Incorrect image dimensions in android when using Bitmap

Question

I have.png image file stored as a resource in my android application. In my code, i am allocationg new Bitmap instance from that image as follow:

Bitmap img = BitmapFactory.decodeResource(getResources(), R.drawable.imgName);

But when I read the image dimensions from the Bitmap object using getWight() and getHeight() methods,

int width = img.getWidth();
int height = img.getHeight();

I am getting different results from the original image... Can some one explain me what am I missing, and how can I retreive the image size?

(My project is complied with android 2.2 - API 8)

Edit: Ok - found out how to get the real dimensions: setting inJustDecodeBounds property of the BitmapFactory.Options class to true as follow:

BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(getResources(), R.drawable.imgName, options);
    width = options.outWidth;
    height = options.outHeight;

The problem now is that the decoder returns null when we send Options argument, so I need to decode again like I did before (without Options argument...) to retrieve Bitmap instance -bizarre, isnt it?

Answer 1

To get exact resource image use:

    BitmapFactory.Options o = new Options();
    o.inScaled = false;
    Bitmap watermark = BitmapFactory.decodeResource(context.getResources(), id, o);

This turns off the automatic screen density scaling.

Update: I'm sure you realized this by now, but inJustDecodeBounds does just that, it finds the dimensions. You will not get an image. That option is generally for doing custom scaling. You end up calling decodeResource twice, the second time setting:

options.inJustDecodeBounds = false;

and making any adjustments to the options based on your:

width = options.outWidth;
height = options.outHeight;

Answer 2

Android scales your image for different densities (in a way for different screen resolutions and sizes). Place a separate copy of your image in drawable-ldpi, drawable-hdpi,drawable-xhdpi , drawable folders.