Re: [Teem-users] uniform resampling of non-uniform data

[David W. <dm...@sc...>]

This worked great -- thanks!!

Dave


On Jul 31, 2004, at 9:49 PM, Gordon Kindlmann wrote:

>
>
> Begin forwarded message:
>
>> From: Gordon Kindlmann <gk...@cs...>
>> Date: Sat Jul 31, 2004  11:44:03 AM US/Mountain
>> To: tee...@li...
>> Subject: Re: [Teem-users] uniform resampling of non-uniform data
>>
>> hi,
>>
>> Great question, and a great place to ask!
>>
>> If you save those numbers into a text file bow.txt, then:
>>
>> echo "0 1" \
>>  | unu reshape -s 2 \
>>  | unu resample -s 256 -k tent \
>>  | unu imap -r -m bow.txt -o bow-256.txt
>>
>> will save a 256-entry lookup table in bow-256.txt, using simple 
>> linear interpolation between the (irregularly spaced) control points. 
>>  Unfortunately, nrrd has no way (not that I know of) to do filtered 
>> sampling on irregularly spaced points.  Actually, I can imagine some 
>> twisted scheme where you warp the values around prior to doing the 
>> lookup, so that effectively the control points are regularly spaced, 
>> and then unwarping afterwards, but off the top of my head I can't see 
>> how to do it.  And its probably moot anyway because "unu rmap" (and 
>> the  nrrdApply1DRegMap() call behind it) can't use a kernel- I felt 
>> that it wouldn't be useful enough.
>>
>> As for doing cubic interpolation, I'd be surprised if you actually 
>> wanted ringing between the control points in a colormap- that would 
>> look awful.  If you just want a touch of blurring between the control 
>> point colors, then you could:
>>
>> echo "0 1" \
>>  | unu reshape -s 2 \
>>  | unu resample -s 256 -k tent -o ramp.nrrd
>>
>> unu resample -i bow.txt -s = x1 -k cubic:1,0 \
>>  | unu crop -min 1 0 -max M M \
>>  | unu inset -i bow.txt -s - -min 1 0 \
>>  | unu imap -r -i ramp.nrrd -m - -o bow-blur-256.txt
>>
>> But having just tried this, and looked at the results, you might 
>> actually want to  do this:
>>
>> unu resample -i bow.txt -s = x1 -k cubic:1,0 \
>>  | unu crop -min 1 0 -max M M \
>>  | unu inset -i bow.txt -s - -min 1 0 \
>>  | unu imap -r -i ramp.nrrd -m - \
>>  | unu resample -s = x1 -k gauss:4,3 -o bow-blur2-256.txt
>>
>> which seems to have a smoother transition around orange.
>>
>> To look at this as an image:
>>
>> unu axinsert -i bow-blur2-256.txt -a 2 \
>>  | unu pad -min 0 0 0 -max M M M+100 \
>>  | unu quantize -b 8 \
>>  | unu save -f pnm | xv -
>>
>>
>> Gordon
>>
>> PS: rm -f ramp.nrrd
>>
>>
>> On Saturday, July 31, 2004, at 10:09 AM, David Weinstein wrote:
>>
>>> Hi,
>>>
>>> I have a colormap (attached below) which has irregular spacing 
>>> (stored in the first column).  How do I use "unu imap" to create a 
>>> colormap with 256 uniformly spaced samples (say, using cubic 
>>> interpolation)?
>>>
>>> Thanks,
>>> Dave
>>>
>>> ==========
>>>
>>> 0 0.453125 0.000000 0.000000
>>> 0.0605 0.753906 0.000000 0.000000
>>> 0.121 0.972656 0.218750 0.000000
>>> 0.146 1.000000 0.313002 0.000000
>>> 0.332 1.000000 0.804688 0.000000
>>> 0.389 0.910156 0.851562 0.000000
>>> 0.529 0.468750 0.886719 0.066406
>>> 0.623 0.113281 0.886719 0.441406
>>> 0.682 0.000000 0.835938 0.640625
>>> 0.771 0.000000 0.664062 0.941406
>>> 0.834 0.000000 0.425781 1.000000
>>> 0.889 0.000000 0.16 1.000000
>>> 0.920 0.000000 0.070312 0.953125
>>> 0.961 0.000000 0.000000 0.687500
>>> 1.0 0.000000 0.000000 0.45
>>>
>>>
>>>
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