Android 图片缩放

//创建一直合适的空白，大小100*100的图片RGB_565会使透明图片变黑建议用ARGB_8888
Bitmap newBitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.RGB_565);
//初始化画布
Canvas canvas = new Canvas(newBitmap);
//将图片缩小到合适位置
canvas.drawBitmap(bitmap, null, new RectF(0, 0, 100, 100), null);
//通过(BitmapDrawable)转换成BitmapDrawable因为Drawable是BitmapDrawable的父类所以直接转换为Drawable
BitmapDrawable bitmapDrawable = new BitmapDrawable(getResources(),newBitmap);
//防止oom回收图片
bitmap.recycle(); 

int width = bitmap.getWidth();
int height = origin.getHeight();
Matrix matrix = new Matrix();
matrix.preScale(ratio, ratio);
Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
origin.recycle();