Here you can find the source of computeInitialSampleSize( BitmapFactory.Options options, int minSideLength, int maxNumOfPixels)
private static int computeInitialSampleSize( BitmapFactory.Options options, int minSideLength, int maxNumOfPixels)
//package com.java2s; import android.graphics.BitmapFactory; public class Main { public static final int UNCONSTRAINED = -1; private static int computeInitialSampleSize(int w, int h, int minSideLength, int maxNumOfPixels) { if (maxNumOfPixels == UNCONSTRAINED && minSideLength == UNCONSTRAINED) return 1; int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 : (int) Math .ceil(Math.sqrt((double) (w * h) / maxNumOfPixels)); if (minSideLength == UNCONSTRAINED) { return lowerBound; } else {// w w w . j av a 2 s .com int sampleSize = Math.min(w / minSideLength, h / minSideLength); return Math.max(sampleSize, lowerBound); } } private static int computeInitialSampleSize( BitmapFactory.Options options, int minSideLength, int maxNumOfPixels) { double w = options.outWidth; double h = options.outHeight; int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 : (int) Math .ceil(Math.sqrt(w * h / maxNumOfPixels)); int upperBound = (minSideLength == UNCONSTRAINED) ? 128 : (int) Math.min(Math.floor(w / minSideLength), Math.floor(h / minSideLength)); if (upperBound < lowerBound) { // return the larger one when there is no overlapping zone. return lowerBound; } if ((maxNumOfPixels == UNCONSTRAINED) && (minSideLength == UNCONSTRAINED)) { return 1; } else if (minSideLength == UNCONSTRAINED) { return lowerBound; } else { return upperBound; } } }