Question about classification (and ENVI implementation)

From: Jonathan Greenberg (greenberg@ucdavis.edu)
Date: Thu Apr 29 2004 - 12:55:22 PDT

  • Next message: Mort Canty: "Re: Question about classification (and ENVI implementation)"

    Recently, I was running the rule classifier on some probability images and
    realized, much to my chagrin, that ENVI has a behavior which I thought is
    incorrect, and I was wondering what is the "real" answer to this situation.
    It deals with when you have ties in the max probability for two or more
    classes. For example:

    Class1,Class2,Class3
    .4,.2,.5
    0,0,0
    .2,.4,.4
    .4,.4,.4

    ENVI will produce the following class map:
    Class3
    Class1
    Class2
    Class1
     -- in the case of a tie, ENVI defaults to the lowest class number. It
    turns out, this behavior IS documented, but this doesn't mean the behavior
    is legitimate. It seems to me that the "correct" output should be:
    Class3
    Class0
    Class0
    Class0

    -> where class0 is unclassified. I suppose my question is a) from a
    classification standpoint, which of these two outputs is "legit", b) how do
    I get envi to produce the 2nd output (what I think is "correct") without
    significant programming, and c) how many of you realized ENVI was doing
    this?

    --j 

    -- 
Jonathan Greenberg
Graduate Group in Ecology, U.C. Davis
http://www.cstars.ucdavis.edu/~jongreen
http://www.cstars.ucdavis.edu
AIM: jgrn307 or jgrn3007
MSN: jgrn307@msn.com or jgrn3007@msn.com

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