Old question, but it might still interest people.
Short anwser :
qemu -nographic -serial mon:stdio -append 'console=ttyS0' binary.img
ttyS0 valid on most PC. it would be something different on ARM system.
Then the serial port and the QEMU are multiplexed on your output. You can switch between them with ctrl-A + C + ENTER.
Long answer: check this blog, it’s awesome.