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/*
* 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.launcher3.graphics;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.util.SparseArray;
import java.util.Arrays;
/**
* Utility class for extracting colors from a bitmap.
*/
public class ColorExtractor {
private final int NUM_SAMPLES = 20;
private final float[] mTmpHsv = new float[3];
private final float[] mTmpHueScoreHistogram = new float[360];
private final int[] mTmpPixels = new int[NUM_SAMPLES];
private final SparseArray<Float> mTmpRgbScores = new SparseArray<>();
/**
* This picks a dominant color, looking for high-saturation, high-value, repeated hues.
* @param bitmap The bitmap to scan
*/
public int findDominantColorByHue(Bitmap bitmap) {
return findDominantColorByHue(bitmap, NUM_SAMPLES);
}
/**
* This picks a dominant color, looking for high-saturation, high-value, repeated hues.
* @param bitmap The bitmap to scan
*/
public int findDominantColorByHue(Bitmap bitmap, int samples) {
final int height = bitmap.getHeight();
final int width = bitmap.getWidth();
int sampleStride = (int) Math.sqrt((height * width) / samples);
if (sampleStride < 1) {
sampleStride = 1;
}
// This is an out-param, for getting the hsv values for an rgb
float[] hsv = mTmpHsv;
Arrays.fill(hsv, 0);
// First get the best hue, by creating a histogram over 360 hue buckets,
// where each pixel contributes a score weighted by saturation, value, and alpha.
float[] hueScoreHistogram = mTmpHueScoreHistogram;
Arrays.fill(hueScoreHistogram, 0);
float highScore = -1;
int bestHue = -1;
int[] pixels = mTmpPixels;
Arrays.fill(pixels, 0);
int pixelCount = 0;
for (int y = 0; y < height; y += sampleStride) {
for (int x = 0; x < width; x += sampleStride) {
int argb = bitmap.getPixel(x, y);
int alpha = 0xFF & (argb >> 24);
if (alpha < 0x80) {
// Drop mostly-transparent pixels.
continue;
}
// Remove the alpha channel.
int rgb = argb | 0xFF000000;
Color.colorToHSV(rgb, hsv);
// Bucket colors by the 360 integer hues.
int hue = (int) hsv[0];
if (hue < 0 || hue >= hueScoreHistogram.length) {
// Defensively avoid array bounds violations.
continue;
}
if (pixelCount < samples) {
pixels[pixelCount++] = rgb;
}
float score = hsv[1] * hsv[2];
hueScoreHistogram[hue] += score;
if (hueScoreHistogram[hue] > highScore) {
highScore = hueScoreHistogram[hue];
bestHue = hue;
}
}
}
SparseArray<Float> rgbScores = mTmpRgbScores;
rgbScores.clear();
int bestColor = 0xff000000;
highScore = -1;
// Go back over the RGB colors that match the winning hue,
// creating a histogram of weighted s*v scores, for up to 100*100 [s,v] buckets.
// The highest-scoring RGB color wins.
for (int i = 0; i < pixelCount; i++) {
int rgb = pixels[i];
Color.colorToHSV(rgb, hsv);
int hue = (int) hsv[0];
if (hue == bestHue) {
float s = hsv[1];
float v = hsv[2];
int bucket = (int) (s * 100) + (int) (v * 10000);
// Score by cumulative saturation * value.
float score = s * v;
Float oldTotal = rgbScores.get(bucket);
float newTotal = oldTotal == null ? score : oldTotal + score;
rgbScores.put(bucket, newTotal);
if (newTotal > highScore) {
highScore = newTotal;
// All the colors in the winning bucket are very similar. Last in wins.
bestColor = rgb;
}
}
}
return bestColor;
}
}
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