docs: public static GrayU8 bitmapToGray( Bitmap input , GrayU8 output , byte[] storage ) {
  		if( output == null ) {
  			output = new GrayU8( input.getWidth() , input.getHeight() );
  		} else {
  			output.reshape(input.getWidth(), input.getHeight());
  		}
  
  		
  		if( storage == null )
  			storage = declareStorage(input,null);
  		input.copyPixelsToBuffer(ByteBuffer.wrap(storage));
  		
  		ImplConvertBitmap.arrayToGray(storage, input.getConfig(), output);
  		
  		return output;
  	}