Decode specific areas of image in Bitmapfactory?

Question

I'm working with GeoTiff/PNG files too large for handling as a whole in my code.

Is there any possibility to decode specific areas (e.g. given by two x,y coordinates) of a file in bitmapfactory? Haven't found anything looking similar at http://developer.android.com/reference/android/graphics/BitmapFactory.html(Android's developer reference).

Thanks!

---

With kcoppock's hint I've set up the following solution.

Though I'm wondering why rect needs to be initialized by Rect(left, bottom, right, top) instead of Rect(left, top, right, bottom)...

Example call:

Bitmap myBitmap = loadBitmapRegion(context, R.drawable.heightmap,
    0.08f, 0.32f, 0.13f, 0.27f);

Function:

public static Bitmap loadBitmapRegion(
    Context context, int resourceID,
    float regionLeft, float regionTop,
    float regionRight, float regionBottom) {

    // Get input stream for resource
    InputStream is = context.getResources().openRawResource(resourceID);

    // Set options
    BitmapFactory.Options opt = new BitmapFactory.Options();
    //opt.inPreferredConfig = Bitmap.Config.ARGB_8888; //standard

    // Create decoder
    BitmapRegionDecoder decoder = null;
    try {
        decoder = BitmapRegionDecoder.newInstance(is, false);
    } catch (IOException e) {
        e.printStackTrace();
    }

    // Get resource dimensions
    int h = decoder.getHeight();
    int w = decoder.getWidth();

    // Set region to decode
    Rect region = new Rect(
            Math.round(regionLeft*w), Math.round(regionBottom*h),
            Math.round(regionRight*w), Math.round(regionTop*h));

    // Return bitmap
    return decoder.decodeRegion(region, opt);

}

Answer 1

You should look into BitmapRegionDecoder. It seems to describe exactly the use case that you are looking for.

Answer 2

I don't know exactly what you mean by "Decode specific areas" but if by decoding you mean, to actually "copy" certain areas of a bitmap, what you can do is make use of canvas in order to get it as shown below:

        Bitmap bmpWithArea = Bitmap.createBitmap(widthDesired, heightDesired, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bmpWithArea);
        Rect area = new Rect(arealeft, areatop, arearight, areabottom);
        Rect actualSize = new Rect(0, 0, widthDesired, heightDesired);
        canvas.drawBitmap(bitmapWithAreaYouWantToGet, area, actual, paintIfAny);

        //And done, starting from this line "bmpWithArea" has the bmp that you wanted, you can assign it to ImageView and use it as regular bmp...

Hope this helps...

Regards!