From left to right - 1-bit bitonal, 8-bit grayscale, and 24-bit color image. https://gyazo.com/4bcbc93350554fdb163a2b8a37e8229a (even easier, the image of the letters is 1 bit, the image of the street is 8 bit and the image of the child is 24) remember that one bit is mandatory only for active ones, then you can modify the alpha in the engine, in your case for example put one image on top of another in layers and play with the opacity (alpha) to get grays :)