Android Bitmap Size Get computeSampleSize(int width, int height, int minSideLength, int maxNumOfPixels)

Description

Compute the sample size as a function of minSideLength and maxNumOfPixels.

Declaration

public static int computeSampleSize(int width, int height,
        int minSideLength, int maxNumOfPixels)

Method Source Code

//package com.java2s;

import android.graphics.BitmapFactory;

public class Main {
    public static final int UNCONSTRAINED = -1;

    /**//from  w  w  w  .  ja  v  a 2 s .c  o m
     * Compute the sample size as a function of minSideLength
     * and maxNumOfPixels.
     * minSideLength is used to specify that minimal width or height of a
     * bitmap.
     * maxNumOfPixels is used to specify the maximal size in pixels that is
     * tolerable in terms of memory usage.
     * <p/>
     * The function returns a sample size based on the constraints.
     * Both size and minSideLength can be passed in as UNCONSTRAINED,
     * which indicates no care of the corresponding constraint.
     * The functions prefers returning a sample size that
     * generates a smaller bitmap, unless minSideLength = UNCONSTRAINED.
     * <p/>
     * Also, the function rounds up the sample size to a power of 2 or multiple
     * of 8 because BitmapFactory only honors sample size this way.
     * For example, BitmapFactory downsamples an image by 2 even though the
     * request is 3. So we round up the sample size to avoid OOM.
     */
    public static int computeSampleSize(int width, int height,
            int minSideLength, int maxNumOfPixels) {
        int initialSize = computeInitialSampleSize(width, height,
                minSideLength, maxNumOfPixels);

        return initialSize <= 8 ? nextPowerOf2(initialSize)
                : (initialSize + 7) / 8 * 8;
    }

    public static int computeSampleSize(float scale) {
        assertTrue(scale > 0);
        int initialSize = Math.max(1, (int) Math.ceil(1 / scale));
        return initialSize <= 8 ? nextPowerOf2(initialSize)
                : (initialSize + 7) / 8 * 8;
    }

    private static int computeSampleSize(BitmapFactory.Options options,
            int minSideLength, int maxNumOfPixels) {
        int initialSize = computeInitialSampleSize(options, minSideLength,
                maxNumOfPixels);

        int roundedSize;
        if (initialSize <= 8) {
            roundedSize = 1;
            while (roundedSize < initialSize) {
                roundedSize <<= 1;
            }
        } else {
            roundedSize = (initialSize + 7) / 8 * 8;
        }
        return roundedSize;
    }

    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 {
            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;
        }
    }

    private static int nextPowerOf2(int n) {
        if (n <= 0 || n > (1 << 30))
            throw new IllegalArgumentException();
        n -= 1;
        n |= n >> 16;
        n |= n >> 8;
        n |= n >> 4;
        n |= n >> 2;
        n |= n >> 1;
        return n + 1;
    }

    private static void assertTrue(boolean cond) {
        if (!cond) {
            throw new AssertionError();
        }
    }
}

Android Bitmap Size Get computeSampleSize(int width, int height, int minSideLength, int maxNumOfPixels)

Description

Declaration

Method Source Code

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