Posted by
Bevic, Jordan on
Dec 22, 2005; 8:35pm
URL: http://imagej.273.s1.nabble.com/Image-Gradient-tp3704168p3704174.html
Dan:
The discrete binning ("vertical banding")is caused by the equalization
algorithm itself, and is not a function of how the image was obtained.
The method involves remapping the image (as in a Look Up Table) using
the cumulative intensity distribution (CD) that has been scaled from
zero to the maximum gray level. Unless your initial histogram is a
straight line from zero to 4096 (so that the scaled CD has values at all
grey levels), there will be some gray values that aren't represented
(this is like missing codes in an analog to digital converter).
Adding noise before equalizing will smooth out the CD, making more gray
levels available in the final image (the final image will still have
noticeable binning, but they will be closer together).
Adding noise after equalizing will spread each bin out, but will not
change their spacing.
Of course, adding noise before and after equalization would give the
smoothest final image.
Jordan Bevic
AVS Engineering
QuadTech
A Subsidiary of Quad/Graphics
Sussex, Wisconsin
414-566-7493 phone
[hidden email]
www.quadtechworld.com
-----Original Message-----
From: ImageJ Interest Group [mailto:
[hidden email]] On Behalf Of
Dan Siler
Sent: Thursday, December 22, 2005 12:41 PM
To:
[hidden email]
Subject: Re: Image Gradient
I have tried histogram equalization from several software packages but
the
images contain severe vertical banding. I don't know if this is caused
by
how the intensities are mapped to the monitor or graphics card or both.
This makes if hard to find vertical flaws. Different monitors/graphic
cards seem to give different results. Does someone have a suggestion on
how to fix this or montitor/graphics card recommendations if that is the
problem. These are 4096 gray scale images.
The images are taken using 4 Mev with a tungstun collimator at the
source
only. Also we are using a linear intensity response CCD 1536 X 1024
detector.
Thanks for your help this has suggested options that may help with the
problem.