Converting Positive Logic to Negative logic. 7 Segment Decoder
That is part of the truth table for a 7-segment decoder that would sink current for segments that are on (for example, to drive a common-anode LED display with open-drain or open-collector outputs). An example of that kind of decoder is the SN7447. The output is '0' for a segment that is on.



If you were sourcing current (for example to drive a common-cathode LED display with emitter followers) then you'd want a '1' wherever the segment is on (the inverse of the above). An example of that kind of decoder is the CD4511.