计算图片缩小比例

    /**     * Calculate an inSampleSize for use in a {@link android.graphics.BitmapFactory.Options} object when decoding     * bitmaps using the decode* methods from {@link android.graphics.BitmapFactory}. This implementation calculates     * the closest inSampleSize that is a power of 2 and will result in the final decoded bitmap     * having a width and height equal to or larger than the requested width and height.     *     * @param options An options object with out* params already populated (run through a decode*     *            method with inJustDecodeBounds==true     * @param reqWidth The requested width of the resulting bitmap     * @param reqHeight The requested height of the resulting bitmap     * @return The value to be used for inSampleSize     */    public static int calculateInSampleSize(BitmapFactory.Options options,            int reqWidth, int reqHeight) {        // BEGIN_INCLUDE (calculate_sample_size)        // Raw height and width of image        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;            // Calculate the largest inSampleSize value that is a power of 2 and keeps both            // height and width larger than the requested height and width.            while ((halfHeight / inSampleSize) > reqHeight                    && (halfWidth / inSampleSize) > reqWidth) {                inSampleSize *= 2;            }            // This offers some additional logic in case the image has a strange            // aspect ratio. For example, a panorama may have a much larger            // width than height. In these cases the total pixels might still            // end up being too large to fit comfortably in memory, so we should            // be more aggressive with sample down the image (=larger inSampleSize).            long totalPixels = width * height / inSampleSize;            // Anything more than 2x the requested pixels we'll sample down further            final long totalReqPixelsCap = reqWidth * reqHeight * 2;            while (totalPixels > totalReqPixelsCap) {                inSampleSize *= 2;                totalPixels /= 2;            }        }        return inSampleSize;        // END_INCLUDE (calculate_sample_size)    }
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