Creating an empty bitmap and drawing though canvas in Android

This is probably simpler than you're thinking:

int w = WIDTH_PX, h = HEIGHT_PX;

Bitmap.Config conf = Bitmap.Config.ARGB_8888; // see other conf types
Bitmap bmp = Bitmap.createBitmap(w, h, conf); // this creates a MUTABLE bitmap
Canvas canvas = new Canvas(bmp);

// ready to draw on that bitmap through that canvas

Here's the official documentation on the topic: Custom Drawing

Do not use Bitmap.Config.ARGB_8888

Instead use int w = WIDTH_PX, h = HEIGHT_PX;

Bitmap.Config conf = Bitmap.Config.ARGB_4444; // see other conf types
Bitmap bmp = Bitmap.createBitmap(w, h, conf); // this creates a MUTABLE bitmap
Canvas canvas = new Canvas(bmp);

// ready to draw on that bitmap through that canvas

ARGB_8888 can land you in OutOfMemory issues when dealing with more bitmaps or large bitmaps. Or better yet, try avoiding usage of ARGB option itself.