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 #39375 is a reply to message #39374]

Wed, 12 May 2004 08:02

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

Craig Markwardt wrote:
> David Fanning <david@dfanning.com> writes:
>
>
>> 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) )
>
>
> Hey David, I'll pile on too. The problem I see with the above
> expression is that there could be an offset between the two images,
> which you are including in your TOTAL expression, and hence biasing
> the rms value. How about the following instead?

The Root Mean Square difference between two images is defined as the
square ROOT of the MEAN of the SQUAREd differences between the images.
If there's an offset between the two images, that offset is supposed to
be squared, and is supposed to contribute to the mean, and therefore to
an increase in the RMS error.

> rms_error = stddev(img_1 - img2)

That's a different statistic, also useful, but it's not the RMS error.

Note: if there's an offset difference, there might also be a scaling
difference. Then the most appropriate statistic to use gets even more
complicated.

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: Sun Oct 12 09:25:45 PDT 2025

Total time taken to generate the page: 9.35976 seconds