Posted by
Michael Schmid on
Jun 21, 2007; 5:54pm
URL: http://imagej.273.s1.nabble.com/Modifying-Image-Histograms-tp3698976p3698984.html
Hi Anthony,
it is a vague question, indeed.
Grayscale? Color? What kind of object? Extended? Small particles?
"Enhance Contrast" without equalizing the histogram, only
saturating a small percentage of pixels, should not mess up
anything (except for astronomical images and the like, where
the maximum intensity of bright stars will be clipped).
If it does not work at all and you have noise in your image,
use despeckle; if you have hot pixels or salt/pepper noise,
use process/noise/remove outliers (needs version 1.38v).
If the contrast between object and background is too weak
because it has blurred edges, unsharp mask will help.
If the object has a different texture than the background, the
variance filter (usually plus some smoothing thereafter) may work.
If you can't threshold the object because of a sloping
background, use "subtract background" or some other background
subtraction plugin, e.g.,
http://www.cs.unc.edu/~cquammen/imagej/
nonuniform_background_removal.html
or
http://www.optinav.com/Polynomial_Fit.htmOf course, the human eye+brains have the advantage of a few million
years development time over any image processing algorithm, so
don't expect that any algorithm will be as good or even better
than what you can see.
Michael
________________________________________________________________
On 21 Jun 2007, at 17:27, Rotella, Anthony M. (GRC) wrote:
> Hello,
>
> I need to threshold a large number of images that are similar,
> but not quite the same. The vast majority threshold satisfactorily
> within the same range, but some are far enough off to throw the
> calculations and the accuracy out the window. Basically, I was
> wondering
> if there is a way to change the images so that the important
> features of
> the histograms of the slices in the stack fit into the same range, but
> so that the pixels still maintain their relative values between each
> other, so the same features of the image still threshold out
> correctly.
> Unfortunately the Autothreshold is way off. I tried Enhance Contrast,
> but makes the images very messy and doesn't work well. Another fix
> to my
> problem is if someone knows how to increase the difference in pixel
> intensities between objects in the foreground and background. I can
> clearly see the difference , but of course, ImageJ can't just do
> what I
> want, and some of the objects that I want to have thresholded out have
> the same intensities as something in the background, maybe somewhere
> else in the image. Unfortunately, I am hesitant to post the images
> on a
> hosting service, but I can e-mail them to anyone that wants to see
> them.
> Thanks, and sorry for the vague question!
>
> Tony Rotella