 The input is only lossless in the 4-diode circuit if only one button is pressed at a time, or if certain problematic multiple key presses are avoided.In the 12-diode circuit, this is not an issue, and there is always a one-to-one correspondence between button presses and input data.However, there are so many diodes that are required to use the method (especially for larger arrays) that there is generally no cost savings over the traditional row-column scan method, unless for some reason the cost of a diode is only a fraction of the cost of an I/O pin, where that fraction is one over the number of I/O lines.