computeSampleSize

转自:http://my.csdn.net/zljk000/code/detail/18212

computeSampleSize方法，返回一个合适的options.inSampleSize值

Java代码

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public class Util {

 

     /*

     * 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.

     *

     * The function returns a sample size based on the constraints.

     * Both size and minSideLength can be passed in as IImage.UNCONSTRAINED,

     * which indicates no care of the corresponding constraint.

     * The functions prefers returning a sample size that

     * generates a smaller bitmap, unless minSideLength = IImage.UNCONSTRAINED.

     *

     * 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.

     */

    publicstatic int computeSampleSize(BitmapFactory.Options options,

            intminSideLength, intmaxNumOfPixels) {

        intinitialSize = computeInitialSampleSize(options, minSideLength,

                maxNumOfPixels);

 

        introundedSize;

        if(initialSize <= 8) {

            roundedSize =1;

            while(roundedSize < initialSize) {

                roundedSize <<=1;

            }

        }else {

            roundedSize = (initialSize +7) / 8* 8;

        }

        returnroundedSize;

    }

     

    publicstatic int computeInitialSampleSize(BitmapFactory.Options options,

            intminSideLength, intmaxNumOfPixels) {

        doublew = options.outWidth;

        doubleh = options.outHeight;

        intlowerBound = (maxNumOfPixels == -1) ?1 :

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

        intupperBound = (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.

            returnlowerBound;

        }

 

        if((maxNumOfPixels == -1) &&

                (minSideLength == -1)) {

            return1;

        }else if(minSideLength == -1) {

            returnlowerBound;

        }else {

            returnupperBound;

        }

    }

     

}