| Re: Search and Replace in 2D Array (Image) [message #66652] |
Thu, 28 May 2009 13:34 |
vikramivatury
Messages: 24
Registered: May 2009
|
Junior Member |
|
|
On May 28, 4:19 pm, "Jean H." <jghas...@DELTHIS.ucalgary.ANDTHIS.ca>
wrote:
> vikramivat...@gmail.com wrote:
>> Hello,
>
>> I have an image "m" which is [1229 x 1229] pixels that contains 1's
>> and 0's. I also have an image "img" which is [1229 x 1229] that
>> contains pixel IDs. For every 1 in image "m" it corresponds to a
>> certain pixel ID in image "img". I am trying to write a loop in IDL
>> that scans through the pixels of image "m" and when its get to a 1,
>> spit out its information from "img". I used the 'where' function (w =
>> where m gt 1.........ids = img(w))
>
> should be GE or EQ, not GT, or you will never have the ones selected
>
> and that worked fine in outputting
>
>> a 1D array of 1510441 pixels, but I am trying to do it for a 2D array
>> using loops.
>
>> img = read_tiff('NP.tif')
>> ids = fltarr(1229,1229)
>
>> for i = 0,1228 do begin
>> for j = 0,1228 do begin
>> if (m(i,j) eq 1.) then begin
>
> Be careful here. Don't use a float if your data is byte/integer. If it
> is of type float, you must do "where X-1.0 lt epsilon"... read David
> Fanning's "the sky is falling" article
>
>> ids(i,j) = img(m(i,j))
>
> This will always be equal to 1. Are you sure you want to subset m here?
>
>> endif
>> endfor
>> endfor
>
>> Any suggestions would be great.
>
>> Thanks,
>> Vikram
>
> "where" remains your friend here.
>
> img = read_tiff('NP.tif')
> ids = fltarr(1229,1229)
> OneIDX = where(m eq 1)
> ids[oneIDX] = img[oneIDX]
>
> If you really want, you can convert back the 1D index to 2D with
> ARRAY_INDICES, but it changes nothing to the above.
>
> Jean
Great! Thats exactly what I wanted. Thanks Jean.
-Vikram
|
|
|
|
| Re: Search and Replace in 2D Array (Image) [message #66653 is a reply to message #66652] |
Thu, 28 May 2009 13:19  |
Jean H.
Messages: 472
Registered: July 2006
|
Senior Member |
|
|
vikramivatury@gmail.com wrote:
> Hello,
>
> I have an image "m" which is [1229 x 1229] pixels that contains 1's
> and 0's. I also have an image "img" which is [1229 x 1229] that
> contains pixel IDs. For every 1 in image "m" it corresponds to a
> certain pixel ID in image "img". I am trying to write a loop in IDL
> that scans through the pixels of image "m" and when its get to a 1,
> spit out its information from "img". I used the 'where' function (w =
> where m gt 1.........ids = img(w))
should be GE or EQ, not GT, or you will never have the ones selected
and that worked fine in outputting
> a 1D array of 1510441 pixels, but I am trying to do it for a 2D array
> using loops.
>
> img = read_tiff('NP.tif')
> ids = fltarr(1229,1229)
>
> for i = 0,1228 do begin
> for j = 0,1228 do begin
> if (m(i,j) eq 1.) then begin
Be careful here. Don't use a float if your data is byte/integer. If it
is of type float, you must do "where X-1.0 lt epsilon"... read David
Fanning's "the sky is falling" article
> ids(i,j) = img(m(i,j))
This will always be equal to 1. Are you sure you want to subset m here?
> endif
> endfor
> endfor
>
> Any suggestions would be great.
>
> Thanks,
> Vikram
"where" remains your friend here.
img = read_tiff('NP.tif')
ids = fltarr(1229,1229)
OneIDX = where(m eq 1)
ids[oneIDX] = img[oneIDX]
If you really want, you can convert back the 1D index to 2D with
ARRAY_INDICES, but it changes nothing to the above.
Jean
|
|
|
|
| Re: Search and Replace in 2D Array (Image) [message #66654 is a reply to message #66653] |
Thu, 28 May 2009 12:39 |
vikramivatury
Messages: 24
Registered: May 2009
|
Junior Member |
|
|
On May 28, 3:28 pm, David Fanning <n...@dfanning.com> wrote:
> vikramivat...@gmail.com writes:
>> I have an image "m" which is [1229 x 1229] pixels that contains 1's
>> and 0's. I also have an image "img" which is [1229 x 1229] that
>> contains pixel IDs. For every 1 in image "m" it corresponds to a
>> certain pixel ID in image "img". I am trying to write a loop in IDL
>> that scans through the pixels of image "m" and when its get to a 1,
>> spit out its information from "img". I used the 'where' function (w =
>> where m gt 1.........ids = img(w)) and that worked fine in outputting
>> a 1D array of 1510441 pixels, but I am trying to do it for a 2D array
>> using loops.
>
>> img = read_tiff('NP.tif')
>> ids = fltarr(1229,1229)
>
>> for i = 0,1228 do begin
>> for j = 0,1228 do begin
>> if (m(i,j) eq 1.) then begin
>> ids(i,j) = img(m(i,j))
>> endif
>> endfor
>> endfor
>
>> Any suggestions would be great.
>
> Well, don't do it like this. :-)
>
> I suggest you investigate LABEL_REGION. *Much* faster!
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Coyote's Guide to IDL Programming (www.dfanning.com)
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
Ok, I will take a look at Label_Regions.
I was just thinking....Is it possible to do something like this
without an if-statment:
img = read_tiff('NP.tif')
ids = fltarr(1229,1229)
w = fltarr(1229,1229)
for i = 0,1228 do begin
for j = 0,1228 do begin
w(i,j) = where m eq 1
ids(i,j) = img(w(i,j))
endfor
endfor
|
|
|
|
| Re: Search and Replace in 2D Array (Image) [message #66655 is a reply to message #66654] |
Thu, 28 May 2009 12:28 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
|
|
vikramivatury@gmail.com writes:
> I have an image "m" which is [1229 x 1229] pixels that contains 1's
> and 0's. I also have an image "img" which is [1229 x 1229] that
> contains pixel IDs. For every 1 in image "m" it corresponds to a
> certain pixel ID in image "img". I am trying to write a loop in IDL
> that scans through the pixels of image "m" and when its get to a 1,
> spit out its information from "img". I used the 'where' function (w =
> where m gt 1.........ids = img(w)) and that worked fine in outputting
> a 1D array of 1510441 pixels, but I am trying to do it for a 2D array
> using loops.
>
> img = read_tiff('NP.tif')
> ids = fltarr(1229,1229)
>
> for i = 0,1228 do begin
> for j = 0,1228 do begin
> if (m(i,j) eq 1.) then begin
> ids(i,j) = img(m(i,j))
> endif
> endfor
> endfor
>
> Any suggestions would be great.
Well, don't do it like this. :-)
I suggest you investigate LABEL_REGION. *Much* faster!
Cheers,
David
--
David Fanning, Ph.D.
Coyote's Guide to IDL Programming (www.dfanning.com)
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
