BitmapFactory。Options.inSampleSize用法

BitmapFactory。Options.inSampleSize用法

BitmapFactory.decodeFile(imageFile);

用BitmapFactory解码一张图片时，有时会遇到该错误。这往往是由于图片过大造成的。要想正常使用，则需要分配更少的内存空间来存储。

BitmapFactory.Options.inSampleSize

设置恰当的inSampleSize可以使BitmapFactory分配更少的空间以消除该错误。inSampleSize的具体含义请参考SDK文档。例如：

BitmapFactory.Options opts = new BitmapFactory.Options();



opts.inSampleSize = 4;



Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

设置恰当的inSampleSize是解决该问题的关键之一。BitmapFactory.Options提供了另一个成员inJustDecodeBounds。

BitmapFactory.Options opts = new BitmapFactory.Options();



opts.inJustDecodeBounds = true;



Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

设置inJustDecodeBounds为true后，decodeFile并不分配空间，但可计算出原始图片的长度和宽度，即opts.width和opts.height。有了这两个参数，再通过一定的算法，即可得到一个恰当的inSampleSize。

查看Android源码，Android提供了一种动态计算的方法。

public 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(BitmapFactory.Options options,



        int minSideLength, int maxNumOfPixels) {



    double w = options.outWidth;



    double h = options.outHeight;







    int lowerBound = (maxNumOfPixels == -1) ? 1 :



            (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));



    int upperBound = (minSideLength == -1) ? 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 == -1) &&



            (minSideLength == -1)) {



        return 1;



    } else if (minSideLength == -1) {



        return lowerBound;



    } else {



        return upperBound;



    }



} 



使用该算法，就可动态计算出图片的inSampleSize。



BitmapFactory.Options opts = new BitmapFactory.Options();



opts.inJustDecodeBounds = true;



BitmapFactory.decodeFile(imageFile, opts);



   



opts.inSampleSize = computeSampleSize(opts, -1, 128*128);  



opts.inJustDecodeBounds = false;



try {



 Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts);



 imageView.setImageBitmap(bmp);



    } catch (OutOfMemoryError err) {



    }