comp.lang.idl-pvwave archive: archive

Home » Public Forums » archive » Re: RMS error

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: RMS error [message #39395 is a reply to message #39392]

Tue, 11 May 2004 15:34

Rick Towler
Messages: 821
Registered: August 1998

Senior Member

"David Fanning" wrote ...
> Julio writes:
>
>> I'd like to calculate Root Mean Square error using a base image and a
>> secondary image. How can I do that? Clues are welcome!
>
> rms_error = Sqrt( Total((img_1 - img2)^2)/N_Elements(img_1) )

A couple of questions:

1) Shouldn't you first cast img_1 and img_2 to something other than byte?
Subtracting byte arrays will result in points that wrap:

IDL> print, 213B-215B
254

When you really want:

IDL> print, 213s-215s
-2

2) Is this correct for true color images? Do you total the square of the
differences for each color plane or do you total the square of the sum of
the differences for each plane? That is:

IDL> print, TOTAL((img_1 - img_2)^2)
56825.0

or:

IDL> dr=reform(img_1[0,*,*] - img_2[0,*,*])
IDL> dg=reform(img_1[1,*,*] - img_2[1,*,*])
IDL> db=reform(img_1[2,*,*] - img_2[2,*,*])

IDL> print, total((dR + dG + dB)^2)
170325.

Now that I think about it the first approach looks correct but since I am
not an image analyst and I don't have even the most basic of references I
thought I would ask.

-Rick

Report message to a moderator

[Message index]

		Re: RMS error By: David Fanning on Thu, 13 May 2004 06:36
		Re: RMS error By: julio on Thu, 13 May 2004 06:22
		Re: RMS error By: Craig Markwardt on Wed, 12 May 2004 08:11
		Re: RMS error By: James Kuyper on Wed, 12 May 2004 08:02
		Re: RMS error By: Paul Van Delst[1] on Wed, 12 May 2004 07:56
		Re: RMS error By: David Fanning on Wed, 12 May 2004 07:42
		Re: RMS error By: Craig Markwardt on Wed, 12 May 2004 07:13
		Re: RMS error By: David Fanning on Tue, 11 May 2004 16:23
		Re: RMS error By: Rick Towler on Tue, 11 May 2004 15:34
		Re: RMS error By: David Fanning on Tue, 11 May 2004 14:14

Previous Topic:	Re: graphics_level
Next Topic:	IDL - fundamental question about image display

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Oct 11 23:07:45 PDT 2025

Total time taken to generate the page: 1.76173 seconds