If you want to copy the pixels of the bitmap to a byte array, the easiest way is:
int height = bitmapFoo.getHeight();
int width = bitmapFoo.getWidth();
pixels = new int[height * width];
bitmapFoo.copyPixelsToBuffer(pixels);
I should warn you that you will have to handle this with care, any other way you will get OutOfMemoryError.
To get All Pixels
bitmapFoo.copyPixelsToBuffer(pixels);
or
bitmapFoo.getPixels(pixels, 0, width, 0, 0, width, height);
To get One Pixel
The two arguments must be two integers within the range [0, getWidth()-1] and [0, getHeight()-1]
int pix = bitmapFoo.getPixel(x, y);