comp.lang.idl-pvwave archive: archive » Re: divide by zero problems

Home » Public Forums » archive » Re: divide by zero problems

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

Re: divide by zero problems [message #15333]

Thu, 13 May 1999 00:00

edward.s.meinel
Messages: 12
Registered: May 1999

Junior Member

C'mon guys, this is IDL not C...

Mark Rehbein <mrehbein@aims.gov.au> wrote:

> Basically, my images have cloud pixels that I have changed to a zero
> value.

OK so far...

> I also have a mask of the image that has values 1 for good pixel
> and 0 for bad pixels (cloud).

So you have new_image = image*mask

> I then add all my images together to get
> a "sum image" and add all my masks together to get a "sum mask".

Oh, then its

FOR i = 0, number_of_images-1 DO BEGIN
image_ sum = image_sum + image[*, *, i]*mask[*, *, i]
mask_sum = mask_sum + mask[*, *, i]
END

> Now to composite or average the images I do the following:
>
> composite=sum image/ sum mask.

i.e., you want to normalize the result. The you should use
something like:

composite = image_sum/(mask_sum + (mask_sum EQ 0))

> In fact I get whole image of
> NaN's in my composite even though my sum image and sum mask have
> decent values in them.

What is the TYPE of image? How many images? image_sum should be declared
at least one TYPE higher than image (if image is BYTE then image_sum
should be INTEGER; if image is INTEGER then image_sum should be LONG;
etc.). If there are more than 256 images then mask_sum should be
declared INTEGER.

Ed Meinel

--== Sent via Deja.com http://www.deja.com/ ==--
---Share what you know. Learn what you don't.---

Report message to a moderator

[Message index]

		Re: divide by zero problems By: edward.s.meinel on Thu, 13 May 1999 00:00
		Re: divide by zero problems By: <asowter on Thu, 13 May 1999 00:00
		Re: divide by zero problems By: korpela on Tue, 11 May 1999 00:00
		Re: divide by zero problems By: davidf on Tue, 11 May 1999 00:00

Previous Topic:	Making an array of structures containing pointers
Next Topic:	coherence test implementation

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 15:47:51 PDT 2025

Total time taken to generate the page: 0.87875 seconds