// width height 实际需要的图片尺寸，为了保证裁剪的图片不变形，最好还是算一下缩放比例，这里就不写了
public static Bitmap loadBitmap(String url, int width, int height)
{
Bitmap bitmap = null;
if (url == null || !new File(url).exists()) return bitmap;
try
{
BitmapFactory.Options opts = new BitmapFactory.Options();
opts.inJustDecodeBounds = true;
BitmapFactory.decodeFile(url, opts);
opts.inSampleSize = calculateSampleSize(opts, width, height);
opts.inJustDecodeBounds = false;
opts.inPreferredConfig = Bitmap.Config.RGB_565;
opts.inPurgeable = true;
opts.inInputShareable = true;
bitmap = BitmapFactory.decodeStream(new FileInputStream(url), null, opts);
bitmap = ThumbnailUtils.extractThumbnail(bitmap, width, height);
return bitmap;
}
catch (Exception e)
{
e.printStackTrace();
}
return bitmap;
}
private static int calculateSampleSize(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;
}sample size就是压缩比例，本质上就是设置恰当的sample size将大的图片尺寸转成相等或略大于我们需要的实际图片尺寸。
inSampleSize*2 是因为官方文档里面提到2的乘方效率最高。
