Judging vs "pointing out a person's fault"

Matthew 7
Do not judge, or you too will be judged. For in the same way you judge others, you will be judged, and with the measure you use, it will be measured to you.
[And so on and so forth]

Matthew 18:15
If your brother [or sister] sins against you, [some manuscripts do not have 'against you'] go and show him [or her] his[her] fault, just between the two of you..........
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Judge : to form a judgement or opinion of; decide upon critically
http://dictionary.reference.com/browse/judge?s=t

"Pointing out a person's fault" and "judging" are not the same, but there is only a thin(and blurry) line separating these two things.

So how do we differentiate what is "judging" and what is "pointing out a person's fault"?