| Re: color value interpolation from colorbar [message #64209 is a reply to message #64128] |
Fri, 05 December 2008 07:17   |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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I would fit a*x^b for red and blue and c+dx for blue.
Ciao,
Paolo
Jeremy Bailin wrote:
> On Dec 4, 9:35�pm, "j.coe...@gmail.com" <j.coe...@gmail.com> wrote:
>> Thanks everyone. �Sorry for the delay, I had to generate the requested
>> pics and create a Picasa web album. �If there is a better way to post
>> images to usenet forums, please let me know.
>>
>> Below is the Picasa link to the two images requested by Vince and
>> Paolo, (1) an example frame grab of a scan, and (2) its colorbar RGB
>> plotted against colorbar location:
>>
>> http://picasaweb.google.com/j.coenia/ColorInterpolation?auth key=H9iPr...
>>
>> To answer Jeremy's question, the colorbar length is 140 pixels or so
>> (scaled here from 1 to 100 on the x axis, which is vertical in the
>> scan). �You can see from the plot that the colorbar sampling is
>> "garbagy." �There are two very bright artifacts, at approximately x=20
>> and x=80. �Such outliers can be tossed or smoothed out somehow I
>> think. �For simplicity, I just sampled the values down the vertical
>> center of the colorbar, as the colorbar tends to bleed a little into
>> the dark background near the edges (more errors).
>>
>> Jeremy's answer makes some sense to me. �So is it possible to
>> reasonably guess the color levels in that artery using the colorbar on
>> the side of the scan? �I know there is no scale on the colorbar --
>> I've been instructed to assume linear gradient from 1 to 100.
>> Radiologists and researchers use these colors; can the computer
>> quantify them to extract more meaningful information?
>>
>> Thanks again.
>
> I think that your colour bar is sampled well enough for the approach I
> suggested to work. You'll need to smooth out your R,G,B curves first,
> though - I would first use Peter's suggestion of taking the mean over
> a few columns within the colour bar, and then I'd pass it through a
> median filter to get rid of the artifacts and further smooth it.
>
> I quite like Peter's approach, actually - assuming that the curves can
> be fit to a sufficiently low-order polynomial, which you'll have to
> check. It should be a lot faster, and is definitely more elegant! The
> approach I suggested should work pretty generically for any bizarre
> colour table, but yours looks it would be reasonably well-behaved once
> smoothed.
>
> -Jeremy.
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