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Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? [message #34744 is a reply to message #34743]

Fri, 11 April 2003 20:02

rmoss4
Messages: 21
Registered: October 2002

Junior Member

Um, that should have been

( b1 - b2 ) gt 0 = 1B i.e. ( b1 - b2 ) = -1 = 255B > 0 = 1

Nevertheless, the point is the same: it is the byte arithmetic that is
causing your confusion.

R

Robert Moss wrote:
> That's what it is. Trust me on this. Here's an example:
>
> Take a single pixel in each band, i.e.
>
> b1 = 17B
> b2 = 18B
>
> Remember, these are both bytes.
>
> Then you get
>
> ( b1 gt b2 ) = 0B
> ( b1 - b2 ) gt 0 = 255B ( b1 - b2 ) = -1 = 255B > 0
>
> Robert Moss, PhD
>
>
>
> xinhai68 wrote:
>
>> I do not think so. You could try using ENVI's self-contained example
>> bhtmref.img to do "b1 gt b2" and "(b1-b2)gt 0" to see the different
>> result.
>
>

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[Message index]

		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: rmoss4 on Sat, 12 April 2003 08:25
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: cshen on Sat, 12 April 2003 02:21
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: David Fanning on Fri, 11 April 2003 20:29
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: rmoss4 on Fri, 11 April 2003 20:02
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: rmoss4 on Fri, 11 April 2003 19:59
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: cshen on Fri, 11 April 2003 17:59
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: rmoss4 on Fri, 11 April 2003 07:10
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: cshen on Thu, 10 April 2003 22:48
		Re: ENVI band math: "b1 gt b2 " , "(b1-b2) gt 0" same or not? By: rmoss4 on Thu, 10 April 2003 19:19

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