0 will result in {@code color2}.</p>
     *
     * @param color1 the first ARGB color
     * @param color2 the second ARGB color
     * @param ratio  the blend ratio of {@code color1} to {@code color2}
     */
    @ColorInt
    public static int blendARGB(@ColorInt int color1, @ColorInt int color2,
            @FloatRange(from = 0.0, to = 1.0) float ratio) {
        final float inverseRatio = 1 - ratio;
        float a = Color.alpha(color1) * inverseRatio + Color.alpha(color2) * ratio;
        float r = Color.red(color1) * inverseRatio + Color.red(color2) * ratio;
        float g = Color.green(color1) * inverseRatio + Color.green(color2) * ratio;
        float b = Color.blue(color1) * inverseRatio + Color.blue(color2) * ratio;
        return Color.argb((int) a, (int) r, (int) g, (int) b);
    }

    /**
     * Blend between {@code hsl1} and {@code hsl2} using the given ratio. This will interpolate
     * the hue using the shortest angle.
     *
     * <p>A blend ratio of 0.0 will result in {@code hsl1}, 0.5 will give an even blend,
     * 1.0 will result in {@code hsl2}.</p>
     *
     * @param hsl1      3-element array which holds the first HSL color
     * @param hsl2      3-element array which holds the second HSL color
     * @param ratio     the blend ratio of {@code hsl1} to {@code hsl2}
     * @param outResult 3-element array which holds the resulting HSL components
     */
    public static void blendHSL(@NonNull float[] hsl1, @NonNull float[] hsl2,
            @FloatRange(from = 0.0, to = 1.0) float ratio, @NonNull float[] outResult) {
        if (outResult.length != 3) {
            throw new IllegalArgumentException("result must have a length of 3.");
        }
        final float inverseRatio = 1 - ratio;
        // Since hue is circular we will need to interpolate carefully
        outResult[0] = circularInterpolate(hsl1[0], hsl2[0], ratio);
        outResult[1] = hsl1[1] * inverseRatio + hsl2[1] * ratio;
        outResult[2] = hsl1[2] * inverseRatio + hsl2[2] * ratio;
    }

    /**
     * Blend between two CIE-LAB colors using the given ratio.
     *
     * <p>A blend ratio of 0.0 will result in {@code lab1}, 0.5 will give an even blend,
     * 1.0 will result in {@code lab2}.</p>
     *
     * @param lab1      3-element array which holds the first LAB color
     * @param lab2      3-element array which holds the second LAB color
     * @param ratio     the blend ratio of {@code lab1} to {@code lab2}
     * @param outResult 3-element array which holds the resulting LAB components
     */
    public static void blendLAB(@NonNull double[] lab1, @NonNull double[] lab2,
            @FloatRange(from = 0.0, to = 1.0) double ratio, @NonNull double[] outResult) {
        if (outResult.length != 3) {
            throw new IllegalArgumentException("outResult must have a length of 3.");
        }
        final double inverseRatio = 1 - ratio;
        outResult[0] = lab1[0] * inverseRatio + lab2[0] * ratio;
        outResult[1] = lab1[1] * inverseRatio + lab2[1] * ratio;
        outResult[2] = lab1[2] * inverseRatio + lab2[2] * ratio;
    }

    static float circularInterpolate(float a, float b, float f) {
        if (Math.abs(b - a) > 180) {
            if (b > a) {
                a += 360;
            } else {
                b += 360;
            }
        }
        return (a + ((b - a) * f)) % 360;
    }

    private static double[] getTempDouble3Array() {
        double[] result = TEMP_ARRAY.get();
        if (result == null) {
            result = new double[3];
            TEMP_ARRAY.set(result);
        }
        return result;
    }

    private interface ContrastCalculator {
        double calculateContrast(int foreground, int background, int alpha);
    }

}