ImageResizer.java 文件源码

/**
 * 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)
}