BitmapUtil.java

package com.yuzhi.fine.utils;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

/**
 * Created by tiansj on 15/11/16.
 */
public class BitmapUtil {

    private static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;
            while ((halfHeight / inSampleSize) > reqHeight && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }
        }
        return inSampleSize;
    }

    // 如果是放大图片，filter决定是否平滑，如果是缩小图片，filter无影响
    private static Bitmap createScaleBitmap(Bitmap src, int dstWidth, int dstHeight) {
        Bitmap dst = Bitmap.createScaledBitmap(src, dstWidth, dstHeight, false);
        if (src != dst) {   // 如果没有缩放，那么不回收
            src.recycle();  // 释放Bitmap的native像素数组
        }
        return dst;
    }

    // 从Resources中加载图片
    public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options); // 读取图片长款
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // 计算inSampleSize
        options.inJustDecodeBounds = false;
        Bitmap src = BitmapFactory.decodeResource(res, resId, options); // 载入一个稍大的缩略图
        return createScaleBitmap(src, reqWidth, reqHeight); // 进一步得到目标大小的缩略图
    }

    // 从sd卡上加载图片
    public static Bitmap decodeSampledBitmapFromSd(String pathName, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(pathName, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        Bitmap src = BitmapFactory.decodeFile(pathName, options);
        return createScaleBitmap(src, reqWidth, reqHeight);
    }
}