//创建一个Options,用于保存图片的参数 BitmapFactory.Options options = new BitmapFactory.Options(); //设置是否只读取图片的参数信息 options.inJustDecodeBounds = true; //由于inJustDecodeBounds被设置为了true,此处只会获得图片的参数信息 //而不会读取到Bitmap对象,也就不会占用内存 BitmapFactory.decodeResource(getResources(), R.id.myimage, options); //获得图片的宽高以及类型 int imageHeight = options.outHeight; int imageWidth = options.outWidth; String imageType = options.outMimeType;

public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {// Raw height and width of image// 图片的原始宽高final int height = options.outHeight;final int width = options.outWidth;// 默认缩放比例为1int inSampleSize = 1;// 如果原始宽高其中之一大于指定的宽高,则需要计算缩放比例// 否则,直接使用原图if (height > reqHeight || width > reqWidth) {// 将图片缩小到一半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.// 计算inSampleSize的值,该值是2的次方,并且能够保证图片的宽高大于指定的宽高while ((halfHeight / inSampleSize) > reqHeight&& (halfWidth / inSampleSize) > reqWidth) {inSampleSize *= 2;}}return inSampleSize;
}

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,int reqWidth, int reqHeight) {// First decode with inJustDecodeBounds=true to check dimensions// 此处将inJustDecodeBounds设置为true,则只解析图片的尺寸等信息,而不生成Bitmapfinal BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeResource(res, resId, options);// Calculate inSampleSize// 此处计算需要的缩放值inSampleSizeoptions.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);// Decode bitmap with inSampleSize set//将inJustDecodeBounds设置为false,以便于解析图片生成Bitmapoptions.inJustDecodeBounds = false;return BitmapFactory.decodeResource(res, resId, options);
}