[Image-SIG] open, show, png, blank

[Chris Mitchell]

>From my understanding of what you are trying to do is remap the dynamic
range of your image.  So in essence you want to set your lowest intensity
to 0 and the highest to 256 (given an 8 bit image).  The transformation
given is non-linear, if you are using this for gel quantification this is a
very very very bad idea.  If it's just screwing around, then it's fine.

So first you say what is the range, (hi-lo), and divide 256 by this to give
your effective intensity per value within your range (so taking a low of
100, a max of 250, each 'point' now represents 1.70 intensity).  You also
want to subtract the lowest intensity from each point to make your new
effective "0 intensity".  This is done dynamically by your given y
equation.  For a linear equation, you would want do use this:

outJ = outI.point(lambda i:(i-y)*x)
So all pixels which were 100 should now map to 0, a pixel of 250 would map
to 255.

On Thu, Feb 9, 2012 at 12:16 PM, Nelson Tong <tongsnelson.ise at gmail.com>wrote:

> >>
> >> On 2/4/12, Randolph Bentson <bentson at holmsjoen.com> wrote:
> >> > Oh, I guess the lambda function should be generalized by
> >> >
> >> > (lo,hi) = outI.getextrema()
> >> > x = 256.0/(hi-lo)
> >> > y = (0-lo)/256.0
> >> > outJ = outI.point(lambda i:i*x+y)
> >
> > I have no experience with these type images, so I don't know if
> > constant values are appropriate. The performance of the generalized
> > mapping seems quick enough, so that may be safer.  BUT, there's
> > one questionable issue with this function: it turns the darkest
> > source pixel to black and the lightest pixel to white. I hope
> > others can provide some comments on that.
>
> I'm not an expert in image processing.  I just want to learn more
> about this since we are talking about the mapping function here.
>
> I don't quite completely understand how this generalized mapping
> function work with im.point().  Given the hi and lo from getextema(),
> I understand that x = 256.0/(hi-lo)
>  is a way to  to adjust the scale parameter to the have a range of
> values  from 0 to 256.  but where does the offset of (y= (0-lo) /256 )
> comes from ? is there any reference anyone can recommend as a tutorial
> about this kind of mapping function?
>
>
>
>
>
>
>
>
> >
> > --
> > Randolph Bentson
> > bentson at holmsjoen.com
> >
> _______________________________________________
> Image-SIG maillist  -  Image-SIG at python.org
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>
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